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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

                            
554 
FXUS64 KHUN 211137
AFDHUN

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

.UPDATE...
For 12Z TAFS.

&&

.NEAR TERM...(This morning) 
Issued at 330 AM CST Tue Nov 21 2017

Surface analysis this morning shows the high pressure ridge axis
nearly bisecting AL as it remains centered over Carolina coast line.
Gradient flow itself is fairly weak, with winds currently under 5
knots across the CWA. GOES R IR bands continue to show a thin layer
of cirrus clouds over parts of S. Middle TN and NE AL
(DeKalb/Jackson). This has kept temps a bit higher compared to obs
site further west. Temps have only dipped into the upper 30s/low 40s
across the TN counties and parts of DeKalb thanks to the cloud cover.
West of I 65 has observed temps already in the low 30s.  

.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
Thursday. 

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.
temps. 

.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 12Z TAFS through 12Z Wednesday morning)
Issued at 537 AM CST Tue Nov 21 2017

VFR conditions will prevail through today. South winds will gradually
veer toward the west through the day today ahead of an approaching
dry cold front. The front is expected to sweep through the area late
tonight/early Wed. morning. While no significant convection is
expected, winds will shift to the north between 3-6Z. 

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...Barron
SHORT TERM...Barron
LONG TERM...17
AVIATION...Barron


For more information please visit our website 
at weather.gov/huntsville.