Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
536 FXUS64 KHUN 210439 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1139 PM CDT Thu Sep 20 2018 .UPDATE... For 06Z TAFS. && .NEAR TERM...(Tonight) Issued at 833 AM CDT Thu Sep 20 2018 Quiet wx conditions prevail across the cntrl TN Valley this Thu evening, as temp trends fall into the lower/mid 80s from their near record highs earlier today. With sfc winds fairly light, these temps should continue to fall into the 70s overnight, with lows early Fri mainly in the upper 60s/near 70F for most spots. Moisture is also gradually spreading into the area from the southeast along a weak sfc trough located west cntrl AL into extreme NW AL. This weak boundary may be a focus for a few showers/tstms later tonight across NW AL, although the prob is fairly low. Showers/tstms may then develop a bit more to the east heading into Fri morning, although rain chances will remain somewhat low for now. .SHORT TERM...(Friday through Saturday) Issued at 250 PM CDT Thu Sep 20 2018 During the day on Friday, convergence increases, as the surface high moves further east and a stronger cold front in the western Great Lakes region gets closer. Should see a better coverage of showers and thunderstorms. Kept 30 to 40 percent chances of activity in the forecast. This trend continues into Friday night, as the front edges slightly closer. Model guidance is split concerning how far south the more concentrated/heavier shower and thunderstorm activity sinks. At this point went a bit below Superblend and closer to GFS with 30 to 50 pop. Expect higher chances of rain to be in northwestern Alabama and southern middle Tennessee. Could see a few stronger storms capable of producing gusty winds and heavier rainfall as shear between 25 and 35 knots impinges on areas near the TN/AL border and in southern middle Tennessee. This doesn't change much on Saturday night, as the front seems to stall in westerly flow. Shower and thunderstorm chances don't change much and heavy rain and gusty winds look to be the biggest threats with stronger thunderstorms. .LONG TERM...(Saturday night through Wednesday) Issued at 250 PM CDT Thu Sep 20 2018 Some changes coming to the forecast in the extended period as a cold front will continue to slowly push ESE from the lower Ohio Valley and Mid-South into the Tennessee Valley. With the upper-ridge sliding off to the east of the Carolinas, this will promote a deeper southwesterly flow, and thus good moisture flux off the Gulf of Mexico. This can be seen with dewpoints which are progged to return to the lower 70s this weekend. This boundary will approach Tennessee/Alabama border on Sunday and serve as a focus for scattered to perhaps numerous showers and thunderstorms along and near it. This activity will be somewhat tied to heating, even with a boundary in place. Therefore, would expect this activity at it's greatest coverage in the afternoon hours -- even with the forcing mechanism in place. The most favored areas for storms will be nearest to the front, across far Northwest Alabama and Southern Middle Tennessee, with this activity becoming more widely scattered along and south of the Tennessee River. The added cloud cover will make for a cooler day as highs in the mid 80s will be common -- around 15 degrees cooler than what we've experienced of late. Models are hinting that the boundary may actually retreat back northward on Monday as the Bermuda high temporarily tries to nose it's way back into the Southern Appalachians. The result, will likely be less clouds and a warmer, drier day. Still, with southwest flow and abundant moisture in place, there will be plenty of ingredients for some scattered showers and storms. The deepening upper-trough will then swing southeast from the Canadian prairies into the Great Lakes and Ohio Valley from Tuesday into Wednesday. This will force a stronger, secondary cold front south into the Tennessee Valley sometime during this timeframe. Thus, more widespread shower and thunderstorm activity, and hopefully some much needed rainfall is possible during the middle of next week. The best dynamics, however, will be well displaced of the region and thus am not expecting any severe risk with this activity. Behind this front, some cooler (more autumn-like) and drier air will filter into the area, which may actually support highs in the upper 70s to lower 80s come late next week! && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1139 PM CDT Thu Sep 20 2018 No changes to previous aviation forecast reasoning. With a weak area of high pressure remaining in place across the srn Atlantic Basin, VFR conds prevail at both main airports. Little change in these conds is xpcted into the day Fri, with mid/high clouds developing across the area as moisture spreads into the area from the south. Some -shra may also begin to develop across parts of the area late tonight into Fri, and in addition to a prevailing VCSH, a PROB30 group was added late in the TAF to account for any precip. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...09 SHORT TERM...KTW LONG TERM...AMP.24 AVIATION...09 For more information please visit our website at weather.gov/huntsville.