Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 101851
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1251 PM CST Sat Dec 10 2016

.SHORT TERM...

This afternoon through Sunday...
Sunny skies and a light northeast flow for this afternoon courtesy
of dry high pressure centered to our north. Temperatures have
warmed up since the cold start to the day. Increased highs a
degree or so and have a range from 45 to 55 degrees.

Overnight, the high pressure drifts eastward. Temperatures should
cool under good radiative conditions this evening. Lows will range
from 25 to 35 degrees. Surface winds will begin responding by
swinging toward the southeast after midnight. Additionally, a low
pressure system approaches the plains by morning and this allows
the winds just above the surface to increase out of the south.
This warm advection regime will increase moisture values and
eventually clouds. Model output does not agree on the timing or
placement of the clouds in the morning but believe these clouds
will begin increasing over east central Alabama by sunrise. There
should be sufficient isentropic lift to get cloud formation.
Therefore, some locations may experience lows a few hours before
sunrise.

With the southerly flow, low level thicknesses and 850 temps
increase on Sunday. So expect the high temperatures to jump to
near normal around 60 in many spots. With clouds and a hint at
some brief easterly influence east, highs may be a tad cooler
near the Georgia state line.

75

.LONG TERM...

Sunday night into Monday morning...
A shortwave trough and associated low pressure system will be
moving through the Great Lakes region and into Ontario. Showers
along a trailing cold front move into the forecast area very late
Sunday night into Monday morning. While the low pressure system
and mid-level shortwave trough will be well removed from the area,
upper-level jet influence, a 45 kt LLJ, and sufficiently high
1000-500 mb mean RH will allow for likely rain chances to be
warranted. With PWATs around 1.1-1.2 inches not expecting anything
heavy, however. Dew points and air temperatures in the 50s through
Monday morning will result in negligible instability. Models are
trending even weaker with instability south of the front Monday
afternoon with dew points barely reaching 60, though air
temperatures will be near 70 in extreme southern counties.
Therefore thunder chances still look low. Expect a band of mainly
light rain showers along the front to slowly sink southward
through the day.

The front will stall out somewhere across the area Monday night
through mid-week. Enough of a southerly component to the low-level
flow will result in isentropic lift and PWATs across the south
will be around 1.3 to 1.4 inches, resulting in continued rain
chances, but still not expecting anything heavy. Models are
beginning to come into enough agreement to begin to bump up rain
chances in the forecast, but rain will continue to be influenced
by where the front is and weak waves developing along it.
Temperatures will be seasonably mild.

A stronger cold front will arrive Wednesday in response to a deep
upper low of Arctic origin moving across southern Canada. There
have been some run to run differences in how quickly moisture
exits the area, but the model runs that have been slower with the
moisture exit have also been slower with the arrival of cold air.
Therefore, expect any remaining moisture to be gone by the time
the cold air arrives. The latest model runs also indicate that the
brunt of this cold air outbreak will miss Central Alabama.

Towards the end of the week, a mid and upper-level trough will
amplify over the western CONUS, with upper-level flow becoming
southwesterly and moist isentropic lift developing ahead of it.
Strong warm advection is expected to keep temperatures warm enough
for only liquid precipitation in Central Alabama beginning on
Friday, but moisture and instability trends will need to be
monitored the following weekend.

32/Davis


&&

.AVIATION...
18Z TAF Discussion.

MVFR ceilings developing Sunday morning, especially east. Surface
high pressure and dry atmosphere will keep skies virtually cloud
free through 06z with a east northeast wind component around 6kts.

Late tonight into Sunday, the high pressure drifts farther east
and a developing low inches toward us from the west. Winds just
above the surface veer quickly and increase from the south between
11-15z. Model solutions and MOS solutions disagree with the
timing and placement of the moisture increase and isentropic lift.
Think there will be some cloud cover and have it developing right
around 12z. Went with ceilings of 015-025 for TOI/MGM/ANB/ASN.

A rainy and unsettled period ensues Monday through Wednesday.

75


&&

.FIRE WEATHER...

Relative humidity values will drop into 20 to 30 percent range this
afternoon. But, winds will be rather light. Moisture begins to
increase Sunday with rain chances returning late Sunday night into
Monday. While the best chances will be late Sunday night into
Monday, rain chances will remain a possibility through the middle of
next week as a front stalls over the area.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     25  54  44  61  50 /   0   0  50  80  40
Anniston    28  54  45  62  52 /   0   0  40  70  50
Birmingham  31  56  49  63  53 /   0   0  40  70  50
Tuscaloosa  28  59  52  66  54 /   0   0  40  70  50
Calera      30  57  49  64  54 /   0   0  30  60  50
Auburn      32  55  48  66  57 /   0  10  30  60  60
Montgomery  29  62  50  71  59 /   0  10  20  60  60
Troy        30  60  51  72  60 /   0  10  30  40  60

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

$$



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