Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 241002

Area Forecast Discussion
National Weather Service Birmingham AL
402 AM CST Fri Feb 24 2017

Today and Tonight.

Expect mostly sunny skies through the day with breezy southerly
winds and warm conditions. Many locations will flirt with record
highs today (see the Climate section below). Forecasted highs at all
four official climate locations break the high temperature record

A cold front will approach Central Alabama from the west by early
evening, along with a broken line of showers and thunderstorms. This
activity will push across the forecast area overnight, exiting the
southeast around sunrise. The main forcing with this system is well
to our north, with a surface low crossing the Great Lakes and upper
level trough remaining very broad over the Deep South. Bulk shear
values directly along the front of 60kts support updrafts, but
low level winds are veered, greatly limiting any tornado
potential. Low level forcing is weak, with a mid level cap ahead
of the front. Lapse rates above the cap and 500mb temps are
supportive of small hail and possibly a few wind gusts, but severe
storms are unlikely and will not add severe wording to the HWO.


Saturday through Thursday.

Any lingering precipitation along the front should quickly exit
the southeast counties Saturday morning. Behind the cold front,
winds will be breezy out of the northwest with 850 mb temperatures
falling to around 0C. This will result in much "colder" high
temperatures (actually only a couple degrees below seasonal
averages) in the 50s north to 60s south. Surface high pressure
will move eastward out the Plains and reach northern AL/Tennessee
by sunrise Sunday morning. Light winds, low dew points, and clear
skies will result in good radiational cooling conditions. Lows
will fall to or below freezing across the north with some upper
20s in the cooler locations. Winds will switch over to the
southeast by Sunday afternoon as the surface high moves off the
Southeast Coast and with warm advection developing temperatures
will recover nicely into the 60s for most locations.

Zonal upper-level flow will become southwesterly Sunday night into
the first half of next week between central/western US broad
upper troughing with embedded shortwaves moving through and a
strengthening upper-level ridge extending from the southern Gulf
to the Bahamas. An initial shortwave will move from the Southwest
US to the Ozarks Sunday into Monday morning while weakening. In
response low-level southerly flow will strengthen Sunday night
into Monday. This will result in isentropic lift and moisture
returning to the area. Isentropic lift precipitation may begin as
early as late Sunday night in the northwest and increase in
coverage across the area through the day on Monday. Due to
moisture transport associated with a 35-40 kt LLJ and PWATs
increasing to 1.3 to 1.4 inches (well above the 90th percentile
for this time of year), rain chances were increased to likely
across portions of the area Monday, Monday night, and Tuesday.
Models have come into better agreement on a slower northward
progression of the warm front Monday which makes sense given that
precipitation north of the warm front will be falling into a
remnant dry air mass. Due to this evaporative cooling forecast
highs on Monday may end up being too warm across the north. Some
thunder will be possible Monday afternoon but instability will
remain elevated rather than surface based during this timeframe.

The warm front will lift northward through the area Monday night
with temperatures rising through the night. A moisture axis will
remain over the area with moist southerly flow continuing to
result in likely rain chances. Models indicate around 500-1000
J/kg of CAPE with mid 60s dewpoints on Tuesday and around 45-50
kts of 0-6 km shear. With steep mid-level lapse rates and low WBZ
heights some stronger storms with hail and gusty winds will be
possible. An isolated severe storm or two (large hail and/or
damaging winds) may be possible Tuesday (or perhaps as early as
Monday night), but without any upper-level forcing or a low-level
focusing mechanism, still do not see anything indicating an
organized threat that would need to go in the HWO. Widespread
clouds/precipitation will also be limiting factors that could keep
these instability values from being realized.

Models diverge on the timing of a stronger shortwave trough moving
from the Southwest US to the Ohio Valley/Great Lakes that will
result in a mid-week frontal passage for our area. The latest GFS
sped up the timing quite a bit with a Tuesday night frontal
passage. The ECMWF has been more consistent run-to-run with a
Wednesday/Wednesday night timing, with better ensemble support,
but there is some spread. The Wednesday/Wednesday night timeframe
remains preferred. Due to differences between models and model
runs regarding timing and various parameters, it is still too
early to determine if there will be any severe storms near the
front. Moisture and instability will be present but upper-level
forcing and low level jet strength remain uncertain. Cooler and
drier conditions will move in behind the front by Thursday.



06Z TAF Discussion.

Except for some low clouds that may or may not develop before
sunrise, VFR conds will prevail during the period. Satellite
imagery indicates very little cloud cover late this evening, but
conditions remain somewhat favorable for cloud formation after 09z
with bases arnd 1500-2000. Cloud cover will likely be patchy, so
went with tempo MVFR cigs between 10z and 14z, with more cloud
cover after sunrise as the air mass heats up quickly. Good low
level mixing during the day should thin out cloud cover after 18z
with scattered clouds. Fog should not be an issue due to moderate
boundary layer winds.




Dry and warm conditions are expected today. A cold front will move
through tonight bringing a chance of a quick shower or storm but
rainfall amounts should be light. Drier air will move in behind
the front for the weekend. RH values will fall to around 30
percent Saturday afternoon with 20 ft winds around 10-12 mph, and
to near 25 percent Sunday afternoon with lighter winds. Critical
fire weather conditions are not expected.



Record high temperatures for Today, February 24:

Birmingham:  78 (1930)
Montgomery:  80 (1890)
Tuscaloosa:  78 (2011)
Anniston:    78 (1982)


Gadsden     78  51  54  29  57 /  10  50   0   0   0
Anniston    79  53  57  31  59 /  10  50   0   0   0
Birmingham  79  50  57  31  60 /  10  50   0   0   0
Tuscaloosa  81  48  58  31  61 /  10  50   0   0   0
Calera      79  52  58  33  60 /  10  50   0   0   0
Auburn      78  57  62  35  60 /  10  30  10   0   0
Montgomery  83  57  63  36  64 /  10  40   0   0   0
Troy        81  58  65  35  64 /  10  30  10   0   0




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