Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 211135

Area Forecast Discussion
National Weather Service Huntsville AL
535 AM CST Sun Jan 21 2018

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 330 AM CST Sun Jan 21 2018

Dry weather prevailed across the greater Tennessee Valley this
morning, thanks to surface high pressure situated east of the
region. Sky conditions ranged from mostly clear east to partly cloudy
west. This discrepancy in sky coverage has resulted in wide
temperatures ranges from west to east. With more clouds, current
temperatures ranged from 44 in Muscle Shoals, to 30 in Ft Payne with
clear skies. An hour or so ago, temperatures in NW Alabama were in
the lower 50s - with similar cold readings over the east. Notably
more lower level moisture was evident further to the west, with
dewpoints ranging from the upper 20s NE Alabama to the mid/upper 30s
west. A weak upper level system moving across the eastern Gulf coast
earlier produced a few light showers across far NW Alabama Saturday
evening. This activity has since dissipated with no precip occurring
over or near the area at the moment.

In contrast to the frigid conditions last week, much warmer weather
will continue today, as a southerly flow around the high east of the
region prevails. Highs today should rise into the mid 60s today,
well above seasonable norms around 51. If more sun occurs
(especially out west), would not be surprised at a few upper 60s by
later this afternoon.

.SHORT TERM...(Tonight through Tuesday)
Issued at 330 AM CST Sun Jan 21 2018

A storm system impacting the Great Basin and Intermountain West with
widespread showers and mountain snowfall, was heading across central
Divide. Surface cyclogenesis was occurring over the eastern NM/CO
plains as this system moves across the Rockies. This new surface low
will deepen and head towards the Great Lakes (reaching them during
Tuesday). A cold front extending south of the low will move across
the forecast area during Monday, bringing widespread showers and a
few thunderstorms. Inter-model comparison this go around was in
reasonably good agreement, bringing the front across the area mainly
in the late morning through late afternoon hours.

There should be strong wind shear preceding the front, along with
minimal instability. Thus again cannot rule strong storms - with the
main threat from strong wind gusts. Some of the storms could be
rotating in a relatively high sheared environment in the late
morning through mid afternoon. With slightly deeper moisture/high
stability to our south, a few marginally severe storms (again from
strong to damaging wind gusts) are a possibility mainly south of the
Tennessee River. The directional shear earlier, becomes more linear
in the afternoon with the front, which should help minimize a larger
scale severe threat. Shower activity should wind down from west to
east Monday evening as the front moves east of the region. Have
included isolated storms within more predominate showers for our
eastern areas early in the early evening. Shower activity should end
before midnight.

Pacific based surface high building in from west will bring more
seasonably cool conditions to the Tennessee Valley for Monday night
and Tuesday. Near freezing night time lows are possible Monday night
with lows in the low/mid 30s. Highs on Tuesday should range in the
upper 40s to around 50.

.LONG TERM...(Tuesday night through Saturday)
Issued at 330 AM CST Sun Jan 21 2018

Quiet and seasonal wx conditions should be ongoing across the cntrl
TN Valley at the start of the long term forecast period. A strong
dome of high pressure out of the mid/srn Plains states will continue
to build ewd into much of the SE region Tue night into Wed, with the
flow pattern aloft turning more towards the W. This should maintain
overall temps near normal trends for this time of the yr, with lows
Tue night right around the 30F mark before rebounding back into the
lower 50s Wed afternoon. Little change in the synoptic pattern is
really anticipated across the region going past mid week, as the sfc
high builds more into the area on Thu and weak upper ridging out of
the srn Plains translates ewd into the wrn/cntrl Gulf states. This
should result in slightly higher afternoon temps Thu, as highs climb
more into the mid 50s for most locations.

Moisture will begin to stream nwd back into the area on Fri, as the
sfc high shifts E and becomes layered across the nrn/mid Atlantic
Basins. With the upper ridge axis also quickly moving ewd over the
region, the brief warming trend should continue thru the end of the
work week, as afternoon highs on Fri climb into the upper 50s/near
60F. The latter half of the global models are still pointing to
another area of low pressure developing over the nrn Plains late
Fri, with the attendant cold front stretching as far S as the wrn
Gulf region. As the sfc low moves E into the Great Lakes around the
first of the weekend period, the front is xpcted to translate ewd
into the Midwest/Lower MS Valley areas. With moisture/cloud cover
continuing to increase into the mid TN Valley, rainfall/showers look
to develop along/ahead of the approaching front, and should begin to
work their way into the area late Fri into Sat. Given the increase
in cloud cover/rainfall, lows Fri night may only fall into the mid
40s for most areas. Highs on Sat though may be able to reach the 60F
mark given some moderate WAA into much of the region.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 535 AM CST Sun Jan 21 2018

Lower level moisture moving over the region has resulted in lower
altitude clouds (mostly above MVFR threshold over NW Alabama).
Could not rule out a brief MVFR deck over the KMSL terminal at the
start of the TAF. VFR weather otherwise should prevail over the
region today. SE winds this morning should become more southerly this
afternoon, then back towards the SE tonight. A storm system forming
over the Rockies will bring more clouds and rain chances to the area
- after this TAF.





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