Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 190012

Area Forecast Discussion
National Weather Service Huntsville AL
712 PM CDT Thu Apr 18 2019

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 146 PM CDT Thu Apr 18 2019

Still a tough forecast with regard to eventual evolutions and
impacts. Warm sector over north AL is very capped per latest 18Z
soundings, with a very dry mid level layer to overcome as well. This
will change quickly as evidenced by 2-3mb/3 hr pressure falls over
central AL into central and southern MS. An axis of dew points in the
m60s is advecting into western AL and eastern MS, and may be feeding
convective development in north central into northeast MS. Will watch
this area closely. More favorable bulk shear and instability is
positioned further south from this area where SPC is likely to issue
a Tornado Watch shortly. Various CAMS seem to point to the severe
convection entering central MS will eventually become a potential
larger scale bowing segment that moves swiftly northeast into north
AL between 00-02Z, and exiting southern TN and northeast AL by around
06Z. This looks plausible, with a strong LLJ acceleration to 60kt+
this evening which should advect deeper moisture northward rapidly.
Then the question is whether this system squelches a possible
secondary area of storms to affect our I-59 corridor after 06Z.
Damaging wind appears to be the main threat, but low level SRH values
should increase rapidly with the LLJ development this evening, so
QLCS tornadoes cannot be ruled out at this point. LCL levels would
need to lower for me to be more concerned here. The threat of locally
heavy rain tonight of 2-3 inches in some areas may pose a flash
flash flood threat as well, but given the isolated nature, have opted
to hold off on a watch.

.SHORT TERM...(Friday through Saturday)
Issued at 146 PM CDT Thu Apr 18 2019

Strong upper trough/cold core will continue to produce good upper
divergence and vertical motion through Friday. The -divQ field
will maximize at midday, so fully expect a full radar of cold core
low-topped showers for much of the day. Blustery northwest winds are
also expected with gusts over 20kt. Temps will likely go nowhere up
given the strong cold advection, clouds and ongoing precip. High may
be lucky to get above 50 in NW Alabama. The center of the 5h low
will be over HSV to the Shoals area by 21Z, and the GFS is showing a
rather distinct bullseye of 0.5-1.0 inch QPF during the afternoon in
our eastern counties. So, if this occurs on top of the 1-2 inches, we
may have some river flooding issues develop in these basins. Again,
holding off on watch, but something to consider in later shifts.

A chilly start is expected Saturday morning in the u30s-l40s. Another
spoke or two of 5h vorticity waves will be rotating around the
departing upper low. This will keep low clouds and a few showers into
Saturday morning, particularly in our northeast counties. The clouds
will be slowest to clear if at all during the day Saturday along the
Cumberland Plateau in northeast AL and southern TN. Further west,
sunshine and a transition to low level warm air advection should
enable temps to reach back into the l60s. On the higher elevations of
the Plateau with the clouds, m-u50s are expected.

.LONG TERM...(Saturday night through Wednesday)
Issued at 146 PM CDT Thu Apr 18 2019

High pressure at the surface will develop over the Northern Gulf of
Mexico, helping reinforce drying and dampen surface winds Saturday
night. Clear skies combined with lower wind speeds will create ideal
radiational cooling conditions. Therefore, low temperatures Sunday
morning will drop into the lower 40s, about 5-10 degrees below
average low temperatures for this time of year; surely the Easter
Bunny will need to remember a jacket when coming to the Tennessee
Valley on Sunday morning. Increasing subsidence as the surface high
envelops the Southeast will allow high temperatures on Easter Sunday
to increase near climatological average, in the mid 70s, with mostly
clear skies.

Confidence is increasing for the forecast next week, as models have
come into much better agreement bringing upper level ridging into the
Mid South early next week. As surface high pressure maintains its
hold over us next Monday and Tuesday, expect warm temperatures in the
upper 70s to low 80s with mostly clear skies. Once the high starts
progressing eastward midweek, southerly return flow will increase
moisture, bringing in more cloud cover and eventually another chance
for showers and thunderstorms late next week.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 712 PM CDT Thu Apr 18 2019

A broad cluster of tsra is working its way ewd into NW/north cntrl AL
heading into the evening hrs this Thu. These tsra have resulted in
some reduced vis near 2SM near the KMSL terminal, with sfc winds
gusting around 30kt. These tsra will continue to move ewd over KHSV
within the hr, and continue to affect both main airports for much of
the evening period. Convective activity should then begin to taper
off from the west overnight, as a cold front approaches the area out
of the Lower MS Valley. Lingering -ra/shra though across the region
will likely result in the development of MVFR cigs later tonight and
into the morning hrs Fri. Sfc winds out of the SSW near 15kt with
higher gusts will turn more towards the WNW around 10-15kt with
higher gusts in the wake of the frontal passage.





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