Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 201056 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
456 AM CST Tue Feb 20 2018

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 347 AM CST Tue Feb 20 2018

Mild temperatures were observed at 07Z in the middle to upper 60s for
most locations. This was due to southerly flow holding at at 5-10kt.
The exception is along the GA border where the western edge of weak
cold air wedging was occurring. Low clouds have edged into far
northeast AL, but do not expect the dense fog now over north central
and northeast GA to reach this area (with the exception of mountaintop
fog due to the clouds).

As as been advertised, a mid and upper level ridge has built off the
southeast U.S. coast, enabling a large southerly fetch of warm and
moist air to flow into the TN valley. Record highs will be neared or
set again today as a result, with forecast soundings supporting
80-81F in the HSV/MSL areas, and upper 70s elsewhere. The low clouds
this morning will likely keep the 4A9/Lookout Mountain area in the
middle 70s.

.SHORT TERM...(Tonight through Thursday)
Issued at 347 AM CST Tue Feb 20 2018

The short range models continue to indicate a weak upper impulse
rotating northward from the Gulf of Mexico around the western portion
of the anti-cyclone. This will generate isolated light showers or
sprinkles tonight into early Wednesday, mainly for areas of eastern
AL into GA. Meanwhile, the NAM/SREF and ECMWF remain constant in the
upper ridge holding the frontal band precipitation to our northwest
and west through Wednesday and possibly into Thursday as well.
Forecast soundings indicate a strong capping inversion in the warm
sector further southeast. In this scenario, the northwest corner of
AL into western portions of southern middle TN will stand the best
chance of showers reaching their areas late Wednesday into Thursday
as the cold front edges close to these areas, but unlikely through
the area. The GFS continues to be the outlier, and aggressively
driving a cold pool and the precipitation band more fully into the TN
valley. Will be siding with the NAM/ECMWF/SREF in this regard to PoP,
with low chances southeast and likely just touching the northwest tip
of AL. Temperatures on Wednesday should still reach the upper 70s to
lower 80s in the warm sector. Thursday is a bit more questionable
with the rain/cloud area north and west, so went with low to middle
70s north, and upper 70s south of the TN River.

.LONG TERM...(Thursday night through Monday)
Issued at 347 AM CST Tue Feb 20 2018

The lingering frontal boundary and warmer than normal temperatures
highlight the extended forecast. The upper ridge is still anchored in
the Western Atlantic, stalling the front to our NW. There is still
some model disagreement on if the front will start to enter the TN
Valley Thurs before lifting back northward Thurs Night/Fri or if it
will remain stalled out to our NW. The GFS is still the one who lets
the front dip into the TN Valley and has the earliest timing with
front compared to the ECMWF, Canadian and NAM who will not let the
front budge until this weekend. Kept in the chance for a few showers
Thurs night with weak lift, the amount of moisture in place and WAA.
Overnight lows will be mild around 60 degrees.

The stubborn ridge starts to break down on Friday as a upper level
trough digs into the Four Corners region. As southerly flow picks up
with the increased pressure gradient, the additional WAA will help
afternoon temps into the upper 70s. Precip chances still linger into
Friday, however just looking at isolated showers.

As the trough ejects from the Four Corners this weekend it will
develop a sfc low near TX/OK that will lift into the MS Valley on
Saturday. Temperatures will be warmer than normal and plentiful
moisture already in place across the region ahead of the front. Highs
on Saturday will be in the lower 70s. The front will push into the
TN Valley Sat Night/Sunday with showers and thunderstorms possible
along and ahead of the front. Models are in better agreement with the
weekend set up, but it is still too early to list any potential
hazards. The front will move out of the area Sunday night/early
Monday, with cooler and drier air filtering in behind it.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 456 AM CST Tue Feb 20 2018

VFR flight weather conditions are expected today. Multi-layer clouds
will develop by late morning into early afternoon. The clouds will be
scattered at 030-035agl with ceilings around 050agl. Isolated light
showers or sprinkles will be possible from these clouds as they lower
to around 020agl (MVFR) tonight, but have left out of the terminals
at this time.





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