Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 271221

Area Forecast Discussion
National Weather Service Huntsville AL
721 AM CDT Mon Mar 27 2017

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 540 AM CDT Mon Mar 27 2017


Quiet wx conditions prevail for now across the cntrl TN Valley, with
temp trends predom in the upper 50s/lower 60s for most locations
under mostly cloudy skies. Strong sly fetch pattern leading well into
the n cntrl Gulf also remains well entrenched over the SE region,
thereby helping to continue ushering moisture into the local area.
The overall pattern though will be changing heading into the daytime
hrs, as strong upper disturbance traversing newd ahead of the main
upper low over the mid Plains translates into the Midwest region.
Latest 00Z ECMWF/GFS have the shear axis stretching into the Mid
South/mid TN Valley areas going into the afternoon/evening periods.
With the buoyant energy/SBCAPE values in the 1500-200 J/kg spreading
into the cntrl TN Valley from the ssw later today coupled with Bulk
Shear values increasing into the 40-50KT range, the potential for
strong/svr tstm development is beginning to look better for most of
the local area. Optimal timing will be from this afternoon into the
evening hrs where better latent heating will be in place and the
upper wave will be approaching the OH Valley states. Given some ample
curvature in the lower levels coupled with Wet Bulb Zero hts just
under 10K ft, rotating cell structures may have enough support in
for the development of large hail to go along with the downward
transfer of convective/damaging wind gusts. Given the increase in
mid/upper forcing suggested by the latest model suites coupled with
0-1/0-3km SRH near 300 m2/s2, a low tornado threat may exists as well
in some of the stronger clusters with embedded mesoscale vortices.

.SHORT TERM...(Tonight through Wednesday)
Issued at 540 AM CDT Mon Mar 27 2017

The threat for severe tstms will continue into the evening hrs, as
the upper disturbance translates further into the OH Valley and the
shear axis becomes more linear across the region. The threat for
strong/svr tstms should then come to an end heading into the late
evening period, as buoyancy/instability weaken and the shear axis
begins to diminish. Parent sfc low associated with the passing upper
trough to the ne should then help the stalled frontal boundary just
to the w to finally begin moving ewd through the area Tue morning,
with lingering showers and perhaps a few tstms coming to an end.
Quiet wx is then xpcted Tue night into Wed, although this latest
frontal passage doesn`t look to result in much of a cool down given
that sfc flow quickly turns back to the e/se by mid week.

.LONG TERM...(Wednesday night through Sunday)
Issued at 540 AM CDT Mon Mar 27 2017

The extended will start off on a dry and mild note ~60 degrees Wed
night before the next system moves in on Thurs with highs in the
upper 70s.

On Thursday, a trough in the S Plains will start to swing NE towards
the Great Lakes. Even though there is more model consistency now
between the GFS and ECMWF, there is still some resolving to do before
Thurs Night/Friday. While the ECMWF was more progressive with the
upper level trough before, it became more linear and the GFS now
holds on to the better upper level dynamics...which is a complete
flip from 24 hrs ago. The GFS sfc low is tracking farther north than
prev runs, not far behind the ECMWF track, however the ECMWF is
showing an additional weak sfc low along the Gulf. The sfc low near
the Gulf could limit or block off our moisture and instability. As it
looks for right now, with strong shear (0-6km of 40-60kts and 0- 1km
of 20-30kts), decent mid-level lapse rates and instability up to 500
J/kg could not rule out some strong to severe storms. Higher
instability will remain to our southwest. Main hazards would be
damaging winds at this time, however this could change with further
models runs and additional model consistency.

As the trough lifts NE, a few disturbances will round the backside
keeping the chance of a few showers and thunderstorms in the forecast
on Friday. However, as the cold front pushes through Friday
afternoon/evening, it will pull in slightly cooler but drier air
ending any lingering precip. A ridge will keep conditions dry and a
few degrees warmer, lower 70s, this weekend.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 721 AM CDT Mon Mar 27 2017

Low clouds, with cloud bases around 1500 ft, have once again become
entrenched across much of the area this early Mon morning, within a
deep sly fetch regime that leads well into the n cntrl Gulf. These
lower clouds may have a tougher time mixing out later this morning as
s flow ushers further Gulf moisture into the area further increasing
the moisture column. MVFR cigs should basically prevail for most of
the day, as shra/tsra increase in response to an upper disturbance
moving across the region. Vis may lower into the IFR range this
afternoon in/near heavier shra/tsra, with vrb winds gusting around
30KT or higher. Precip should then off this evening as the upper wave
passes off to the ne, although MVFR cigs look to prevail well into
the early morning period Tue.





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