Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 200833

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

.NEAR TERM...(Today and Tonight)
Issued at 233 AM CST Mon Nov 20 2017

A fairly active and amplified upper flow pattern is expected to bring
several mid-level shortwave troughs across the eastern half of the
country as a synoptic ridge builds over the Desert Southwest. The
resulting continental polar airmass intrusions will keep temperatures
cooler and dry conditions in place. Meanwhile, above normal
temperatures are forecast over the Desert Southwest.

A continental polar airmass underneath a surface high pressure
system centered just to the northwest over the MS River Valley and a
clear sky is allowing temperatures to drop below freezing this
morning. As a result, will keep the freeze warning in effect through
8AM as most locations should experience a hard freeze over the coming

After sunrise, temperatures should gradually rebound into the low to
mid 50s today underneath a sunny to mostly sunny sky. The high
pressure system should move east today causing weak northerly winds
(around 5 MPH) to veer to the southeast. Though not expecting a big
warm up tonight, overnight low temperatures should moderate somewhat
into the mid to upper 30s with slightly higher temperatures near the
TN River.

.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 06Z TAFS through 06Z Monday night)
Issued at 1137 PM CST Sun Nov 19 2017

With a strong area of high pressure building ewd into the region, VFR
conds are xpcted thru the TAF period.


AL...Freeze Warning until 8 AM CST this morning for ALZ001>008-016.




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