Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
000 FXUS64 KHUN 130525 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1125 PM CST Wed Dec 12 2018 .UPDATE... For 06Z TAFS. && .NEAR TERM...(Tonight) Issued at 814 PM CST Wed Dec 12 2018 High pressure at the sfc continues its slow advance off the coast of GA/SC, with a cold front well NW of the area approaching the mid-MS River Valley. This setup is allowing S/SW flow to develop in the tightening pressure gradient to the NW over portions of AR/TN/MS, which will shift E/SE over the next 12 hours or so. A look at regional radars shows a few echoes approaching NW AL, extending back into Ern AR. METARS sporadically show a few -RA reports along the MS River, but not much between here and there. Much of what's falling is rather light and is evaporating before it hits the ground (thanks to dewpoint depressions of 15-20 degrees). Models keep much of this light activity NW of the CWFA for tonight As such, much of tonight will be dry, with the bulk of the rain not arriving until late in the day tomorrow. For tonight, all wx elements are on track at this hour for lows to fall into the middle 30s E/lower 40s W. Therefore, no major changes were warranted for the public forecast update this evening. .SHORT TERM...(Thursday through Friday) Issued at 252 PM CST Wed Dec 12 2018 This setup changes little during the day on Thursday, with a strong upper low pushing east from Colorado/New Mexico into Oklahoma and Texas. A decent low level jet develops between 30 and 45 knots ahead of this feature and its associated surface low. However, deeper moisture remains well west of the area over Louisiana and Mississippi. Very strong upper level jet shown with this feature associated as the subtropical and main jet stream phases. Not looking at any instability both at the surface and aloft in most guidance during the afternoon and evening hours on Thursday. However, precipitation chances really ramp up towards midnight and overnight. Warmer temperatures are expected with lows only dropping into the mid 40s to around 50 degrees due to cloud cover and warm air advection. Friday should be even warmer (highs in the mid to upper 50s) with continued high precipitation chances, as the surface low and associated storm system moves east into Mississippi. Some guidance does show some surface based instability edging into our extreme southwestern counties in the afternoon, but only about 100 to 500 J/KG. With such a strong wind field this could still be enough where if that is realized some stronger storms are possible. However, at this time that is extremely uncertain. Friday evening models show cold air aloft moving with the upper low over the area and some elevated instability (though surface based instability goes away). This could lead to a extended potential of stronger storms into the evening hours. Main threat could be small hail. Saturday looks showery, as the surface/upper low continue to slowly exit the area. At this point, little instability is shown. Temperatures should be a bit cooler with highs only in the upper 40s/lower 50s. .LONG TERM...(Friday night through Tuesday) Issued at 252 PM CST Wed Dec 12 2018 A strong upper low will be swinging through the TN Valley on Saturday night, exiting to our northeast by daybreak. Forecast models differ on just how quickly the low moves out of the area, with the ECWMF the slowest. The main implication for this would be the potential for lingering light showers through the overnight hours, but for now have precip ending by midnight. Regardless, lingering cloud cover will keep overnight lows mild for this time of year, with temps only falling to around 40 by daybreak on Sunday. An upper ridge will begin to build into the Plains on Sunday, while the upper trough axis pushes through the eastern CONUS. This will keep northwest flow aloft over the TN Valley, with surface flow generally to the north as high pressure builds into the region. The ridge will move through the Mississippi Valley on Monday and into the TN Valley by Tuesday, with high pressure remaining at the surface. This will keep dry conditions over the area for much of the long term period, with temperatures right around seasonal norms (highs in the low-mid 50s, lows in the low-mid 30s). && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1125 PM CST Wed Dec 12 2018 VFR conds will prevail at both KHSV/KMSL terminals through mid/late afternoon Thursday. Gusty S winds will be sustained between 10-15mph, with gusts up to 20-25mph possible. Closer to or shortly after 00Z Friday, rain will overspread the terminals, expanding in coverage after 06Z Friday. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...12 SHORT TERM...KTW LONG TERM...73 AVIATION...12 For more information please visit our website at weather.gov/huntsville.