Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 270837

Area Forecast Discussion
National Weather Service Huntsville AL
337 AM CDT Thu Jun 27 2019

.NEAR TERM...(Today)
Issued at 337 AM CDT Thu Jun 27 2019

Showers and thunderstorm activity that prompted some warnings around
midnight have dissipated. A new cluster of showers and thunderstorms
have developed in northwestern Tennessee since. This look to be on
the west edge of a weak area of low pressure near extreme
southwestern Kentucky. Models move this feature southward today
towards northern Mississippi. Based on radar trends, this activity
should begin to push southward near the northwestern MS/AL border
shortly after daybreak (7 AM to 8 AM). This activity may weaken as it
does so, since the atmosphere was stabilized by overnight
convection. However, by the late morning and afternoon hours, expect
daytime heating and renewed moisture advection to push instability
quite a bit higher. Several models are forecasting between 2500 and
3500 J/KG of SBCAPE. With this forcing pushing into the area with the
surface low, believe enough forcing will couple with the instability
to produce more widespread shower and thunderstorm activity. DCAPE
values between 800 and 1000 J/KG and the ample instability should
provide enough impetus for at least an isolated damaging wind threat.
Very weak shear will likely provide for primarily a quick microburst
type threat with any severe thunderstorms. However, given
instability hail up to the size of quarters cannot be ruled out.

.SHORT TERM...(Tonight through Saturday)
Issued at 337 AM CDT Thu Jun 27 2019

Shower and thunderstorms activity looks like it could hang on into
the evening hours tonight, before dissipating. Two things should
contribute to this. The surface low should be moving more to the
west shifting forcing more westward and we should lose the effects of
daytime heating. We could see patchy fog if widespread rainfall is
realized. Left this out for now, with uncertainty that occurs
sometimes with summertime convection. Most guidance brings slightly
drier air into the region Thursday night. So lows look like they will
drop into the mid to upper 60s.

By Friday morning, most guidance moves the center of the area of low
pressure into eastern Arkansas. At the same time, models show a weak
shortwave moving southeast through the Mid-Atlantic states. A
reflection of the forcing with this feature extends southwest into
the Tennessee Valley in most guidance. The combination of being on
the eastern edge of forcing associated with the surface low over
Arkansas and forcing extending southwest from the Mid-Atlantic states
should keep scattered showers and thunderstorms in the forecast
Friday afternoon and evening. This activity should dissipate by the
early evening hours. Lows should be slightly warmer as well only
dropping into the upper 60s to lower 70s.

Saturday looks drier, but a weak boundary still may be just south of
or across northern Alabama. With afternoon heating isolated to
scattered shower and thunderstorm development looks reasonable.
Should be warm still with highs in the upper 80s to lower 90s. Heat
index values should remain in the mid to upper 90s.

.LONG TERM...(Saturday night through Wednesday)
Issued at 337 AM CDT Thu Jun 27 2019

The extended will be almost textbook late June/early July weather
for the TN Valley, as robust (not overwhelming!) high pressure parks
itself over the region and doesn`t let go. A backdoor front will make
an attempt to push down the lee of the Appalachians Sunday, but it
is merely a glancing blow and should not have much effect locally.
Ensembles suggest a weak trough developing over the Plains and MS
Valley--just in time for July 4th of course--but aside from the
presence of the trough, timing/details remain murky at this range.

The outcome of all this is generally 20-30% PoPs, focused each
afternoon/evening, with higher values coming around the middle of
next week. Blended guidance suggests a persistence forecast for both
high (low-mid 90s) and low temperatures (around 70/low 70s). This is
reasonable based upon slightly above heights. Nothing about the
pattern lends itself to any targets of opportunity, so the blended
guidance will be mostly adopted as-is.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1200 AM CDT Thu Jun 27 2019

A few remaining clusters of shra/tsra may linger near the two main
terminals into the overnight hrs, and a VCTS group has been added
thru 08Z. These -tsra may affect the KHSV terminal between 06Z and
08Z, providing MVFR CIGS or VSBYS. For now, included a tempo group
of -tsra at KHSV. Some light fog or MVFR cigs may are also possible
for a few hrs early Thu morning. VFR conds should then prevail for
much of the day Thu, with mainly just some sct mid/high clouds in
place. Iso/sct shra/tsra are again possible later in the day Thu as
well, although confidence is low on exact placement/timing.





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