Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 112150

Area Forecast Discussion
National Weather Service Birmingham AL
350 PM CST Tue Dec 11 2018

Through Tonight.

After a foggy/icy and cold morning, we have finally cleared out
with lots of sunshine around Central Alabama. Surface ridging over
Southeast Texas and Louisiana today will slide eastward to
encompass the entire Gulf Coast tonight. We should have clear
skies initially this evening and near calm winds that will allow
readings to fall off quickly. However, we are expecting some
cirrus clouds to move in during the late evening toward and after
midnight. We have dried out some today. That and the high cirrus
will aide in our favor. We don`t want to drop off too quick and too
soon to reach our dew point. Currently not looking at a repeat
fog event from last night. Will certainly be keeping an eye on the
cirrus to monitor their progress toward us this afternoon into
this evening.


Wednesday through Saturday.

Surface high pressure persists across the region on Wednesday,
helping to moderate our high temps in the afternoon. An upper level
low and associated shortwave trough swing through the Great Lakes
Region Wednesday evening with the main upper level jet spreading
east to west across TN. Synoptic lift associated with the upper jet
will increase cloud cover Wednesday night into Thursday morning,
which will help keep our low temps in the 40s.

On Thursday, a deepening trough digs through the Rockies and
develops a surface low over TX. Right now, model guidance suggests a
pre-frontal shortwave will slide through MS Thursday afternoon, so
we`ll see an increase in rain chances from west to east Thursday
evening and becoming widespread in the overnight hours. As this
occurs, the surface low continues to strengthen, which will increase
the pressure gradient across the area, leading to some gusty winds
ahead of and with the widespread rain. Some guidance suggest some
elevated instability could work its way into our area Thursday
evening into early Friday morning, but it`s not much instability.
Just in case, I`ve added mention for a slight chance of thunder with
the widespread rain. Directional shear profiles aren`t overly
impressive, the lapse rates are fairly weak, and the best
instability is behind the pre-frontal shortwave. Therefore, I`m not
including any mention of severe in the HWO. By Friday evening, the
best rain chances will be in the northeast as the main cold front
continues to lift generally from the west-southwest to the
northeast. The upper level low is still over Central AL through the
afternoon on Saturday, so I can`t rule out some lingering showers
through the evening hours on Saturday. Overnight Saturday into
Sunday, the upper level low is east of our area. Some wrap-around
moisture may lead to some lingering showers in the northeastern-most
counties, but I`ve capped those PoPs at 15-20% for now.


Sunday thru Tuesday morning.

The upper level low has progressed eastward along with associated
precipitation. North/northwesterly flow begins to dominate the
upper levels and surface high pressure builds in from the west on
Sunday. Timing and uncertainties regarding moisture return for
the next system still remain inconsistent. Therefore, have held
off on mentionable PoPs for Monday through Tuesday morning.



18Z TAF Discussion.

Visibilities are improving as noted by obs and visible satellite
showing fog confined to generally west of I-65 and mainly south
of I-20 and decreasing/retreating southwestward with every scan.
With that said, only have an MVFR mention for an hour or less at
BHM and TCL. After that, we finally clear out with a VFR forecast
for the next 24 hours and only some high cirrus possible for
tonight into Wednesday with overall lighter winds as surface
ridging builds over the Gulf Coast States.




Rain free conditions are expected through Wednesday thanks to
surface ridging, ahead of the next system Thursday into Friday.
Afternoon relative humidity values remained in the 40s to 50s for
many today but a few saw 30s in some spots. On Wednesday afternoon,
40s and 30s are expected. There are no fire weather concerns at
this time.


Gadsden     28  52  39  55  47 /   0   0  10  30  90
Anniston    28  54  40  57  47 /   0   0  10  20  90
Birmingham  31  54  44  58  50 /   0   0  10  40  90
Tuscaloosa  31  56  45  60  49 /   0   0  10  60  90
Calera      29  55  43  58  49 /   0   0  10  40  90
Auburn      30  54  41  56  49 /   0   0  10  20  90
Montgomery  30  58  43  61  52 /   0   0  10  30  90
Troy        29  57  42  61  53 /   0   0   0  30  90





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