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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 201949

Area Forecast Discussion
National Weather Service Huntsville AL
249 PM CDT Thu Sep 20 2018

.NEAR TERM...(Tonight)
Issued at 250 PM CDT Thu Sep 20 2018

The Muscle Shoals area was able to climb to 99 degrees more than 
once this afternoon. A decent cumulus deck has formed that will 
likely help to keep highs from possibly climbing over 100 degrees. 
Most guidance continues to show a fairly solid cumulus deck continue 
to become more widespread and move northward tonight towards southern
middle Tennessee. 

Slightly better convergence/deeper moisture, should allow this cloud
cover to maintain itself overnight. Several models do show some 
scattered precipitation developing as well. Based on soundings, this 
should be mainly showers and possibly an isolated thunderstorm. 
Although forcing is better, it is still very meager, so only included
a 20 to 30 percent chance in overnight, primarily after midnight. 

.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 agood 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 18Z TAFS through 18Z Friday afternoon)
Issued at 1220 PM CDT Thu Sep 20 2018

VFR conditions are expected through the TAF period. As forcing
increases near and west of the I-65 corridor, there may be just 
enough lift and moisture to produce isolated to widely scattered 
convection near both terminals around midnight tonight. However, due
to uncertainty, left specific mention of precipitation and MVFR cigs
out of terminals and just included a broken deck at 7000 feet for 
now. If -TSRA or lower cigs impact either terminal after 06Z, then 
MVFR or lower vsbys/cigs could briefly occur through 21/13Z. Better 
SHRA chances and thicker cloud cover should develop near both 
terminals after 13Z through 18Z. Included a tempo group to account 
for this with MVFR cigs. 





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