Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 221723
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1223 PM CDT Sun Apr 22 2018

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 909 AM CDT Sun Apr 22 2018

A moisture/mid level boundary lifted north across the area this
morning and this was the focusing mechanism for showers and a few
embedded thunderstorms. HREF did indicate some weak MUCAPE (<200
J/kg) over the area this morning and potentially lingering into the
late morning hours. Radar and satellite imagery suggest waves
ejecting out of the upper low to our west have been the trigger for
additional development. We`ll have a few of these more isolated
storms move up into the area through the early afternoon. Then as the
upper level system shifts east the main precip axis begins to move
over the area and showers/storms become more widespread.

In terms of the environment, soundings and hires guidance suggest
a more saturated sounding this afternoon with very limited
instability. Shear will be on the stronger side 60-80kts but with
little to no instability only expecting a few embedded, mainly
elevated thunderstorms. Then as the upper low enters the TN Valley,
lapse rates steepen and but the cold front will be sweeping across
the area. Could see a stronger storm or two along the front but
confidence in that is low. Thinking is that with the better
instability bottled up to our south we`ll see more widespread storms
develop south of the area and this could really limit chances in the
TN Valley. HIRES guidance quickly ends precip overnight but with the
vort max lingering near the area could still see a few isolated to
scattered storms develop.

Models do show a stronger LLJ develop this afternoon 40-60kts with
the stronger winds over the eastern half of the area. So, won`t make
any changes to the Wind Advisory we have in effect for this evening.

.SHORT TERM...(Tonight through Tuesday)
Issued at 406 AM CDT Sun Apr 22 2018

Breezy to windy conditions across the east ate expected this evening
with widespread showers and isolated thunderstorms. Fortunately,
stability values remain on the low side with extreme wind shear
values. The NAM was showing over 2000 m2/s2 helicity values at
Huntsville late this evening, indicative of strong winds aloft. The
winds should diminish pretty rapidly from SW-NE after midnight, as
the strongest forcing exits the region.

Cloudy skies and widespread showers and isolated thunderstorms will
continue on Monday. The parent low from the latest guidance should
move across the Mid South and dissipate, while a comma head precip
shield moves across the Tennessee Valley Monday night into Tuesday.
A more stable atmosphere as the low exits to the east of the region
will remove thunder from the forecast for Tuesday, along with lower
rain chances. Rainfall totals upwards of 3 inches are possible by
late Tuesday, which could produce hydrological concerns.

.LONG TERM...(Tuesday night through Saturday)
Issued at 406 AM CDT Sun Apr 22 2018

Upper low/trough axis will continue to lift newd away from the cntrl
TN Valley Tue night, as lingering showers over NE AL quickly taper
off to the E during the evening period. Any lull in the rainfall
though is xpcted to be short lived heading into Wed, as another
amplifying trough pattern over the Plains states drops into the
Midwest/SE regions. As this occurs, another weak sfc boundary will
translate ewd into the region, with a shallow influx of moisture
increasing just ahead of the approaching front. Weak dynamic forcing
along the front should provide the means for some development of sct
showers Wed/Wed night, before rainfall again tapers off to the E with
the passage of this next front. The latter half of the global models
are suggesting little in the way of any cold air advection in the
wake of this next frontal passage on Thu, with afternoon highs
Wed/Thu climbing mainly into the upper 60s/near 70F. Overnight temps
Tue/Wed nights also look to remain fairly similar, with lows mainly
in the lower 50s or around the 50F mark.

After another brief dry spell Thu night, as high pressure over the
srn Plains quickly moves ewd across the wrn/cntrl Gulf regions, the
00Z ECMWF/GFS are hinting at yet another weak frontal boundary out of
the nrn/mid Plains traversing sewd into the Midwest/OH Valley states
Fri/Fri night. Most of the better forcing/lift looks to remain N of
the cntrl TN Valley, although just enough moisture may be in place
below H7 to result in a few showers thru Fri night, before drier air
above H85 mixes into the area for the start of the weekend period.
The influx of slightly drier air may at least allow overnight lows
Fri night to fall more into the mid 40s for most locations. This
doesn`t look to have much affect though on afternoon temps Sat, with
highs again climbing predom into the upper 60s/near 70F under mostly
sunny skies.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1223 PM CDT Sun Apr 22 2018

The earlier line of showers/storms has lifted to the north leaving
mainly light rain and MVFR cigs between 1,000-2,000ft. An upper level
system to our west will push east through the afternoon/evening and
bring a batch of moderate to heavy rain across the terminals. IFR
cigs/vis are possible with the heavier showers, otherwise expect MVFR
conditions. Winds increase out of the E/SE as the low nears the area
with gusts of 25-30kts possible from HSV east towards GA. The KMSL
terminal may see gusts up to 20-25kts. A cold front will lower rain
chances from west to east late tonight into early Monday morning.
However, scattered light rain could continue for much of Monday.

Have kept thunder out of the TAFs at this time as we haven`t seen any
lightning activity to our S/SW recently. Plus any storms that do form
will be embedded in the heavier rain and thus likely elevated.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Wind Advisory from 4 PM this afternoon to 1 AM CDT Monday for
     ALZ006>010-016.

TN...Wind Advisory from 4 PM this afternoon to 1 AM CDT Monday for
     TNZ076-096-097.

&&

$$

NEAR TERM...Stumpf
SHORT TERM...RSB
LONG TERM...09
AVIATION...Stumpf


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