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Area Forecast Discussion

FXUS64 KHUN 281151

Area Forecast Discussion
National Weather Service Huntsville AL
651 AM CDT THU JUL 28 2016

For 12Z TAFs.


(Issued 322 AM CDT THU JUL 28 2016)

Latest water vapor imagery shows a subtropical high off the
southeast Atlantic Coast and a stronger high over the Desert
Southwest. Meanwhile, a weak trough axis extended through the
Mississippi Valley region. At the surface, a weak area of low
pressure extended across the southern MS Valley, with a weak
boundary trailing eastward and southward from this low. An area of
showers continues to slowly push to the northeast across western TN
and northern MS in response to a vorticity max in the base of the
longwave trough. Much of the forecast area remains under the
influence of the subtropical high, with slightly drier air noted
across the TN Valley. This will change as we move into the morning
hours, as the axis of the trough shifts east, as does the upper
ridge. Though for the next few hours, a few light showers may
develop, with cloud cover will keep temps from dropping too much
through sunrise.

The ongoing showers to our west are expected to enter west Alabama
toward the mid to late morning hours, as the trough axis shifts
northeastward. Although cloud cover will limit the daytime heating,
strong southerly flow will continue to push warm and moist Gulf air
into the area. Forecast soundings show PW values rising from 1.8 to
2.2 inches by the afternoon. Meanwhile, forecast CAPE values will
rise to near 1000 j/kg. These factors, combined with the enhanced
lift from the upper trough, will lead to a greater coverage of
thunderstorms than we have previously seen. However, confidence is
still somewhat low and therefore will keep PoPs to the likely
category. Locally heavy rainfall will be possible, though the dry
soil moisture will limit the likelihood of flash flooding, unless
precip rates are high. Max temperatures will greatly depend on the
coverage of thunderstorms, though highs will be a few degrees below
those observed yesterday due to the cloud cover expected.

The upper trough will weaken by sunset, with the main piece of
energy shifting to the east. The coverage and intensity of lingering
showers and thunderstorms will become limited and will likely
diminish entirely by midnight. The forecast area will remain under a
broad and weak upper level trough through much of the weekend, as the
subtropical ridge moves well south of the area. Several disturbances
are expected to develop and move through the longwave trough, which
will provide for scattered thunderstorms, generally in the afternoon
through early evenings. Much of the forecast will
depend on mesoscale features, as the synoptic lift will generally
remain weak. Have maintained the 50 PoP in for Friday through Sunday,
with lower rain chances during the overnight periods.

The upper level high over the desert SW will strengthen over the
weekend, and push eastward during the day Monday. The broad upper
trough over much of the eastern CONUS will strengthen slightly in
response to the upper ridge. This will put the forecast area in weak
northwest flow aloft Sunday night and Monday, with guidance showing
a vort max developing over the upper midwest and moving southeast
into the area. However, given the uncertainty on day 5, will
maintain our 40 PoPs in for this period. The remainder of the forecast
will be dominated by the upper level ridge, with rain chances
depending on mesoscale interactions.



For 12Z TAFs: Regional sfc obs and recent satellite data suggest that
MVFR stratus deck is firmly entrenched across the region this
morning, with cloud bases in the 1500-2500 ft range. Although a few
lgt shra will be psbl during initial hrs of the forecast, it appears
that best chance for -ra will come btwn 28/14-20Z as an upper-level
disturbance tracks newd over nrn AL. Sfc winds will increase to 10g18
kts from the sw during this period, as well. Pcpn will end from sw-
to-ne over the course of the aftn with cigs expected to temporarily
improve as this occurs. However, stratus deck will likely begin to
build down arnd sunset, with IFR cigs anticipated at both terminals
by 29/05Z. Another weak disturbance approaching the region after
midnight should result in an increase in convection btwn 06-12Z, and
VCTS has been included to address this potential. Sfc winds will
remain from the wsw at speeds arnd 5 kts for second half of TAF



.HUN Watches/Warnings/Advisories...



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