FXUS63 KIWX 050122 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 822 PM EST Wed Dec 4 2024 .KEY MESSAGES... - Lake effect snow, gusty winds, and reduced visibility are expected this evening overnight into Thursday. Wind gusts up to 50 mph are possible, especially near the lake. - A winter storm warning and winter weather advisory are in effect for southwest Michigan and northern Indiana. Hazardous travel is possible in these areas. - Arctic air arrives Wednesday night with wind chills in the single digits to below zero. The cold will last through Friday. - Friday and Saturday will be dry, then rain is expected Sunday night and Monday. && .UPDATE... Issued at 822 PM EST Wed Dec 4 2024 Strong arctic cold front now just reaching BEH and SBN with impressive 50-60 mph gusts will continue east through the remainder of the forecast area this evening. The stronger gusts have been on the southern fringe of an organized line(s) of convection tracking through southern MI. Ptype has quickly changed over to a burst of moderate/heavy wet snow given intense dynamic/evaporative cooling with visby's briefly down to a quarter/half mile within the line as it tracks east-southeast through southern MI, possibly clipping far northeast IN and nw OH later this evening. Have opted to handle with a SPS for now as a marginal temp profile and lagging influx of arctic air likely keeps this initial activity from being a true snow squall/flash freeze situation. Warmer and less organized convective activity to the south likely limits impacts, removed from the more robust ascent plume associated with a vigorous vort max tracking through lower Michigan. Forecast is on track otherwise with no changes to headlines overnight into Thursday as we transition over to a wind driven lake effect event in our wnw flow LES belts. && .DISCUSSION... Issued at 228 PM EST Wed Dec 4 2024 A deepening clipper like system traverses the northern Great Lakes today into Thursday. Strong gradient winds across the area will have some likihood of being brought to the surface today as the morning clouds move eastward and mixing slowly gets started. The majority of the winds are forecast to stay under 40 mph today. It will be when the strong shortwave dives across Lake MI and its attendant arctic front moves through the area that we get our higher impact outcomes. In terms of wind, the greatest chance for 40+ mph winds appears to come at night when the cold air arrives on top of the warmth of the mid to upper 30 degree highs to cooling into the teens tonight. This is going to have to rely on the cold air doing the majority of the mixing in this case to allow for more than an hour or two of cold front forced gusts. This is outside of normal timing climatology for when gusts really surpass advisory criteria, which is during the morning hours. Although this could be influenced by the amount of warm advection events we have that often create an inversion to limit coupling by the afternoon. Still think this is strong enough to go with an SPS for areas south of US-30 this evening into the overnight. Should there be any wet roadways from precip across the area today, there is a chance for some flash freezing, although wind gusts and the normally dry nature of these systems may cut down on those chances. The other longer-lasting impact will be the snow. Trajectories finally swivel around to northwest around or just after 00z this evening. Initially, winds are nearly unidirectional and with minimal shear to shread dominant banding. However, by 12z, stronger shear around 15 kts through the cloud bearing layer may be enough to break up any remaining single banding and allow for more of a multibanded set up for Thursday. The trend will also be to have the lake-induced inversions drop from a good 700 mb/9500 ft to below that 7500 ft threshold for better lift early Thursday morning. The trend will also be to lose moisture content through the lowest 1 km of the profile and the inversion heights drop during the morning as well. By the morning, HREF guidance seems to indicate that the Michigan counties of Cass and St Joseph and portions of Berrien county will be on their way to reaching warning criteria with 6 to 8 inches by 12z. It may take a little bit more effort for the southern row of counties in the warning to attain their snow threshold especially if it is going to be less efficient and if there's a trend towards a multiband orientation. HREF snowfall brings the 3 to 6 totals over 24 hrs by 12z Thursday morning to 6 to 8 inches by Thursday evening in St Joseph and parts of Elkhart. Still, it appears the best area for lowered visibility both from fractured snow flakes and blowing and drifting snow appears to be the closer you are to Lake MI where the strongest winds are expected to be and some snow pack still remains from our last event, but some of the visibility issues may extend farther downstream of Lake MI as well and this could help verify those warnings at an impact-based level. 30 kt gusty winds are expected to last through the morning, but dissipate during the afternoon. Lake effect snow continues through the day Thursday, but may even sputter and start into Thursday night as that's when trajectories finally turn more southerly. Mentioned the teens for lows tonight, but highs Thursday and Friday struggle reach freezing with a majority in the mid 20s to around 30 both days. The worst wind chills are below zero south of US-30 tonight with the strong gusty winds helping out there. Finally, the north and western side of the approaching surface high pressure begins influencing the area with warm advection around midday Friday. Expect dry weather, then, Friday as result. Saturday, a sprawling warm front from a low pressure system in Canada scrapes our north. Am skeptical anything comes out of it based on moisture profiles, but the NAM solution indicates it might. As a result of the warm front and the high pressure system stalling in the Gulf of Mexico, warm advection sets up and allows temperatures to arrive back in the 40s on Sunday. This is all in the nick of time because the upper low in the southwestern US through all this time finally meanders northward toward the area Sunday night into Monday with chances for rain. We'll have to see how much snowpack exists at that point and heavy it rains because all that rain/meltwater goes somewhere and it may be into the rivers. Additionally, we'll have to see what happens to road temperatures because there could be some onset freezing rain. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 534 PM EST Wed Dec 4 2024 Arctic front on track to plow through KSBN by 01z and KFWA by 2-3z with ~40 kt gusts and convective rain/snow showers immediately along and behind. Brief reductions in visby's to less than a mile possible with snow showers/squalls, with some rain potentially mixing in initially. Attention thereafter will turn to the lake effect response as cold/strong west-northwest flow trajectories overspread the relatively warmer lake waters overnight into Thursday. This lake plume to primarily remain north of KFWA with times of light snow showers and cigs in the high MVFR to low VFR category. Lake effect snow multibands will be in and out of KSBN with variable flight conditions (LIFR to MVFR) overnight into tomorrow, with some improvement possible later Thursday as drier air starts to lower inversion heights and the overall intensity of the LES. West winds will continue to gust up to near 30 knots otherwise into Thursday. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...Winter Storm Warning until 1 AM EST Friday for INZ005-006-104. Winter Weather Advisory until 1 AM EST /midnight CST/ Friday for INZ007>009-014-103-116-204. Wind Advisory until 4 AM EST /3 AM CST/ Thursday for INZ012- 013-015-017-018-020-022>027-032>034-203-216. OH...None. MI...Winter Storm Warning until 1 AM EST Friday for MIZ078-079-177- 277. Winter Weather Advisory until 1 AM EST Friday for MIZ080. MARINE...Gale Warning until 1 PM EST Thursday for LMZ043-046. && $$ UPDATE...Steinwedel DISCUSSION...Roller AVIATION...Steinwedel