Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 211636 AAB

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
1036 AM CST Sat Jan 21 2017

.NEAR TERM...(Rest of Today)
Issued at 1036 AM CST Sat Jan 21 2017

Quite a busy weather day across the Tennessee Valley earlier this
morning. An area of showers and embedded thunderstorms moved over the
region from the SSW-NNE, bringing another bout of rainfall ranging
from a quarter to one-half inch, and upwards of an inch in some
spots. Local and regional radars indicated the showers now exiting
far NE Alabama and our southern middle Tennessee counties. Skies west
of this were actually clearing somewhat, with some blue peeking in
between post system mid/high clouds.

The strong and severe storms stayed well to our south this morning,
as a strong upper level system moved in a west to east manner across
the southern part of AL, keeping the strongest lift, shear, moisture
convergence out of this area. Another system was beginning to form
over the central Red River region of OK/TX. As this next system moves
to the east, it will bring a warm front northward across the
Tennessee Valley tonight. This will bring another bout of strong to
severe convection to the area during the late evening and overnight.
How much sun and subsequent temperature recovery could make a
difference on how strong storms become later this evening.

For the rest of the day, have sped up the departure of clouds and
shower activity even faster than the night shift did (which was
faster than previous guidance suggested). Thus with more expected
direct sun and/or sun through high clouds, highs today should
recover to around 70 over our western and some of our central areas
this afternoon. Raised highs upwards of a few degrees out west, with
mainly a degree or two most spots in our central areas. Additional
clouds in advance of the next system should return in the late
afternoon. We`ll address this further as more model input comes in.

.SHORT TERM...(Tonight through Monday)
Issued at 220 AM CST CST Sat Jan 21 2017

The models seem to be converging on their synoptic solution across
our region tonight through Monday. Strong upper jet energy will help
to intensify an upper low over TX/OK tonight with it moving eastward
into the lower MS Valley near Memphis Sunday morning. A bimodal
convective event appears to be setting up over the Southeast U.S. as
a result tonight into Sunday. Cold core convection with the upper low
and along the pseudo-occluded and warm fronts will develop late this
afternoon and evening in AR/north MS and lift north and northeast
into western TN/KY/northern AL tonight. Discrete supercells with
large hail are quite possible with this activity, possibly extending
southeast into northern AL and southern TN tonight after 03-06Z
tonight. The threat for tornadoes will be rather low given low level
CAPE is rather low, while steep mid level lapse rates contribute
to the total CAPE located in the favorable hail growth layer.
Better overall thermodynamics and low and deep layer bulk shear
values will occur in central and southern AL into GA more closely
tied to the low level jet where a separate MCS is likely to take
place both tonight, and again on Sunday. Thus, the SPC outlook looks
pretty good with a more marginal-slight risk of severe weather in
north AL and southern middle TN.

Will there be a "break" Sunday morning before the upper low pivots
into AL? Possibly, but not much of one since dPVA will be strong.
The NAM/GFS/ECWMF are now all in much better consensus with a
secondary surface low that deepens rapidly from the FL panhandle
northeast into western SC/NC on Sunday into Sunday Night. The
heaviest deformation QPF is now located just to our east. So, not as
concerned about our flood potential with this system.

On Monday, we will continue to see an axis of shower activity shift
east of the area through the day. Windy conditions are expected on
Monday due to the very tight pressure gradient that results from a
more phased surface low that takes shape over the central
Appalachians. Gusts of 30-35 mph are expected, especially in the
higher terrain of northeast AL/southern TN.

.LONG TERM...(Tuesday through Friday)
Issued at 220 AM CST CST Sat Jan 21 2017

Agreement among medium range models/ensembles is quite good on a
pattern change for rest of the work week. While ridging will briefly
build back over the region Tuesday in the wake of the departing low,
another deep north Pacific trough--and a return to reality for late
January--will quickly erode that ridge by the end of the week.

Conditions behind the front Tuesday will be more seasonable than the
recent warm spell, but temperatures will recover nicely ahead of the
front Wednesday. The main rain chances come Wednesday along the
front, although even these do not look robust due to limited
moisture advection. Isolated showers will persist into Thursday as
the trough deepens and a shortwave pivots around the base of the
trough. In this regime with persistent troughing over the eastern
CONUS, temperatures will fall back to around/just below normal for
late January (50/30).


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 515 AM CST Sat Jan 21 2017

Low clouds with ceiling AOB 010AGL (IFR) have entered north central
and northeast AL including KHSV. It is less certain these clouds
will reach KMSL so have not included as of yet. The northern extent
of a large complex of showers and thunderstorms will affect both KHSV
and KMSL this morning. Moderate showers may reduce visibility to
~3SM at times at KHSV. Lighter rain is expected at KMSL with VFR
still remaining possible this morning. A few rogue lightning strikes
are possible, but it is too uncertain to include at this time and
amendments may be necessary. VFR flight weather conditions are
anticipated this afternoon before low clouds redevelop this evening
in the 010-020agl range. Additional showers and thunderstorms are
expected, especially after 06Z. Some of these could be strong with





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