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Area forecast discussion
National Weather Service Birmingham Alabama
606 PM CST sun Dec 15 2019

Update...
aviation discussion.

&&

Short term...
/updated at 1218 PM CST sun Dec 15 2019/
through tonight.

There's been a varied presence of clouds across central Alabama
this afternoon. Moisture in the low levels + warm advection and
lift will aid in a continued presence/re-development of low clouds
tonight. Patchy fog is possible overnight into Monday morning,
with a southerly breeze tending to preclude dense fog. Lows
tonight will run in the 50s.

Monday and Tuesday.
/Severe potential late Monday into early Tuesday/

There's a sharp thermal gradient toward our west this afternoon,
where a surface low is forecast to develop early Monday beneath a
positively-tilted upper trough. This low is projected to move
northeastward from the arklamiss region to the Tennessee Valley by
late in the day. This path should tend to keep surface wind
trajectories from veering too much during the event. Forecast
soundings across central Alabama show good directional and speed
shear with height. At 0-1 km, hodograph curvature should result in
srh values of 250-350 m2/s2. Combined with bulk shear values
running 45-55 knots, the environment is supportive of organized
and rotating storms. Href mean cape values are around 450-750 j/kg
with a low-end probability of localized values closer to 1,000
j/kg. This seems to be a consistent ceiling for this event,
typical of a cold-season system, yet is a sufficient amount for
severe storms given the strong shear. Also, a plume of mid-level
lapse rates in the 7c range, located over the interior west Gulf
of Mexico region Sunday afternoon, will move northeast through
Monday. These values are supportive of deep convection. Storm Mode
and a couple limiting factors will determine if the
aforementioned variables are able to be realized and allow this
system its full potential. Based on the parameters and setup, all
of central Alabama is under a threat for severe storms late Monday
into early Tuesday.

Convection will favor forcing associated with the front, with a
mixed storm Mode expected. It's plausible that we'll see semi-
discrete cells near the larger band of storms featuring segments
and clusters. The storms will carry a threat of a few tornadoes,
damaging straight-line winds, and hail as they move across
central Alabama. Due to the orientation of the convective line and
storm motions, training rainfall is probable. We don't anticipate
a significant flood threat, but minor flooding could occur in
urban, low-lying, and poor-drainage areas.

A cold front will complete its passage across central Alabama on
Tuesday. Clouds will linger, with much cooler air arriving on a
breezy northwest wind. Clouds will begin to vacate the region
heading through the night, with lows at or below 32 degrees.

89^gsatterwhite

Long term...
/updated at 1218 PM CST sun Dec 15 2019/
Wednesday through Saturday.

Fair weather is forecast Wednesday and Thursday with afternoon
highs in the 50s. The next system will bring increased cloudiness
for Friday and Saturday, with a chance of rain heading into the
weekend.

89^gsatterwhite



&&

Aviation...
00z taf discussion.

A stratus deck with cigs hovering around 3kft is pushing to the
north this evening, leaving mostly clear skies at most terminals to
start the forecast period. Could see sct to bkn cigs at anb and asn
over the next couple hours but cigs should remain just above MVFR
criteria.

The break in cig height restrictions will be short-lived, as low
clouds will redevelop tonight, with heights falling to IFR. Patchy
fog is also possible, primary at more sheltered locations and
valleys, as low level southerly winds will remain elevated
overnight. Increasing low level winds ahead of an approaching storm
system will allow for a period of low level wind shear for terminals excluding mgm
and toi.

Showers and storms will impact all terminals Monday and Monday
night. Isolated to scattered showers could develop before sunrise
Monday, with activity becoming more widespread by Monday afternoon.
Best chance of rain and storms will come after 17/00z.

14



&&

Fire weather...

Varied cloudiness continues Sunday evening, with widespread low
clouds expected to develop overnight. Rain and storms are forecast
late Monday through early Tuesday, some of which may be severe.
Breezy northwesterly winds are expected on Tuesday, easing
overnight. Rain-free weather is expected for Wednesday and
Thursday, with the next system bringing increased cloudiness for
Friday and a chance of showers by Saturday.

&&

Preliminary point temps/pops...
Gadsden 54 68 42 54 27 / 30 60 100 30 0
Anniston 55 70 46 58 28 / 20 40 90 40 0
Birmingham 57 70 44 52 29 / 30 70 100 20 0
Tuscaloosa 59 74 42 50 28 / 20 80 90 10 0
Calera 57 71 44 53 28 / 20 50 90 30 0
Auburn 53 70 53 62 31 / 10 20 90 70 0
Montgomery 57 74 50 61 31 / 20 30 90 60 0
Troy 55 74 53 65 32 / 10 10 90 70 0

&&

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