725
FXUS64 KBMX 242348
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
548 PM CST Sun Nov 24 2024

...New SHORT TERM, AVIATION...

.SHORT TERM...
(This evening through Monday)
Issued at 545 PM CST SUN NOV 24 2024

A zonal flow aloft coincides with a surface ridge now centered to
our southeast. Low-level flow, generally from the surface through
850 mb, now prevails a S to SSW direction promoting a slow
increase of warm air advection that will persist tonight. This
will support an increase in low clouds and some patchy fog. Thus,
tonight`s lows may occur around or just after Midnight before
clouds/advection increase. The troposphere will continue to
moisten through tomorrow ahead of a cold front and associated band
of light/moderate rain showers that will pass over the area, and
this is discussed in the long-term. Highs tomorrow are in the 70s
with variable cloudiness.

40/Sizemore

&&

.LONG TERM...
(Monday night through next Saturday)
Issued at 309 PM CST SUN NOV 24 2024

Key messages:

- High (60-80%) rain chances Wednesday night into Thanksgiving,
  with high uncertainty regarding how quickly precipitation exits
  on Thanksgiving.

- Low probabilities (less than a Level 2 out of 5 risk) for
  severe storms Wednesday night into Thanksgiving, with high
  uncertainty on timing and if probabilities will increase.

- Much colder temperatures for the rest of the holiday weekend and
  into the following week.

Fairly active/progressive pattern in the long term forecast
period, as several relatively low amplitude waves move through
fast/somewhat quasi-zonal flow through the southern CONUS, along
the base of broad but strengthening troughing over the northern
CONUS. Initial trough will move through the Midwest and Ohio
Valley Monday night, sending a cold front through Central Alabama
during that time. Better height falls will remain north of the
area, but sufficient height falls and a modest 30kt 850mb jet will
allow a fairly narrow band of light to moderate showers to move
through Monday night. Activity will begin to diminish as it moves
southeastward Tuesday morning and becomes further removed from the
upper forcing, but latest guidance suggests it will make it a bit
further southeast than previously indicated. Activity will be
light, with probabilities of exceeding a half inch of rain near
zero. Probabilities for thunder are non-zero but less than 15%.
Low temperatures for areas ahead of the front will be mild.
Without strong CAA behind the front highs on Tuesday will still be
above normal.

Next system is currently located off the coast of the Pacific
Northwest. There continues to be spread in the ensemble members
regarding the amplitude and speed of the wave after it crosses the
Rockies. Cluster analysis indicates about 60% of total ensemble
members (90% of GEFS members, 45% of EPS members, and 40% of GEPS
members) with a weaker, slower wave, 30% of total ensemble
members (3% of GEFS members, 45% of EPS members, and 45% of GEPS
members) with a stronger, quicker wave, and a remaining ~10% with
a more intermediate solution. So especially considering the
underdispersive nature of the GEFS it would be premature to pick
one scenario over the other. Either scenario would favor high rain
chances late Wednesday night into early Thanksgiving morning,
while the quicker scenario would result in a drier (but cool)
Thanksgiving afternoon vs a wetter scenario. A stronger wave
would be of more concern for severe weather potential with a
stronger wave of low pressure developing along the front, and
associated enhanced low-level mass response and hodograph
curvature, with a potential isolated tornado threat Wednesday
night. The slower scenario would result in a more of a wind/hail
threat on Thanksgiving, with decreasing low-level shear even as
instability increases. A limiting factor with the slower scenario
would also be a tendency for storms to be quickly undercut by the
surging strong cold front with flow parallel to the front.

Will note that while temps/dew points aren`t that impressive at
the surface Wednesday night, temperatures aloft will be chilly
with steepening mid-level lapse rates of 6.5 to 7 C/km. This could
potentially allow a supercell updraft to over-perform if it can
get going and become sustained. Severe probabilities at this time
remain less than 15% (slight risk) caliber, so will forego
messaging given the Days 4-5 timeframe. But a marginal risk could
become necessary for parts of the area Wednesday night depending
on guidance trends overnight tonight as we get into the Day 3
timeframe.

Behind the Thanksgiving system, cool and generally dry conditions
are expected for the rest of the holiday weekend. Majority of
ensemble members are dry with a shortwave Saturday night, but did
add in some slight chance PoPs in deference to a few ensemble
members. If these members with precipitation were to verify,
temperatures would likely be a few degrees warmer than indicated
in the deterministic forecast and thus only liquid precipitation
is mentioned. Long range indications show some Arctic air moving
into much of the central and eastern CONUS next week with
probabilities of below normal temperatures near 80%.

32/JDavis

&&

.AVIATION...
(00Z TAFS)
Issued at 545 PM CST SUN NOV 24 2024

VFR conditions are currently observed across Central Alabama
airfields this evening with light southerly winds 5 kts or less.
However, moisture increases will support an increase in low
stratus tonight, and I`ve placed most TAF sites at MVFR cigs late
tonight into tomorrow morning. IFR cigs (and patchy fog) are not
out of the question, but confidence was too low for 00z TAF
inclusion.

Winds will increase to 5-10 kts tomorrow afternoon prevailing
southwesterly. Cigs will rise back into VFR during that time before
another decrease to MVFR tomorrow night along with SHRA and an
approaching cold front.

40/Sizemore

&&

.FIRE WEATHER...

Rain showers will move across central Alabama Monday night,
associated with a frontal passage, though amounts are likely to
average less than 0.25 inch. Afternoon minimum RHs will remain above
critical thresholds over the next few days. 20-foot winds will be
southwesterly on Monday around 10 mph with a few gusts near 20
mph, and northerly on Tuesday decreasing to less than 10 mph by
the afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     41  73  50  62 /   0   0  70  10
Anniston    45  73  53  63 /   0   0  60  10
Birmingham  49  73  51  61 /   0   0  70  10
Tuscaloosa  48  74  53  63 /   0   0  70  10
Calera      48  75  54  63 /   0   0  70  10
Auburn      47  73  58  68 /   0   0  40  30
Montgomery  48  77  60  69 /   0   0  40  30
Troy        47  75  60  70 /   0  10  30  30

&&

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

$$

SHORT TERM...40/Sizemore
LONG TERM....32/JDavis
AVIATION...40/Sizemore