785
FXUS64 KBMX 031117
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
517 AM CST Wed Dec 3 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 515 AM CST WED DEC 3 2025

 - Stubborn overcast conditions this morning will continue through
   at least midday, with clouds hopefully mixing out during the
   early afternoon hours.

 - Below average temperatures are anticipated for most of the next
   seven days, along with multiple rounds of light to moderate
   rainfall from Thursday through Saturday.

 - Another 1-2 inches of rainfall is expected through Saturday,
   potentially approaching 3 inches along and south of the I-85
   corridor. However, no flooding impacts are expected.


&&

.DISCUSSION...
(Today through next Tuesday)
Issued at 326 AM CST WED DEC 3 2025

This Morning through Thursday:

It appears that I`ll be using the most non-scientific method
possible in order to make the best forecast over the next 12
hours: Looking out the window! As was the concern last night at
this time while looking at some of the high-res guidance members,
forecast soundings, and HREF probabilities, much of the region is
socked in with post-frontal stratus clouds. In fact, the GOES-19
Night Fog product shows low stratus still in place as far west as
eastern Arkansas and the bootheel of Missouri and actually
expanding to the north. As a result, the forecast over the next 12
hours has been completely overhauled through mid-morning today to
account for the overcast conditions. It`s very interesting to note
that there are still some guidance members that think it should be
completely clear right now, due to the fact that the very shallow
layer of moisture near the surface simply can`t be resolved by
guidance with course vertical resolution. With the NBM
incorporating the full suite of model guidance members, it
actually contaminates the sky cover forecast, lowering it to
broken or even scattered values. Again, by simply looking out the
window and satellite imagery the sky cover forecast was manually
adjusted to 100 for at least the next six hours.

Our 00z sounding from yesterday evening presents the current
mesoscale and synoptic setup very well. Following the frontal
passage yesterday, very shallow cold air advected southward over
the top of already moist conditions at the surface. Meanwhile,
temperatures aloft have become much warmer above 800mb with dry
westerly flow and even southwesterly flow at 500mb. Upward
vertical motion in the upper levels is actually ongoing with
divergence aloft as a vort max approaches from the southwest.
Based on some prior case studies performed by our office over the
years, by looking at isentropic surfaces the current overcast
conditions could be developing and persisting due to a local
rising of pressure surfaces (or pressure tendency) now that the
depth of the cold air has increased over the region. When the
pressure tendency rises, it can cause just enough rising motion on
the isentropic surfaces for the clouds to develop or be
maintained if there`s enough moisture present in the lowest
levels. That is occurring despite the overall isentropic descent
over the region post-frontal passage and negative pressure
advection. With the moisture at the lowest levels essentially
trapped by the inversion and very low mixing ratios being advected
southward along a similar isentropic surface, these clouds are
going to persist for quite a while. We should finally see the
clouds eventually mix out by this afternoon as sufficient surface
heating occurs and mixing ratios increase. No doubt, lots of
complex interactions are currently ongoing!

Temperatures through sunrise are expected to fall a few degrees
due to weak cold air advection still ongoing or will hold mostly
steady due to the overcast conditions. It`s amazing that in just
three days time we`ve gone from the possibility of seeing upper
teens in the colder northern valleys to only upper 20s and lower
30s as of the current forecast. Based on how quickly the stratus
clouds are able to mix out, the diurnal trend will also be
affected. I`ve gone with a slower warm-up through midday followed
by a faster warming trend during the afternoon, expecting clouds
to clear fairly quickly. Further updates may be needed to forecast
highs today if clouds hang on just a little longer than
anticipated

The next wave within the southwesterly flow aloft and southern
stream will arrive by Thursday as moisture spreads in aloft.
Forecast soundings are indicating that the column aloft should be
able to moisten enough for light rain or sprinkles to fall perhaps
as far north as the I-20 corridor by midday Thursday. We should
see lots of returns on radar, but some of it will not actually be
able to reach the surface. Farther to the south, at least steady
light rains are expected along the Highway 80/I-85 corridor
southward through Thursday afternoon. Highs should remain on the
cool side in the mid to upper 40s due to widespread clouds and
rain.

Friday through Early Next Week:

Isentropic upglide will ramp back up once again during the day on
Friday with overrunning moisture streaming northeast from the
Gulf. Another surface low is expected to develop near Mobile Bay
and move east through the Florida Panhandle. The heaviest rainfall
for our CWA will be north of the low once again, or the I-85
corridor southward. For Saturday, rain chances will greatly depend
on the depth of another approaching 500mb shortwave trough
ejecting eastward from the Four Corners States. The deeper the
trough, the more of a southwesterly flow aloft can be achieved and
thus moistening of the atmospheric column along with isentropic
lift for additional stratiform rain to develop. At this time, the
best rain chances will continue to remain across the southeastern
half of the forecast area, but a subtle change in the strength of
the shortwave would mean much higher rainfall coverage by Saturday
afternoon. For Sunday and into early next week, forecast
confidence decreases as long-range guidance disagrees with how the
evolution of a longwave trough will occur over the eastern CONUS
by Monday and Tuesday. One scenario is drier and colder with
northwest flow, while the other is more progressive with stronger
shortwave activity and a wetter overall setup as Gulf moisture
gets involved once again. The drier and cooler persistence
forecast remains for now through next Tuesday.

56/GDG

&&

.AVIATION...
(12Z TAFS)
Issued at 515 AM CST WED DEC 3 2025

MVFR ceilings are in place across all terminals as a large stratus
deck remains parked over the Southeast US. VFR ceilings return by
18Z for all sites. Light winds and VFR conditions then persist
through the end of this TAF cycle.

95/Castillo

&&

.FIRE WEATHER...

Rain-free conditions are expected today despite overcast
conditions lasting through at least midday. An additional round
of soaking rainfall moves into the region by Thursday evening. 1-2
inches of rain are anticipated, perhaps as high as 3 inches along
and south of the I-85 corridor which will continue to help
mitigate current drought conditions. Otherwise, MinRH values will
hover in the 50-60% range through the weekend, and Fire Weather
concerns will remain limited due to wet fuels.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     50  31  49  38 /   0   0  30  80
Anniston    50  33  49  40 /   0   0  40  90
Birmingham  49  35  49  40 /   0   0  50  90
Tuscaloosa  51  35  49  41 /   0  10  60  90
Calera      52  34  49  40 /   0   0  60  90
Auburn      52  36  48  42 /   0   0  60 100
Montgomery  51  36  47  43 /   0   0  80 100
Troy        52  37  48  43 /   0   0  80  90

&&

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

$$

DISCUSSION...56/GDG
AVIATION...95/Castillo