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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 130525

Area Forecast Discussion
National Weather Service Huntsville AL
1125 PM CST Wed Dec 12 2018

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 

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

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. 





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