Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/20/22

Area Forecast Discussion
National Weather Service Louisville KY
909 PM EST Wed Jan 19 2022 .Forecast Update... Issued at 855 PM EST Wed Jan 19 2022 Well...Arctic front just passed thru SDF...and latest AMDAR sounding (SDF to MDW) from 0054z has big dry layer 900 mb to 720 mb. This corresponds well with mid deck cloud ceilings from MDH thru EVV and up to HNB. This area has much limited precip shield and pireps have been reporting lgt to mdt chop in this area. Meanwhile further south a large rain shield is along and south of the parkways. Cold front pushing east and the precip shield from W KY with strong nw winds pushing it east. There is a brief thin area of sleet from Butler, Warren, and Grayson counties on dual pol and wx reports. This transition will not last long, before turning over to all snow in next 90 min. Between 930 est and 2 am...there will be the 4 to 5 hour of accumulating snow between the parkways. Still like 1 to 3 in this area. Further north we are contemplating on how to handle areas along and north of the Ohio River in S IN. This just in...light snow at the NWS office and temps have dropped 5 degrees in last 2 hrs. && .Short Term...(Tonight through Thursday evening) Issued at 249 PM EST Wed Jan 19 2022 ...Accumulating Snow Still Expected Tonight... By 00Z the cold front will be just exiting the southeast corner of the LMK CWA in the Lake Cumberland region, ushering in much colder air. Patchy light rain has developed along and ahead of the front from Kentucky to Texas, with light snow behind the boundary over the Midwest. As cold air pours into the region, light rain this afternoon will transition to snow this evening into the late night hours. A wintry mix is possible during the transition, but should be fairly quick as the cold air pushes in...likely less than two hours at any one spot. The snow and the cold are the larger stories for tonight. Snow will fall tonight as the upper trough axis remains off to our west this evening and a 5H speed max swings into the Tennessee Valley late tonight. Cross-sections and soundings show high RH in the DGZ. There is also some negative EPV present but it is quite weak, and theta-e surfaces show little if any instability. Mid-level frontogenesis is much weaker than what we saw with the January 6 event and moves through more quickly. So, a broad area of light snow is expected, with possibly some embedded moderately enhanced bands of snowfall. HREF shows only a very small chance of snowfall rates exceeding an inch per hour, and only for a couple of hours late tonight. The most likely area to be affected by any locally higher snowfalls would be the southern Blue Grass, generally from the Lebanon and Danville areas ENE into eastern Kentucky. Will still go with general amounts of 1-3" in the advisory area, with perhaps 2-4" in the Blue Grass. Unfortunately confidence in snowfall totals has actually decreased today, with some data sources coming in with lesser amounts of snow. WPC Super Ensemble at Lexington shows a mean of 1.5" and almost all members are below 3.5". However, WSSI does still support advisory- level snow and there is enough support in the data to stick with the higher amounts we had been advertising previously. In addition, winds behind the front will become gusty tonight, with gusts of 20-25mph possible (gusts over 30 mph have been observed upstream). For anyone out on the roads tonight (which is not recommended) this will add to the difficult conditions in driving snow. Wind chills will fall into the 5-15 degree range by morning. Road surface temperatures are expected to fall below freezing around midnight, and air temperatures will bottom out in the upper teens to lower 20s by dawn. So, any moisture that freezes from the rain this afternoon plus snow on top of it will rapidly lead to snowy/icy conditions that will likely persist into Thursday. Tomorrow will be much quieter with winds subsiding and no precipitation expected with partly to mostly cloudy skies as strong high pressure advances from the Dakotas to Iowa. Temperatures will mostly stay in the 20s. && .Long Term...(After midnight Thursday night through Wednesday) Issued at 300 PM EST Wed Jan 19 2022 The main story for the long term will be the below normal temperatures for the bulk of the forecast period. Long range forecast models 7-day temperature anomalies have KY ranging 5 to 10 degrees below normal. This matches up with the 5 to 7 day 500 mb anomalies from both the EURO/GFS showing a general troughiness across the eastern half of the CONUS with ridging across the western US. Strong arctic high settles in over the Ohio Valley to end the work week. Lows to start Friday will be cold with morning minimums in the low/mid teens, despite sunshine and good subsidence from the sfc high, highs in the afternoon will only reach the mid/upper 20s. A few weak shortwaves will propagate through the Great Lakes over the weekend but per model soundings, we will remain too dry in the low levels for there to be any precipitation. Highs will be in the low/mid 30s on Saturday and a few ticks warmer Sunday in the mid/upper 30s. Our attention then turns to the possibility of another storm system impacting the Ohio Valley by Tuesday. Cut-off low over the Gulf of California will eject eastward across TX Monday into Tuesday as an upper-level trough drops southward over the Dakotas and into the Great Lakes by Tuesday. Long range models tend to agree that a sfc low develops along the LA Gulf coast Monday night into Tuesday morning but differ significantly on how deep the trough becomes over the Great Lakes and on the strength of the system as it tracks along the Gulf Coast into the southeastern US by Tuesday evening. For now, will introduce the slight chance of rain/snow across most of KY on Tuesday with highs in the mid/upper 30s. && .Aviation...(00Z TAF Issuance) Issued at 605 PM EST Wed Jan 19 2022 Main impacts: -- Precip type changeover this evening -- Gust potential, BWG/LEX wind shift -- Low ceilings, and low vis in snow Discussion: Wind shift associated with the Arctic cold front is through HNB and SDF, and on the doorstep of BWG. Precip is still all rain, though anything that gets into HNB now will immediately be snow. Changeover is pending at all three sites in KY, and could have a period of SNPL mix before going to all snow late this evening. Cig/vis should both drop into IFR once precip is all snow, and should stay that way until just after midnight. Best chances and most persistent IFR will be in LEX, whereas snow will hang on the longest at SDF, possibly until the end of the inbound traffic push around 08-09Z. Wind gusts from the N or NNW will be just shy of 20 kt. Will break out to a mid-level deck before daybreak, but expect a stratus deck to fill in with morning mixing, leaving ceilings in the barely-VFR category for a lot of the day. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...Winter Weather Advisory until 8 AM EST /7 AM CST/ Thursday for INZ084-089>092. KY...Winter Weather Advisory until 8 AM EST /7 AM CST/ Thursday for KYZ023>043-045>049-053>057-061>067-070>078-081-082. && $$ Update...JDG Short Term...13 Long Term...BTN Aviation...RAS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
942 PM CST Wed Jan 19 2022 .UPDATE... Issued at 911 PM CST Wed Jan 19 2022 The forecast remains on track this evening for lake-effect snow showers to move through portions of northwest Indiana. Radar trends this evening have continued to show bands of snow showers developing and moving on shore east of Gary, IN with more recent scans showing a more dominant band developing just offshore of western Lower Michigan. Forecast soundings continue to show a favorable environment across portions of Porter County with ample low-level moisture, steep low-level lapse rates, and strong ascent forcing going through the snow growth region. Some uncertainty still remains in where exactly the best convergence axis and the aforementioned dominant band will set up, but hazardous travel from snow covered roads and reduced visibilities due to steady snow should be expected through the night and into the day Thursday. For this threat, the Winter Weather Advisory remains in effect until 6 PM CST Thursday evening. For the rest of the forecast area, we are in for a quiet and bitterly cold night with temperatures continuing to drop into the single digits. Blustery north-northwest winds will also continue gust around 20 to 25 mph which will create very cold subzero wind chills in the minus 10 to minus 20 range heading into Thursday morning. Temperatures on Thursday will remain cold with highs struggling to reach 20 degrees, but skies will be mostly cloud- free for northeastern Illinois with partly cloudy skies for portions of northwest Indiana not experiencing lake-effect snow showers. Yack && .SHORT TERM... Issued at 315 PM CST Wed Jan 19 2022 Through Thursday night... The two primary areas of interest in the short term forecast continue to be the swath of lake-effect snow slated to move over portions of northwest Indiana tonight and tomorrow and the bitter cold expected the next couple of nights. No changes were made to the going Winter Weather Advisory that goes into effect at 6pm this evening and is currently set to expire at 6pm Thursday for Porter County. Lake effect snow has already begun to fall over parts of southwestern Michigan and will scoot southward along the lakeshore over the next several hours. Snow is anticipated to begin falling on northeastern Porter County as early as around 4:00 PM and propagate southwestward to include much of Porter County and portions of northern and eastern Lake County shortly thereafter with light flurries possible in surrounding areas. Most model guidance has been contaminated by the National Ice Center`s January 18th ice analysis and says that most of the Illinois and Indiana nearshore zones of Lake Michigan are ice-covered heavily limiting the amount of fetch over this area as well as positioning the land breeze convergence farther east than it may end up in reality. However, since the portion of the lake that plays into this system is practically ice-free, this means the coverage of accumulating snow will likely be stretched ~5-10 miles west of where most model guidance suggests. Snow rates will pick up through the evening with the heaviest rates occurring in northern Porter County overnight and into early to mid tomorrow morning when we see the greatest amount of low level convergence and vertical motion in conjunction with sfc-850mb lapse rates of 7 K/Km or greater and lake-induced EL`s over 7,000 ft. At this time, snow rates could reach upwards of one inch per hour in this area. This spawns concerns regarding the morning commute tomorrow, particularly along the I-80/90/94 corridors as well as I-65 north of Rt. 30. Slippery road conditions and reduced visibilities can be expected through the entirety of the morning commute. If you`re driving in this area tomorrow morning, allow yourself plenty of extra travel time. This snow will lighten up through the morning though remain in the area through much of the afternoon. Some guidance is picking up on the potential development of a mesolow tomorrow afternoon which could keep the snow, albeit lighter snow, falling in the area through at least Thursday evening. At this time, some light flurries are also possible near the Illinois lakeshore. The highest snow totals will likely be found in northern and northeastern Porter County where several inches are probable, with localized 6"+ amounts possible. Big question is do we see this occur with a longer duration of light to moderate rates, or does an intense single band move in by Thursday morning as shown by some of the recent CAM solutions. Observational trends will need to be monitored closely this evening. Should confidence increase on heavy snowfall rates and higher impacts to the Thursday morning commute, may need to consider a warning upgrade. The rest of Porter County and northeastern Lake County are expected to receive around an inch of snow. All the while, the rest of the CWA will remain precipitation-free through the short term. In other news, a cold air mass being pulled in from the northwest and fueled by a positively tilted trough aloft will drop temperatures into the single digits for most of the CWA by early tomorrow morning. Gusts near 20 mph will pull wind chills down below zero area-wide with wind chills around 15 below zero expected in the far west suburbs and approaching 20 below zero in the far northwest CWA. Highs reaching only the teens tomorrow will be followed by another night with temperatures dropping into the single digits and likely below zero for some. Calm winds tomorrow night and Friday morning, however, will not result in much of a wind chill factor. Doom/Castro && .LONG TERM... Issued at 315 PM CST Wed Jan 19 2022 Friday through Wednesday... The theme through the long term an unsettled and colder than normal pattern, with multiple snow chances this weekend into early next week. Anomalous western ridging (+PNA) will connect with ridging spiking to the north of Alaska (-EPO), keeping a deep mid-level trough axis centered from Hudson Bay through the Great Lakes, favoring the colder than normal temperature regime. None of the systems look particularly moisture-laden, but do have favorable cold thermal profiles to work with as well as thermal gradients for some temporary better snowfall rates in the broad Midwest region. Obviously the low amplitude and speedy movement of these systems makes them difficult to place and time in the extended. Overall, the forecast thoughts and adjustments to the National Blend of Models (NBM) were similar to the previous few shifts. On Friday, 1035-1038 mb high pressure will centered over the area to start with a cold morning as a result and then only recovering to the upper teens to mid 20s in the afternoon. With potential southern Lake Michigan meso-low possibly still lurking near the extreme northwest Indiana and immediate Illinois shoreline, have a chance for flurries and slight snow shower chance mentioned. The high pressure will exit southeast Friday night, resulting in gradually increasing southerly winds and temperatures flatlining or slowly rising. The first disturbance we`re watching on Saturday is along/ahead of a cold front packing a reinforcing surge of cold air. Limited moisture and light QPF output on the guidance but decent forcing with lift temporarily aligned with DGZ saturation amidst cold advection could squeeze out a dusting to a few tenths of snow, which we`re messaging in the grids as a chance of of light snow. Breezy southwest winds ahead of the front will make for a "milder" Saturday topping out in the upper 20s to lower 30s. The "clipper highway" or "clipper train" pattern will feature 24-36 hour intervals of these systems moving into the broader mid- upper MS Valley/western Great Lakes region. 500 mb ensemble mean shows the core of the strongest 500 mb winds oriented toward our general direction. Predictability is still low on the specifics of these low amplitude disturbances several days out, but what we can say is regular chances of light to moderate snow accumulations are possible, depending on the tracks each individual clipper takes. There is a coherent signal for the next, stronger clipper on Sunday among the 12z operational models, along with a weak surface low reflection passing to our southwest and south. Looking at the ensemble members, there is plenty of spread as is to be expected, but with consistent enough signal the past few cycles, adjusted PoPs up to mid chance range. Current timing favors Sunday morning for most areas for threat of light snow accumulation and slippery travel. Forecast soundings show a deep DGZ, so if lift is aligned with DGZ, could see temporary moderate rates of fluffy/high ratio snow. The next clipper threat will follow closely on the heels of Sunday`s wave. There is a good signal for Monday or later Monday into Tuesday but very large ensemble member spread in short-wave trajectory and timing. Monday daytime is currently favored for the mid chance PoPs I-80 and north, with lower PoPs through Monday night. At the end of the period, there is a strong signal at this lead time for another shot of Arctic air driven in ahead of incoming ~1040 mb high pressure. Exactly how cold it gets will be determined by the snow cover extent. At the least in this set- up, expect the lake effect machine to reinvigorate. Should a southern stream wave and surface low track off to our northeast as shown by a few guidance members, this scenario could even threaten the Illinois side with lake effect snow Tuesday into Wednesday. For now, have adjusted to low chance PoPs for the Illinois shore and far northwest Indiana. Castro/MTF && .AVIATION... For the 00Z TAFs... There are no major aviation concerns through the next 24 to 30 hours. All terminals will remain largely cloud-free with north to northwest winds gradually decreasing in magnitude through the TAF period. Aircraft arriving or departing toward the east may encounter icing while flying through a lake-effect stratocumulus deck over Lake Michigan. Such lake effect snow showers (and associated MVFR stratocumulus clouds) may occasionally get within 10 miles of GYY through the next 18 to 24 hours but the majority of activity is expected to remain to the east. The wind direction at ORD/MDW may attempt to flop north to northeasterly 21-00Z tomorrow as a surface high pressure system approaches from the northwest, though wind speeds are expected to be at or below 8kt (if not lower) should such a change in direction occur. Borchardt && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...Winter Weather Advisory...INZ002 until 6 PM Thursday. LM...Heavy Freezing Spray Warning...Winthrop Harbor to Burns Harbor until 9 AM Thursday. Small Craft Advisory...IL nearshore waters until 9 AM Thursday. Small Craft Advisory...IN nearshore waters until 6 PM Thursday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at: