Area Forecast Discussion
Issued by NWS Huntsville, AL

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547
FXUS64 KHUN 280453
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1153 PM CDT Mon Mar 27 2017

.UPDATE...
For 06Z TAFS.

&&

.NEAR TERM...(Rest of tonight)
Issued at 919 PM CDT Mon Mar 27 2017

Continuing to monitor a line of strong thunderstorms moving through
NW AL, producing some large hail. Ahead of the line, a recycled
rain cooled environment from the previous activity will limit the
widespread severe thunderstorm threat through the next few hours.
However, dew points hovering around 60F and MUCAPE ~ 500j/kg will not
completely kill the threat. Hi res guidance is suggesting this line
to shift out of the CWA ~6-8Z.

No changes were made to the afternoon forecast package due to active
weather.

.SHORT TERM...(Tuesday through Wednesday)
Issued at 300 PM CDT Mon Mar 27 2017

Isolated to scattered thunderstorms remain possible over areas south
and east of the NW Alabama Quad Cities Tuesday morning. These storms
will end from NW to SE as a cold front moves across the region during
the day. Another mild to warm spring day is forecast with highs
warming into the low/mid 70s. The above noted frontal boundary will
become stationary; oriented west to east south of the area later
Tuesday and Tuesday night. Slightly cooler and drier air filtering in
from the NW will produce lows into the lower/mid 50s. There could be
patchy fog formation late Tuesday night, mainly within and near wind
sheltered areas and locations that were affected by recent heavy
rainfall.

Wednesday, the boundary south of the area will return northward as a
warm front, and bring a slight chance of showers/thunderstorms in
the afternoon. Given limited amounts and timing of instability, did
not continue rain chances into Wednesday night. The frontal boundary
will move ever so further north during the night-time, setting up
another busy day convective wise on Thursday...

.LONG TERM...(Wednesday night through Sunday)
Issued at 300 PM CDT Mon Mar 27 2017

Models continue to diverge a bit concerning the eastward progression
of the storm system moving from Kansas/Oklahoma towards the
Tennessee Valley on Thursday. Based on the strong ridge it is moving
into over the Great Lakes region into the Mid-Atlantic region, think
the slower solution is more likely. Thus kept precipitation chances
isolated east of I-65 early on Thursday. West of I-65 enough forcing
and low-level moisture convergence should be in place in northwestern
Alabama for widespread shower and thunderstorm development.

Models diverge a bit concerning how far north the surface low and
thus how far north the warm front with this system sets up. This
would affect the amount of instability in place along and ahead of
the approaches storm system. Models are in fairly good agreement that
surface based instability around 500 J/kg is in place in the
morning. Along with 40 to 50 knots of Bulk Shear in place and some
low level turning of winds, severe storms producing damaging winds
are possible. These parameters continue and spread slowly east into
the late afternoon hours ahead of the system near and west of I- 65.
Surface based instability climbs to between 1000 and 1500 J/KG in
models (maybe a bit higher depending on how far north the warm front
makes it). Morning precipitation should keep the best instability in
place near and east of I-65. This would enhance damaging wind
potential and tornado potential as the afternoon would progress in
those areas. Luckily, low level helicity values forecast at this time
do suggest any tornadoes that develop would be fairly weak in
nature. As even stronger forcing moves into northern Alabama ahead of
a fairly strong cold front, strong to severe storms could last into
the early evening hours. However, by midnight the atmosphere should
be too worked over by precipitation to produce more than ordinary
showers and thunderstorms. Models diverge how quickly showers push
east of the area on Friday. Forecast models indicate a blend of this
timing and leans towards the later exiting time into Georgia late
Friday afternoon.

High pressure builds into the Tennessee Valley behind the front
Saturday night into Sunday, as another storm system develops
somewhere over southwestern Texas or Oklahoma. The surface high
should keep forcing and better moisture advection to our west in
Mississippi until Sunday evening. This should also keep highs and
lows cooler (highs in the upper 60s to lower 70s/lows in the upper
40s to lower 50s) Friday night through Sunday. By Sunday evening
into Monday, these parameters should become stronger over northern
Alabama and Southern Middle Tennessee. At this time, this system
does not look as unstable as previous systems. Strong storms look
possible, but surface based instability does not looks as good. Rain
chances really pick up Monday into Monday night as this systems
pushes east through the area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1153 PM CDT Mon Mar 27 2017

An earlier line of convection has now moved to the southeast of the
KMSL and KHSV terminals, with little to no precip expected through
the next 24 hours. VFR conditions will give way to MVFR cigs around
08Z, as low level moisture remains elevated and low stratus moves in
from the north. Although there may be some light fog, surface winds
in the 5 to 10 kt range should keep most of the fog at bay. Cigs will
lift through the morning, with VFR conditions returning around 19Z.
A cold front will also drift southward, shifting surface winds to the
northwest between 15Z and 19Z.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...Barron
SHORT TERM...RSB
LONG TERM...KTW
AVIATION...73


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