Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 191736
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1136 AM CST Sun Nov 19 2017

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 1000 AM CST Sun Nov 19 2017

The cold front that brought showers/thunderstorms and strong winds to
the Tennessee Valley yesterday has continued its movement further
eastward. The front was trailing south of a surface low over SE
Quebec, then moving in an west-east manner across the New England
region, to the southeast across the North Carolina Outer Banks, and
near Gainesville FL. A much cooler airmass west of this front has
become entrenched across the eastern 2/3`s of the CONUS, thanks to
cool surface high pressure centered over West Texas.

Despite the high being the main controlling feature, residual lower
level moisture wrapping around the departing cyclone was sending
stratus SSE across the Tennessee Valley from Middle Tennessee. Short
term model output has these clouds thinning and moving more to the
east as the day progresses. Thus our more western areas should
experience more sun versus more clouds over the east. Despite a
presence of the clouds or not, a much colder day is in store for the
Tennessee Valley. After highs in the upper 60s and lower 70s
yesterday, highs will struggle into the upper 40s to lower 50s.
Northwest winds in the 5-15 mph range should produce wind chill
values, making it feel 5-10 degrees cooler - especially in more
exposed locations.

As noted below in the previous Short Term area, a hard freeze looks
likely for the entire forecast area tonight, except in locations
near and downwind of large bodies of water.

.SHORT TERM...(Tonight through Tuesday night)
Issued at 225 AM CST Sun Nov 19 2017

As high pressure settles in over the area this evening winds begin to
taper off and become light after midnight. Dewpoints are forecast to
drop into the low to mid 20s. Couple those two things with clear
skies and it should be a good radiational cooling night with lows in
into the mid 20s. Did end up tweaking temps down a degree from
previous forecasts. These values warrant the issuance of a Freeze
Warning for much of NW and north central AL. NE AL and our TN
counties have experienced freezing conditions earlier this year and
will not be included in this issuance. The high begins to shift east
on Monday with winds turning to the E/SE by the afternoon hours.
Sunny skies and slight WAA will allow highs Monday to reach the mid
to upper 50s.

Monday into Tuesday: a trough moving along the Gulf Coast begins to
pivot/lift NE into southern GA. A few waves embedded in the flow are
forecast by latest guidance to move just south of the area. Models
are surprisingly consistent in showing a few spotty showers
developing over eastern AL and central to NW GA. These appear to be
generated off of a convergence axis and likely aided by the
shortwaves moving overhead. But soundings continuing to show a very
dry atmosphere over the TN Valley so the forecast will remain dry
through the short-term. We will see an increase in high level clouds
on Tuesday but that should be it. Highs reach into the lower 60s for
much of the area. The only exception will be across NE AL with highs
in the mid to upper 50s. Lows Tuesday morning and Wednesday morning
warm back above the freezing mark with values in the mid 30s.

.LONG TERM...(Wednesday through Saturday)
Issued at 225 AM CST Sun Nov 19 2017

The mean synoptic scale trough pattern will prevail over the eastern
half of the country while ridging will build over the desert
southwest. This will create a dichotomy of temperatures with warm
(possibly record breaking heat) over the desert southwest, while
cool (below normal) weather largely prevails across the eastern half
of the country. Within the persistent northwesterly flow setup from
Manitoba to the southeast, several mid-level shortwave troughs will
track southeast bringing dry reinforcing cold fronts. A couple of
these shortwave troughs will amplify the southern flank of a longwave
trough moving across the MS River Valley and Gulf coast. By
Wednesday a second mid-level shortwave trough will have caused a
split polar jet flow pattern to develop with the southern portion
stretching further south than normal (over the central Gulf of
Mexico) while the northern portion of the polar jet remains over the
Great Lakes/Southern Canada. A cold front will accompany this
shortwave trough pushing over the TN Valley early on Wednesday
morning.

Antecedent dry environment with little in the way of moisture
advection will result in no precipitation with this cold front.
Temperatures will struggle to rise into the low to mid 50s on
Wednesday. Then, another freeze is expected on Wednesday night as
surface anticyclone moves close to the TN Valley from the Ozarks/MS
River Valley.  By Thanksgiving Day, the cutoff low located just off
the northern Gulf coast will be inducing widespread showers over
Florida and southern GA. Meanwhile, a mostly sunny and cold, day is
expected across the TN Valley with highs in the low to mid 50s.

Friday will be a little warmer with daytime highs in the mid to
upper 50s as the high pressure system becomes compressed between the
cutoff low (moving over the Atlantic coastlines of FL/GA) and next
shortwave trough moving across the northern Plains. Some variability
in trajectory and also potential for at least low level moisture
advection may increase the potential for light precip on Saturday
into Saturday night. However, will keep the area dry
Saturday/Saturday night given the uncertainty on the moisture
return.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1136 AM CST Sun Nov 19 2017

Residual VFR stratus moving across areas east of I-65 from the NW
should continue to thin and diminish this afternoon, as drier and
colder air from the north filters in across the region. NW winds
should veer to the north, but become light/variable shortly after
sunset, with clear skies expected. Light SE winds are forecast to
develop a few hours after sunrise Monday morning.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Freeze Warning from 9 PM this evening to 8 AM CST Monday for
     ALZ001>008-016.

TN...NONE.
&&

$$

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


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