075 FXUS64 KHUN 140515 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1215 AM CDT Thu Mar 14 2019 .UPDATE... For 06Z TAFS. && .NEAR TERM...(Rest of tonight) Issued at 948 PM CDT Wed Mar 13 2019 Near term model progs are in agreement in forecasting the impressive deep-layer cyclone over the western high Plains to slowly lift northeastward into the mid-MO Valley by 12Z. As this occurs, the pressure gradient across the local CWFA will increase to 6-8 mb, supporting an increase in south-southeasterly flow throughout the night. Due to this, as well as some mixing of intense southerly flow associated with the low-level jet, we have issued a Wind Advisory for all forecast zones through 14Z. Although sustained winds will likely fall shy of criteria, frequent gusts to 35 MPH should occur, and may result in a fair number of downed trees (especially given the moist nature of the local topsoil). Otherwise, based on latest model guidance, it appears as if large scale ascent related to the low to our west will be maximized across the region overnight, and should be enhanced further by a glancing blow from a weak wave peripheral to the main synoptic scale cyclone. Widespread shower and thunderstorm activity to our west has thus far been concentrated in the vicinity of a weak surface trough/streamline confluence axis, that is expected to become even more diffuse throughout the night as the peripheral wave ejects rapidly north- northeastward into the eastern Great Lakes. However, as this occurs, the axis of deeper convection is expected to translate eastward into northwest AL early Thursday morning, and POP/weather grids have been adjusted to reflect this reasoning. Otherwise, minor changes were made to temperature and sky cover grids to reflect recent trends in observations. .SHORT TERM...(Thursday through Friday night) Issued at 328 PM CDT Wed Mar 13 2019 An unsettled period is expected for Thursday and Thursday night, as the parent low moving to the NE reaches the western Great Lakes region by the afternoon. Despite the main low being rather deep, it will be further away from the Tennessee Valley - which in itself tends to reduce severe weather potential. But strong lift with the approaching front, warmer than normal temperatures and available moisture will make for a strong to severe thunderstorm potential, especially in the afternoon and evening. The SPC has our western 2/3's of our area in a Slight Risk, with the rest of NE Alabama and SE Franklin County TN in a Marginal Risk. The main risks associated with the stronger or severe thunderstorms would be damaging outflow wind gusts. A tornado or two also cannot be ruled out. Even with widespread showers and storms, one last warm day is in the forecast, with high temperatures into the low/mid 70s. A cold front trailing south of the low will sweep across the region late Thu night, helping to end shower activity from west to east. A reality check (yes it is still winter) will be realized with lows cooling into the mid 40s west to lower 50s east. Cooler weather will makes it return on Friday with highs only in the mid/upper 50s. Skies should clear in time for Friday night, with lows falling into the mid 30s. .LONG TERM...(Saturday through Tuesday) Issued at 328 PM CDT Wed Mar 13 2019 The long term period will start well below normal with a broad longwave trough across the eastern US. At the surface a high will be moving into the OH Valley and result in a push of cold/dry air into the TN Valley. Locations north of the TN River will likely drop below freezing for a few hours Saturday night into Sunday. On Sunday models indicate a clipper type system moving through the broad longwave trough and while we'll see some continued CAA with this feature. This system should increase the winds enough to keep temps just above freezing Sunday night into Monday. High temps over the weekend won't make it out of the 50s, which is below the normal high of 61-62 for this time of year. The surface high shifts east early next week and winds become more southerly with time. Expect highs to warm into the lower 60s and stay near normal through the week. Lows will also gradually warm but values will stay in the 30s to lower 40s. Looking towards the middle to end of next week models are starting to come into better agreement that a trough will dig south and result in a round of scattered showers Wed/Thur. There is still some uncertainty as this is really the first run that models have started to show this. So, have kept PoPs low given the uncertainty. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1009 PM CDT Wed Mar 13 2019 No changes from previous aviation forecast reasoning, with weather conditions at the terminals this TAF period dictated by the motion of a deep-layer cyclone to our west. Warm/moist advection is expected to continue overnight, with the base of the stratus layer descending to around 1500 ft by 07Z. Strengthening atmospheric lift will also translate to a band of SHRA/embedded TSRA, which will mainly impact northwest AL during the early morning hours Thursday. Thus, we have included SHRA/VCTS at MSL during this period, with only VCSH at HSV due to uncertainty on eastward extent of this activity. A second band of convection will likely evolve along a Pacific cold front as it sweeps eastward across the region late tomorrow aftn/tomorrow evening, with VCTS reintroduced at MSL/20Z and HSV/22Z, and prevailing TSRA for MSL beginning at 22Z. Although some fluctuations in ceiling heights are possible, especially early tomorrow aftn, we have indicated cigs in the 1500-3000 ft range for the entire forecast period. SSEly sfc flow will increase further into the 22G32 knot range as the pressure gradient contracts overnight, but should veer to SW and subside late in the period as the cold front approaches from the west. Skies will clear rapidly in the wake of the cold front, with VFR conds and lgt WNW flow returning late tomorrow evening. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Wind Advisory until 9 AM CDT Thursday for ALZ001>010-016. TN...Wind Advisory until 9 AM CDT Thursday for TNZ076-096-097. && $$ NEAR TERM...70/DD SHORT TERM...RSB LONG TERM...Stumpf AVIATION...70/DD For more information please visit our website at weather.gov/huntsville.