Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 021724

Area Forecast Discussion
National Weather Service Huntsville AL
1124 AM CST Fri Dec 2 2016

For 18Z TAFS.


.NEAR TERM...(Rest of Today)
Issued at 923 AM CST Fri Dec 2 2016

After a chilly start to the morning, temps have started to rebound
with sunrise, rising 5-10 degrees in the last hour. This puts 9AM
temps in the lower to upper 40s.

Surface high pressure will settle into the area today with sunny
skies this morning giving away to cirrus clouds this evening ahead of
the next system out to the west. Weak cold advection will continue
today but highs will still reach into the upper 50s.

.SHORT TERM...(Tonight through Sunday night)
Issued at 335 AM CST Fri Dec 2 2016

A trough digging through the desert southwest today will end up over
NW Mexico by this evening. Due to how far south the trough digs it
taps into sub-tropical moisture and strong winds aloft will carry
this increased upper level moisture into the region tonight.
Increasing high level clouds should help to keep temperatures near
the mid to upper 30s tonight.

The forecast for Saturday night through Sunday is quite
interesting and complex. All of the guidance is in agreement that
very strong WAA will develop over the region during this period in
response to western trough and shortwaves being ejected out ahead of
it. However, the high pressure from Friday lingers to our NE and
winds will remain out of the E/NE and some models hint at a some CAD
developing. The core of the warm air in the low to mid-levels is
expected to remain anchored along the Gulf Coast and the strong WAA
will occur aloft.

Latest forecast soundings suggest rapid saturation aloft in response
to the strong WAA during the day Saturday. But E/NE winds help to
keep dry air in place beneath this layer. This first shortwave is
forecast to arrive into the area Saturday afternoon with precip
spreading from west to east Saturday night. Analyzing the QPF fields
from the latest guidance suggest the possibility of a boundary
developing that should enhance QPF numbers from Saturday night
through Sunday afternoon. Unfortunately, where this boundary sets up
is still uncertain as the GFS/NAM place it over the region, while the
ECMWF/GEM keep it just south of the area. The exact position will be
crucial as it could mean the difference of 1-2 inches of rain vs
0.5-0.75 inches of rain. Due to the uncertainty in where this will
set up, ended up using a blend of guidance for QPF values, which has
the current forecast between the two ranges mentioned above. In any
case it will be some welcome rainfall.

As mentioned above, we will remain in the "cool" sector of the storm
and temps on Sunday struggle to reach the 50 degree mark and it will
likely be a cold rainy day. By the afternoon/evening the shortwave
shifts east of the area and have lowered PoPs to reflect this.
However, the lower levels are expected to remain saturated and we
should end up with periods of light rain/possibly drizzle continuing
through Sunday night.

.LONG TERM...(Monday through Thursday)
Issued at 335 AM CST Fri Dec 2 2016

The brief break in the more widespread precip will end after
daybreak on Monday. Precip will spread northward through the day, as
low to mid level moisture advection quickly returns and the upper
low moves into the Arklatex region. Ongoing showers will continue
through much of the evening and overnight hours, and the upper low
is expected move just to our northwest between 06Z and 12Z Tuesday.
Meanwhile, a warm front will lift northward as the associated
surface low moves towards the mid MS Valley. Dewpoints reach into
the mid to upper 50s, however expect the area to remain fairly
capped as the ongoing precip prevents us from warming too much. Mid
level lapse rates will steepen in response to the cooling temps
aloft, and elevated thunderstorms are possible. However expect these
to be isolated and embedded in the widespread rainfall. Given the
stronger lift associated with this low, rain may be heavy at times
and we are forecasting up to an inch of additional rainfall with this
wave of showers.

The upper low will quickly race off to the NE on Tuesday, with
another break in precip Tuesday afternoon and through the overnight
hours. Uncertainty increases for the next system, as the GFS and
ECMWF are roughly 12 hours off on the progression of another upper
trough. The trough is expected to eject east of the Rockies on
Tuesday, and quickly amplify as it moves through the Central Plains.
A strong arctic cold front will accompany the trough and move
towards the TN Valley late Wednesday. The GFS has precip moving
through quickly during the overnight hours, with the front moving
east of the area by daybreak Thursday. Meanwhile, the ECMWF has
precip beginning around daybreak Thursday and pushing east of the
area late Thursday afternoon. Given these timing differences, leaned
somewhat closer to the ECMWF as the GFS seems to have slowed down
slightly as well, leaving a chance of precip in for the east on
Thursday. This also means slightly warmer temps than the blended
guidance, with lows on Thursday morning just above freezing.
Although it is day 6/7 and model discrepancies remain high, if the
arctic air moves in quicker than the precip can exit this might give
us our first shot at snow flurries. Of course this will not be any
impact to the area as we will not have enough moisture and lift to
lead to accumulations, but after the above normal temps in November,
it`s certainly a change in pace.

The arctic air will quickly move into the forecast overnight
Thursday. While models are in slight disagreement over how quickly
that will occur, there is increased confidence of temps well below
normal for the Friday and maybe Saturday timeframe. Many models show
temps remain at or below freezing, with a few slightly higher. Our
record low maximum temp for Huntsville is 30 degrees and at this
point, we are not forecast to be several degrees above this.
However, we may be looking at record breaking cold weather next


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1124 AM CST Fri Dec 2 2016

VFR conditions and winds of 5-10 knots are expected through the TAF





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