Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 111718
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1118 AM CST Mon Dec 11 2017

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today and Tonight)
Issued at 824 AM CST Mon Dec 11 2017

It`s going to be quite the pleasant day although it`s chilly this
morning. 8am temps are slow to warm and still in the lower to upper
30s but should warm quickly in the next few hours. Weak southerly
flow continues today which will continue the warming trend in the
temps. Did not make any edits to highs today, just to the temp trend
and highs should still reach to the mid to upper 50s, probably 60 in
a few spots.

An Alberta clipper/short wave will dive down towards the area this
afternoon bringing a reinforcing cold front through by
midnight. Clouds will increase along the front but no precipitation
is expected. Current forecast lows are in the middle 30s but will be
tricky depending on the timing of the cold front and the overall
cloud coverage.

.SHORT TERM...(Tuesday through Wednesday night)
Issued at 226 AM CST Mon Dec 11 2017

There is enough moisture and weak lift on Tuesday morning across
southern middle TN (mainly Franklin County) to support a light
rain/snow mix between 12-17Z. Not much in accumulations is expected
given the dry air above the -10C level, but definitely something to
monitor. The most noticeable feature will be the breezy northwesterly
surface winds of 10-15 MPH gusting to 20 MPH as strong cold air
advection ensues. Depending on the speed of the cold air, could see
high temperatures actually occurring in the early morning hours on
Tuesday. Temperatures should rise modestly from overnight lows in
the low to mid 30s to the low 40s due to the strong cold air
advection and mostly cloudy sky conditions.

The mid-level shortwave trough should merge with another approaching
embedded shortwave trough moving southeast on the southern flank of
the Canadian upper low over Quebec/Ontario on Tuesday. Clouds should
clear on Tuesday night yielding a very cold night in the low to mid
20s (possibly teens over southern middle TN). Little solar
modification of the airmass will take place on Wednesday, but weak
southwest surface flow will begin to push the airmass northeast. This
will mean a SW (higher) to NE (lower) gradient in daytime highs in
the mid to upper 40s. And then, yet another fast moving shortwave
trough (second Alberta clipper system) will move over the Midwest on
Wednesday afternoon arriving over the TN Valley late on Wednesday
night. Forecast soundings show a rather dry airmass below 700 mb. So,
will keep dry forecast in place ahead of the front expected on
Thursday.

.LONG TERM...(Thursday through Sunday)
Issued at 226 AM CST Mon Dec 11 2017

Region will remain in a west-northwest flow pattern aloft Thursday
into Friday.  Clipper-type low will be dropping through the eastern
OH valley into the central Appalachians on Thursday bringing a cold
front through during the day.  At this time, the models indicate
little moisture and weak UVV to support measurable precipitation at
this time.  A shortwave dropping south through the Plains quickly
follows behind on Friday will dig a stronger positive tilt wave
through the southeast U.S. This will likely generate rainfall along
the front from the northern Gulf of Mexico northeast through
northern FL and southern GA. An upper ridge then quickly amplifies
over the Southeast on Saturday with good southwest low level flow and
warm advection. Highs should reach the m-u50s quite easily Saturday
afternoon. Another shortwave trough arrives on Sunday, this time
being of Pacific origin. Strong mid level warm air advection may be
enough to generate some mid level cloud Saturday night, but will
leave dry until Sunday when the surface cool front arrives. There is
a wide disagreement with this system between a more bullish/wetter
GFS and drier ECMWF. This looks to be mainly due to the ability of
the GFS to advect deeper moisture northward, while the ECMWF is a bit
delayed in this regard. Will stick close to suggested blended PoP
guidance for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1118 AM CST Mon Dec 11 2017

Light and variable winds this morning will steadily become SW around
8-12kts in the next hour or so and through the afternoon. A cold
front will move through west to east this evening, probably around 4z
at KMSL and 5Z at KHSV, possibly off an hour in either direction. A
strong jet will accompany the front leading to LLWS for a few hours
with the passage. Winds will still be gusty through the day Tuesday
with gusts 18-20kts possible. Mid level ceilings will move in with
the front and may lower to 3-4kft in the afternoon. This is still a
bit far out to say for certain.

&&

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

$$

NEAR TERM...LN
SHORT TERM...SL.77
LONG TERM...17
AVIATION...LN


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