Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 231109
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
609 AM CDT SAT JUL 23 2016

.UPDATE...
For 12Z TAFs.

&&

.DISCUSSION...
(Issued 243 AM CDT SAT JUL 23 2016)
A muggy night out there with temps in the lower to upper 70s across
the area with dew points in the lower to mid 70s. Mid and high level
clouds have helped to keep the temps up and should stay overhead for
the rest of the night.

Synoptically speaking an upper trough is passing off the east coast
of the northeastern states with a ridge developing over the central
parts of the U.S which we are just on the eastern fringe of.
Embedded in that is a disturbance forming a weak upper low that is
currently somewhere in the MO/KY/TN region. This can be seen well in
water vapor imagery and IR imagery with the area of high clouds
spinning around that area. This feature will continue to sink south-
southeast today.

A couple of important changes were made to the forecast today after
looking at the latest model guidance. For one, cloud cover looks to
be much higher than previously thought and higher than what we saw
yesterday. It also looks like the precip coverage will be slightly
higher. Both of these will lead to lower high temps which will be a
few degree lower than the previous forecast, in the lower 90s.
However, it doesn`t look like we will mix out as well today with the
increased moisture which will keep dew points in the lower 70s, maybe
even a degree higher than forecast after thunderstorms move through.
So even with the lower temps, heat indices will still be 100-105,
slightly higher in some locations, so the heat advisory will continue
as is.

In terms of thunderstorms today, that upper low is more lift than
usual for this time of year and couple that with plenty of moisture
and PW values above 2 inches, thinking we could have thunderstorm
coverage higher than the scattered/50% in the forecast at this time.
The cloud cover will limit instability and the bases will be higher
than previous days so the chance of a severe storm is very low. The
thunderstorm activity may linger into the evening hours but it
should be dry overnight with lows in the lower to mid 70s.

Sunday/Monday will return to a more summer like pattern with weak
high pressure over the area and enough afternoon instability for
isolated to scattered thunderstorms, one or two of which could be
strong. Highs will still be in the mid 90s which will lead to heat
index values of 100-105 degrees. A weak frontal boundary will move
towards the area Monday night but will only provide slightly cooler
conditions as we move into Tuesday.

A fairly consistent pattern is setting up past Tuesday. Weak mid
level ridging remains in place through the week with a broad upper
trough making its way east up north of the Great Lakes. With a
continued southerly flow and dew points in the lower 70s, enough
instability will be realized each day as well as steep lapse rates to
support scattered afternoon/evening thunderstorms which linger into
the early evening hours. Friday/Saturday look to be the best chances
simply due to the mid level ridge breaking down. Each day could have
one or two severe storms like most afternoons in the summer but there
aren`t any distinguishing features to help determine if one day has a
better chance.

Highs each day Tue-Sat will be near normal, in the lower 90s with
lows each night in the lower 70s.

LN

&&

.AVIATION...
For 12Z TAFs: sct shra were now moving across KMSL due to a weak
upper disturbance and 8h convergence over wrn TN. Cloud tops were
warming attm but with daytime heating and good instability, expect
more sct shra/tsra to develop by late mrng/early aftn. Coverage of
shra/tsra may be a little more today than yesterday, especially over
KMSL. Will go with vcsh at both tafs this mrng then vcts by the aftn
with a tempo group at KMSL. Shra/tsra should begin to taper after 00z
tonight. Otherwise expect mainly vfr conditions, except mvfr in tsra,
thru the fcst period.

007

&&

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

TN...Heat Advisory until 7 PM CDT this evening for TNZ096.

&&

$$

For more information please visit our website
at weather.gov/huntsville.



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