Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/24/16


Area Forecast Discussion
National Weather Service Grand Rapids MI
917 PM EST Fri Dec 23 2016 LATEST UPDATE... Update .SYNOPSIS... Issued at 320 PM EST Fri Dec 23 2016 Precipitation will move through the area overnight, consisting primarily of snow from the I-96 vicinity north. Farther south towards I-94 and southeast towards Lansing, a wintry mix with rain is expected which will greatly reduce snow accumulations. Another system will bring primarily rain to the area Christmas night into Sunday. Christmas Day could be foggy ahead of this system as more humid air moves into the area and across snow covered areas. After highs approach 50 on Monday, temperatures will return to much more seasonal readings into the middle of next week. && .UPDATE... Issued at 917 PM EST Fri Dec 23 2016 Made a few tweaks to the weather and POP grids. Current obs and radar trends show the rain/snow line across roughly the I-96 corridor. GRR has been going back and forth the past hour. Will have snow as p type across the northern half of the forecast area with a rain snow mix across the southern half. Temperatures and dew points where rain is mixing in are high enough to avoid the mention of freezing rain, but we will have to watch this. Also ended the precip earlier than previous forecast based on latest hi-res models and radar trends. Will have it all done before 12Z Saturday. && .SHORT TERM...(This evening through Sunday night) Issued at 320 PM EST Fri Dec 23 2016 No significant changes to previous thinking in the update with minimal impacts anticipated. Dry slot is starting to fill in thanks to deeper convection developing over IA into IL. ACARS soundings upstream reflect a fairly strong warm layer, but air is quite dry and wet bulb cooling should help reduce temperatures fairly rapidly. Models have been quite consistent with respect to total accumulations which boosts forecast certainty. We are concerned about fog on Christmas Day as dewpoints climb above freezing with residual snowpack. This could be somewhat hazardous with rapid visibility changes possible for drivers passing open fields. Leading edge of precipitation could be freezing rain due to wet bulb cooling and initial lack of deep saturation. However, ice accumulations should be negligible and short lived however before heavier precipitation arrives as rain. .LONG TERM...(Monday through Friday) Issued at 320 PM EST Fri Dec 23 2016 Rain showers associated with the big storm over the Plains will be exiting the cwa Monday morning. Colder air will flow back over the cwa. High temperatures Tuesday will be 20 degrees colder than those on Monday. However, the air won`t be quite cold enough for significant lake effect snow. As a result, only isolated to scattered snow showers are expected Tuesday. A trough moving across the upper Midwest will likely generate some light snow Wednesday night-Thursday night. The snow may mix with and/or change to rain south of I-96 Thursday afternoon before changing back to snow late Thursday. A surge of colder air will likely result in snow showers Thursday night into Friday as high temperatures Friday remain in the 20s. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 645 PM EST Fri Dec 23 2016 Snow will bring widespread IFR conditions overnight with conditions becoming MVFR on Saturday morning and into the afternoon. Southeast winds aob 10 knots will go west by 12Z Saturday. && .MARINE... Issued at 320 PM EST Fri Dec 23 2016 No changes planned. Current SCA headlines for the overnight hours look on track, but evening shift may elect to fine tune expiration times with new guidance. Christmas Day will likely have substantial fog in addition to strengthening offshore winds. && .HYDROLOGY... Issued at 1211 PM EST Fri Dec 23 2016 Little has changed in the last 24 hours with respect to short term concerns. The long term looks increasingly more active with several waves of precipitation, varying in duration and magnitude. After coordination with the River Forecast Center this morning, we decided to cover expected river rises with a statement (RVS). At this time Sycamore Creek, the Looking Glass River and the Maple River all head near or above advisory levels. Crests are forecast to occur Monday into Tuesday. Confidence is low, but the statement at least raises awareness through the holiday weekend and mitigate any surprises early next week. Thoughts from yesterday concerning warm ground temperatures and gradual snowmelt are still in play. That has not changed. The key factor therein lies the amount of liquid precip and pace of snowmelt late Sunday into Monday. Once temperatures fall back below freezing next week, it is likely to slow/halt runoff. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Small Craft Advisory until 7 AM EST Saturday for LMZ845>849. && $$ UPDATE...Ostuno SYNOPSIS...TJT SHORT TERM...TJT LONG TERM...04 AVIATION...Ostuno HYDROLOGY...JAM MARINE...TJT
AREA FORECAST DISCUSSION
National Weather Service Northern Indiana
840 PM EST Fri Dec 23 2016 .SYNOPSIS... Issued at 354 PM EST Fri Dec 23 2016 Pockets of light rain will give way to areas of drizzle overnight. A second storm system will bring a slight chance of drizzle or freezing drizzle with areas of fog early Christmas morning followed by warmer temperatures and rain Sunday afternoon through Monday. && .UPDATE... Issued at 838 PM EST Fri Dec 23 2016 00Z DTX/ILX raobs illustrate rapid saturation ongoing across the area this evening. Continued strong warm advection resulting in primarily rain and expected so going forward especially as vigorous mid level dryslot spreads ewd out of IL. Prior fcst snow accums were drastically cut north and eliminated south as upstream observational trends and radar indicate drizzle will become the dominant precip type behind current arc of shra moving through. However no problems expected as surface temps remain above freezing tonight. && .SHORT TERM...(This Evening through Saturday) Issued at 355 PM EST Fri Dec 23 2016 Recent aircraft soundings continue to indicate a very dry layer under 700 mb. Precipitation was having a hard time reaching the ground through mid afternoon, although some very light snow was reported west of Chicago and light drizzle or rain near Monticello. Given forecast wet bulb temperatures and dynamic cooling, will continue to maintain light snow accumulations, mainly north of highway 6 as the upper level system moves across the area. Otherwise, travel impacts appear marginal with surface temperatures falling to near freezing tonight. There could be some icy spots where rain or melted snow freezes overnight. Skies should stay cloudy to mostly cloudy Saturday with light winds. && .LONG TERM...(Saturday Night through Friday) Issued at 355 PM EST Fri Dec 23 2016 An intense upper low and associated winter storm will be moving across the Dakotas Sunday night. An occluding front with a surge of moisture well ahead of this system will bring a variety of weather to the forecast area late Saturday night into Monday. A cool east flow Saturday night along with a significant low level inversion should cause areas of fog to form. Patchy drizzle and freezing drizzle area possible. The increasing moisture over snow covered areas should help the fog to persist through Sunday night. Highs Monday should be close to the relatively cool record high of 54 degrees at Ft Wayne. All of the precipitation should fall as rain Sunday night and Monday given low level temps near 10C and surface temperatures well above freezing. Hydrologic issues appear to be limited given rainfall less than a half an inch and snow water equivalents between 0.5 and 1.0. Another system will bring a chance for a rain/snow mix during the middle of the week. && .AVIATION...(For the 00Z TAFS through 00Z Saturday Evening) Issued at 644 PM EST Fri Dec 23 2016 Sw disturbance over sw WI will continue newd through nrn lower MI overnight. Fairly vigorous downstream low level warm advection underway attm although boundary layer moisture lags. As such general light rain as unfolded within warm sector and expected to predominate this evening as both forcing and best low level moisture flux strips off to the east after midnight. Otherwise shallow cold advection wing wraps in late tonight and looks to effective cap a saturated boundary layer in place on Sat with low ifr based cloud cigs as a result. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...NONE. && $$ UPDATE...T SYNOPSIS...JT/Skipper SHORT TERM...Skipper LONG TERM...Skipper AVIATION...T Visit us at www.weather.gov/iwx Follow us on Facebook...Twitter...and YouTube at: www.facebook.com/NWSNorthernIndiana www.twitter.com/nwsiwx www.youtube.com/NWSNorthernIndiana
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
921 PM CST Fri Dec 23 2016 .UPDATE... 921 PM CST Snow banding that has mainly affected far northern Illinois will be coming to end within the next hour or so. Earlier there were occasional moderate/heavy rates and enough to produce accumulations of 1 to locally 2 inches near the Wisconsin border. Precipitation over next few hours for the rest of the area is either brief light rain or patchy drizzle. Extensive stratus deck and very minimal cool advection behind cold front passage tonight means that temperatures will basically flatline from current readings. With a saturated boundary layer or minimal dewpoint depressions at most, have maintained patchy fog through much of Saturday morning. Will need to monitor for dense fog development, particularly over deeper snow cover areas in Illinois once winds drop off toward daybreak, but do not yet have enough confidence to add it into grids. With temperatures in some areas at or just above freezing, cannot rule out isolated slick spots on less traveled roads, elevated surfaces and parking lots/sidewalks overnight into Saturday morning. Based on current trends with stratus deck on fog product satellite and light northwest low level flow turning nil Saturday with a strengthening inversion developing, have increasing confidence that we`ll be socked in with low clouds the rest of the weekend. So temperatures likely won`t change all that much overall from current levels until warm front passage later Sunday. Have reduced diurnal temperature change from previous forecast to trend forecast in that direction. Finally, forecast soundings on Saturday night suggest that moisture depth will be quite shallow and likely not conducive to drizzle formation, casting doubt on small drizzle and freezing drizzle potential mentioned in grids. Did not remove drizzle from forecast, but will brief incoming shift on these concerns. Castro && .SHORT TERM... 139 PM CST Through Saturday... KLOT Radar confirms we are still contending with some dry air locally, but we are seeing some lighter to moderate precipitation at times in a more convective looking nature, some rain...some snow...possibly some sleet. Forcing is increasing ahead of the next more potent shortwave entering KS/NE and some lead energy ahead of that to provide our lift later this afternoon and evening. Amdar soundings this afternoon do depict dry air below 800 mb but these are down from earlier. Wet bulb zero heights are also only about 1000 ft, mainly due to the low level warmer surface conditions. Period of best forcing is 3 pm till about 8 pm or so, where accums seem on track for north central Illinois. Forecast soundings now with the slightly lower wet bulb zero heights suggest that snow will largely be the dominant precipitation type during the peak forcing period, albeit with some initial rain or sleet possible. If forcing is strong enough, for more than just brief periods of time, some slushy wet light accums can be expected elsewhere mainly north of the interstate 80 corridor during the wet moderate snowfall at times, but pavement temps above freezing too in these areas so these may be limited to the grass and elevated surfaces too. Regardless, it should be a bit messy for a few hours later today. Rain is favored for areas well south and east. We transition to a drizzle later this evening, getting back below or near freezing overnight when precipitation is largely ending. Could be a brief window of FZDZ but pavement temps are near or above freezing as well. Fairly benign weather is expected on Saturday with high pressure centered over the Ohio valley and extending northwest to our area. Temperatures will hold largely above freezing in 30s to possibly near 40 in the south. Continued low level warm advection will keep a strong temperature inversion, and will lock any low level clouds in place for much of the day. We could see some breaks, especially north. KMD && .LONG TERM... 238 PM CST Saturday night through Friday... Main concerns in the extended are drizzle/freezing drizzle late Saturday night into Sunday morning and then another period of precip mid to late next week. Freezing drizzle is still expected to form Saturday night into Christmas morning. Temperatures will range from around freezing south of I-80 to below freezing everywhere else so a glaze is likely on elevated surfaces. Slick spots are possible Christmas morning especially on bridges and overpasses. Confidence is medium in freezing drizzle coverage and how much of a glaze will form on roads so no headlines are expected at this time. Areas of fog are also possible as warm, moist air will be moving in. The next low takes shape Sunday over the plains with warm air advection continuing through the day. High temps will range from around 40 along the IL/WI state line to near 50 well south of I-80. Debated raising temps even further, but am unsure how well the warmer air will warm the surface given foggy and drizzly conditions. Rain continues Sunday night and shifts east of the forecast area Monday. Monday`s high temps will occur around midnight because temps will slowly fall throughout the day behind the low`s cold front. Drier and more seasonal temps return with lows in the low to mid 20s Monday night. High pressure scoots over the region Tuesday, and the upper level ridge rolls overhead Wednesday. Highs on Wed will be in the mid to upper 30s. Guidance then differs with the upper level trough and surface low mid and late next week. The ECMWF`s trough is further south and has more precip. Kept a slight chance to chance of precip through Thursday given the differences. Lows will dip below freezing so precip types change from rain to snow in response to the surface temps. We remain under the upper level low through the end of the week. Lake effect precip may persist into Friday morning, but otherwise, conditions look quiet with seasonal temps. JEE && .AVIATION... For the 00Z TAFs... Challenging aviation forecast all around. First, should be a lull in the steadier precip to start the TAF cycle with perhaps just some drizzle or light fog/mist. Narrow (but long) ENE-WSW oriented band of precip northwest of the Chicago terminals seems likely to remain NW of Chicago with just some isolated snow showers south of the band this evening. At RFD, this band looks to have a good shop of lasting for several hours this evening with periodic bursts of moderate snow possible, before snow ends there later this evening. South of the steadier snow band, CIGS have been slow to drop thus far and with precip intensity easing up, confidence is lower in IFR CIGS quickly developing this evening. Have pushed back the onset of IFR CIGS several hours, but confidence is low and cannot rule out an earlier arrival. Will continue to closely monitor trends this evening and amend when/if needed. Later tonight into Saturday, most guidance shows skies clearing out Saturday, however if stratus does develop as expected tonight, climo/pattern recognition would suggest it likely persisting with MVFR CIGS through the day Saturday. Confidence is low in CIGS forecast later tonight and beyond, but opted to maintain persistence from previous forecast which would fit conceptual model. Izzi && .MARINE... 238 PM CST South to southwest veer to northwest overnight as a cold front passes over the lake. High pressure moves over the lake Saturday and winds become east behind it. A strong low develops over the plains Sunday and lifts north through Sunday night. It still looks like a small craft advisory and gale headline will be needed as southeast winds increase. The low passes over Ontario Monday and another round of southwest gales is possible Monday mainly over the northern half of the lake. Still too far out to issue a watch. High pressure follows the low mid week as does another low pressure trough. Persistent west to northwest winds are forecast from Wed night through Fri. JEE && .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