Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 222021
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
321 PM CDT Sat Jul 22 2017

.NEAR TERM...(Tonight)
Issued at 321 PM CDT Sat Jul 22 2017

Strong daytime heating and unusually high amounts of moisture in the
atmosphere has resulted in isolated shower/thunderstorm development
around the Tennessee Valley. The upper ridge that helped bring the
very warm to hot conditions across the southern CONUS continued on a
weakening trend, as more moisture and upper level support from our
south slowly creeps northward. Precipitable water amounts from
morning soundings were in the 1.7 to 1.9 inch range. So far, very
warm to hot temperatures have occurred across the Tennessee Valley,
with highs in the low/mid 90s so far. Corresponding heat indexes have
risen to as high as 110 at KHSV last hour, others ranged in the 103
to 108 range.

With a loss of daytime heating, shower activity should wane during
the early evening. Expect another warm night with lows only in the
low/mid 70s. Have placed patchy fog within and near the river
valleys. More of it is possible, especially in and near places that
received a good dose of rain earlier.

.SHORT TERM...(Sunday through Monday)
Issued at 321 PM CDT Sat Jul 22 2017

Forecast precip water amounts from the NAM and GFS both suggest in
the 1.9 to 2.1 inch range into Monday. Thus locally very heavy rains,
gusty winds and frequent lightning are possible with the stronger
storms.

Shower activity should once again reform mainly late Sunday morning,
continuing into the afternoon. Some of the storms during Sun could
become strong, with gusty winds the main threat. Torrential rainfall
and intense lightning is also a possibility in the strongest storms.
With more clouds than sun, some relief from the heat is expected,
with highs in the upper 80s to lower 90s. Even with the cooler
temperatures, apparent temperatures over portions of northwest
Alabama could still approach 105 for a brief time. Given uncertainty
with this, held off on another Heat Advisory for Sunday this issuance.

Weak upper level support moving northward from the south, along with
a southward moving outflow boundary and/or gravity wave Monday
should result in numerous showers and thunderstorms across the
Tennessee Valley. With more clouds and showers, even cooler
conditions will greet the start of a new work week, with highs in the
mid 80s to around 90.

.LONG TERM...(Monday night through Friday)
Issued at 321 PM CDT Sat Jul 22 2017

The extended will once again start out with a upper-level ridge
anchored across the central portion of the country. A shortwave
combined with a sfc cold front moving into the TN Valley on Tuesday
will develop scattered showers and thunderstorms. It will be moving
into an atmosphere with PWATs are almost 2 inches but shear is weak.
Gusty winds and heavy rainfall will be main hazards. Daytime highs
will be near normal, reaching the upper 80s to 90 degrees.

The latter half of the week will see diurnal showers and
thunderstorms with near normal temps in the upper 80s to lower 90s.
Don`t forget about the heat index! Values will be around 100 degrees
Wed-Fri. With the ridge still anchored and a trough sweeping across
the Great Lakes, northwesterly flow aloft will set up across much of
the region. The GFS is still coming in more confident with the
northwesterly flow sending a disturbance into the area on Thurs/Thurs
Night. The ECMWF is slower and keeping it to our north. Put in
scattered showers/storms on Thurs with isolated lingering into Thurs
night to accommodate for the model discrepancies. A front will
approach the area from the north on Friday brining additional showers
and thunderstorms. Storms could be strong with BUFR soundings
showing PWATs possibly over 2 inches and a fair amount of CAPE. Kept
POPs as scattered until model runs get a better timing of the front.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1227 PM CDT Sat Jul 22 2017

Strong daytime heating and high amounts of atmospheric moisture has
resulted in the development of clouds, and isolated to scattered
convection. Given radar trends, expect coverage to increase into the
mid/late afternoon. Given the high amounts of precipitable water in
the atmosphere, the stronger storms will be capable of producing
strong outflow winds over 40kt, torrential rainfall and frequent
lightning. Slow cell movement could produce a somewhat longer period
of reduced CIG/VIS values, if storms occurs at a terminal. Shower
chances will decrease this evening and tonight. Given showers in
progress, residual moisture, light winds, and mostly clear skies
could result in fog before daybreak Sunday - which was added to the
TAF.

&&

.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 TNZ076-096.

&&

$$

NEAR TERM...RSB
SHORT TERM...RSB
LONG TERM...JMS
AVIATION...RSB


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