Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 261332

Area Forecast Discussion
National Weather Service Huntsville AL
832 AM CDT Thu Apr 26 2018

.NEAR TERM...(Rest of Today)
Issued at 813 AM CDT Thu Apr 26 2018

Upper low continues to spin across the Deep South this morning,
generally situated across northern Mississippi. Regional radar shows
precipitation associated with the warm conveyor belt extending from
the north central Gulf of Mexico into Middle Tennessee.
Precipitation rotating around the cold core/upper low was noted
across northwest MS/southwest TN. So far, precipitation amounts have
been pretty decent generally in the 1/4 to 1/2 inch range. Steady
rainfall will persist for several more hours across northeast Alabama
with a brief break noted west of I-65 later this morning.

The 06z/12z high res guidance shows a general increase in convective
precip underneath the upper low as it slides eastward today. Despite
fairly weak lapse rates beneath 700 millibars this seems reasonable
given PWATs hovering around an inch and broad scale ascent associated
with the low. Am not overly keen on thunder potential for the
afternoon given the aforementioned low level lapse rates but you can
never rule out thunder with the passage of a closed low. Thus will
maintain isolated wording for now. Current temps are running in the
lower to middle 50s and we will be hard pressed to warm more then 5
to 8 degrees under full overcast and occasional precip. That`s
reflected well in current max temps. Morning update will be issued
shortly mainly for timing and trends.

.SHORT TERM...(Tonight through Friday night)
Issued at 238 AM CDT Thu Apr 26 2018

A shallow cool airmass rushes in behind the departing system and
should result in a low level inversion developing tonight. With
recent rainfall and whatever rain we get today expect some moisture
to be trapped beneath this inversion and patchy fog/low level stratus
to develop tonight. The benefit of the fog/low clouds will be that
temps never really get a chance to bottom out and lows remain in the
mid to upper 40s.

An elongated/sheared vorticity axis moving across the Plains today
ends up producing two distinct upper level systems overnight. One
moves across OK/TX and the other stronger system across the Great
Lakes. The OK/TX system continues to drop S/SE and will pass to our
S/SW on Friday. Models do show some remnants of the sheared vorticity
axis and have it going across the area Friday afternoon. There might
be just enough lift and lingering low level moisture to support a few
isolated light showers Friday afternoon. Have low end PoPs for
Friday to account for this. Otherwise, expect mainly dry and partly
cloudy skies on Friday. With the late April sun, even with a few
clouds around we should be able to warm up into the upper 60s to
lower 70s on Friday. High pressure moving in behind this feature
remains to our west and keeps the stronger CAA at bay for Friday
night. Expect temps to be close to Thursday nights values, maybe even
a degree or two warmer.

.LONG TERM...(Saturday through Wednesday)
Issued at 238 AM CDT Thu Apr 26 2018

An upper-trough centered over the eastern Great lakes, extending
south along the spine of the Appalachian Mountains will continue to
pull away from the Tennessee Valley this weekend. In its wake, high
pressure will build into the area from the west, which will promote a
mostly clear and sunny sky -- along with dry weather this weekend
into early next week. Initially, north to northeasterly flow will
help to keep temperatures in check by a few degrees this weekend,
with highs warming into the upper 60s to lower 70s. These readings
are about 5-8 degrees below normal for late April despite the ample

The aforementioned high will intensify as it shifts east into the
Tennessee Valley, eventually becoming established over the Southern
Appalachians by Tuesday (just east of the area). With winds veering
back to the south to southwest, moisture will gradually be on the
rise, along with temperatures. Breezy SW winds will enhance warming,
along with increased thickness values and temperatures aloft (~ 5
degrees Celsius higher at 850 mb) by Tuesday and Wednesday. This
will result in highs reaching to upper 70s to lower 80s by the middle
of the new week. A cold front advancing southeast from the Central
Plains and Missouri Valley will approach the Mid South late in the
period. Will likely see result in some denser cloud cover late
Wednesday into Wednesday night. However, any shower/thunderstorm
activity should remain well to the northwest. Most guidance is
holding off on any PoPs/QPF until late in the week, beyond the scope
of this forecast package.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 626 AM CDT Thu Apr 26 2018

A low pressure system has brought light to moderate showers to both
terminals as of 11z. The system will track across the area and result
in a continuation of light rain and MVFR cigs with bases between
1,000-2,500ft. Rain begins to taper off this afternoon as the system
exits the area to the east. But low clouds will linger for much of
the overnight period with some patchy fog possible. Still uncertain
just how widespread and dense fog might be tonight so have kept out
of current TAFs. Winds switch to the NW this afternoon as the system
moves off to the east.





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