Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
000 FXUS64 KHUN 232001 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 201 PM CST Sat Feb 23 2019 .NEAR TERM...(Tonight) Issued at 200 PM CST Sat Feb 23 2019 A crazy day continues weatherwise. Luckily we had a small break from the more concentrated heavier rainfall we have had over the past several days this morning. However, a line of showers and thunderstorms has been moving east from eastern Arkansas into western Mississippi. Ahead of this line, clouds have broken up some near a warm front that has moved just north of Tupelo into western Tennessee. Strong advection of much warmer and more moist air along with some sunshine has allowed temperatures to climb into the lower 70s with dewpoints in the upper 60s. This has created between 1000 and 3000 J/KG of surface based CAPE in that area. Further east in northern Alabama, this advection has not been quite as strong and cloud cover a bit more entrenched. So surface based CAPE values have only climbed to between 500 and 1000 J/KG at this time. Strong values of bulk shear, helicity, and steep mid level lapse rates are all in place over these areas ahead of the approaching line of developing storms. Thus, a tornado watch was issue west of Alabama for Mississippi and western Tennessee, eastern Arkansas, and northeastern Louisiana through 8 PM. Some scattered showers and thunderstorms have also developed ahead of that near the AL/MS border. Over northwestern Alabama, between some insolation and strong warm/moist air advection surface and elevated instability should continue to increase west of I-65. Expect mainly scattered showers and thunderstorms to continue to develop over the next few hours. Believe stronger to severe thunderstorm development may hold off until around 2 or 3 pm, when stronger low level forcing occurs and better instability is in place. Any discrete storms that do form over the next few hours ahead of the line will need to be watch closely for tornadoes. Expect the watch to be extended eastward sometime between 3 and 6 PM. This will mainly depend on how quickly any scattered thunderstorm activity really gets going. Likely would be a tornado watch. Given all the other parameters in place, large hail and damaging winds will be possible this afternoon and evening as this consolidating line of thunderstorms pushes east across the area through midnight or just afterwards. Based on observational, satellite imagery, and model guidance: the line of thunderstorms ahead of the front should move very quickly aided by a strong southwesterly to westerly mean flow ahead of this storm system. Another round of heavy rainfall between 1 and 2 inches with locally higher amounts near 3 inches is expected late this afternoon through tonight with this activity. The main dynamics with this system do lift northeast late this evening into the overnight hours with this system. This should keep the heaviest rainfall will mainly be in northwestern Alabama into southern middle Tennessee and the worst of the severe weather potential near that area as well. .SHORT TERM...(Sunday through Monday) Issued at 200 PM CST Sat Feb 23 2019 Finally, a break from the wet weather still holds in model guidance on Sunday onward through Monday. Cooler and drier air will move into the area during this period. Highs will drop into the 50s and lows into the 30s under sunny skies. .LONG TERM...(Monday night through Friday) Issued at 200 PM CST Sat Feb 23 2019 This dry and sunny trend will continue through Tuesday. Models are continuing to have a hard time handling weak upper level disturbance that move through a modifying zonal flow and precipitation associated with it Tuesday night through next weekend. For now kept with blended model output with a slight warming trend and isolated to widely scattered showers off and on during that period. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 1137 AM CST Sat Feb 23 2019 LIFR cigs (~400 ft) will persist at KMSL while IFR cigs (~600 ft) will persist at KHSV through 22Z. A warm front will lift north of the area during the early afternoon, with some improvement to the cigs expected by 22Z, though cigs will still remain around 1500 ft. A cold front will push through the region late tonight, with showers and thunderstorms moving across the region ahead of the front. The bulk of this activity should reach KMSL between 01Z and 03Z and KHSV between 03Z and 05Z. These storms will produce gusty winds and the potential for severe hail. Isolated storms are possible ahead of this, and have introduced -TSRA at KMSL by 22Z and KHSV by 01Z. Timing is uncertain, so amendments may become necessary later in the afternoon. Storms will end between 03Z and 05Z, with conditions quickly improving at the terminals as the cold front moves through the region. Outside of thunderstorms, winds will remain gusty through the day and into the morning hours on Sunday. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Flash Flood Watch until midnight CST tonight for ALZ001>010-016. TN...Flash Flood Watch until midnight CST tonight for TNZ076-096-097. && $$ NEAR TERM...KTW SHORT TERM...KTW LONG TERM...KTW AVIATION...73 For more information please visit our website at weather.gov/huntsville.