Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 080507
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1107 PM CST Wed Dec 7 2016

.UPDATE...
For 06Z TAFS.

&&

.NEAR TERM...(Tonight)
Issued at 930 PM CST Wed Dec 7 2016

Strong SWLY flow in the mid/upper levels helped to create an
inversion over the region for much of the day today. This combined
with lingering moisture in the low-levels created the stratus deck
today. However, as observations and 00Z soundings indicate drier air
has filtered in, clearing the stratus deck. The strong SWLY winds
though will continue to advect mid/upper level moisture into the
region and we should remain overcast tonight.

The question for tonight though is how fast does the Arctic airmass
over the Central Plains make it into the region and will we have any
precip with it? Latest surface analysis would suggest the front is
over northern Arkansas as of 03Z. Timing this out it would move it
through between 07Z to 12Z tonight. Regional radar imagery shows some
very light precip has developed along front and with a few weak
shortwaves caught in the strong SWLY flow. Used a blend between raw
model guidance, time-lagged ensembles, and forecast soundings and
believe that the drier air at the surface should keep any measurable
precip at bay. However, the SWLY flow continues throughout the night
and will allow for some moisture to be advected into the region in
the mid-levels. The lift with the front and weak shortwaves may be
enough to allow for very light precip to fall in the form of
sprinkles to possibly an isolated flurry. Tried to time out the
arrival of the coldest temperatures aloft and at the surface for when
to add the mention of an isolated flurry, and came up with between 3
AM to 6 AM.

Confidence in any precip and the type remains very low. Will watch
closely what occurs to our west over AR/MS to see if we can
potentially remove all precip tonight. Clouds should keep
temperatures from dropping very quickly tonight but with the arrival
of the Arctic airmass, lows Thursday morning will be in the low to
mid 30s.

.SHORT TERM...(Thursday through Friday)
Issued at 228 PM CST Wed Dec 7 2016

The arctic airmass will quickly build in on Thursday, and the
tightening pressure gradient will make for a very chilly day. Highs
will generally be in the upper 30s to lower 40s and will combine
with 10 to 15 kt winds to create wind chills in the 30s through much
of the day. Strong CAA will continue overnight THursday, with lows
plummeting into the teens to lower 20s. Winds will remain in the 5
to 10 kt range, and wind chill values may dip into the single digits,
especially in the higher terrain. Conditions are not expected to warm
much during the day on Friday, as the center of the surface high
becomes nestled across the area. Highs are forecast to remain in the
30s, and will not rise above freezing until noon.

.LONG TERM...(Friday night through Tuesday)
Issued at 228 PM CST Wed Dec 7 2016

Clear skies and a surface high directly over the area will allow
temperatures to drop into the upper teens to around 20 degrees again
on saturday morning. Zonal flow develops aloft on Saturday afternoon
into Sunday, as another disturbance develops over the Midwestern
states. This should make highs a bit more bearable, reaching the
lower 40s in most locations. However, higher elevations may still
remain in the lower to mid 30s.

Overnight, although some moisture is advected northward via
developing southwesterly low level flow, lows will still drop to
around between 32 and 36 degrees west of I-65. With breezy conditions
developing, wind chills could drop into the lower 20s or upper teens
in higher elevations. Further east lows in the upper 20s look
possible. However, expect by 8 AM temperatures to rebound quickly
via strong southerly low level flow to between 35 and 40 degrees
everywhere. Some developing cloudy conditions can be expected, but
not precipitation is expected through 9 or 10 am on Sunday.

Increasing moisture advection and lift ahead of the disturbance will
produce some isolated/scattered showers in northwestern alabama by
the mid to late morning hours on Sunday. Strong southerly low level
flow should also warm temperatures back into the 50s during the day
on Sunday. These showers should shift east later in the day on Sunday
into Sunday night and become more widespread. Models are in fairly
good agreement on timing early with this system. They produce 1/4 to
3/4 of an inch of rainfall over the area by Sunday evening. It will
be close if we have a mix of light rain/snow sunday morning, but at
this point keeping all rain, with temperatures 33 to 35 degrees in
most locations or higher. Expect lows on Monday to climb back into
the lower 40s via the strong southerly flow.

As we progress through the day on Monday, synoptic models diverge
very significantly. ECMWF slows the front down quite a bit and keeps
widespread showers over northern alabama and Southern Middle
Tennessee into the early afternoon hours, before moving
precipitation into Georgia. For now, going with Superblend for
consistency sake, given the large spread in model solutions and
keeping a 30-40 percent chance of rain in the forecast on Monday
(although the actual forecast might end up being 20 percent or less
given such different solutions concerning frontal movement). Either
way, highs will be in the 50s again on Monday.

Synoptic models are in good agreement again by Tuesday, with cool
temperatures and fairly zonal flow in place. By Wednesday models
show a weak frontal boundary setting up over the Ohio Valley
southwest into the northern Tennessee. This could produce some very
light precipitation over the area Tuesday night into Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1100 PM CST Wed Dec 7 2016

The drier air at the surface arrived a bit quicker than thought with
the 00Z issuance and the MVFR stratus deck has cleared. An Arctic
front is expected to move across the area tonight through Thursday
morning and drop clouds back down to 5,000ft. Winds remain out of the
NW through the period but increase after 12Z with speeds around
10kts. A few gusts of 15kts to possibly 20kts are possible Thursday
afternoon.

&&

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

$$

NEAR TERM...Stumpf
SHORT TERM...73
LONG TERM...KTW
AVIATION...Stumpf


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