Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 261526
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
926 AM CST Sun Feb 26 2017

.NEAR TERM...(Rest of Today)
Issued at 925 AM CST Sun Feb 26 2017

A cold start to Sunday with temps around the TN Valley in the mid to
upper 20s. The exception was our TN counties where values were in the
lower 20s. Surface high pressure that built into the area last night
will begin to transition eastward today. This will take us out of a
CAA regime and heights through much of the atmosphere are expected to
warm throughout the day. With clear skies and increasing heights
aloft, temperatures are expected to warm 5-10 degrees above Saturdays
values. Highs this afternoon will range from the mid 50s across the
eastern half of the area to lower 60s over the western half. By this
afternoon we will start to see some increasing high level cloud cover
as a low pressure system over the TX panhandle begins to shift east.
But these will be too thin to have any impact on high temps.

The current forecast is in good shape and made only minor tweaks to
the trends.

.SHORT TERM...(Tonight through Tuesday)
Issued at 235 AM CST Sun Feb 26 2017

Expect thick cloud cover above 15,000 feet to arrive around midnight
in northwestern Alabama. This should be thick enough to produce
mostly cloudy conditions. This will spread east overnight. At the
same time, models develop a broad shortwave within the main flow
aloft over Oklahoma/Texas. The east fringe of upper level energy
ahead of this feature is forecast to push into the western edge of
the surface ridge after midnight on Sunday, with isolated to widely
scattered showers developing in northwestern Alabama by then. On
Monday morning, as stronger low level moisture advection is expected,
rain chances will increase. This is mainly due to the energy with
the weakening shortwave pushing into central Mississippi and northern
Alabama. Kept a 50 to 80 chance of rain west of I-65 Monday morning.
Models are quite different after mid-day on Monday concerning the
location of higher chances of rain. At this time going with a blend
of both the ECMWF and GFS. Keeping 50-60 percent chance of rain
across most of the area.

Models keep weaker upper level energy moving across central/northern
Alabama Monday night into Tuesday. Enough instability aloft is
forecast by most models to include isolated thunderstorms Monday
night into Tuesday morning. Although more surface based instability
will be in place on Tuesday morning, a strong 700 mb CAP will be in
place as well. By Tuesday afternoon, models are hinting that the CAP
may break late in the afternoon. If that happens some strong storms
are possible, maybe even a few marginally severe (especially in
northwestern Alabama). Main severe thunderstorm threats look to be
damaging winds or a brief, weak tornado if the CAP breaks.

.LONG TERM...(Tuesday night through Saturday)
Issued at 235 AM CST Sun Feb 26 2017

A stormy middle of the week looks more likely across the Tennessee
Valley. A few items of note that will get things going... An upper
level system currently moving southward along the British Columbia
coast will intensify somewhat over the next day as it moves across
the Pacific Northwest. Another upper low now located near 34N142W
will move eastward, and combine with the more eastward system. This
fortified system will move to eastward and becoming neutrally tilted
by the middle of the week, as it moves across the Mid Mississippi
Valley. While it tracks across the Continental Divide on Monday, it
will induce surface cyclogenesis east of the Colorado Front Range.
This next surface low should move to the ENE, reaching the Great
Lakes region during Wed morning. The models through that time-frame
are in reasonably good agreement with the position/strength of the
surface low.

This system`s cold front on Wednesday morning should extend SW to
Missouri, and to east/central Texas. Strong lift with and ahead of
the front will bring scattered showers and a few thunderstorms
Tuesday night, with rain chances increasing as the front and upglide
preceding this system increases. Went with Definite rain chances for
most of our area, and Likely just for our further southeast areas
during Wednesday.

The map/plain view and point soundings during this period points to
a potential for strong to severe storms, especially on Wednesday. The
best chances for severe weather appears will occur mainly to our
north, closer to the main surface low and where moisture convergence
and shear values appear will be maximized. A severe threat will
continue given elevated convective forecast values, including SHERBS3
values above 1 across most of the Deep South north of I-20. The
GFS/ECMWF still point to a possible convective line moving west to
east across the region during Wednesday. Timing of the front becomes
varied depending upon the model, with the GFS back to a slightly
faster timing than the ECMWF. Further down the line and well north of
here, even more dramatic differences between the base GFS and EC
regarding the surface low. The GFS "goes to town" taking a slightly
further north and much deeper solution than the EC, beginning Wed
night, which would account for a faster QLCS/front passage.
Strong/damaging wind gusts appear to main threats from the stronger
storms.

Drier and cooler conditions, with daily high/lows a tad below
seasonable norms will return on Thursday, as the front exits further
to the east, and a Pacific based surface high builds eastward. This
dry trend should continue into Friday and Saturday. High temps by Sat
should return to or just above seasonable levels, which happen to be
around 61F.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 540 AM CST Sun Feb 26 2017

VFR conditions are expected throughout the TAF period at both
terminals. A few showers may impact the KMSL terminal after 07/06Z.
However, due to expected isolated to widely scattered coverage, only
a VCSH was added between 07/06Z and 07/12Z and cigs were lowered to
8000 feet.


&&

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

$$

NEAR TERM...Stumpf
SHORT TERM...KTW
LONG TERM...RSB
AVIATION...KTW


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