115 FXUS64 KHUN 092353 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 553 PM CST Mon Dec 9 2019 .UPDATE... For 00Z TAFS. && .NEAR TERM...(Tonight) Issued at 313 PM CST Mon Dec 9 2019 A mild and windy day is underway across the area, with current temperatures in the lower to middle 60s. Huntsville International Airport is a few tenths shy of 65 degrees, which is about 10 degrees above normal for this time of year. Showers have developed to the W of the CWFA and have slowly meandered Ewrd through the day. This activity is expected to arrive in NW AL within the hour, and will fill in as it overspreads the area tonight. Some moderate to heavy rainfall is expected ahead of the approaching cold front, which is currently diving SE toward the area over the Mid-MS River Valley, and slated to arrive in NW AL around sunrise Tuesday. Morning lows will be cooler in NW AL, bottoming out in the upper 30s/lower 40s, with places in SErn portions of the area in NE AL bottoming out in the lower/middle 50s. A Wind Advisory remains in effect through midnight tonight, though areal observations may support canceling this a few hours early. The last item of note tonight is that we may have a few rumbles of thunder embedded within the moderate/heavy rainfall, and this is accounted for in the grids/HWO. .SHORT TERM...(Tuesday through Wednesday) Issued at 313 PM CST Mon Dec 9 2019 By far the biggest story of the forecast period revolves around the potential for winter weather tomorrow afternoon/evening and into tomorrow night. I'll start with this: accumulating snowfall is likely with this frontal passage. The big question is exactly how much snow we'll get when it's all said and done. Model guidance has continued to come in quicker with the progression of the front, and therefore colder air arrives quicker and definitely in time to transition the moisture into a wintry mix and eventually all-snow. Moderate to heavy rainfall will occur overnight and into the early morning hours as the front arrives in NW AL around daybreak. Colder air is lagging behind the frontal passage by about 50-100 miles (currently over portions of AR and MO), so temperatures aren't going to plummet in the wake of the front. Temps will therefore slowly decrease through the morning hours and a changeover to a rain/snow mix is expected in NW AL and Srn Middle TN between ~12-2PM, and locations along a Moulton to Huntsville to Scottsboro line ~2-4PM. Locations SE of that, including Cullman, Guntersville, and Fort Payne are looking at maybe a 4-6PM timeframe for changeover. Taking a look at cross sections and determining deformation zones, there is a period of time where enhanced lift at 700mb occurs overhead, and therefore may enhance snowfall rates tomorrow evening. Though this is a small ~3 hour window, this may lead to higher snowfall rates for a few select locations across the area. Overall, snowfall totals look to be around a dusting to half an inch in NW AL and Srn Middle TN, dwindling as you head to the South/East. A few spots in Nrn areas may receive up to 1", which is Winter Weather Advisory Criteria for our office. For now, will not officially be issuing that just yet, and will allow one more run of the models to come in for the midnight shift to officially decide to pull the trigger. Confidence is not high enough at this point today to issue that product this far out. Assuming we get a little deformation banding setting up, realistically, we could see 1-1.5" in some spots, if not a little higher. Some short-term models have gone with MUCH higher amounts, but am not biting on that given the current atmospheric profiles in place. The snow that falls for us will be a wet/sloppy snow, melting on contact with roadways/the ground that's currently in the 50s. Temperature profiles hug the 0 degree isotherm in the lower third of the atmosphere, and even with evaporational cooling, temps don't fall much below a couple of degrees below 0, so the type of snow is important here (wet/sloppy) in regarding the eventual accumulations. Several observational sites reported 51-54F degree ground temperatures currently, and that was this morning before ambient temperatures rose into the middle 60s this afternoon. This will further help to melt the already wet snow as it falls. So, will we see snow? YES. Will it impact travel Tuesday afternoon or Wednesday morning? Most likely, NO. Soundings are indicative of a rain/snow mix transitioning to a wet snow Tuesday afternoon/evening, and then temperatures slowly fall to around freezing by midnight. From there, you're only talking about 2-4 degrees lower by sunrise (official morning lows). There is always the chance for a slick spot on an elevated roadway surface on Wednesday morning given the fact that bridges don't have the luxury of retaining insolation/heat. Therefore, winds behind the front will drop temperatures of those roadways, but this wind will also help dry up the wet/soggy snow and help it evaporate on roadway surfaces as well. In all, temperatures Wednesday morning will fall into the upper 20s/lower 30s, and this is not drastic enough to flash-freeze any remaining puddles across the area. Caution should be used when traveling, as always, when there's winter weather, but I really don't think this is the event to 'shut the city down' or ' buy lots of bread and milk' or anything like that. Dry air entrainment in the wake of the front will make for an abrupt end to the wintry weather across the area, with clouds clearing out quickly around sunrise Wednesday. Despite CAA, Wednesday will be a sunny and windy day, further melting any lingering snow. Daytime highs will actually climb into the middle 40s, with even a few upper 40s possible, so again, we're not expecting any widespread issues with this event. .LONG TERM...(Wednesday night through Sunday) Issued at 313 PM CST Mon Dec 9 2019 A large dome of high pressure will continue to lift NE across the mid Atlantic/NE states Thu, with a developing return flow pattern beginning to usher moisture back into the region. The flow pattern over the SE states will also begin to back toward the SW, as a longwave upper trough pattern drops sewd into the mid/srn Plains. This will at least result in one more day of dry/quiet wx conditions Thu, before shower activity begins to develop/spread nwd out of the cntrl Gulf states Thu night into Fri. Overall temps look to trend quite seasonal Thu into Thu night, with highs in the lower 50s and lows predom in the upper 30s/near 40F. Synoptic scale differences remain between the latter half of the global model runs, with the 12Z GFS showing that broad longwave upper trough pattern translating ewd across the region. The 12Z ECMWF on the other hand trends a bit more progressive with the upper trough axis tempo closing off and diving a bit further to the south into the Gulf states. The sfc reflection in the ECMWF shows a potential sfc wave forming across the extreme north Gulf region and quickly lifting NE across the srn Atlantic states, while the GFS suggests an inverted sfc trough quickly developing/moving east over the NE Gulf. The ECMWF solution would have a bit more shower activity spreading into the mid TN Valley, although for now will stick with the ongoing forecast suggesting chc POPs developing near the end of the work week, before tapering off to the east Sat. Temps look to remain fairly seasonal thru the weekend, with highs mainly in the mid/upper 50s while lows trend predom in the mid 30s/around 40F. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 553 PM CST Mon Dec 9 2019 Shower activity preceding a strong cold front, that was draped from east of Chicago, to far NE Arkansas and south of the Texas Metroplex, should move across the terminals in the predawn hours. A rumble or two of thunder cannot be ruled out in the heaviest showers overnight. SW winds in the 5-15kt range, occasionally gusty will veer to the NW, increasing into the 10-20 mph range after daybreak. Mainly MVFR CIG/VIS values should continue tonight, a few brief IFR or lower values are possible in the heavier showers. Showers should change to a wintry mix in the afternoon as colder air becomes more prevalent. No accumulations on ground surfaces are expected, however a dusting or light icing cannot be ruled out on elevated and exposed surfaces. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...12 SHORT TERM...12 LONG TERM...09 AVIATION...RSB For more information please visit our website at weather.gov/huntsville.