918 FXUS64 KHUN 290913 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 313 AM CST Sat Feb 29 2020 .NEAR TERM...(Today) Issued at 312 AM CST Sat Feb 29 2020 Water vapor this morning shows a pronounced upper level trough from the upper Great Lakes south to the Tennessee Valley. Light showers associated with a shortwave along the base of the trough are lingering this morning across the forecast area, but precip should diminish by sunrise as it continues to push off to our east. Dry conditions are then expected for the remainder of leap day with afternoon temperatures warming into the lower 50s. .SHORT TERM...(Tonight through Monday) Issued at 312 AM CST Sat Feb 29 2020 Benign weather conditions continue tonight through the first half of Sunday before another chance of rain reaches the region Sunday evening as a front lifts northward through the Tennessee Valley. Warm air advection from southwesterly flow will warm daytime temperatures into the 60s, which will feel quite nice after several below normal days. Light to moderate rain develops along the aformentioned front and quickly overspreads the area on Sunday evening. Have increased PoPs on Monday compared to overnight blends as model guidance is showing better agreement in the placement of the front. The front is expected to stall across southern TN/northern AL, which result in more rounds of rain through the day Monday. Have introduced slight chance of thunderstorms overnight Sunday, but a better chance for thunder exists on Monday as better instability moves overhead. With rain and thunderstorms expected, temperatures Monday remain nearly constant upper 50s to lower 60s. .LONG TERM...(Tuesday through Friday) Issued at 312 AM CST Sat Feb 29 2020 The extended period will be characterized by mild temperatures and a significant period of wet weather Tuesday through Wednesday night. Some appreciable differences between the GFS/Canadian and the ECMWF solutions still exist regarding the evolution, timing, and track of this system. Regardless, all models show the potential for several rounds of moderate to heavy rainfall during the aforementioned period. Accordingly, the threat for widespread flash/areal flooding issues exist during the middle part of the upcoming week. Additionally, river flooding is expected along the Tennessee River watershed, especially the tributaries of the main stem Tennessee River -- which may last through at least the end of next week. By Tuesday morning, a slow moving warm front will be lifting north through the Tennessee Valley ahead of a developing upper-level storm system to the west of the region. This feature will generate widespread moderate to heavy rain showers and some isolated thunderstorms (thanks to some modest elevated instability) that will slowly trek across the region. Combined with the rainfall that already will have occurred on Monday, expect some flooding issues to develop during this window, especially in areas where training occurs. The next question for the next 24-36 hours will be where this boundary ends up stalling which will ultimately depend on how this system evolves. The GFS and Canadian favor a solution that initially lifts this boundary just to the north of the area Tuesday afternoon/evening. However, by Tuesday night into Wednesday, the front will then shift back into North Alabama as the northern stream trough over the Central Plains merges with a deepening upper-low across Texas and the Mississippi Delta. With strong cyclogensis taking place in this solution, another round of moderate to heavy rainfall would occur on Wednesday, exacerbating ongoing flooding issues and potentially sending some of our rivers into minor to moderate flooding. The ECMWF on the other hand does not merge the two systems, indicating the northern stream trough will remain well north of the area, while moving the upper low (which weakens into an open wave) across the Deep South and Southern Appalachians Wednesday into Thursday. Rainfall totals with this solution would be a little bit lower, but we'd still get a solid period of moderate to heavy rainfall, albeit later during a Wednesday night into Thursday morning period. All this to say, confidence is increasing for a sizable flood threat during the middle part of week, with only some questions regarding the timing and evolution of the storm system. With the NAM starting to come into agreement with the GFS/Canadian solutions, have favored this in our forecast for now. This puts storm total QPF in the 4-5" range from 12 Monday through 18z Thursday across our entire area. Depending on where this boundary sets up, these values may need to be adjusted further in the coming days. Some good news is that behind this system subtropical ridging eventually looks to build in, promoting some dry weather through the end of next weekend. Additionally, we should be able to expect plenty of sunshine to accompany high temperatures in the 60s. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 1032 AM CST Fri Feb 28 2020 Light showers ahead of a cold front will continue to push through the TN Valley for the next 2-3 hours. At higher elevations, a snow mix is possible, but this is not likely at MSL and HSV. Light northwest winds continue tonight before skies clear in the morning. Southerly flow returns tomorrow evening with clear skies expected overnight. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...GH SHORT TERM...GH LONG TERM...AMP.24 AVIATION...30 For more information please visit our website at weather.gov/huntsville.