Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 211816

Area Forecast Discussion
National Weather Service Huntsville AL
116 PM CDT Tue Sep 21 2021

.NEAR TERM...(Tonight)
Issued at 115 PM CDT Tue Sep 21 2021

Upper level diffluence in advance of the approaching cold front will
continue to produce thunderstorms across western TN into northern MS
late this afternoon in a plume of MLCAPEs of 2000-2500 j/kg. CAMS
suggest a weakening trend as they arrive in northwest AL and middle
TN this evening, as they encounter lower CAPEs. However, fully expect
these showers and thunderstorms to continue across the rest of north
AL and southern middle TN. Then, another band of showers and
thunderstorms will occur with the cold front and more closely tied to
the strong shortwave trough axis that digs southeast into the lower
OH and TN valleys. This area of precipitation will likely be mostly
east of the I-65 corridor by 12Z/Wed. Again, locally excessive
rainfall is possible due to saturated soils.

.SHORT TERM...(Wednesday through Thursday)
Issued at 115 PM CDT Tue Sep 21 2021

The precipitation, cold front and shortwave will have exited our
eastern counties by ~15Z/Wed. Lower clouds may linger into the
midday hours due to strong low level cold air advection. Deeper
mixing will yield gusts of 15-20kt through much of the day, with
temperatures squeaking out 70-73 degrees in valley areas with
sufficient sunshine, while staying in the middle to upper 60s at most
atop the higher Cumberland plateau areas. Winds will diminish late
Wednesday night sufficiently to allow temperatures to fall into the
upper 40s in southern middle TN and the highest elevations of
northeast AL, with around 50 expected in urban valley locations.
Thursday`s high do not appear they will eclipse Wednesday, with lower
70s in valleys and upper 60s atop the higher plateaus.

.LONG TERM...(Thursday night through Monday)
Issued at 115 PM CDT Tue Sep 21 2021

Early autumn weather will be in full swing during the extended
period. After morning lows in the middle to upper 40s Friday
morning, low level ridging/subsidence may allow for a few degrees
of warming Friday afternoon with highs in the lower to middle 70s.
Another progressive shortwave will push through the Great Lakes and
OH/TN valley regions on Saturday, but the lower to mid levels of the
atmosphere will be too dry to support much in the way of clouds and
no precipitation this far south. High temperatures will be
progressively warmer through the weekend into early next week with
building heights and a slow eastward transition to the surface and
850 mb ridge into the far southeast U.S. Expect high temperatures in
the upper 70s to lower 80s Sunday and lower 80s for most valley
locations on Monday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1149 AM CDT Tue Sep 21 2021

Conditions should transition to VFR by 18Z, but scattered SHRA or
TSRA may still be possible which could temporarily lower conditions
to MVFR or IFR. After 00Z, in advance of a cold front, additional
SHRA and TSRA are expected to enter NW AL and travel east across
north AL and southern middle TN through 06Z. MVFR ceilings of
020-025agl are likely during this period. A cold front will bring
another round of SHRA and possibly TSRA along and behind the frontal
passage, which should reach KMSL by 08Z and KHSV by 10Z. A marked
wind shift to the northwest is expected with 10-15kt sustained winds
and gusts over 20kt through the remainder of the period. Ceilings
will remain at 010-020agl (MVFR), although improvement to VFR may
occur by 18Z/22.





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