Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 260000
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
700 PM CDT Tue Apr 25 2017

.UPDATE...
For 00Z TAFS.

&&

.NEAR TERM...(Tonight)
Issued at 300 PM CDT Tue Apr 25 2017

Clear skies are forecast again tonight but with a little more drier
air in place and a slight S/SE wind expected overnight, fog won`t be
nearly as widespread as it was this morning. Dewpoint depressions
will be the smallest across the eastern half of the area and have
added patchy fog to valley locations. Lows tonight will be in the mid
50s.

.SHORT TERM...(Wednesday through Thursday night)
Issued at 300 PM CDT Tue Apr 25 2017

Raw model guidance seems to be under doing the highs on Wednesday
with those forecasting highs in the lower 80s. With a 850/700mb jet
of 30-40kts lifting NE through the TN/MS/AL area on Wednesday, we can
expect a breezy day with some portion of these higher wind values
mixing down to the surface. 850mb temps of 17 to 19C would support
afternoon highs in the mid to upper 80s. The better mixing, warm
temps aloft, will combine with drier air and lead to temps above what
is the latest raw model guidance for highs. Nudged highs into the mid
to upper 80s for much of the area.

For Wednesday night into Thursday, guidance has been consistent in
showing a system digging E/SE through the four corners region and
into the ArkLaTex area on Wednesday. This is expected to generate
convection over AR/LA/MO Wednesday afternoon with a likely QLCS/MCS
moving east during the overnight hours. Models are in good agreement
in moving this feature across the TN Valley after 06Z Thursday into
early Thursday morning. There are still questions as to whether or
not this line will be able to hold together as it moves east and if
it does could it be surface based?

Right now, with the warm 850mb temps on Wednesday, there isn`t much
in the way of cooler temps being advected into the area to remove the
mid-level CAP and models are pointing to this region of warm temps
aloft continuing all the way up until the line moves across the area.
However, there could be a mixture of strong vertical motions and
rain cooled air, arriving ahead of the line of thunderstorms to allow
for a brief window around sunrise Thursday morning that thunderstorms
could become surface based (confidence in this though is very low).
Think the warm temps and generally dry atmos. profile will limit
storms somewhat and as storms cross the area they are forecast to be
primarily elevated.

Now with that said, shear with these storms will be strong with
50-60kts of 0-6km shear and 40kts of 0-1km shear due to a 80-90kt
500mb jet moving across the area. Hodographs are also interesting
with a good turning of the wind with height. So this event will need
to be watched, as storms even elevated could be strong to potentially
severe.

The line is forecast to quickly exit the area to the east Thursday
morning. But the lingering cloud cover behind the system and weak
CAA will lead to temps in the low to mid 70s. Thursday night lows
drop into the mid to upper 50 with patchy fog possible.

.LONG TERM...(Friday through Monday)
Issued at 300 PM CDT Tue Apr 25 2017

The stalled cold front will lift back northward as a warm front
during the day on Friday. Daytime highs will reach the low/mid 80s
as breezy southerly flow accompanies the warm front. This will
provide a lifting mechanism for showers and thunderstorms in the
morning/early afternoon, while daytime heating in the afternoon hours
will drive more scattered summertime convection. Question still
remains on how strong the storms will be associated with the warm
front. The front weakens as it moves into the TN Valley ~12-15Z.
Shear of ~40kts is better in the morning then weakens in the
afternoon.  Moisture return will not be a problem as dewpoints will
get up into the 60s and PWATs over an inch. With the warm temps and
good low level moisture instability is forecast to be ~2000 J/kg or
more.

Southerly flow picks up on Saturday ahead of the next storm system
swinging out of the Rockies. Daytime highs will soar into the upper
80s towards 90 degrees with a few showers and thunderstorms possible
as weak disturbances pass through.

As the sfc low lifts northeastward from TX up towards the Great
Lakes, the associated cold front will move into the TN Valley Sunday
night into Monday. Moisture ahead of the front will continue to feed
into the region as PWATs encroach 2" by Sunday night. With CAPE
~1000 J/kg and 0-6km shear of 40-50kts, there is a potential for
severe storms. The GFS continues to be the faster run, however it is
picking up on a possible sfc low near the Gulf, so will have to watch
for any coastal convection that would affect our severe storm
potential.

If you are looking for a cool down, it will arrive on Monday.
Showers and thunderstorms will be exiting the forecast area but high
temps will only be in the 70s!

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 700 PM CDT Tue Apr 25 2017

With a sfc ridge of high pressure in place over the cntrl Gulf
states, VFR conds are xpcted through the TAF period.

&&

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

$$

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


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