KHUN issues Area Forecast Discussion (AFD) valid 2019-12-10T15:44:00Z 238 FXUS64 KHUN 101544 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 944 AM CST Tue Dec 10 2019 .NEAR TERM...(Rest of Today) Issued at 944 AM CST Tue Dec 10 2019 While rain abounds on regional radars for the moment, the TN Valley is waiting with bated breath as the changeover to frozen precipitation is on the doorstep of NW AL. We've gotten a report of Sleet in Waterloo about half an hour ago, and this trend is expected to march E/SE across the area through the day. Not a lot has changed with respect to the eventual snowfall amounts, as ground temperatures are still in the 50s. The cold front has already pushed S/E of the CWFA, extending from the Appalachians SWwrd into Srn MS/LA. The cold air is lagging a bit, with temperatures in the 30s just now on the doorstep of NW AL.The changeover will slowly overtake the TN Valley through the day, with a changeover to all-snow expected in NW AL ~Noon, in HSV ~2PM, and in Fort Payne ~4PM. Given the fact that a lot of melting will occur with the warm ground temperatures, accumulations will be limited to a dusting to perhaps up to 0.5", with a few spots receiving upwards of 1" possible when it's all said and done this evening. Temperatures by sunset are expected to be in the lower to middle 30s, and will bottom out in the upper 20s to lower 30s by morning. Travel impacts are not expected given the melting anticipated, as many accumulations will just remain on grassy surfaces. For the public forecast update this morning, only minor tweaks were made to hourly grids to follow in line with observational trends. Most wx elements were on track and major changes weren't warranted. .SHORT TERM...(Tonight through Thursday) Issued at 518 AM CST Tue Dec 10 2019 The areas mentioned above will definitely see the changeover to snow in the early evening hours. Expect the most accumulation of snowfall to occur north of the Tennessee River. In these areas amounts around one half of an inch look reasonable. Localized amounts around 1 inch also look possible in higher elevations of southern middle Tennessee. Thinking is still that warm ground temperatures will help limit snowfall totals, despite this activity lasting into the evening hours before moving southeast of the area shortly after midnight. However, temperatures should drop in the upper 20s to around 30 degrees around 6 AM on Wednesday. This will refreeze any remaining moisture. However, due to breezy conditions and drier air moving quickly into the area after midnight, widespread hazardous conditions are not expected. Therefore, a Special Weather Statement will continue to highlight this threat. A cold day remains on tap for Wednesday, despite clearing skies. High temperatures are not expected to climb above 50 degrees. Higher elevations above 1200 feet may only warm to the lower 40s. Slightly warmer conditions are expected both Wednesday night and Thursday. Lows in the lower 30s and highs in the lower 50s are expected. .LONG TERM...(Thursday night through Monday) Issued at 518 AM CST Tue Dec 10 2019 Global models continue to suggest that broad cyclonic flow will exist across the CONUS at the beginning of the extended period, with deep-layer southwesterly winds expected to strengthen across the TN Valley Thursday night as a lower-latitude shortwave trough migrates through the southern Plains. At the surface, a modest increase in southeasterly flow is anticipated during this same period due to the sharpening gradient between a strong high over northern New England and a developing cyclone over the north central Gulf of Mexico. The resultant increase in atmospheric lift and northward advection of moisture will become increasingly favorable for expansion of light rain into the region from the south on Thursday evening, with perhaps a few rounds of moderate rainfall during the morning hours on Friday, as this is the period when large scale ascent will be maximized ahead of the approaching mid-level trough. It appears as if this initial shortwave will lift northeastward across the region during the late morning/early afternoon hours, leading to a lower coverage of rainfall during the late afternoon. Consensus guidance indicates that another vort max will cross the region Friday night, perhaps resulting in the regeneration of light rainfall early Saturday morning. A final episode of light rain will be possible late Saturday afternoon, as a northern stream wave spreads east-southeastward into the OH Valley, sending a cold front southeastward through the region. However, due to weakening low-level convergence along this boundary, we have only included a slight-low chance POP (highest for the east). Low temperatures will remain mild on Friday and Saturday mornings due to both cloud cover and moist southwesterly flow, with readings in the l-m 40s expected both periods. A slightly cooler airmass will likely enter the region in the wake of the cold front, with lows falling back into the mid 30s Sunday morning. Highs will warm from the lower 50s on Friday into the m-u 50s Saturday, as stratus clouds should scatter during the morning hours. As for the end of the extended period, models indicate that an unamplified zonal flow aloft will result in a dry period for most of the day on Sunday. However, another longwave trough is expected to develop from the northern Plains into the southwestern CONUS late this weekend, resulting in a return to moist southwest flow on Sunday night and Monday. Chances for precipitation will begin to increase once again late Sunday night, with a fairly widespread coverage of rain anticipated on Monday as an inverted surface trough builds northeastward into the region from the Gulf coast. Although not specifically mentioned in the forecast at this time, a few thunderstorms will be possible on Monday, along with an increasing threat for locally heavy rainfall. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday morning) Issued at 600 AM CST Tue Dec 10 2019 A cold front has now pushed southeastward across both terminal locations, with NW flow currently reported at HSV/MSL. Periods of lgt RA/SHRA in the the wake of the front will continue to impact both airports this morning, before the transition to a mixture of RA/SN occurs arnd 20Z. Although cigs/vsby will predominately be in the MVFR range, a brief period of IFR conditions could occur in snow this evening, and AWW issuance may be warranted at both terminals prior to the onset of the wintry precipitation. Conds will improve by the end of the TAF period, as colder/drier air finally begins to spread southeastward in the wake of the cold front. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...12 SHORT TERM...KTW LONG TERM...70/DD AVIATION...DD/KTW For more information please visit our website at weather.gov/huntsville.