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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 152006

Area Forecast Discussion
National Weather Service Huntsville AL
306 PM CDT Sun Jul 15 2018

.NEAR TERM...(Tonight)
Issued at 306 PM CDT Sun Jul 15 2018

Active afternoon across the Tennessee Valley, with scattered to
numerous storms in progress as of 20z. Any diurnal convection will 
diminish after sunset. However, additional showers and storms 
associated either with the boundary that is entering NW AL or the 
boundary elongated to our west just across the MS border could linger
into this evening and into the overnight hours. The combo of PWAT 
values remaining over 2", weak shear, slow storm motion and CAPE 
values of 2-3,000 J/kg into this evening will allow for a strong 
storm or two with heavy rainfall, gusty winds and frequent lightning 
as the main threats. Especially for locations that have already 
received rainfall, localized flash flooding is possible. 

Starting this morning off with mainly BKN/OVC clouds and the early 
start of convection put limited solar heating somewhat and probably the
possibility of reaching heat advisory criteria across NW AL. 
However, decided to keep the heat advisory in place due to the fact 
that locations who have received a peak of sunshine have quickly 
rebounded their temps. Thus, a few isolated spots could see peak HIs
close to 105 degrees. See the heat advisory for additional 
information. Otherwise, cloudy conditions will keep overnight lows at
bay, with temps reaching the lower 70s. 

.SHORT TERM...(Monday through Tuesday Night)
Issued at 306 PM CDT Sun Jul 15 2018

As an upper-level trough swings across southern Canada, it will
continue to break down the ridge that was anchored across the 
Southeast. This will place us in a northwesterly flow pattern,
allowing a series of disturbances to dive down into the region. At
the sfc, a low moving out of the Great Lakes will pull a cold front 
into the TN Valley by Tuesday morning. With moist and unstable 
conditions, scattered to numerous showers and storms are possible 
Monday and Tuesday. Heavy rainfall, gusty winds and frequent 
lightning will again be the main threats with PWATS still ~2" and 
CAPE 1000-2000 J/kg. Steering flow will slightly improve, allowing 
for storms to have a lower chance of producing flooding. The increase
in storm coverage and cloud cover will limit heating, and thus temps
should only reach around 90 degrees. This will keep heat index 
values below heat advisory criteria over the next couple days. As the
front pushes through late Tuesday and drier air filters in, storm 
chances will decrease allowing for a drier air mass to work in by 
Tuesday night.

.LONG TERM...(Wednesday through Saturday) 
Issued at 306 PM CDT Sun Jul 15 2018

Large area of high pressure is xpcted to be in place across the 
Great Lakes/OH Valley states to start off this part of the forecast 
package, with a cold front located just south of the cntrl TN Valley.
Some slightly drier air between H5-H85 should also be in place over 
the area thx to the passage of the front earlier, which should offset
much in the way of rain chances except for perhaps the far SW corner
of the forecast area where slightly better convergence near the 
front may allow for a few showers/tstms thru Wed. Temps will still be
seasonably warm with highs in the upper 80s/near 90F, although the 
drier air will keep afternoon heat indices more in the lower/mid 90s.

Rain chances begin to gradually increase Thu/Fri, as the front to the
south rebounds to the north as a warm front. With the warm front
moving nwd, a low pressure system out of the mid Plains states also
looks to translate ewd into the Midwest/OH Valley areas, which should
help with the influx of moisture into the region. The latter half of
the global models are also suggesting an upper shrtwv/trough carving
thru the Great Lakes, placing the region in more of a nwly flow 
regime. All of this should result in sct showers/tstms developing 
across the mid TN Valley by Fri and persisting into the weekend. Even
with the increase in rainfall, highs still look to be fairly 
seasonal for this time of the yr, with temps again maxing out near 
the 90F mark for most locations, while overnight lows trend predom in
the upper 60s to lower 70s.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1221 PM CDT Sun Jul 15 2018

Prevailing forecast will be VFR with a tempo of MVFR conditions this
afternoon as thunderstorm coverage increases. Thunderstorms will
diminish with sunset, however additional convection is possible
before the end of the TAF period. Kept with a VCTS starting at 15Z 
due to low confidence in timing. 


AL...Heat Advisory until 6 PM CDT this evening for ALZ001>003.




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