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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 211759

Area Forecast Discussion
National Weather Service Huntsville AL
1159 AM CST Tue Nov 21 2017

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 1159 AM CST Tue Nov 21 2017

Despite light winds, temperatures across the region have risen into
the mid and upper 50s. Will make adjustments here too and send out
another update shortly. 

Previous 10 AM issuance....

If you prefer dry/mild weather, today should be shaping up like 
that. An area of high pressure that brought the chilly conditions to 
the region yesterday morning (and not as cool this morning) has 
continued building eastward. It was now situated off of the east 
coast and north of Bermuda. An anticyclonic flow around it has firmly
placed the Tennessee Valley in a light southerly flow.

Somewhat deeper moisture, and a few light showers were in progress
along parts of the Gulf coast. These showers, and more clouds were
moving NNE from the western Florida panhandle to across eastern
Alabama and much of Georgia. In fact, the lower clouds have spread
westward over Ft Payne. West of here, periods of more high clouds 
were spreading to the east as a surge of high altitude moisture heads
eastward, rounding large scale troughing extending southward along 
the Mississippi Valley region. 

The lower clouds should remain across parts of NE Alabama, and even
retrogress west of the Cumberland Plateau; or across Winchester
during some of the afternoon. The remainder of the region should 
experience more sun - and somewhat warmer high temperatures. The sun
and light southerly flow should help high temperatures rise into the
lower 60s. 

.SHORT TERM...(Today through Thursday) 
Issued at 330 AM CST Tue Nov 21 2017

Our gradual warming trend will continue today as deeper southerly
flow develops ahead of an approaching cold front, progged to pass
through the region early Wednesday. Regardless of the warmer temps
and slight moisture return from the south, ridging through around H7
along with a decent subsidence inversion in place will keep rain
chances minimal. It is worth noting that a few global and regional
models were hinting at a possibility of some showers today for parts
of DeKalb and eastern Jackson associated with a surge of moisture
from the Gulf. However, expect that feature to remain east of the CWA
as the mid/upper level trough will swing through the area during the
afternoon hours. 

Late Tuesday/early Wednesday timeframe will feature a dry cold front
quickly shifting through the area, helping to reinforce some cooler 
than average temps. Thanks to the cold air advection, temps on 
Wednesday will likely only push into the upper 40, maybe mid 50s for 
our southern zones. Expect temps to fall into the upper 20s by early

This cold air mass will gradually moderate by Thursday. Low level
flow will start to lose its northern component as the ridge shifts
east, however mid/upper level winds will keep N/NW flow in place. So
while temps will be warmer Thursday and Friday morning compared to
the previous day, we will still trend below average for mid/late Nov.

.LONG TERM...(Friday through Monday)
Issued at 330 AM CST Tue Nov 21 2017

On Day 4 (Fri) an upper shortwave axis will be dropping southeast 
through the TN valley into the existing trough position over the 
central Gulf Coast and Gulf of Mexico. This will produce little more
than a few high clouds with the baroclinic zone/surface low will be 
developing/moving northeast across the FL peninsula and east of the 
Carolinas. A sprawling high pressure ridge will follow behind from 
the central Appalachians through the western Gulf Coast on Friday. 
Then, another shortwave and fast moving cold front will drop 
southeast Friday night into Saturday morning (GFS) and Saturday 
during the day (ECMWF). The suggested blends yield high temps in the 
upper 50s/lower 60s Saturday, followed by about a 10 degree drop for 
highs on Sunday. With the surface high on the GFS dropping right over
the TN valley (and the ECMWF ridge over the area as well) ideal 
conditions for radiational cooling are expected. This means another 
widespread hard freeze is likely again on Monday morning with raw 
model dew points suggesting lows could drop into the 20s areawide. 
The models depict a rather quick airmass modification on Days 7-8 as 
a mid to upper level ridge shift east into the southeast U.S.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1159 AM CST Tue Nov 21 2017

VFR conditions should continue across the TAF sites. An area of
stratus moving northward from the Gulf across eastern Alabama should
remain east of the KHSV terminal into the evening. Otherwise periods
of high clouds will continue. A dry cold front arcing from north and
central Indiana, to near St Louis and Amarillo will move to the 
southeast, moving across the region tonight. No weather of
consequence is expected, except that S-SW winds will become NW 
after the front passes. Northwest winds should increase into the 
10-20 kt by late Wednesday morning. 





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