Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 221108

Area Forecast Discussion
National Weather Service Huntsville AL
608 AM CDT Tue Aug 22 2017

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 354 AM CDT Tue Aug 22 2017

The rest of the overnight hours looks like it will remain to be mild
and muggy with temps not getting out of the lower 70s. Only major
addition to the near term was adding in patchy fog for the lake and
valley locations. Over the past few hours, a few locations saw
visibilities lower and nighttime microphysics RGB satellite data is
highlighting some fog in the valley locations. As a trough digs
across the Great Lakes today, it will weaken the ridge across the
Southeast. Combined with southwesterly winds returning moisture to
the area and daytime highs in the lower 90s, isolated diurnal
convection is possible. This will also give way to heat index values
around 100 degrees this afternoon!

.SHORT TERM...(Tonight through Thursday Night)
Issued at 354 AM CDT Tue Aug 22 2017

A sfc low located north of the Great Lakes will send a cold front
all way down to the TN Valley on Wednesday. As the cold front
encroaches tonight, scattered showers and thunderstorms will spread
into the TN Valley. Greater coverage is expected as the front moves
in on Wednesday. With cloudy skies and convection the daytime highs
will be a few degrees below normal in the mid 80s. As the front
pushes through the forecast area, expect showers/storms to taper off
Wednesday night as drier and cooler air begins to filter in.
Overnight lows will be in the mid 60s. Thursday will be precip free
as high pressure builds in and reinforces the cooler/drier air.
Daytime highs will also be in the mid 80s but the overnight lows will
be in the lower 60s with southern middle TN possibly dipping into
the upper 50s providing a little taste of Fall.

.LONG TERM...(Friday through Monday)
Issued at 354 AM CDT Tue Aug 22 2017

Synoptically on Friday, an upper trough will be moving off to the
northeast with surface high pressure building in from the north. A
weak ridge also is trying to build in from the southeast. At the
same time, the remnants of TS Harvey look to make a come back and
the guidance is consistent with it moving into the SE Texas coast on
Friday. The eventual track of these remnants will impact how wet/dry
the local area is for the long term. Either way, Friday and Friday
night should stay dry with a cool/dry northerly flow at the surface
and westerly flow aloft.

On Saturday, a vort max extending from Harvey will interact with
increased moisture thanks to surface winds shifting to the
southeast, in response to a surface feature off to the east. This
could cause isolated to scattered showers and storms to form, mostly
in areas east of Huntsville. This wave will remain across the area
through at least Monday.

Differences in how guidance handles Harvey start to become apparent
on Sunday with the GFS picking it up into a trough by Sunday night
with the ECMWF not picking it up, with a slower moving trough, until
Wednesday. If the GFS verifies, widespread showers and thunderstorms
would be possible Sunday night into Tuesday night with gusty winds
as well. The ECMWF still ejects the shortwave mentioned earlier into
the area which strengthens the confidence for the chance POPs in the
forecast Sunday into Monday but there is a break before the Harvey
remnants move through Tuesday.

In terms of temperatures, highs will be in the mid 80s Fri-Sun with
little change on the synoptic scale. Then, highs are forecast to be
cooler, in the lower 80s, due to the enhanced chance for
rain/clouds. Lows will generally be in the mid 60s.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 607 AM CDT Tue Aug 22 2017

VFR conditions will prevail through the TAF period at both KMSL and
KHSV. Isolated diurnal afternoon showers and thunderstorms are
possible today but with the uncertainty of exact timing and location
did not include them in the TAF at this time. Greater coverage of
convection is expected towards the end of the TAF period with an
approaching front and winds becoming northwesterly.





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