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Area Forecast Discussion

126
FXUS64 KHUN 262328 AAA
AFDHUN

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
628 PM CDT FRI AUG 26 2016

.UPDATE...
For 00Z TAFs.

&&

.SYNOPSIS...
(Issued 307 PM CDT FRI AUG 26 2016)

The prevailing ridge across the Southeast/Appalachian states will
keep the region hot and humid with various rounds of mainly
afternoon thunderstorms through the weekend. Further to the
northwest, a longwave trough moving across western/central
Canada/Intermountain West will actually act to dampen the ridge over
the next 3 days. The upper flow pattern then looks to transition to
an omega block pattern across north America later next week with the
TN valley in NW flow.

Meanwhile, scattered storms have developed along a convergence
boundary over central AL to northern MS. This convergence boundary
will likely remain the focus for storms until this evening.

SL.77
&&

.DISCUSSION...
(Issued 307 PM CDT FRI AUG 26 2016)

The scattered storms are expected to prevail into the early evening
hours with gusty winds of 30-40 MPH possible with any of the
stronger storms. After storms diminish/dissipate, patchy fog will be
possible overnight with patchy dense fog possible near rivers,
lakes, and valleys. Then, on Saturday, expecting this convergence
boundary to dissipate/move off to the north due to shift in the upper
ridge position towards the central Appalachians. As this shift in the
ridge position continues, the TN valley will be positioned on the SW
flank of the ridge. An inverted trough/weak vorticity max rotating
around the southern flank will approach on Saturday afternoon over
the central/northern GA/NE AL. As a result, anticipate isolated
thunderstorms to develop again, especially over NE AL. Greater areal
coverage in storms may be possible depending on the timing of the
trough as instability will be maximized during the afternoon. With
wind shear values quite low, any storms that develop will be pulse-
like with potential for microbursts. Primary impacts will be gusty
winds up to 40 MPH with very heavy rainfall. In addition,
temperatures will still be quite hot and humid with temperatures
rising into the low 90s, which with dewpoints in the 70s, will
translate to heat index value rising close to 105.

Similar conditions are anticipated on Sunday as the upper flow
pattern begins to transition to a more dampened ridge as the polar
jet trough moves up and over the ridge. With the dampening ridge, kept
the isolated thunderstorm chances in place for the afternoon
especially over NE AL where greater speed convergence within the flow
is noted in the mid levels.

Though the ridge will be weaker during the early part of the week,
weak northeasterly flow is expected which may advect drier air aloft
acting to limit deep convective updrafts. Nevertheless, will keep
isolated thunderstorms in the forecast through Monday and Tuesday
with similar daytime highs in the 90s. The main difference may be
somewhat `cooler` dewpoint temperatures which may keep heat index
values below 100. The upper flow pattern then begins to transition
to an omega flow pattern by day 7/8. In the meantime, on Wednesday
and Thursday have kept isolated thunderstorms in the forecast with
highs in the 90s and lows in the 70s.

This does not take into effect any of the possible impacts from
Invest 99L. At this point, too much uncertainty on the track, storm
integrity, and intensity still exist with this tropical wave to even
incorporate any impacts for the end of next week.

SL.77

&&

.AVIATION...
For 00Z TAFs: Next wave of TSRA will affect KHSV through 01Z, then
could affect KMSL 01-02Z. Even some weaker storms have been
producing gusts around 40 kt so the TAFs will reflect this for now.
After this, short term models suggest storms weakening and
dissipating. With all the rain occurring today, fog is likely if we
are able to get any clearing; will stick with MVFR visibility though
IFR/LIFR is possible. Storms should be more isolated tomorrow.

BCC

&&

.HUN Watches/Warnings/Advisories...
AL...NONE.
TN...NONE.
&&

$$

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at weather.gov/huntsville.



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