Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/05/16


AREA FORECAST DISCUSSION
NWS BUFFALO NY
616 AM EST SUN JAN 3 2016 .SYNOPSIS... AN ARCTIC FRONT WILL CROSS THE REGION TODAY WITH SNOW SHOWERS AND BETTER ORGANIZED LAKE EFFECT SNOW EAST OF THE LAKES. WIDESPREAD LAKE EFFECT SNOW WILL THEN CONTINUE SOUTH OF THE LAKES SUNDAY NIGHT AND MONDAY WITH VERY COLD TEMPERATURES. HIGH PRESSURE WILL BRING A RETURN TO DRY WEATHER TUESDAY WITH TEMPERATURES MODERATING TO ABOVE NORMAL AGAIN DURING THE SECOND HALF OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... A FAST MOVING CLIPPER OVER SOUTHERN QUEBEC THIS MORNING WILL RACE ACROSS NORTHERN NEW ENGLAND TODAY. IN THE WAKE OF THIS CLIPPER A SHARP MID LEVEL TROUGH WILL DIG INTO THE EASTERN LAKES AND NEW ENGLAND...DRIVING A STRONG ARCTIC FRONT SOUTHWARD ACROSS THE REGION THIS AFTERNOON. THE ARCTIC FRONT MAY PRODUCE A BRIEF BURST OF SNOW SHOWERS IN MANY AREAS...BUT MORE IMPORTANTLY WILL ENHANCE LAKE EFFECT SNOW EAST OF THE LAKES TODAY. OFF LAKE ERIE... STILL JUST A FEW FLURRIES FALLING AS OF 11Z EAST OF LAKE ERIE. A RECENT AMDAR SOUNDING SHOWS ABOUT -10C AT THE BASE OF THE INVERSION...NOT QUITE COLD ENOUGH FOR DENDRITIC CRYSTAL GROWTH. THE UNFAVORABLE CLOUD MICROPHYSICS SO FAR HAVE JUST SUPPORTED TINY FLAKES AND FLURRIES. THIS SHOULD CHANGE SHORTLY AS DEEPER MOISTURE IS ABOUT TO MOVE OVER LAKE ERIE FROM THE NORTH...WHICH WILL BEGIN TO LIFT THE INVERSION AND COOL THE COLUMN...PRODUCING BETTER DENDRITIC CRYSTAL GROWTH. EXPECT SNOW TO BLOSSOM BY MID MORNING FROM SOUTHERN ERIE AND WYOMING COUNTIES DOWN THE CHAUTAUQUA COUNTY LAKESHORE. LAKE INDUCED EQUILIBRIUM LEVELS IMPROVE TO AROUND 8K FEET LATER THIS MORNING...WHICH SHOULD SUPPORT MORE WIDESPREAD LAKE EFFECT SNOW ACROSS THE WESTERN SOUTHERN TIER AS BOUNDARY LAYER FLOW BECOMES MORE WESTERLY. LATER THIS AFTERNOON THE ARCTIC FRONT WILL CROSS LAKE ERIE. THIS SHOULD BRING A PERIOD OF ENHANCED SNOWFALL RATES MAINLY FROM SOUTHERN ERIE COUNTY INTO THE CHAUTAUQUA RIDGE AS CONVERGENCE FROM THE ARCTIC FRONT INTERACTS COOPERATIVELY WITH CONVERGENCE FROM LAKE EFFECT AND UPSLOPE PROCESSES. BY THIS EVENING FLOW QUICKLY BECOMES NORTHWEST IN THE WAKE OF THE ARCTIC FRONT...WITH LAKE EFFECT TRANSITIONING INTO UPSLOPE SNOW ALONG THE CHAUTAUQUA RIDGE. THERE MAY BE A BRIEF WINDOW DURING THE LATE AFTERNOON AND EARLY EVENING FOR AN UPSTREAM CONNECTION TO LAKE HURON...BUT THIS QUICKLY MOVES WEST TO NEAR ASHTABULA OHIO THIS EVENING AS BOUNDARY LAYER FLOW BECOMES NNW. FOR TODAY THROUGH TONIGHT EXPECT THE GREATEST AMOUNTS ACROSS THE HIGHER TERRAIN OF THE CHAUTAUQUA RIDGE...WITH 6-10 INCHES OF ACCUMULATION COMING IN SEVERAL DIFFERENT WAVES. EXPECT MORE ON THE ORDER OF 4 TO 6 INCHES ACROSS SOUTHERN ERIE AND WESTERN WYOMING COUNTIES. OFF LAKE ONTARIO... LIGHT SNOW ACROSS JEFFERSON COUNTY AS OF 11Z SHOULD QUICKLY BLOSSOM INTO MORE ORGANIZED LAKE EFFECT SNOW BY MID MORNING NEAR WATERTOWN AS MOISTURE DEEPENS AND EQUILIBRIUM LEVELS RISE IN RESPONSE TO INCREASING LARGE SCALE ASCENT. LATER THIS MORNING BOUNDARY LAYER FLOW WILL BECOME MORE WESTERLY AND FORCE INTENSIFYING LAKE EFFECT SNOW TO THE TUG HILL. MESOSCALE MODEL GUIDANCE CONTINUES TO HIT THIS BAND HARD TODAY...WITH HIGH SNOWFALL RATES SUGGESTED IN THE NCAR 3KM MESOSCALE ENSEMBLE AND OTHER HIGH RESOLUTION GUIDANCE. INSTABILITY MAY GROW STRONG ENOUGH AND DEEP ENOUGH INTO THE MIXED PHASE REGION TO SUPPORT SOME THUNDER AND 2-3 INCH PER HOUR SNOWFALL RATES. THIS AFTERNOON THE ARCTIC FRONT WILL CROSS LAKE ONTARIO AND LIKELY MERGE WITH THE LAKE EFFECT SNOW BAND...MOVING TO THE SOUTHEAST CORNER OF THE LAKE. THIS WILL TAKE A BAND OF HEAVY SNOW SOUTH ACROSS OSWEGO COUNTY...WITH A BURST OF SNOW POSSIBLY MOVING ONSHORE IN NORTHERN CAYUGA AND WAYNE COUNTIES AS WELL. FARTHER WEST...EXPECT A BURST OF SNOW SHOWERS FROM ROCHESTER WEST ACROSS THE NIAGARA FRONTIER WITH THE PASSAGE OF THE ARCTIC FRONT AND WESTERN PORTION OF THE LAKE ONTARIO BAND. BOUNDARY LAYER FLOW QUICKLY BECOMES NORTHWEST THIS EVENING AND NORTHERLY OVERNIGHT. THIS WILL SET THE STAGE FOR A WIDESPREAD SPRAY OF LIGHT TO MODERATE LAKE EFFECT SNOW SHOWERS SOUTH OF LAKE ONTARIO COVERING MUCH OF THE AREA FROM OSWEGO COUNTY WESTWARD TO THE NIAGARA FRONTIER. LAKE INDUCED EQUILIBRIUM LEVELS REMAIN AROUND 8K FEET OVERNIGHT WITH A FAVORABLE LAYER OF DENDRITIC CRYSTAL GROWTH IN THE SHALLOW CLOUD LAYER BELOW. DESPITE THE SHORT NORTHERLY FETCH... STRONG THERMODYNAMICS AND FAVORABLE CLOUD MICROPHYSICS SHOULD SUPPORT SOME DECENT ACCUMULATIONS ALONG THE SOUTH SHORE OF THE LAKE WITH THE GREATEST AMOUNTS FOCUSING ON THE GENESEE VALLEY INCLUDING ROCHESTER INTO PORTIONS OF THE NORTHERN FINGER LAKES. EXPECT THE GREATEST TOTALS FOR TODAY AND TONIGHT TO FOCUS ON THE TUG HILL WITH 6-12 INCHES...MOST OF WHICH FALLS TODAY PRIOR TO THE ARCTIC FRONTAL PASSAGE. EXPECT 3-5 INCH AMOUNTS TO THEN BE COMMON TONIGHT ALONG THE SOUTH SHORE OF LAKE ONTARIO FROM OSWEGO COUNTY WESTWARD TO ORLEANS COUNTY...INCLUDING THE GREATER ROCHESTER AREA. THE REST OF THE NIAGARA FRONTIER MAY SEE AN INCH OR TWO WITH NARROW MULTIPLE BANDS COMING OFF THE WEST END OF THE LAKE IN NORTHERLY FLOW. && .SHORT TERM /MONDAY THROUGH TUESDAY/... LAKE EFFECT SNOW WILL CONTINUE SOUTH OF LAKE ONTARIO AND ERIE ON MONDAY AS OUR FIRST ARCTIC BLAST OF THE SEASON HOLDS HIGH TEMPERATURES IN THE LOW TEENS AND SINGLE DIGITS. A SHARP TROUGH DIGGING INTO THE UPPER GREAT LAKES THIS MORNING IS DRIVING AN ARCTIC AIRMASS SOUTHWARD ACROSS ONTARIO AND THE HUDSON BAY. 850 MB TEMPERATURES UNDER THIS TROUGH AS ANALYZED UNDER - 20C... WITH SURFACE OBS THIS MORNING SHOWING TEMPERATURES DOWN INTO THE TEENS F BELOW ZERO NEAR THE HUDSON BAY. THIS AIRMASS WILL BE IN PLACE OVER THE FORECAST AREA BY MONDAY MORNING... WITH A WELL ESTABLISHED NORTHERLY FLOW BETWEEN THE SURFACE HIGH BUILDING INTO THE UPPER GREAT LAKES AND THE SURFACE LOW OFF THE NORTHEAST COAST. LAKE EFFECT SNOWS WILL BE STILL BE ONGOING MONDAY MORNING SOUTH OF THE LAKES. BY MONDAY MORNING... THE STEERING FLOW WILL BE ALMOST DUE NORTHERLY... WHICH RESULTS IN THE SHORTEST FETCH POSSIBLE ACROSS LAKE ONTARIO INTO THE SOUTH SHORE OF THE LAKE. LAKE INSTABILITY AND LOW-LEVEL MOISTURE WILL BE BEST IN THE MORNING BEFORE RIDGING BUILDING IN ALOFT LOWERS THE CAPPING INVERSION BY THE AFTERNOON MONDAY INTO MONDAY NIGHT. THUS EXPECT NUMEROUS NARROW SNOW BANDS ACROSS THE COUNTIES SOUTH OF THE LAKE... STRETCHING FROM THE NIAGARA FRONTIER ACROSS TO ROCHESTER TO FAR WESTERN OSWEGO COUNTY. HIGHER SNOWFALL RATES WILL BE CONFINED TO AREAS CLOSEST TO LAKE ONTARIO (NORTH OF THE THRUWAY... BUT HIGHEST ALONG THE LAKE SHORE)... AND FROM ABOUT ORLEANS COUNTY ACROSS TO NORTHERN CAYUGA COUNTY WHERE THE FETCH ACROSS THE LAKE IS SLIGHTLY WIDER THAN FOR THE NIAGARA FRONTIER. SNOWFALL ACCUMULATIONS DURING THE DAY MONDAY ARE EXPECTED TO BE GENERALLY AROUND 2 TO 3 INCHES IN THE MORE IDEAL LOCATIONS... WITH AMOUNTS TAPERING OFF TO AN INCH OR LESS OUTSIDE OF THESE AREAS. VERY LOCALIZED HIGHER AMOUNTS ARE ALWAYS POSSIBLE IF ONE OF THESE NARROW BANDS LINGERS OF ONE AREA FOR AN EXTENDED PERIOD OF TIME. OFF LAKE ERIE.. THE CHAUTAUQUA RIDGE IN CHAUTAUQUA COUNTY WILL PICK UP ANOTHER INCH OR SO ON MONDAY WITH A COMBINED SHORT FETCH ACROSS LAKES ONTARIO AND ERIE INTO THE UPSLOPE PRONE REGION. INTERIOR PORTIONS OF THE SOUTHERN TIER WILL LIKELY SEE VERY LITTLE IF ANY SNOWFALL. SNOW WILL TAPER OFF RATHER QUICKLY INTO MONDAY NIGHT AS THE CAPPING INVERSION LOWERS UNDER THE RIDGING BUILD IN... WITH MAINLY LAKE CLOUDINESS LINGERING SOUTH OF THE LAKES. OTHERWISE... SKIES WILL START TO CLEAR IN THE NORTH COUNTRY... AND MONDAY NIGHT WILL BE ANOTHER VERY COLD NIGHT WITH LOWS MAINLY IN THE SINGLE DIGITS WITH SOME BELOW ZERO READINGS IN THE NORTH COUNTRY. TEMPERATURES WILL START A SLOW REBOUND ON TUESDAY AS THE PROGRESSIVE PATTERN QUICKLY BUILDS RIDGING ACROSS THE FORECAST AREA. HIGHS ON TUESDAY WILL BE BACK INTO THE 20S. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... HIGH PRESSURE DRIFTS EAST OF THE AREA BY THE MIDDLE OF NEXT WEEK WITH MODERATING SOUTHWESTERLY FLOW BRINGING TEMPERATURES BACK TO A LITTLE ABOVE NORMAL FOR WEDNESDAY AND THURSDAY WITH A PERIOD OF DRY WEATHER. THE NEXT CHANCE OF PRECIPITATION COMES IN THE FORM OF RAIN LATE FRIDAY THROUGH SATURDAY. LOOKING FARTHER AHEAD... THERE REMAINS CLEAR SIGNALS IN THE LONGER RANGE FORECASTS FROM THE GFS/EC AND CFS FOR TEMPERATURES TO TURN BELOW NORMAL FROM ABOUT JANUARY 11 THROUGH THE MIDDLE PORTION OF THE MONTH. WITH LAKE TEMPERATURES STILL RUNNING ABNORMALLY WARM AFTER A RECORD BREAKING WARM DECEMBER... A TURN TO BELOW OR MUCH BELOW NORMAL TEMPERATURES SHOULD SIGNAL AN INCREASE OF LAKE EFFECT SNOW EVENTS AS WELL. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/... LAKE EFFECT SNOW WILL DEVELOP THIS MORNING EAST OF THE LAKES WITH AREAS OF IFR. THIS WILL MAINLY IMPACT THE KJHW AND KART TERMINALS THROUGH MIDDAY. THIS AFTERNOON A SHARP ARCTIC FRONT WILL CROSS THE REGION WITH A FEW BRIEF BURSTS OF SNOW SHOWERS AND BRIEF IFR IMPACTING MOST OF THE TERMINALS. LAKE EFFECT SNOW WILL FOCUS SOUTHEAST OF THE LAKES AT THIS TIME NEAR KJHW AND KFZY. TONIGHT LOW LEVEL FLOW BECOMES NORTHERLY...WHICH WILL PRODUCE A WIDE SPRAY OF LIGHT TO MODERATE LAKE EFFECT SNOW SOUTH OF BOTH LAKES WITH AREAS OF IFR VSBY. THE MOST PERSISTENT IFR SHOULD BE FOUND AT KROC AND KJHW...BUT SOME MAY DEVELOP AT KBUF AND KIAG AS WELL LATE TONIGHT. OUTSIDE OF THE LAKE EFFECT AND ARCTIC FRONTAL SNOW SHOWERS EXPECT WIDESPREAD MVFR CIGS AND VFR VSBY. OUTLOOK... MONDAY...MVFR/IFR WITH SNOW SHOWERS AND LAKE EFFECT SNOW. TUESDAY THROUGH THURSDAY...VFR. && .MARINE... HIGH END SMALL CRAFT ADVISORY CONDITIONS WILL REMAIN IN PLACE THROUGH TODAY WITH STRONG WESTERLY WINDS TO THE SOUTH OF A CLIPPER LOW PASSING THROUGH SOUTHERN QUEBEC. AN ARCTIC COLD FRONT WILL CROSS THE LOWER LAKES LATER THIS AFTERNOON. WINDS WILL BECOME NORTHERLY BEHIND THE ARCTIC FRONT AND MAINTAIN MORE MODEST SMALL CRAFT ADVISORY CONDITIONS TONIGHT THROUGH MONDAY. HIGH PRESSURE WILL BRING A RETURN TO LIGHTER WINDS BY TUESDAY. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...LAKE EFFECT SNOW WARNING UNTIL 4 PM EST THIS AFTERNOON FOR NYZ007-008. LAKE EFFECT SNOW WARNING UNTIL 1 PM EST MONDAY FOR NYZ006. LAKE EFFECT SNOW ADVISORY FROM 3 PM THIS AFTERNOON TO 1 PM EST MONDAY FOR NYZ002>005-014. LAKE EFFECT SNOW WARNING UNTIL 1 AM EST MONDAY FOR NYZ019-020- 085. LAKE EFFECT SNOW ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR NYZ012. MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LEZ020. SMALL CRAFT ADVISORY UNTIL 7 PM EST MONDAY FOR LEZ040-041. SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR LOZ030. SMALL CRAFT ADVISORY UNTIL 1 AM EST TUESDAY FOR LOZ042>045. && $$ SYNOPSIS...HITCHCOCK NEAR TERM...HITCHCOCK SHORT TERM...CHURCH LONG TERM...CHURCH AVIATION...HITCHCOCK MARINE...HITCHCOCK
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AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
235 PM CST TUE JAN 5 2016 .UPDATE... 1128 AM CST NO SIGNIFICANT CHANGES TO GOING FORECAST. PRIMARY TWEAK WAS TO ADJUST HIGH TEMPERATURES UP A DEGREE OR TWO TOWARD BUT NOT AS WARM AS MAV/LAV GUIDANCE. THIS YIELDS HIGHS IN THE LOWER 30S NORTH OF I-88 WHERE THE DEEPER SLEET COVER IS AND GENERALLY MID 30S SOUTH OF I-88. AIRCRAFT SOUNDINGS AND RAP/HRRR FORECAST SOUNDINGS SUGGEST MIXING SHOULD TOP OUT AROUND 900 MB TODAY...AND MIXING DOWN FROM THIS LEVEL SUPPORTS AT LEAST TEMPS AS WARM AS FORECAST HIGHS. A FEW UPPER 30S ARE POSSIBLE IN CENTRAL ILLINOIS COUNTIES...BUT CONSIDERING THAT THERE IS STILL SLEET COVER ACROSS THE AREA...UPPER 30S READINGS SHOULD BE LOCALIZED. HIGH CLOUDS WILL GRADUALLY INCREASE AS A WEAK UPPER DISTURBANCE MOVES ACROSS THE AREA. PRESSURE GRADIENT ON BACK SIDE OF EXPANSIVE HIGH PRESSURE TO THE EAST AND WEAK LOW PRESSURE OVER THE HIGH PLAINS WILL SUPPORT SOUTH TO SOUTH-SOUTHWEST WINDS 10-15 MPH WITH OCCASIONAL GUSTS IN THE 15-20 MPH RANGE. RC && .SHORT TERM... 305 AM CST THROUGH WEDNESDAY... A QUIET FIRST 36 HOURS OF THE FORECAST WITH THE ACTION ALL WEDNESDAY NIGHT AND BEYOND. CONCERNS REMAIN ON LIGHT FREEZING PRECIPITATION AND/OR SNOW LATE WEDNESDAY NIGHT AND THURSDAY MORNING. ANY CHANGES TO THIS PART OF THE FORECAST HAVE BEEN MAINLY TWEAKS AND REFINING AREA...WITH STILL MORE OF AN EMPHASIS IN CHANCES/DURATION IN NORTH CENTRAL ILLINOIS. STOUT CANADIAN HIGH PRESSURE OF 1038MB CENTERED OVER THE EASTERN GREAT LAKES WILL EASE EASTWARD TODAY WITH ITS BACKSIDE SOUTHERLY WINDS HAVING ALREADY OUSTED THE STRATOCUMULUS. PATCHES OF HIGH CLOUDS WILL DRIFT OVER TODAY AS A LOW AMPLITUDE UPPER RIDGE ALSO MOVES ON EAST. HIGHS ARE EXPECTED TO BE RIGHT AROUND NORMAL. A LIGHT SOUTHERLY WIND WILL ALLOW TEMPERATURES TO BE A TAD MILDER TONIGHT. CLOUDS SHOULD THICKEN MORE ON WEDNESDAY BUT A MODIFYING LOWER ATMOSPHERE SHOULD SUPPORT MID 30S IN THE NORTHERN SNOW COVERED AREAS TO UPPER 30S IN THE SOUTH. WITH TEMPERATURES NOT FAR ABOVE FREEZING IN NORTH CENTRAL ILLINOIS...THIS AREA WILL BE MOST FAVORED TO DIP BELOW FREEZING PRIOR TO PRECIPITATION CHANCES LATER THAT NIGHT. MTF && .LONG TERM... 213 PM CST WEDNESDAY NIGHT THROUGH TUESDAY... THE EXTENDED PERIOD LOOKS TO BE QUITE ACTIVE...WITH SEVERAL PRECIPITATION-PRODUCING SYSTEMS INTO THE WEEKEND AND THEN AN INTRUSION OF COLD ARCTIC AIR SUNDAY INTO NEXT WEEK. THE FIRST SYSTEM TO AFFECT THE REGION WILL BE A RELATIVELY MINOR AMPLITUDE SHORT WAVE TROUGH WHICH WILL LIFT NORTHEAST ACROSS THE FORECAST AREA WEDNESDAY NIGHT. DESPITE SOUTH-SOUHTWEST LOW LEVEL WINDS...FORECAST SOUNDINGS INDICATE THAT THESE LAYERS ARE INITIALLY QUITE DRY...WITH RETURN OF GULF MOISTURE BLOCKED BY EXPANSIVE SURFACE HIGH PRESSSURE RIDGE AXIS WHICH EXTENDS FROM THE MID-ATLANTIC BACK ACROSS THE GULF COAST STATES INTO TEXAS. LOW LEVEL MOISTURE DOES BEGIN TO FLOW NORTH-NORTHEASTWARD AROUND THE WESTERN PERIPHERY OF THE HIGH...THOUGH IT APPEARS TO LAG THE BETTER FORCING WITH THE INITIAL WEAKENING SHORT WAVE. MODELS HAVE GENERALLY TRENDED SLOWER WITH LIGHT QPF PRIMARILY JUST OFF TO THE WEST OF THE CWA THROUGH 12Z THURSDAY MORNING. WHILE THE INITIAL SHORT WAVE PULLS AWAY TO THE NORTHEAST EARLY THURSDAY...GUIDANCE DOES EVENTUALLY SPREAD LIGHT QPF INTO THE CWA DURING THE DAY PRIMARILY IN THE WEST/SOUTHWEST AS PERSISTENT 20-25 KT SOUTHWEST WINDS RESULT IN WEAK BUT PERSISTENT ISENTROPIC ASECNT WHICH CONTINUES TO WORK TO SATURATE THE LOW LEVELS FROM THE TOP DOWN. WHILE PRECIPITATION IS EXPECTED TO BE LIGHT...P-TYPE IS A CONCERN AS SURFACE TEMPERATURES ARE EXPECTED TO BE NEAR FREEZING LATE WEDNESDAY NIGHT/EARLY THURSDAY MORNING...AND THIS COMBINED WITH INITIALLY DRY LOW LEVELS (AND WET-BULB COOLING IMPLICATIONS) WOULD SUPPORT A FROZEN OR FREEZING P-TYPE MIX OF SLEET/SNOW/FREEZING RAIN INTO THURSDAY MORNING BEFORE PERISTENT WARM/MOIST ADVECTION WARMS THE COLUMN AND RAISES SURFACE TEMPERATURES ABOVE FREEZING FROM SOUTH TO NORTH THROUGH MID-DAY/EARLY AFTERNOON. LIGHT QPF IMPLIES MINIMAL SLEET/SNOW ACCUMULATION POTENTIAL...THOUGH ANY LIGHT FREEZING RAIN COULD CAUSE SOME LIGHT GLAZING MAINLY ON ELEVATED SURFACES AND THIN/UNTREATED PAVEMENT SUCH AS SIDEWALKS... DRIVEWAYS AND SOME PARKING LOTS. WEAKENING DEEP LAYER FORCING BEHIND DEPARTING SHORT WAVE SHOULD ALLOW PRECIP TO TRANSITION MAINLY TO A LIGHT RAIN/DRIZZLE WITH TEMPS ABOVE FREEZING THURSDAY AFTERNOON AND HIGHS FROM THE MID-30S NORTH TO THE LOW 40S FAR SOUTH. ATTENTION THEN TURNS BACK TO THE SOUTHWEST...AND TO A STRONGER MID-LEVEL SHORT WAVE DEVELOPING OVER THE SOUTH-CENTRAL PLAINS WITH A CLOSED 500 MB CENTER WHICH LIFTS NORTHEAST INTO THE MID- MISSISSIPPI VALLEY BY FRIDAY MORNING AND ACROSS THE FORECAST AREA ON FRIDAY. RENEWED AND STRONGER DEEP FORCING FOR ASCENT ATOP NOW SATURATED LOW-MID LEVELS IS EXPECTED TO PRODUCE AN AREA OF MORE WIDESPREAD LIGHT-MODERATE RAIN ACROSS THE CWA THURSDAY NIGHT INTO FRIDAY AS THE SHORT WAVE AND ITS ASSOCIATED SURFACE LOW APPROACH AND TRANSIT THE AREA. P-TYPE EXPECTED TO BE ALL RAIN AT THIS TIME...WITH SURFACE TEMPS ABOVE FREEZING AND LOWER PORTION OF FORECAST SOUNDINGS SATURATED AND WARMER THAN 0C. SOME DIFFERENCES IN THE MODEL DETAILS REMAIN DURING THIS PERIOD...THOUGH THERE IS GENERAL OVERALL AGREEMENT IN RAIN AMOUNTS UP AROUND A HALF INCH OR SO ESPECIALLY ACROSS THE WESTERN PARTS OF THE CWA CLOSER TO THE EXPECTED MID-LEVEL CIRCULATION TRACK. IT SHOULD BE NOTED THAT THIS TRACK MAY SHIFT AS THIS IS STILL DAY 4 OF THE FORECAST WHERE MODELS STILL SHOW SOME VARIATION. PRECIP INTENSITY WILL LIKELY DIMINISH TO DRIZZLE/LIGHT RAIN AGAIN FRIDAY AFTERNOON AS THE MID- LEVEL WAVE AND SURFACE LOW EVENTUALLY LIFT NORTHEAST OF THE CWA. LIGHT RAIN/DRIZZLE MAY CONTINUE FRIDAY NIGHT AS ANOTHER WEAK SHORT WAVE TROUGH TRAVERSES THE REGION...POSSIBLY MIXING WITH OR CHANGING TO SOME LIGHT SNOW OVER NORTHWEST IL AFTER MIDNIGHT AND ACROSS THE AREA SATURDAY AS COLDER AIR STARTS TO FILTER IN BEHIND SURFACE COLD FRONT TRAILING FROM THE LOW DEPARTING TO OUR NORTHEAST. A FEW LIGHT SNOW SHOWERS COULD LINGER INTO SATURDAY NIGHT AS WEAK UPPER TROUGH COMPLETES ITS TRANSIT. FARTHER NORTH...A DEEP UPPER TROUGH/CLOSED LOW DEVELOPS OVER CENTRAL CANADA AND DIGS SOUTHEAST ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION SATURDAY NIGHT THROUGH MONDAY. THIS LEADS TO THE DEVELOPMENT OF A LARGE AMPLITUDE EASTERN NORTH AMERICAN UPPER TROUGH AND A QUICK TRANSITION TO SIGNIFICANTLY COLDER WEATHER SUNDAY INTO NEXT WEEK AS 850 MB TEMPS DROP TO AROUND -20C MONDAY. DURING THAT PERIOD HIGHS WILL LIKELY STRUGGLE TO RISE OUT OF THE TEENS DURING THE DAY...WITH LOWS IN THE SINGLE DIGITS ACROSS MUCH OF THE FORECAST AREA. RATZER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * BRIEF WINDOW OF MVFR THROUGH AFTERNOON. BMD //DISCUSSION...UPDATED 20Z... AFTERNOON CUMULUS BECAME A LITTLE MORE WIDESPREAD THAN PREVIOUSLY EXPECTED RESULTING IN SOME BKN HIGH END MVFR CIGS MOVING INTO THE CHICAGO AREA. STILL ANTICIPATE IMPROVEMENT AROUND SUNSET THIS EVENING. PREVIOUS DISCUSSION...18Z... QUIET WEATHER ON TAP FOR THE TERMINALS THROUGH THE FORECAST PERIOD. HIGH PRESSURE IS CENTERED NEAR THE UPPER OHIO VALLEY THIS AFTERNOON RESULTING IN MODEST SOUTH-SOUTHWEST FLOW ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA. OCCASIONAL GUSTS INTO THE MID TO HIGH TEENS ARE EXPECTED THROUGH THE AFTERNOON AND SHOULD TAPER WITH SUNSET. ALSO CANNOT RULE OUT FEW/SCT CUMULUS 020-025 DEVELOPING THIS AFTERNOON...AND ALSO DISSIPATING WITH SUNSET. HIGH AND MID LEVEL CLOUD COVER WILL INCREASE THIS EVENING AND TONIGHT. EXPECT VFR CONDITIONS THROUGH THE PERIOD. BMD //ORD AND MDW CONFIDENCE...UPDATED 20Z... * HIGH. BMD //OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z... WEDNESDAY NIGHT...CHANCE OF WINTRY MIX OF PCPN TOWARD DAYBREAK. CIG/VIS BECMG MVFR LATE NIGHT. THURSDAY....WINTRY MIX OF PCPN EARLY CHANGING OVER TO RAIN AND/OR DRIZZLE IN THE AFTERNOON AND CONTINUING THROUGH THE NIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. FRIDAY...RAIN/DRIZZLE LIKELY THROUGH THE DAY AND CONTINUING OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SATURDAY...CHANCE OF RAIN OR SNOW THROUGH THE DAY...CHANGING OVER TO SNOW OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SUNDAY...CHANCE OF LINGERING LIGHT SNOW MORNING. MVFR CIG/VIS POSSIBLE MORNING. OTRW...VFR/WX NIL. MONDAY...VFR/WX NIL. KREIN && .MARINE... 234 PM CST MAIN MARINE FORECAST CONCERN IS THE SOUTHWESTERLY GALES OCCURRING ON THE NORTHERN PORTION OF THE LAKE THIS AFTERNOON THROUGH EARLY WEDNESDAY MORNING. GRADIENT HAS TIGHTENED ACROSS THE NORTHERN LAKES TODAY BETWEEN HIGH PRESSURE ALONG THE EAST COAST...AND AN AREA OF LOW PRESSURE MOVING ACROSS HUDSON BAY. SEVERAL SHORE SITES REPORTING 30+ KTS AS OF 2 PM CST...WITH PORT INLAND ALONG THE NORTH SHORE CURRENTLY REPORTING 35 KT GALES. GALES ARE EXPECTED TO CONTINUE THROUGH THIS EVENING...THOUGH FORECAST MODELS HAVE TRENDED TOWARD WINDS DECREASING A LITTLE SOONER PRE-DAWN WEDNESDAY MORNING...AND HAVE MOVED UP THE END OF THE GALE WARNING TO 3 AM CST. OTHERWISE...THE GRADIENT LOOKS TO WEAKEN MORE SUBSTANTIALLY DURING THE DAY WEDNESDAY...AS A WEAK AREA OF LOW PRESSURE MOVES INTO THE UPPER MIDWEST. SOUTH WINDS WILL BEGIN TO BACK TO THE SOUTHEAST-EAST THURSDAY NIGHT AND FRIDAY...AS ANOTHER DEEPER LOW LIFTS TOWARD THE WESTERN LAKES AND EVENTUALLY PASSES ACROSS LAKE MICHIGAN FRIDAY NIGHT. STRONG ARCTIC HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST LATE IN THE PERIOD...WITH WEST-NORTHWEST WINDS PICKING UP AND TEMPERATURES PLUMMETING SUNDAY INTO EARLY NEXT WEEK. FOR THE ILLINOIS AND INDIANA NEARSHORE WATERS...SOUTHWEST WINDS OCCASIONALLY GUSTING 20 KTS OR A LITTLE HIGHER THIS AFTERNOON. WINDS WILL GRADUALLY DIMINISH TO LESS THAN 20 KT LATER TONIGHT. RATZER && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
214 PM CST TUE JAN 5 2016 .UPDATE... 1128 AM CST NO SIGNIFICANT CHANGES TO GOING FORECAST. PRIMARY TWEAK WAS TO ADJUST HIGH TEMPERATURES UP A DEGREE OR TWO TOWARD BUT NOT AS WARM AS MAV/LAV GUIDANCE. THIS YIELDS HIGHS IN THE LOWER 30S NORTH OF I-88 WHERE THE DEEPER SLEET COVER IS AND GENERALLY MID 30S SOUTH OF I-88. AIRCRAFT SOUNDINGS AND RAP/HRRR FORECAST SOUNDINGS SUGGEST MIXING SHOULD TOP OUT AROUND 900 MB TODAY...AND MIXING DOWN FROM THIS LEVEL SUPPORTS AT LEAST TEMPS AS WARM AS FORECAST HIGHS. A FEW UPPER 30S ARE POSSIBLE IN CENTRAL ILLINOIS COUNTIES...BUT CONSIDERING THAT THERE IS STILL SLEET COVER ACROSS THE AREA...UPPER 30S READINGS SHOULD BE LOCALIZED. HIGH CLOUDS WILL GRADUALLY INCREASE AS A WEAK UPPER DISTURBANCE MOVES ACROSS THE AREA. PRESSURE GRADIENT ON BACK SIDE OF EXPANSIVE HIGH PRESSURE TO THE EAST AND WEAK LOW PRESSURE OVER THE HIGH PLAINS WILL SUPPORT SOUTH TO SOUTH-SOUTHWEST WINDS 10-15 MPH WITH OCCASIONAL GUSTS IN THE 15-20 MPH RANGE. RC && .SHORT TERM... 305 AM CST THROUGH WEDNESDAY... A QUIET FIRST 36 HOURS OF THE FORECAST WITH THE ACTION ALL WEDNESDAY NIGHT AND BEYOND. CONCERNS REMAIN ON LIGHT FREEZING PRECIPITATION AND/OR SNOW LATE WEDNESDAY NIGHT AND THURSDAY MORNING. ANY CHANGES TO THIS PART OF THE FORECAST HAVE BEEN MAINLY TWEAKS AND REFINING AREA...WITH STILL MORE OF AN EMPHASIS IN CHANCES/DURATION IN NORTH CENTRAL ILLINOIS. STOUT CANADIAN HIGH PRESSURE OF 1038MB CENTERED OVER THE EASTERN GREAT LAKES WILL EASE EASTWARD TODAY WITH ITS BACKSIDE SOUTHERLY WINDS HAVING ALREADY OUSTED THE STRATOCUMULUS. PATCHES OF HIGH CLOUDS WILL DRIFT OVER TODAY AS A LOW AMPLITUDE UPPER RIDGE ALSO MOVES ON EAST. HIGHS ARE EXPECTED TO BE RIGHT AROUND NORMAL. A LIGHT SOUTHERLY WIND WILL ALLOW TEMPERATURES TO BE A TAD MILDER TONIGHT. CLOUDS SHOULD THICKEN MORE ON WEDNESDAY BUT A MODIFYING LOWER ATMOSPHERE SHOULD SUPPORT MID 30S IN THE NORTHERN SNOW COVERED AREAS TO UPPER 30S IN THE SOUTH. WITH TEMPERATURES NOT FAR ABOVE FREEZING IN NORTH CENTRAL ILLINOIS...THIS AREA WILL BE MOST FAVORED TO DIP BELOW FREEZING PRIOR TO PRECIPITATION CHANCES LATER THAT NIGHT. MTF && .LONG TERM... 213 PM CST WEDNESDAY NIGHT THROUGH TUESDAY... THE EXTENDED PERIOD LOOKS TO BE QUITE ACTIVE...WITH SEVERAL PRECIPITATION-PRODUCING SYSTEMS INTO THE WEEKEND AND THEN AN INTRUSION OF COLD ARCTIC AIR SUNDAY INTO NEXT WEEK. THE FIRST SYSTEM TO AFFECT THE REGION WILL BE A RELATIVELY MINOR AMPLITUDE SHORT WAVE TROUGH WHICH WILL LIFT NORTHEAST ACROSS THE FORECAST AREA WEDNESDAY NIGHT. DESPITE SOUTH-SOUHTWEST LOW LEVEL WINDS...FORECAST SOUNDINGS INDICATE THAT THESE LAYERS ARE INITIALLY QUITE DRY...WITH RETURN OF GULF MOISTURE BLOCKED BY EXPANSIVE SURFACE HIGH PRESSSURE RIDGE AXIS WHICH EXTENDS FROM THE MID-ATLANTIC BACK ACROSS THE GULF COAST STATES INTO TEXAS. LOW LEVEL MOISTURE DOES BEGIN TO FLOW NORTH-NORTHEASTWARD AROUND THE WESTERN PERIPHERY OF THE HIGH...THOUGH IT APPEARS TO LAG THE BETTER FORCING WITH THE INITIAL WEAKENING SHORT WAVE. MODELS HAVE GENERALLY TRENDED SLOWER WITH LIGHT QPF PRIMARILY JUST OFF TO THE WEST OF THE CWA THROUGH 12Z THURSDAY MORNING. WHILE THE INITIAL SHORT WAVE PULLS AWAY TO THE NORTHEAST EARLY THURSDAY...GUIDANCE DOES EVENTUALLY SPREAD LIGHT QPF INTO THE CWA DURING THE DAY PRIMARILY IN THE WEST/SOUTHWEST AS PERSISTENT 20-25 KT SOUTHWEST WINDS RESULT IN WEAK BUT PERSISTENT ISENTROPIC ASECNT WHICH CONTINUES TO WORK TO SATURATE THE LOW LEVELS FROM THE TOP DOWN. WHILE PRECIPITATION IS EXPECTED TO BE LIGHT...P-TYPE IS A CONCERN AS SURFACE TEMPERATURES ARE EXPECTED TO BE NEAR FREEZING LATE WEDNESDAY NIGHT/EARLY THURSDAY MORNING...AND THIS COMBINED WITH INITIALLY DRY LOW LEVELS (AND WET-BULB COOLING IMPLICATIONS) WOULD SUPPORT A FROZEN OR FREEZING P-TYPE MIX OF SLEET/SNOW/FREEZING RAIN INTO THURSDAY MORNING BEFORE PERISTENT WARM/MOIST ADVECTION WARMS THE COLUMN AND RAISES SURFACE TEMPERATURES ABOVE FREEZING FROM SOUTH TO NORTH THROUGH MID-DAY/EARLY AFTERNOON. LIGHT QPF IMPLIES MINIMAL SLEET/SNOW ACCUMULATION POTENTIAL...THOUGH ANY LIGHT FREEZING RAIN COULD CAUSE SOME LIGHT GLAZING MAINLY ON ELEVATED SURFACES AND THIN/UNTREATED PAVEMENT SUCH AS SIDEWALKS... DRIVEWAYS AND SOME PARKING LOTS. WEAKENING DEEP LAYER FORCING BEHIND DEPARTING SHORT WAVE SHOULD ALLOW PRECIP TO TRANSITION MAINLY TO A LIGHT RAIN/DRIZZLE WITH TEMPS ABOVE FREEZING THURSDAY AFTERNOON AND HIGHS FROM THE MID-30S NORTH TO THE LOW 40S FAR SOUTH. ATTENTION THEN TURNS BACK TO THE SOUTHWEST...AND TO A STRONGER MID-LEVEL SHORT WAVE DEVELOPING OVER THE SOUTH-CENTRAL PLAINS WITH A CLOSED 500 MB CENTER WHICH LIFTS NORTHEAST INTO THE MID- MISSISSIPPI VALLEY BY FRIDAY MORNING AND ACROSS THE FORECAST AREA ON FRIDAY. RENEWED AND STRONGER DEEP FORCING FOR ASCENT ATOP NOW SATURATED LOW-MID LEVELS IS EXPECTED TO PRODUCE AN AREA OF MORE WIDESPREAD LIGHT-MODERATE RAIN ACROSS THE CWA THURSDAY NIGHT INTO FRIDAY AS THE SHORT WAVE AND ITS ASSOCIATED SURFACE LOW APPROACH AND TRANSIT THE AREA. P-TYPE EXPECTED TO BE ALL RAIN AT THIS TIME...WITH SURFACE TEMPS ABOVE FREEZING AND LOWER PORTION OF FORECAST SOUNDINGS SATURATED AND WARMER THAN 0C. SOME DIFFERENCES IN THE MODEL DETAILS REMAIN DURING THIS PERIOD...THOUGH THERE IS GENERAL OVERALL AGREEMENT IN RAIN AMOUNTS UP AROUND A HALF INCH OR SO ESPECIALLY ACROSS THE WESTERN PARTS OF THE CWA CLOSER TO THE EXPECTED MID-LEVEL CIRCULATION TRACK. IT SHOULD BE NOTED THAT THIS TRACK MAY SHIFT AS THIS IS STILL DAY 4 OF THE FORECAST WHERE MODELS STILL SHOW SOME VARIATION. PRECIP INTENSITY WILL LIKELY DIMINISH TO DRIZZLE/LIGHT RAIN AGAIN FRIDAY AFTERNOON AS THE MID- LEVEL WAVE AND SURFACE LOW EVENTUALLY LIFT NORTHEAST OF THE CWA. LIGHT RAIN/DRIZZLE MAY CONTINUE FRIDAY NIGHT AS ANOTHER WEAK SHORT WAVE TROUGH TRAVERSES THE REGION...POSSIBLY MIXING WITH OR CHANGING TO SOME LIGHT SNOW OVER NORTHWEST IL AFTER MIDNIGHT AND ACROSS THE AREA SATURDAY AS COLDER AIR STARTS TO FILTER IN BEHIND SURFACE COLD FRONT TRAILING FROM THE LOW DEPARTING TO OUR NORTHEAST. A FEW LIGHT SNOW SHOWERS COULD LINGER INTO SATURDAY NIGHT AS WEAK UPPER TROUGH COMPLETES ITS TRANSIT. FARTHER NORTH...A DEEP UPPER TROUGH/CLOSED LOW DEVELOPS OVER CENTRAL CANADA AND DIGS SOUTHEAST ACROSS THE UPPER MIDWEST AND GREAT LAKES REGION SATURDAY NIGHT THROUGH MONDAY. THIS LEADS TO THE DEVELOPMENT OF A LARGE AMPLITUDE EASTERN NORTH AMERICAN UPPER TROUGH AND A QUICK TRANSITION TO SIGNIFICANTLY COLDER WEATHER SUNDAY INTO NEXT WEEK AS 850 MB TEMPS DROP TO AROUND -20C MONDAY. DURING THAT PERIOD HIGHS WILL LIKELY STRUGGLE TO RISE OUT OF THE TEENS DURING THE DAY...WITH LOWS IN THE SINGLE DIGITS ACROSS MUCH OF THE FORECAST AREA. RATZER && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * BRIEF WINDOW OF MVFR THROUGH AFTERNOON. BMD //DISCUSSION...UPDATED 20Z... AFTERNOON CUMULUS BECAME A LITTLE MORE WIDESPREAD THAN PREVIOUSLY EXPECTED RESULTING IN SOME BKN HIGH END MVFR CIGS MOVING INTO THE CHICAGO AREA. STILL ANTICIPATE IMPROVEMENT AROUND SUNSET THIS EVENING. PREVIOUS DISCUSSION...18Z... QUIET WEATHER ON TAP FOR THE TERMINALS THROUGH THE FORECAST PERIOD. HIGH PRESSURE IS CENTERED NEAR THE UPPER OHIO VALLEY THIS AFTERNOON RESULTING IN MODEST SOUTH-SOUTHWEST FLOW ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA. OCCASIONAL GUSTS INTO THE MID TO HIGH TEENS ARE EXPECTED THROUGH THE AFTERNOON AND SHOULD TAPER WITH SUNSET. ALSO CANNOT RULE OUT FEW/SCT CUMULUS 020-025 DEVELOPING THIS AFTERNOON...AND ALSO DISSIPATING WITH SUNSET. HIGH AND MID LEVEL CLOUD COVER WILL INCREASE THIS EVENING AND TONIGHT. EXPECT VFR CONDITIONS THROUGH THE PERIOD. BMD //ORD AND MDW CONFIDENCE...UPDATED 20Z... * HIGH. BMD //OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z... WEDNESDAY NIGHT...CHANCE OF WINTRY MIX OF PCPN TOWARD DAYBREAK. CIG/VIS BECMG MVFR LATE NIGHT. THURSDAY....WINTRY MIX OF PCPN EARLY CHANGING OVER TO RAIN AND/OR DRIZZLE IN THE AFTERNOON AND CONTINUING THROUGH THE NIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. FRIDAY...RAIN/DRIZZLE LIKELY THROUGH THE DAY AND CONTINUING OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SATURDAY...CHANCE OF RAIN OR SNOW THROUGH THE DAY...CHANGING OVER TO SNOW OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SUNDAY...CHANCE OF LINGERING LIGHT SNOW MORNING. MVFR CIG/VIS POSSIBLE MORNING. OTRW...VFR/WX NIL. MONDAY...VFR/WX NIL. KREIN && .MARINE... 300 AM CST IN THE NEAR TERM...WINDS ARE SHIFT TO SOUTH-SOUTHWEST AS HIGH PRESSURE SAGS SOUTHEAST...EXTENDING FROM SRN QUEBEC THROUGH THE MIDDLE MISSISSIPPI VALLEY AND LOW PRESSURE DEEPENS OVER HUDSON BAY. A STRENGTHENING PRESSURE GRADIENT///STRONGEST OVER THE NORTHERN PORTION OF THE LAKE WILL LEAD TO A PERIOD OF SOUTHWEST GALES ACROSS NORTHERN LAKE MICHIGAN FROM THIS MORNING THROUGH EARLY WEDNESDAY MORNING...BEFORE EASING BACK TO 20-25 KT BY LATER WEDNESDAY. WITH A SLIGHTLY WEAKER GRADIENT OVER THE SOUTHERN PORTIONS OF THE LAKE...WINDS SHOULD REMAIN UNDER GALE FORCE LEVELS. FOR THE NEARSHORE WATERS...WINDS WILL BE OFFSHORE AND WITH WEAK WARM ADVECTION...DO NOT EXPECT STRONGER WINDS TO MIX DOWN TO THE SURFACE UNTIL FLOW REACHES THE OPEN WATERS...SO EXPECT PREVAILING WINDS OVER THE NEARSHORE WATERS TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS. HOWEVER...AN OCCASIONAL GUST TO 25-30KT WILL BE POSSIBLE TOWARD THE NEARSHORE-OPEN WATERS BOUNDARY. LOW PRESSURE WILL EVENTUALLY DEVELOP OVER THE SOUTHERN PLAINS LATE WEDNESDAY NIGHT AND THURSDAY...WHICH WILL LIFT NORTHEAST TO THE WESTERN GREAT LAKES BY LATE FRIDAY. THE LOW IS EXPECTING TO BE IN A WEAKENING PHASE AS IT CROSSES THE SOUTH END OF THE LAKE FRIDAY NIGHT. GUSTY WEST WINDS WILL LIKELY DEVELOP IN THE WAKE OF THE LOW SATURDAY NIGHT AND BEYOND...AS STRONG HIGH PRESSURE AND AN INTRUSION OF COLD ARCTIC AIR SPREAD INTO THE REGION SUNDAY INTO NEXT WEEK. KREIN && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
153 PM CST TUE JAN 5 2016 .UPDATE... 1128 AM CST NO SIGNIFICANT CHANGES TO GOING FORECAST. PRIMARY TWEAK WAS TO ADJUST HIGH TEMPERATURES UP A DEGREE OR TWO TOWARD BUT NOT AS WARM AS MAV/LAV GUIDANCE. THIS YIELDS HIGHS IN THE LOWER 30S NORTH OF I-88 WHERE THE DEEPER SLEET COVER IS AND GENERALLY MID 30S SOUTH OF I-88. AIRCRAFT SOUNDINGS AND RAP/HRRR FORECAST SOUNDINGS SUGGEST MIXING SHOULD TOP OUT AROUND 900 MB TODAY...AND MIXING DOWN FROM THIS LEVEL SUPPORTS AT LEAST TEMPS AS WARM AS FORECAST HIGHS. A FEW UPPER 30S ARE POSSIBLE IN CENTRAL ILLINOIS COUNTIES...BUT CONSIDERING THAT THERE IS STILL SLEET COVER ACROSS THE AREA...UPPER 30S READINGS SHOULD BE LOCALIZED. HIGH CLOUDS WILL GRADUALLY INCREASE AS A WEAK UPPER DISTURBANCE MOVES ACROSS THE AREA. PRESSURE GRADIENT ON BACK SIDE OF EXPANSIVE HIGH PRESSURE TO THE EAST AND WEAK LOW PRESSURE OVER THE HIGH PLAINS WILL SUPPORT SOUTH TO SOUTH-SOUTHWEST WINDS 10-15 MPH WITH OCCASIONAL GUSTS IN THE 15-20 MPH RANGE. RC && .SHORT TERM... 305 AM CST THROUGH WEDNESDAY... A QUIET FIRST 36 HOURS OF THE FORECAST WITH THE ACTION ALL WEDNESDAY NIGHT AND BEYOND. CONCERNS REMAIN ON LIGHT FREEZING PRECIPITATION AND/OR SNOW LATE WEDNESDAY NIGHT AND THURSDAY MORNING. ANY CHANGES TO THIS PART OF THE FORECAST HAVE BEEN MAINLY TWEAKS AND REFINING AREA...WITH STILL MORE OF AN EMPHASIS IN CHANCES/DURATION IN NORTH CENTRAL ILLINOIS. STOUT CANADIAN HIGH PRESSURE OF 1038MB CENTERED OVER THE EASTERN GREAT LAKES WILL EASE EASTWARD TODAY WITH ITS BACKSIDE SOUTHERLY WINDS HAVING ALREADY OUSTED THE STRATOCUMULUS. PATCHES OF HIGH CLOUDS WILL DRIFT OVER TODAY AS A LOW AMPLITUDE UPPER RIDGE ALSO MOVES ON EAST. HIGHS ARE EXPECTED TO BE RIGHT AROUND NORMAL. A LIGHT SOUTHERLY WIND WILL ALLOW TEMPERATURES TO BE A TAD MILDER TONIGHT. CLOUDS SHOULD THICKEN MORE ON WEDNESDAY BUT A MODIFYING LOWER ATMOSPHERE SHOULD SUPPORT MID 30S IN THE NORTHERN SNOW COVERED AREAS TO UPPER 30S IN THE SOUTH. WITH TEMPERATURES NOT FAR ABOVE FREEZING IN NORTH CENTRAL ILLINOIS...THIS AREA WILL BE MOST FAVORED TO DIP BELOW FREEZING PRIOR TO PRECIPITATION CHANCES LATER THAT NIGHT. MTF && .LONG TERM... 305 AM CST WEDNESDAY NIGHT THROUGH MONDAY... AN ACTIVE JET WITH NUMEROUS STORM SYSTEMS OVER THE CENTRAL AND EASTERN NORTH PACIFIC WILL FUNNEL INTO THE WESTERN CONUS DURING THE REMAINDER OF THE WEEK AND EVENTUALLY CARVE OUT A BROAD LONGWAVE TROUGH BY FRIDAY. TWO CORE SHORT WAVE TROUGHS WILL INITIALLY MOVE EASTWARD INTO THE MIDWEST...THE FIRST STILL APPEARING TO MOVE OVER OUR AREA LATE WEDNESDAY NIGHT AND THURSDAY MORNING DAMPENING AS IT DOES...LIKELY DUE TO INFLUENCE OF THE MID- ATLANTIC HIGH. THIS BRINGS THE LIGHT MIXED PRECIPITATION CHANCES. A SECOND SHORT WAVE WITH DEEPER REFLECTION PASSES OVER ON THURSDAY NIGHT INTO FRIDAY BRINGING MORE WIDESPREAD LIQUID PRECIPITATION. GLOBAL GUIDANCE IS IN FAIR AGREEMENT WITH SUCH AN EVOLUTION DURING THIS WEDNESDAY NIGHT THROUGH PERIOD AND HAVE FOLLOWED MORE CLOSELY THAN THE NAM OR SREF AT THIS JUNCTURE. FOR LATE WEDNESDAY NIGHT AND THURSDAY MORNING...LIGHT ADIABATIC OMEGA ON THE SATURATING SURFACES ACROSS THE MID-MISSISSIPPI VALLEY SUPPORTS PATCHY LIGHT PRECIPITATION POSSIBLY MAKING IT INTO NORTH CENTRAL ILLINOIS AS WEDNESDAY NIGHT PROGRESSES AND OVER OTHER PARTS OF THE CWA EARLY THURSDAY MORNING. WARM LAYERS ALOFT ARE FORECAST PRIMARILY BETWEEN 0.5C AND 2.5C...ALLOWING FOR AT THE LEAST PARTIAL MELTING. GIVEN THE LIGHT OMEGA FORECAST AND ASSOCIATED GUIDANCE QPF...FORCING SEEMS LIKE IT MAY NOT BE ENOUGH FOR THINGS TO WET BULB TO SNOW...SO CONTINUE WITH AN INCLUSION OF FREEZING RAIN IN THE FORECAST AS WELL AS POSSIBLY SLEET. AGAIN QPF LOOKS LIGHT SO THE CONCERN WILL BE A LIGHT GLAZE ESPECIALLY IF OVERLAPPING THE THURSDAY MORNING COMMUTE IN SOME AREAS. THE SECOND SHORT WAVE BRINGS BETTER SUPPORT FOR LIFT AND MOISTURE...WITH FAIRLY GOOD 925-700MB MOISTURE CONVERGENCE. SO CONTINUE WITH HIGH POPS THURSDAY NIGHT THROUGH FRIDAY. AT TIMES OMEGA LOOKS LIKE IT DROPS OFF YET STILL A DEEP SATURATED LAYER BELOW ANY ICE...SO MENTION DRIZZLE AS WELL AS RAIN IN THE FORECAST. HAVE RAINFALL VALUES FORECAST FROM A WPC AND WELL VERIFYING MODEL BLEND AND THE MAGNITUDES ARE AROUND ONE HALF INCH AT THIS TIME. AFTER THAT POINT THE PATTERN GETS MESSY FOR SPECIFICS GIVEN THE BROADNESS OF THE UPPER TROUGH IMPINGING INTO THE REGION. THIS WARRANTS QUITE A BIT OF PRECIPITATION CHANCES FRIDAY AND SATURDAY...AND WHILE NOT PRESENTLY MENTIONED THE POSSIBILITY ON SUNDAY AND MONDAY IN A COLD ADVECTION PATTERN IS NOT ZERO. ONE THING THAT IS MORE CONFIDENT IS THAT TEMPERATURES WILL BE TRENDING DOWNWARD AS THE WEEKEND PROGRESSES WITH UPSTREAM COLDER AIR SINKING SOUTHWARD AND ABLE TO BE TAPPED BY NORTHWEST WINDS BEHIND SUCCESSIVE SHORT WAVE TROUGHS. HAVE LEANED TOWARD A QUICKER COOLER SOLUTION ON SATURDAY WITH MORE CHANCES FOR SNOW OR AT LEAST RAIN OR SNOW. ITS A LITTLE MORE MUDDY TO TELL IF SOME MODERATE SNOW CHANCES COULD EXIST SATURDAY OR SATURDAY NIGHT...OR IF IT WILL BE JUST LIGHT. GIVEN THE PLACEMENT BETWEEN INTERACTING JETS...ONE OF WHICH IS A BUCKLING NORTHERN STREAM...CERTAINLY CANNOT RULE IT OUT IN THE REGION. TEMPERATURES VERY WELL COULD FALL DURING ONE OR BOTH DAYS THIS COMING WEEKEND AS THICKNESSES DROP AND LOW-LEVEL NORTHWESTERLY FLOW INCREASES. WHILE OUR CWA MAY LOSE A GOOD PART OF MOST OF ITS SNOW COVER THROUGH THIS WORK WEEK WITH THE RAIN AND TEMPERATURES A HANDFUL OF DEGREES ABOVE FREEZING...THE SNOW PACK WILL BE INTACT IMMEDIATELY UPSTREAM /NORTHWEST/ AND HELP ENSURE THE CANADIAN POLAR AIR MASS IS NOT MODIFIED MUCH AT ALL AS IT EXPANDS INTO THE REGION. THE SIGNAL FOR COLD AIR HAS BEEN THERE AT LEAST SEVERAL DAYS IN THE LONG RANGE GFS AND ECMWF AND SUPPORTED BY CURRENT TELECONNECTIONS SIGNALS...SO LOOKING MORE POSSIBLE THAT THE COLD AIR GETS REINFORCED EARLY NEXT WEEK. PRESENTLY IN THE LONG RANGE DETERMINISTIC FORECAST WE HAVE TEMPERATURES MONDAY MORNING IN THE SINGLE DIGITS IN MANY AREAS WITH WIND CHILLS OF -5 TO -15. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 20Z... * BRIEF WINDOW OF MVFR THROUGH AFTERNOON. BMD //DISCUSSION...UPDATED 20Z... AFTERNOON CUMULUS BECAME A LITTLE MORE WIDESPREAD THAN PREVIOUSLY EXPECTED RESULTING IN SOME BKN HIGH END MVFR CIGS MOVING INTO THE CHICAGO AREA. STILL ANTICIPATE IMPROVEMENT AROUND SUNSET THIS EVENING. PREVIOUS DISCUSSION...18Z... QUIET WEATHER ON TAP FOR THE TERMINALS THROUGH THE FORECAST PERIOD. HIGH PRESSURE IS CENTERED NEAR THE UPPER OHIO VALLEY THIS AFTERNOON RESULTING IN MODEST SOUTH-SOUTHWEST FLOW ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA. OCCASIONAL GUSTS INTO THE MID TO HIGH TEENS ARE EXPECTED THROUGH THE AFTERNOON AND SHOULD TAPER WITH SUNSET. ALSO CANNOT RULE OUT FEW/SCT CUMULUS 020-025 DEVELOPING THIS AFTERNOON...AND ALSO DISSIPATING WITH SUNSET. HIGH AND MID LEVEL CLOUD COVER WILL INCREASE THIS EVENING AND TONIGHT. EXPECT VFR CONDITIONS THROUGH THE PERIOD. BMD //ORD AND MDW CONFIDENCE...UPDATED 20Z... * HIGH. BMD //OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z... WEDNESDAY NIGHT...CHANCE OF WINTRY MIX OF PCPN TOWARD DAYBREAK. CIG/VIS BECMG MVFR LATE NIGHT. THURSDAY....WINTRY MIX OF PCPN EARLY CHANGING OVER TO RAIN AND/OR DRIZZLE IN THE AFTERNOON AND CONTINUING THROUGH THE NIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. FRIDAY...RAIN/DRIZZLE LIKELY THROUGH THE DAY AND CONTINUING OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SATURDAY...CHANCE OF RAIN OR SNOW THROUGH THE DAY...CHANGING OVER TO SNOW OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SUNDAY...CHANCE OF LINGERING LIGHT SNOW MORNING. MVFR CIG/VIS POSSIBLE MORNING. OTRW...VFR/WX NIL. MONDAY...VFR/WX NIL. KREIN && .MARINE... 300 AM CST IN THE NEAR TERM...WINDS ARE SHIFT TO SOUTH-SOUTHWEST AS HIGH PRESSURE SAGS SOUTHEAST...EXTENDING FROM SRN QUEBEC THROUGH THE MIDDLE MISSISSIPPI VALLEY AND LOW PRESSURE DEEPENS OVER HUDSON BAY. A STRENGTHENING PRESSURE GRADIENT///STRONGEST OVER THE NORTHERN PORTION OF THE LAKE WILL LEAD TO A PERIOD OF SOUTHWEST GALES ACROSS NORTHERN LAKE MICHIGAN FROM THIS MORNING THROUGH EARLY WEDNESDAY MORNING...BEFORE EASING BACK TO 20-25 KT BY LATER WEDNESDAY. WITH A SLIGHTLY WEAKER GRADIENT OVER THE SOUTHERN PORTIONS OF THE LAKE...WINDS SHOULD REMAIN UNDER GALE FORCE LEVELS. FOR THE NEARSHORE WATERS...WINDS WILL BE OFFSHORE AND WITH WEAK WARM ADVECTION...DO NOT EXPECT STRONGER WINDS TO MIX DOWN TO THE SURFACE UNTIL FLOW REACHES THE OPEN WATERS...SO EXPECT PREVAILING WINDS OVER THE NEARSHORE WATERS TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS. HOWEVER...AN OCCASIONAL GUST TO 25-30KT WILL BE POSSIBLE TOWARD THE NEARSHORE-OPEN WATERS BOUNDARY. LOW PRESSURE WILL EVENTUALLY DEVELOP OVER THE SOUTHERN PLAINS LATE WEDNESDAY NIGHT AND THURSDAY...WHICH WILL LIFT NORTHEAST TO THE WESTERN GREAT LAKES BY LATE FRIDAY. THE LOW IS EXPECTING TO BE IN A WEAKENING PHASE AS IT CROSSES THE SOUTH END OF THE LAKE FRIDAY NIGHT. GUSTY WEST WINDS WILL LIKELY DEVELOP IN THE WAKE OF THE LOW SATURDAY NIGHT AND BEYOND...AS STRONG HIGH PRESSURE AND AN INTRUSION OF COLD ARCTIC AIR SPREAD INTO THE REGION SUNDAY INTO NEXT WEEK. KREIN && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
AREA FORECAST DISCUSSION
NWS CHICAGO/ROMEOVILLE IL
1128 AM CST TUE JAN 5 2016 .UPDATE... 1128 AM CST NO SIGNIFICANT CHANGES TO GOING FORECAST. PRIMARY TWEAK WAS TO ADJUST HIGH TEMPERATURES UP A DEGREE OR TWO TOWARD BUT NOT AS WARM AS MAV/LAV GUIDANCE. THIS YIELDS HIGHS IN THE LOWER 30S NORTH OF I-88 WHERE THE DEEPER SLEET COVER IS AND GENERALLY MID 30S SOUTH OF I-88. AIRCRAFT SOUNDINGS AND RAP/HRRR FORECAST SOUNDINGS SUGGEST MIXING SHOULD TOP OUT AROUND 900 MB TODAY...AND MIXING DOWN FROM THIS LEVEL SUPPORTS AT LEAST TEMPS AS WARM AS FORECAST HIGHS. A FEW UPPER 30S ARE POSSIBLE IN CENTRAL ILLINOIS COUNTIES...BUT CONSIDERING THAT THERE IS STILL SLEET COVER ACROSS THE AREA...UPPER 30S READINGS SHOULD BE LOCALIZED. HIGH CLOUDS WILL GRADUALLY INCREASE AS A WEAK UPPER DISTURBANCE MOVES ACROSS THE AREA. PRESSURE GRADIENT ON BACK SIDE OF EXPANSIVE HIGH PRESSURE TO THE EAST AND WEAK LOW PRESSURE OVER THE HIGH PLAINS WILL SUPPORT SOUTH TO SOUTH-SOUTHWEST WINDS 10-15 MPH WITH OCCASIONAL GUSTS IN THE 15-20 MPH RANGE. RC && .SHORT TERM... 305 AM CST THROUGH WEDNESDAY... A QUIET FIRST 36 HOURS OF THE FORECAST WITH THE ACTION ALL WEDNESDAY NIGHT AND BEYOND. CONCERNS REMAIN ON LIGHT FREEZING PRECIPITATION AND/OR SNOW LATE WEDNESDAY NIGHT AND THURSDAY MORNING. ANY CHANGES TO THIS PART OF THE FORECAST HAVE BEEN MAINLY TWEAKS AND REFINING AREA...WITH STILL MORE OF AN EMPHASIS IN CHANCES/DURATION IN NORTH CENTRAL ILLINOIS. STOUT CANADIAN HIGH PRESSURE OF 1038MB CENTERED OVER THE EASTERN GREAT LAKES WILL EASE EASTWARD TODAY WITH ITS BACKSIDE SOUTHERLY WINDS HAVING ALREADY OUSTED THE STRATOCUMULUS. PATCHES OF HIGH CLOUDS WILL DRIFT OVER TODAY AS A LOW AMPLITUDE UPPER RIDGE ALSO MOVES ON EAST. HIGHS ARE EXPECTED TO BE RIGHT AROUND NORMAL. A LIGHT SOUTHERLY WIND WILL ALLOW TEMPERATURES TO BE A TAD MILDER TONIGHT. CLOUDS SHOULD THICKEN MORE ON WEDNESDAY BUT A MODIFYING LOWER ATMOSPHERE SHOULD SUPPORT MID 30S IN THE NORTHERN SNOW COVERED AREAS TO UPPER 30S IN THE SOUTH. WITH TEMPERATURES NOT FAR ABOVE FREEZING IN NORTH CENTRAL ILLINOIS...THIS AREA WILL BE MOST FAVORED TO DIP BELOW FREEZING PRIOR TO PRECIPITATION CHANCES LATER THAT NIGHT. MTF && .LONG TERM... 305 AM CST WEDNESDAY NIGHT THROUGH MONDAY... AN ACTIVE JET WITH NUMEROUS STORM SYSTEMS OVER THE CENTRAL AND EASTERN NORTH PACIFIC WILL FUNNEL INTO THE WESTERN CONUS DURING THE REMAINDER OF THE WEEK AND EVENTUALLY CARVE OUT A BROAD LONGWAVE TROUGH BY FRIDAY. TWO CORE SHORT WAVE TROUGHS WILL INITIALLY MOVE EASTWARD INTO THE MIDWEST...THE FIRST STILL APPEARING TO MOVE OVER OUR AREA LATE WEDNESDAY NIGHT AND THURSDAY MORNING DAMPENING AS IT DOES...LIKELY DUE TO INFLUENCE OF THE MID- ATLANTIC HIGH. THIS BRINGS THE LIGHT MIXED PRECIPITATION CHANCES. A SECOND SHORT WAVE WITH DEEPER REFLECTION PASSES OVER ON THURSDAY NIGHT INTO FRIDAY BRINGING MORE WIDESPREAD LIQUID PRECIPITATION. GLOBAL GUIDANCE IS IN FAIR AGREEMENT WITH SUCH AN EVOLUTION DURING THIS WEDNESDAY NIGHT THROUGH PERIOD AND HAVE FOLLOWED MORE CLOSELY THAN THE NAM OR SREF AT THIS JUNCTURE. FOR LATE WEDNESDAY NIGHT AND THURSDAY MORNING...LIGHT ADIABATIC OMEGA ON THE SATURATING SURFACES ACROSS THE MID-MISSISSIPPI VALLEY SUPPORTS PATCHY LIGHT PRECIPITATION POSSIBLY MAKING IT INTO NORTH CENTRAL ILLINOIS AS WEDNESDAY NIGHT PROGRESSES AND OVER OTHER PARTS OF THE CWA EARLY THURSDAY MORNING. WARM LAYERS ALOFT ARE FORECAST PRIMARILY BETWEEN 0.5C AND 2.5C...ALLOWING FOR AT THE LEAST PARTIAL MELTING. GIVEN THE LIGHT OMEGA FORECAST AND ASSOCIATED GUIDANCE QPF...FORCING SEEMS LIKE IT MAY NOT BE ENOUGH FOR THINGS TO WET BULB TO SNOW...SO CONTINUE WITH AN INCLUSION OF FREEZING RAIN IN THE FORECAST AS WELL AS POSSIBLY SLEET. AGAIN QPF LOOKS LIGHT SO THE CONCERN WILL BE A LIGHT GLAZE ESPECIALLY IF OVERLAPPING THE THURSDAY MORNING COMMUTE IN SOME AREAS. THE SECOND SHORT WAVE BRINGS BETTER SUPPORT FOR LIFT AND MOISTURE...WITH FAIRLY GOOD 925-700MB MOISTURE CONVERGENCE. SO CONTINUE WITH HIGH POPS THURSDAY NIGHT THROUGH FRIDAY. AT TIMES OMEGA LOOKS LIKE IT DROPS OFF YET STILL A DEEP SATURATED LAYER BELOW ANY ICE...SO MENTION DRIZZLE AS WELL AS RAIN IN THE FORECAST. HAVE RAINFALL VALUES FORECAST FROM A WPC AND WELL VERIFYING MODEL BLEND AND THE MAGNITUDES ARE AROUND ONE HALF INCH AT THIS TIME. AFTER THAT POINT THE PATTERN GETS MESSY FOR SPECIFICS GIVEN THE BROADNESS OF THE UPPER TROUGH IMPINGING INTO THE REGION. THIS WARRANTS QUITE A BIT OF PRECIPITATION CHANCES FRIDAY AND SATURDAY...AND WHILE NOT PRESENTLY MENTIONED THE POSSIBILITY ON SUNDAY AND MONDAY IN A COLD ADVECTION PATTERN IS NOT ZERO. ONE THING THAT IS MORE CONFIDENT IS THAT TEMPERATURES WILL BE TRENDING DOWNWARD AS THE WEEKEND PROGRESSES WITH UPSTREAM COLDER AIR SINKING SOUTHWARD AND ABLE TO BE TAPPED BY NORTHWEST WINDS BEHIND SUCCESSIVE SHORT WAVE TROUGHS. HAVE LEANED TOWARD A QUICKER COOLER SOLUTION ON SATURDAY WITH MORE CHANCES FOR SNOW OR AT LEAST RAIN OR SNOW. ITS A LITTLE MORE MUDDY TO TELL IF SOME MODERATE SNOW CHANCES COULD EXIST SATURDAY OR SATURDAY NIGHT...OR IF IT WILL BE JUST LIGHT. GIVEN THE PLACEMENT BETWEEN INTERACTING JETS...ONE OF WHICH IS A BUCKLING NORTHERN STREAM...CERTAINLY CANNOT RULE IT OUT IN THE REGION. TEMPERATURES VERY WELL COULD FALL DURING ONE OR BOTH DAYS THIS COMING WEEKEND AS THICKNESSES DROP AND LOW-LEVEL NORTHWESTERLY FLOW INCREASES. WHILE OUR CWA MAY LOSE A GOOD PART OF MOST OF ITS SNOW COVER THROUGH THIS WORK WEEK WITH THE RAIN AND TEMPERATURES A HANDFUL OF DEGREES ABOVE FREEZING...THE SNOW PACK WILL BE INTACT IMMEDIATELY UPSTREAM /NORTHWEST/ AND HELP ENSURE THE CANADIAN POLAR AIR MASS IS NOT MODIFIED MUCH AT ALL AS IT EXPANDS INTO THE REGION. THE SIGNAL FOR COLD AIR HAS BEEN THERE AT LEAST SEVERAL DAYS IN THE LONG RANGE GFS AND ECMWF AND SUPPORTED BY CURRENT TELECONNECTIONS SIGNALS...SO LOOKING MORE POSSIBLE THAT THE COLD AIR GETS REINFORCED EARLY NEXT WEEK. PRESENTLY IN THE LONG RANGE DETERMINISTIC FORECAST WE HAVE TEMPERATURES MONDAY MORNING IN THE SINGLE DIGITS IN MANY AREAS WITH WIND CHILLS OF -5 TO -15. MTF && .AVIATION... //ORD AND MDW CONCERNS...UPDATED 16Z... * SLY-SSWLY WINDS GUSTING TO 16-18 KT. KREIN/DEUBELBEISS //DISCUSSION...UPDATED 12Z... HIGH PRESSURE WILL SLIDE TO THE EAST TODAY WHILE LOW PRESSURE DEVELOPS OVER THE WESTERN PLAINS. SLY WINDS WILL INCREASE THROUGH THE DAY...WHILE VEERING TO SSWLY. SUSTAINED WINDS OF 10-15KT ARE LIKELY BY LATE MORNING WITH GUSTS OF 18-20KT PERSISTING THROUGH LATE AFTERNOON. CONDITIONS WILL BE VFR THROUGH THE PERIOD WITH NO SIG WX OR OPERATIONALLY SIGNIFICANT CLOUD COVER. KREIN //ORD AND MDW CONFIDENCE...UPDATED 16Z... * MEDIUM CONFIDENCE IN MAGNITUDE OF WINDS. * HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS. KREIN/DEUBELBEISS //OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z... WEDNESDAY NIGHT...CHANCE OF WINTRY MIX OF PCPN TOWARD DAYBREAK. CIG/VIS BECMG MVFR LATE NIGHT. THURSDAY....WINTRY MIX OF PCPN EARLY CHANGING OVER TO RAIN AND/OR DRIZZLE IN THE AFTERNOON AND CONTINUING THROUGH THE NIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. FRIDAY...RAIN/DRIZZLE LIKELY THROUGH THE DAY AND CONTINUING OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SATURDAY...CHANCE OF RAIN OR SNOW THROUGH THE DAY...CHANGING OVER TO SNOW OVERNIGHT. MVFR CIG/VIS LIKELY...IFR CONDITIONS POSSIBLE. SUNDAY...CHANCE OF LINGERING LIGHT SNOW MORNING. MVFR CIG/VIS POSSIBLE MORNING. OTRW...VFR/WX NIL. MONDAY...VFR/WX NIL. KREIN && .MARINE... 300 AM CST IN THE NEAR TERM...WINDS ARE SHIFT TO SOUTH-SOUTHWEST AS HIGH PRESSURE SAGS SOUTHEAST...EXTENDING FROM SRN QUEBEC THROUGH THE MIDDLE MISSISSIPPI VALLEY AND LOW PRESSURE DEEPENS OVER HUDSON BAY. A STRENGTHENING PRESSURE GRADIENT///STRONGEST OVER THE NORTHERN PORTION OF THE LAKE WILL LEAD TO A PERIOD OF SOUTHWEST GALES ACROSS NORTHERN LAKE MICHIGAN FROM THIS MORNING THROUGH EARLY WEDNESDAY MORNING...BEFORE EASING BACK TO 20-25 KT BY LATER WEDNESDAY. WITH A SLIGHTLY WEAKER GRADIENT OVER THE SOUTHERN PORTIONS OF THE LAKE...WINDS SHOULD REMAIN UNDER GALE FORCE LEVELS. FOR THE NEARSHORE WATERS...WINDS WILL BE OFFSHORE AND WITH WEAK WARM ADVECTION...DO NOT EXPECT STRONGER WINDS TO MIX DOWN TO THE SURFACE UNTIL FLOW REACHES THE OPEN WATERS...SO EXPECT PREVAILING WINDS OVER THE NEARSHORE WATERS TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS. HOWEVER...AN OCCASIONAL GUST TO 25-30KT WILL BE POSSIBLE TOWARD THE NEARSHORE-OPEN WATERS BOUNDARY. LOW PRESSURE WILL EVENTUALLY DEVELOP OVER THE SOUTHERN PLAINS LATE WEDNESDAY NIGHT AND THURSDAY...WHICH WILL LIFT NORTHEAST TO THE WESTERN GREAT LAKES BY LATE FRIDAY. THE LOW IS EXPECTING TO BE IN A WEAKENING PHASE AS IT CROSSES THE SOUTH END OF THE LAKE FRIDAY NIGHT. GUSTY WEST WINDS WILL LIKELY DEVELOP IN THE WAKE OF THE LOW SATURDAY NIGHT AND BEYOND...AS STRONG HIGH PRESSURE AND AN INTRUSION OF COLD ARCTIC AIR SPREAD INTO THE REGION SUNDAY INTO NEXT WEEK. KREIN && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO