Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 210523
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1223 AM CDT Thu Sep 21 2017

.UPDATE...
For 06Z TAFS.

&&

.NEAR TERM...(Rest of tonight)
Issued at 919 PM CDT Wed Sep 20 2017

Surface high pressure over the region continued to provide light
winds. Despite the surface ridge, strong late summer heating and
available moisture earlier resulted in isolated to scattered
convection, mainly to our north. A more stable environment with
evening cooling has helped to dissipate that activity. Otherwise a
warm night for the near Autumn season, with 9 PM temperatures in the
lower 70s.

Night time lows should cool to the mid/upper 60s under generally
clear skies. This again will make fog formation a good possibility
across parts of the Tennessee Valley. Some of this fog could become
locally dense before daybreak Thursday, especially in and near the
valley locations and near large bodies of water.

On-going forecasts from the day crew were overall good shape. Did
make minor changes, mainly with fog timing, delayed an hour or so.
The fog should continue through the 9 AM timeframe before completely
dissipating, especially if dense fog occurs.

.SHORT TERM...(Thursday through Friday)
Issued at 219 PM CDT Wed Sep 20 2017

Through Friday, the 850-500mb ridge will build over the OH and MS
Valleys.  Along the eastern fringe of the ridge, weak vorticity
waves will continue to drop south.  These along with local forcing
along the Plateau and Mountains may induce scattered
shower/thunderstorm development on Thursday and perhaps on Friday as
well.  Otherwise, will go with near persistence temperature
forecasts both days with highs in the mid 80s to around 90. Will
also maintain patchy valley fog both Thursday and Friday Nights as
well.

.LONG TERM...(Friday night through Tuesday)
Issued at 219 PM CDT Wed Sep 20 2017

Upper-ridge over the Tennessee Valley will shift north into the
Great Lakes by Saturday as a weak area of low pressure along FL/AL
the Gulf Coast becomes more magnified as it drifts into Central
Alabama. The increased lift, along with sufficient boundary layer
moisture will allow for scattered thunderstorms to develop during
the afternoon and evening, with the best coverage along and south of
the Tennessee River. This feature will linger around the region
enough on Sunday and Monday to also warrant a few isolated afternoon
storms. In general through, the broad ridge over the eastern CONUS
should promote a fairly dry and mostly clear forecast each day
through at least the middle of the upcoming work week. Highs in the
85-90 degree range are expected each day, with nighttime lows in the
low to mid 60s. As is typical this time of year, the mostly clear
sky and light winds may result in patchy fog development near
rivers/lakes overnight as well.

Late in the period, a longwave trough will push east from the Rocky
Mountains into the Ohio Valley. This feature will likely bring with
it a stronger front into the Tennessee and lower Mississippi River
valleys -- and perhaps some better chances for storms. Additionally,
this could usher in a cooler, more autumn-like air mass to end
September and start October. Still some differences in the model
with respect to timing 7-8 days out, so did not get too specific
with the details this far out. Stay tuned!

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1223 AM CDT Thu Sep 21 2017

VFR conditions at the start of the TAF should become MVFR with 3-5
miles surface visibility from fog forming. Reductions to IFR 1SM at
KMSL to 2SM at KHSV are possible before daybreak Thu. Fog that forms
should dissipate a couple of hours after sunrise, with VFR weather
returning. Strong late summer heating, available moisture, and an
approaching upper level system could bring isolated to scattered
afternoon convection. As such, have added a VCTS for both airports
for the mid/late afternoon. Light southerly winds overnight and Thu
AM should become northerly around 5kt in the afternoon. Winds again
should become light and variable after sunset.

&&

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

$$

NEAR TERM...RSB
SHORT TERM...17
LONG TERM...AMP.24
AVIATION...RSB


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