Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 250002

Area Forecast Discussion
National Weather Service Birmingham AL
602 PM CST Fri Feb 24 2017

For 00Z Aviation.



Forecast has been on track today with the temperature trends only
varying a degree or so from the hourly forecast. Have tweaked
temperatures slightly to account for a few sites consistently
trending 2-3 degrees warmer than previously forecasted, but
overall minor changes across Central AL. Sunny skies with only
scattered cumulus across the area. All climate sites (Birmingham,
Montgomery, Tuscaloosa, and Anniston) have broken the daily high
temperature records today.
A cold front moves through the region later tonight, associated
with an upper low moving through the Great Lakes region. Most of
the stronger forcing remains well to our north, though the 0-6
bulk shear magnitudes are around 50-55kts, which would support
organized updrafts. However, forecast soundings show largely
veered hodographs - limiting any tornado potential. Model
soundings also show a capped environment around 700-750mb, which
is verifying as indicated by the CU fields parallel with the
general low-level flow. Just haven`t seen enough evidence in the
models or temp/dewpoint trends to give me confidence in the severe
potential, so will not add anything to the HWO today. I wouldn`t
be surprised to see some stronger storms with small hail and/or
gusty winds, especially up in the northern and northeastern
counties where the better instability and shear overlap, but
storms will likely remain below severe limits. CAMs show much of
the convection occurring along the front late tonight and into the
overnight hours in the form of a broken line, thus have left PoPs
at around 50% along the front as it moves through Central AL.
Current timing from previous forecast seems to still be valid with
the front and best rain chances entering our northwestern
counties around or just before midnight and moving southeastward
across the area through the overnight hours. By sunrise tomorrow
morning, the front should be exiting Central AL, ending the rain


Saturday through Thursday.

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.



00Z TAF Discussion.

Overall thinking has not changed too much this forecast. The main
change was to limit the mention of thunder at the terminals.
Conditions start off VFR across the area with southerly winds
decreasing in their gustiness. A strong cold front will enter
Central Alabama this evening and exit south and east around 12z.

It appears there will be a limited timeframe of MVFR ceilings in
the frontal zone. Therefore, mentioned these restrictions
generally from 06-11z at TCL/BHM/EET/ASN/ANB. Reduced the mention
of thunder to VCTS with a tempo of SHRA. It appears that our
overall forecast only has a 50 percent chance of it even raining
with limited deep layer moisture. At this time, lightning is
showing up along the front as far south as Kentucky. Will monitor
this activity through the evening closely for any changes. This
was also focused on the front and any pre-frontal activity may
need a time adjustment.

Removed mention of thunder at MGM/TOI and have VCSH. The time
frame is a bit later from generally 09-13z. Once again monitor any
pre-frontal activity for a time change on precip mention.

Clear and breezy on Saturday with northwest winds mainly 10 to




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     51  54  29  57  38 /  50   0   0   0  10
Anniston    53  57  31  59  41 /  50   0   0   0  10
Birmingham  50  57  31  60  43 /  50   0   0   0  10
Tuscaloosa  48  58  31  61  44 /  50   0   0   0  20
Calera      52  58  33  60  44 /  50   0   0   0  10
Auburn      57  62  35  60  44 /  40  10   0   0   0
Montgomery  57  63  36  64  44 /  40   0   0   0  10
Troy        58  65  35  64  44 /  30  10   0   0   0




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