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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

                            
432 
FXUS64 KHUN 201729
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1129 AM CST Mon Nov 20 2017

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 847 AM CST Mon Nov 20 2017

With an exception of locations just downwind of large bodies of
water, a growing season hard freeze affected nearly all of the
Tennessee Valley last night. The lowest temperature noted thus far 
was 19 in Winchester, with just about all other locations having 
lows of at least 28 degrees. As of the present, temperatures across 
the forecast area have risen above 32 degrees. As such, a Non- 
Precipitation Warning for Freezing temperatures was allowed to expire
at 8 AM.

The forecast otherwise for the rest of the day should feature
slightly warmer temperatures, as generally sunny skies prevail 
across the the southeast CONUS. A shield of high clouds associated 
with a slight dip in the upper jet should persist through the day. 
High temperatures later this afternoon should rise into the low/mid 
50s, a category or two warmer than yesterday. Lighter winds from the
southeast and south will make for more comfortable conditions for 
those working outdoors today. The removal of the Freeze Warning and 
minor forecast updates for today were recently sent.

.SHORT TERM...(Tuesday through Wednesday night)
Issued at 233 AM CST Mon Nov 20 2017

By this point in the forecast (Tuesday), a sheared mid-level 
shortwave moving within the northwesterly flow over the northern 
Plains will rapidly move underneath a deepening shortwave trough over
the Great Lakes. Meanwhile, low-level clouds are expected to develop
just off the coast of GA and move northwest towards eastern Alabama.
Antecedent southeasterly flow will advect modified air towards the TN
Valley on Tuesday which combined with the daytime heating will mean
daytime highs should reach into the low 60s. It is possible that some
very light precipitation could reach the ground over northeast
Alabama on Tuesday afternoon within the 'warm air' advection zone, 
but due to the very dry airmass in place, not confident enough to
include in the forecast.

A reinforcing cold front moving ahead of the shortwave trough moving
over the Midwest on Tuesday is expected to arrive over the TN Valley
on Tuesday night into Wednesday morning. Forecast soundings and
moisture transport products do show the potential for cloud cover
both at the low-levels (above 850 mb) and mid-levels pre- and post-
frontal. Nevertheless, these same profiles also show very dry surface
layers. So, will keep the dry forecast. The primary change will be to
the temperatures on Wednesday. Current guidance is cooler with the
daytime highs post-frontal passage on Wednesday morning. Given the
source region and speed of this front, incorporating highs in the mid
to upper 40s (NW) and low 50s (SE). In addition, northerly winds of
10-15 MPH will make it feel cold on Wednesday. After sunset,
temperatures should drop quickly below freezing again which will
given a cold start to Thanksgiving Day.

.LONG TERM...(Thursday through Sunday)
Issued at 233 AM CST Mon Nov 20 2017

A dry and seasonably cool weather pattern will remain over the 
region from days 4-7.  The trough in the eastern Gulf of Mexico will 
be enhanced by another shortwave dropping south on Thu-Fri with a 
Gulf surface low becoming more defined and lifting northeast across 
the FL peninsula on Friday into Saturday.  The surface ridge planted 
across the southern into the east central CONUS will narrow and 
weaken during this time as another cold front drops southeast 
through the OH into the TN valley.  This as amplification of the 
upper trough over the eastern CONUS occurs.  Timing of this frontal 
passage looks to be on Saturday afternoon and will likely be precip-
free. After highs in the 50s Thursday and Friday, we may reach the 
lower 60s just before this front passes, then decline again into the 
upper 40s to lower 50s for highs on Sunday, followed by another 
freeze Sunday night into Monday morning.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1129 AM CST Mon Nov 20 2017

Surface high pressure moving eastward across the region will continue
to produce VFR weather for the TAF period. Scattered to occasionally
broken high altitude clouds will affect the region into Tuesday 
morning, as a weak upper system moves across the SE States. Light SE
winds today will become light/variable tonight, then light from the
south a few hours after daybreak on Tuesday. 

&&

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

$$

NEAR TERM...RSB
SHORT TERM...SL.77
LONG TERM...17
AVIATION...RSB


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at weather.gov/huntsville.