Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 210820

Area Forecast Discussion
National Weather Service Huntsville AL
220 AM CST Sat Jan 21 2017

.NEAR TERM...(Today)
Issued at 220 AM CST CST Sat Jan 21 2017

Thus far, the veil of CI/CS is helping to negate the potential for
radiation fog. Given the narrow T/Td spreads, we should see at least
patchy fog develop before showers arrive before daybreak. Speaking
of which, the latest HRRR/short range model reflectivity suggests
that the strong/severe t-storms from developing MCS in MS/LA will be
directed mainly to our south and southeast this morning. The northern
stratiform region of the MCS will likely affect our area. We will
maintain thunderstorms as some lightning remains possible. The
precip should exit our eastern counties before midday. We will leave
a small chance in for redevelopment, but it would appear the
afternoon hours should be mainly dry. Subsidence behind this system
should allow for partial clearing and temps to warm nicely into the
m-u60s for highs.

.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 06Z TAFS through 06Z Saturday night)
Issued at 1104 PM CST Fri Jan 20 2017

VFR conditions and light winds at the current time and through the
next few hours. Due to current trends and the thick layer of higher
clouds moving in, removed the 4SM visibility from the TAFS. Vis may
briefly dip below 6SM but confidence is not high enough to keep in
the TAFS.

A system from the south looks like it will now impact the terminals
with rain after 12z from the west and move fairly quickly to the
east. Also added a brief TEMPO for thunderstorms. Should see a break
in the afternoon with VFR CIGS. Another round of showers and
thunderstorms then impacts the terminals after 03Z Sunday.





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