Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 271550

Area Forecast Discussion
National Weather Service Huntsville AL
950 AM CST Mon Feb 27 2017

.NEAR TERM...(Rest of Today)
Issued at 950 AM CST Mon Feb 27 2017

An area of light-moderate rain has just about pushed across the
Huntsville CWFA this morning, faster than just about any short-
range model had predicted even within the last 2-3 hours. GOES-East
visible imagery even indicates some partial clearing ongoing in
extreme northwest Alabama at this point--and some blue sky is even
visible from this office--though it may not last very long.
Temperatures areawide are consistently in the mid 40s in the wake of
the rainfall.

The newest short-range models (HRRR and the like) suggest that this
is just about it for us today in terms of rain, as the weak mid-level
shortwave pushes east in this progressive pattern. The forecast PoPs
will be updated to show a downward trend for the rest of the day.
Satellite trends suggest that the clearing will be short-lived with
more clouds filling in later this morning, but many areas may still
see a brief glimpse of sunshine. Temperatures should rebound nicely
behind the rainfall, as they have already done in parts of north
Mississippi and west Tennessee. Blended guidance continues to show
upper 50s, which may be a little optimistic but attainable with the
brief clearing.

.SHORT TERM...(Tonight through Wednesday)
Issued at 415 AM CST Mon Feb 27 2017

Scattered rain chances should continue tonight. Added thunder to the
mix after midnight as greater instability is realized. Milder
temperatures are in the forecast with lows only in the low/mid 50s.
Another system moving in will bring likely shower/thunderstorm
chances on Tuesday. Rain chances again should be reduced somewhat
Tuesday evening, but should pick up late in the night, as the main
system approaches. Some of the storms Tuesday evening/overnight
especially out west could become strong, with gusty winds the main

The upper system noted above over the western CONUS will track
eastward and spawn a surface low east of the Rockies today. This
next low will move towards the Great Lakes during Wednesday, and
bring a strong cold front eastward. This front as it nears will help
produce widespread showers and thunderstorm. Most of the convective
parameters are on the high side as they have been the past few runs;
all suggestive of a severe weather episode for the Tennessee Valley -
with damaging wind gusts the main threat. Large hail and a few
tornadoes are also possible too, especially if breaks occur in a
squall line as it moves across the region on Wed. Dewpoint values
during Wed should rise into the lower 60s area wide, with 0-3km
helicity values between 200-400 m/s (at times higher), and CAPE
values around 500 j/kg. The Day-3 Convective Outlook shows similar
trends yesterdays Day-4 outlook indicated. The GFS again was the
quicker of the models concerning timing with the front/Quasi-Linear
Convective System or QLCS. But the ECMWF was indicating a further
southward and deeper surface low than it had yesterday, which could
enhance overall storm strength. The severe threat will end from NW to
SE during the course of the day as the QLCS moves across the region.
Timing from the GFS has it well SE of the forecast area before dusk,
while the EC was delayed by 3-5 hours or so.

.LONG TERM...(Wednesday night through Sunday)
Issued at 415 AM CST Mon Feb 27 2017

Most of the very active wx should be just about thru NE AL with the
onset of this part of the forecast package, as showers/tstms continue
to quickly taper off from the w with the passage of the cold front.
The latter half of the model suites point to the sfc boundary moving
ewd into the mid/srn Atlantic basins late Wed evening, with the
associated convective line in tow. This in turn will allow a strong
dome of high pressure out of the mid/srn Plains states to build ewd
into the SE region into early Thu, as clouds begin to gradually sct.
High pressure out of the nrn Plains will actually become reinforced
across the cntrl TN Valley by Fri, under mostly clr/sunny skies. This
should allow for a brief cooling trend going into the weekend period,
as overall temps trend closer to seasonal values. Rain chances may
then work their way back into the forecast by the end of weekend
period, as the sfc high translates ewd into the srn Atlantic and
return/sly flow develops across much of the region. With the slow
increase in returning moisture, weak isentropic lift may provide
enough support for sct showers into the new week.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 554 AM CST Mon Feb 27 2017

VFR weather across the region will deteriorate this morning, as an
area of showers affecting north and central Mississippi moves towards
and across the Tennessee Valley. An embedded thunderstorm cannot be
ruled out today within the heaviest showers, but chances of them are
too low for inclusion into the TAF. CIG/VIS values should be reduced
into the MVFR range in shower activity today. Higher moisture values
and low clouds should continue tonight after the showers exit to the
east - continuing MVFR flying weather. IFR CIG reductions look
possible across the area late in the TAF.





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