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Area Forecast Discussion

FXUS64 KHUN 230245 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
945 PM CDT FRI JUL 22 2016

Kept sky cover generally cloudy through the overnight and maintained
slight shower/thunderstorm chances.


Shower activity that affected parts of the Tennessee Valley earlier
today has either moved south of the region and/or faded with a loss
of daytime heating. Despite a rather early start of shower and
thunderstorm this afternoon afternoon, very warm to hot conditions
were realized across the area. Both the Albertville and Muscle Shoals
airports both exceeded 105 degree heat indexes during the peak
heating earlier today, thanks to high enough humidity values.

Strong upper level ridging sprawled across the Southern Plains and
Rockies (in the 598 decameter height range at 500 mb) was sending a
northerly flow over the region. Other former convection within this
flow was headed toward the region. Given an already unstable lower
atmosphere and weak upper support moving this way, decided to stay
with lower end rain chances for the overnight. As is usually the case
in the summer, numerical models have a tough time forecasting the
if`s and when`s of convection...even in the short term. The HRRR was
hinting at convection moving in to our NE areas late tonight; with
the new NAM showing something similar --- then merging this activity
with others from our NW before daybreak Saturday morning. That being
said, most spots should remain dry. But those that receive showers
will be affected by locally heavy downpours, gusty winds and frequent

More clouds than sky is expected for the overnight. This should help
temper fog formation for the most part before sunrise tomorrow. These
clouds, especially if they last into Saturday morning will have an
effect on high temperature potential later on. Right now, will keep
the Heat Advisory going for tomorrow. But it could be removed later
tonight if new guidance suggests cooler conditions to end the week.



(Issued 714 PM CDT FRI JUL 22 2016)
For 00Z TAFs: Lingering ra will likely end at the MSL terminal within
first 30 min of TAF period, and with no convection currently slated
to impact HSV will mention no pcpn at onset of either TAF. Although
several outflow bndrys remain in the area to initiate isold
shra/tsra, expect conds to remain VFR this evening, with bkn/ovc as
and cs decks, and lgt/vrbl winds. A stronger disturbance currently
dropping swd thru the lower OH valley region is forecast to shift
slowly sswwd across the area late tonight and tomorrow, resulting in
a greater coverage of convection. This disturbance will likely lead
to regeneration of shra/tsra to the nw of the area after midnight,
with activity spreading/developing ssewd into the terminals just
before or around sunrise -- and lingering thru first part of the
morning. Tempos for tsra and vsby/cig reductions have been included
during this period, but timing may need to be adjusted. Threat for
storms tomorrow aftn will be dependent on coverage of morning
activity, but we have included vcsh thru end of TAF period along with
bkn-ovc cigs aob 8 kft.



(Issued 254 PM CDT FRI JUL 22 2016)
The 19z surface analysis indicated that a weak trough was moving
southward out of western Kentucky and an area of showers/storms were
developing along and ahead of the boundary. Will continue with at
least slight chance to chance pops into the evening hours as the
widely scattered/scattered storms are expected to further shift
southeast into the forecast area. The short term models are in decent
agreement involving the development of scattered showers/storms
toward sunrise on Saturday and have bumped up pops slightly into the
chance category especially after 10z Saturday.

On Saturday, scattered showers/storms are expected to continue to
develop across portions of the forecast area by the afternoon. Will
continue with the heat advisory into Saturday as there is a level of
uncertainty involving morning shower/storm development. There is also
expected to be higher RH values present and warming occurring into
Saturday afternoon, which will result in heat indices moving into
criteria by Saturday afternoon. Will continue with chance pops for
Sunday, due to the remnants of the old boundary being in place across
the area, afternoon heating and high PWAT values contributing to the
rain chances.

By Monday, the focus will turn to a weak cold front that will be
moving southeast into the Ohio valley region. Scattered
showers/storms will develop ahead of the boundary across middle
Tennessee and into north Alabama by the afternoon and will continue
with higher chance pops. The GFS and ECMWF models indicate that the
weakening boundary will slowly shift southward through middle
Tennessee on Tuesday and will eventually dissipate by early
Wednesday. The bulk of the shower/storm activity associated with the
dying boundary should move northeast of the forecast area by
Wednesday, with lesser chances of showers and storms possible. By
late Wednesday/early Thursday, another mid level trough and weak
frontal boundary will follow a southeast movement into the Ohio
valley region. Scattered showers/storms will again be possible on
Thursday and into Friday as the boundary sinks southward to near the
forecast area into middle Tennessee. Will go with higher chance pops
for Thursday and Friday and will keep temps close to GFS/ECMWF
guidance through the extended forecast period.



.HUN Watches/Warnings/Advisories...
AL...Heat Advisory until 7 PM CDT Saturday for ALZ001>008-016.

TN...Heat Advisory until 7 PM CDT Saturday for TNZ096.



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at weather.gov/huntsville.

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