Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 250056

Area Forecast Discussion
National Weather Service Huntsville AL
756 PM CDT Tue Apr 24 2018

.NEAR TERM...(Tonight)
Issued at 800 PM CDT Tue Apr 24 2018

Latest radar trends showers a more widespread area of light to
moderate rainfall over Moore county in Tennessee extending northwest
into the Lewisburg area of Tennessee. This activity is moving
southeast across Lincoln, Moore, and western Franklin counties.
Further southeast and west of this activity, more isolated to widely
scattered showers are occurring. Newest mesoscale models are picking
up on this activity better than previous runs and keep a showers
moving southeast into Jackson county Alabama through 10 or 11 PM.
This looks reasonable based on a bit more of a southerly push of
forcing with the broad upper low to our northeast seen in satellite
imagery. Thus have increased chances of precipitation east of a line
from Fayetteville to Hytop, AL significantly through 11 PM. As the
upper low pushes more to the east around midnight, believe rain
chances will die out quickly. Although winds should stay between 5
and 10 mph with some higher gusts this evening, some patchy fog is
possible after midnight. This may be the case especially in
northwestern Alabama which should see more clearing and in wind
sheltered locations. Winds should keep it from becoming dense though.
Based on expected combination of cloud cover and winds, raised low
temperatures a bit into the mid 50s in north central Alabama. Cooler
lows in the lower 50s look reasonable in northwest Alabama and in the
Fort Payne area.

.SHORT TERM...(Wednesday through Thursday night)
Issued at 202 PM CDT Tue Apr 24 2018

For Wednesday, there should be a break in the shower activity as the
TN Valley experiences shortwave ridging. Somewhat warmer daytime
highs will occur with upper 60s to low 70s expected. Meanwhile, a
shortwave trough currently moving across the Intermountain West and
Central Plains will be moving southeast. As it does so, the trough
becomes positively tilted with the northern flank of it becoming
sheared. The effect of the shearing may bring additional cloud cover
southward on Wednesday but precipitation should hold off until later
Wednesday afternoon as a strengthening LLJ ahead of this shortwave
sends warmer and saturated air northeast. Then, have included a
gradual increase in POPs starting over the NW zones initially, but as
the trough tracks further south will see the gradient in POPs
occurring more from south to north as precipitation spreads
northward. Forecast soundings and plan view depiction is showing a
low-level to mid-level cold pool developing on Thursday as that
shortwave trough moves closer. This increase in low-level lapse rates
will increase conditional instability. This along with the strong
forcing could cause thunderstorm development especially on Thursday
afternoon and south of the TN River. There may also be small hail and
gusty winds up to 30 MPH given the combination of low freezing
layers and potential pulse like deep convective updrafts. As a
result, have added isolated thunderstorms for that area generally
south of the TN River and also increased POPs areawide. This
shortwave trough should then move quickly off to the northeast
bringing an end to storm activity and shower activity on Thursday

.LONG TERM...(Friday through Monday)
Issued at 202 PM CDT Tue Apr 24 2018

The only precipitation chance during the extended period will be on
Friday, and it is an uncertain one given model differences. That
being how far south the next upper shortwaves digs, with resultant
-divQ fields. With such displacement of the northern stream, suspect
that the ECMWF is closer to reality. However, for consistency sake,
will keep a 20 PoP going (near suggested blended guidance).

After this, synoptics favor a welcome dry and warm period through
the weekend into early next week with northwesterly 5h flow through
Sunday, before a high amplitude ridge shifts east into the upper MS
valley into the TN valley. At the surface, a 1030mb high shifts off
the mid Atlantic coastline on Monday, with a corresponding 8h high
off the Carolinas. This will produce a modest southerly flow and
increase thickness values to support highs well into the 70s and
possibly lower 80s. Lead shortwaves ejecting from next trof advancing
into the Rockies may arrive by late in Day 7 (night) period into Day
8, but will keep rain chances out through Monday night until this
becomes more certain.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 653 PM CDT Tue Apr 24 2018

Showers may linger through 01Z at KHSV before pushing south of the
terminal. Clouds are tricky, with some areas including KMSL already
clearing out. This should continue at KMSL until around 2Z, when
additional VFR mid/high cigs push back into the area. Winds look to
be gusty this evening before dropping off to around 5 knots after 05Z
at both terminals. KMSL may clear out again as well after 5Z, which
should produce some mvfr vsbys despite winds. Models hint at cigs
below 3000 feet returning after 05Z or 06Z at KMSL and KHSV. Not as
sure about KMSL, but if fog forms with fairly clear skies despite
winds, KMSL could see MVFR/IFR cigs/vsbys between 08Z and 12Z. Fairly
confident that a predominant MVFR deck will occur at KHSV starting
at 06Z. Some guidance drops cigs below 1000 feet, but will leave out
of terminals for now.





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