Area Forecast Discussion
Issued by NWS Huntsville, AL

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965
FXUS64 KHUN 292024
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
324 PM CDT Sat Apr 29 2017

.NEAR TERM...(Tonight)
Issued at 300 PM CDT Sat Apr 29 2017

Current satellite imagery shows forcing from the shortwave moving
into northern Alabama at this time. Given very unstable airmass in
place (SBCAPE 2000-3500 J/KG) and DCAPE values between 1000 and 1200
J/KG, the strongest storms could become marginally severe producing
wind gusts around 60 mph and small hail. Given the cap still in
place, believe coverage will remain isolated to widely scattered at
best. Models still push this forcing east of northern Alabama around
10 PM. Expect activity to dissipate by then after losing daytime
heating. It will be a warm night with lows around 70 degrees.

.SHORT TERM...(Sunday through Monday)
Issued at 300 PM CDT Sat Apr 29 2017

Current satellite imagery shows a mesoscale convective complex
developing over northern Louisiana. This is south of the main frontal
boundary over Oklahoma northeast into Missouri and northern Indiana.
As this front develops and pushes slowly east toward the Tennessee
Valley, this may affect the evolution of the pre-frontal trough axis
on Sunday and how far east it initially develops. Most synoptic
operational models do not show this feature, including the NAM12.
These operational models hold off shower and thunderstorm activity
with the prefrontal trough axis until between 4 PM and 8 PM in
northwestern Alabama and continue this activity through the overnight
hours. However, after midnight with lessening instability the severe
storms do not look as likely east of I-65. Either way the timing
works out, the threats remain similar to previous forecasts. The main
threat will be damaging winds. A tornado or two cannot be ruled out
(mainly west of I-65). Heavy rainfall between 1 and 2 inches with
locally higher amount up to 3 inches look possible given strong
forcing and high instability. A few showers could linger into Monday
as drier and cooler air moves into the region.

.LONG TERM...(Monday night through Friday)
Issued at 300 PM CDT Sat Apr 29 2017

The cold front responsible for much of the active wx ending
the weekend period should be well e of the TN Valley into
the Atlantic Basin going into Tue, as high pressure out of the
srn Plains quickly works its way into the SE region. Other than
perhaps a brief shot of cooler/drier air during the first half
of the new work week, little relief in overall temps is xpcted with
this frontal passage thru mid week, as the low level wind field veers
back to the se/s and the flow pattern aloft turns more toward the
wsw. Afternoon temps both Tue/Wed look to return close to 80F, as
another upper trough pattern drops well into the srn Plains states.

Unfortunately, there is a large disconnect with the progression of
this upper trough axis and its associated sfc wave between the latest
12Z guidance and the previous 00Z model runs. The latest model suites
are now hinting at a more vigorous upper low/trough system gradually
traversing enewd into the wrn/cntrl Gulf states for the second half
of the work week, compared to the faster 00z solutions. This scenario
does at least maintain showers/tstms developing Wed/Thu, as the
initial sfc wave and its associated cold front translate ewd across
the cntrl TN Valley. However, the prob may now exists for secondary
sfc waves to develop along the upper low/trough axis lingering back
to the w. This now results in iso/sct showers into Fri as the upper
low/trough gradually moves ewd across the cntrl Gulf region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 111 PM CDT Sat Apr 29 2017

VFR conditons are expected most of the forecast period. Windy
conditions are expected with with southerly winds of 10-20 mph with
gusts to around 30 mph through the early evening hours. Wind should
less overnight to around 15 knots. Model guidance indicates some
brief low cloudiness may lower cigs into the mvfr realm just after
daybreak on Sunday. Even stronger winds are expected on Sunday. May
have to introduce wind shear in next issuance on Sunday.


&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Wind Advisory from 10 AM to 10 PM CDT Sunday for ALZ001>010-016.

TN...Wind Advisory from 10 AM to 10 PM CDT Sunday for TNZ076-096-097.

&&

$$

NEAR TERM...KTW
SHORT TERM...KTW
LONG TERM...99
AVIATION...KTW


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at weather.gov/huntsville.



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