Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 251720

Area Forecast Discussion
National Weather Service Huntsville AL
1220 PM CDT Mon Sep 25 2017

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 947 AM CDT Mon Sep 25 2017

Satellite this morning shows a weak low pressure system sitting just
off the AL/FL Gulf Coast and a broad upper level high to our NW. Flow
through the mid/upper levels will be out of the S/SE. Some hires
guidance indicates a weak piece of energy breaking off the low and
moving up through the area later today. While any forcing with this
will be weak, combined with the warm daytime temps and dewpoints
in the upper 60s, it`s possible an isolated storm could bubble up.
However, modifying the BMX and OHX soundings for this afternoon only
shows at most 500 J/kg of ML-CAPE and there is an inversion just
above 700mb that might prevent CI. So, on the fence on pulling PoPs
for today but will wait and see what the CU field looks like here in
a few hours. In either case though it would only be one or two storms
that develop, so PoPs remain below 20 percent. No other adjustments
are needed at this time.

.SHORT TERM...(Tonight through Wednesday)
Issued at 345 AM CDT Mon Sep 25 2017

The overall wx pattern definitely turns more quiet starting tonight,
with the only real concern some more patchy dense fog possible across
the sheltered/valley areas and near bodies of water. Overnight temps
will again be similar to the last couple of mornings, with lows well
in the mid 60s for most locations. Quiet and unseasonably warm wx
should then be the trend into mid week, with the sfc/upper ridge
remaining fairly stagnant from the NE/mid Atlantic states swwd into
much of the region. Afternoon highs will again climb well into the
mid/upper 80s both Tue/Wed while overnight lows remain predom in the
mid 60s. Latest model runs are still showing the well advertised cold
front dropping out of the Plains states and approaching the local
area from the NW late Wed. The sfc boundary though may not start to
cross thru the cntrl TN Valley until late Wed afternoon into Wed
evening, with the brunt of the cooler air displaced a bit wwd behind
the lead front.

.LONG TERM...(Wednesday night through Sunday)
Issued at 345 AM CDT Mon Sep 25 2017

At the start of the longer term, an upper level Rex-style block was
situated across Europe, helping to maintain a generalized troughing
west and ridging east setup across the greater North American
domain. This block will break down somewhat after the middle of the
week, allowing troughing across the North Atlantic to advance
somewhat further to the east. Another item of interest, a speed
max/upper level system currently moving ashore the Alaska
Panhandle, will induce upper level troughing near the Great Lakes;
with it amplifying southward to the Appalachians and Mid Atlantic
region. This trough will in part help weaken and begin a NE movement
of Hurricane Maria from the continent, forecast to be east of the
VA/NC border on Wednesday.

The above noted trough digging southward will help bring a cold
front across the Tennessee Valley during the Wednesday evening to
early Thursday time frame. With the lion`s share of atmospheric
moisture remaining well to our southwest, will stay with a dry
forecast with the front passage. Cooler air NW of the front, as
promised should start bringing a noticeable cooler trend for daily
high/low temperatures for the later half of the week into early next
week. A reinforcing dry front is forecast to move across the area
during late Friday. Highs on Thursday, in the low/mid 80s will be
the last 80s this week. Even cooler conditions on Friday, with highs
in the upper 70s, and in the mid 70s for the Sat/Sun/Mon timeframe.
Lows in the mid 60s Wednesday night, will cool into the mid 50s for
Friday night through Sunday night. Normal high/low temperatures on
Sunday, or October 1st are around 80/55 for reference.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1220 PM CDT Mon Sep 25 2017

High pressure over the OH Valley continues to control the weather
over the TN Valley. VFR conditions are expected for much of the TAF
period with cigs at or above 3,500 ft. An isolated shra/tsra is
possible in NW AL and in TN this afternoon but probs are too low to
include in TAFs. Tonight patchy fog is possible and could see brief
periods at MSL where vsbys drop below 1 mile, as has been the case
for the past few mornings. Winds remain light and variable through
the period.




NEAR TERM...Stumpf

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