Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 240003

Area Forecast Discussion
National Weather Service Birmingham AL
703 PM CDT Mon Apr 23 2018

For 00Z Aviation.


This Afternoon and Tonight

The main surface low is still near northwestern TN this afternoon,
with an occluded front stretched into northwestern Georgia with a
triple point surface low, near I-20 just east of the state line.
From there a warm front bisects Georgia and then the cold front
stretches south to just west of Eufaula and Dothan. Expect the
warm and cold fronts to clear the area shortly, but the occluded
front will remain in the same general area for some time being as
the main upper level low remains stacked over the region. This
will continue to allow several lobes of energy to transfer around
the bottom of the upper low and will continue to spark showers
with each passing lobe. So will continue to mention scattered to
numerous showers in the north with isolated to scattered in the
south. These are very efficient rain makers so even a brief shower
could bring up to a tenth of inch of rain to the area. Most of
the activity will decrease in coverage during the evening with the
loss of the daytime heating. Thicker clouds will once again
develop tonight and lower through the overnight period with
partly to mostly cloudy skies through the night. Rain chances are
highest in the north with the proximity to the low, but drizzle
may be possible anywhere.


Tuesday through Sunday.

The pesky vertically stacked upper low will continue to drift
eastward over Kentucky and Tennessee on Tuesday, finally pushing
away from the area as it crosses the Appalachians Tuesday night.
Wraparound low-level moisture and cool air aloft will continue to
promote scattered light showers across the area in a speckled
pattern. A spoke of energy/surface trough will be pushing eastward
across the northern counties during the morning hours Tuesday,
resulting in the best coverage of showers being over the northeast
counties, while daytime heating will promote additional development
by afternoon. Clouds will help keep temperatures in the upper 60s to
low 70s. CAMs indicate that isolated showers may linger into the
early evening, before deep layer north-northwesterly flow brings in
drier air. There will still be enough low-level moisture for low
clouds to hang around overnight Tuesday night, however.

The southern portion of a shortwave trough currently over the
northwestern CONUS will break off and move southeastward as a
compact/potent shortwave into Oklahoma Wednesday afternoon and move
towards the area Wednesday night. The cold front will remain
northwest of the area during the day on Wednesday, but increasing
mid and upper-level moisture could result in a few showers reaching
the ground across the northern counties. Dew points will remain in
the 50s ahead of the front, as surface winds remain northwesterly.
The best dynamics and moisture look to be post-frontal, so not
expecting anything strong/severe with this front.
Models are indicating that a weak wave of low pressure may develop
along the front, resulting in an area of light to moderate mainly
stratiform rainfall that moves through late Wednesday night and
Thursday aided by strong upper-level forcing. Therefore PoPs have
been increased during these periods and may need to be increased
further if ensemble spread decreases.

Another strong shortwave in the northwest flow aloft and associated
cold front moves through Friday, re-enforcing the eastern CONUS
trough. Moisture return looks very limited ahead of this wave, but
the dynamics may be enough to squeeze out some showers with nothing
strong to severe expected with this system either. Upper-level
ridging will build over much of the CONUS over the weekend ahead of
troughing along the West Coast and behind the departing eastern
CONUS trough. Thus it looks likely that we will see our first dry
weekend in a while with highs in the 70s and spectacular conditions
for outdoor activities.



00Z TAF Discussion.

Generally accepted the trend from the previous forecast package.
The best upward motion and lift remains north and east, so have
removed the VCSH from all terminals but ANB/ASN. Even some thunder
was indicated with this activity but the chances its near a
terminal is slim. The upper low and its associated cold air aloft
will keep clouds in the forecast. Model soundings moisten back up
in the lowest levels. Therefore, the northern sites will see the
drop into MVFR 05-08z and near IFR by around daybreak. Isentropic
lift at varying levels over Central Alabama and soundings
indicating some low level lift may be enough for some light
drizzle. Kept this mention in the forecast with a slight drop in
vis. Winds generally westerly at 5kts overnight. Confidence in the
lower clouds south is a bit less so dropped mention at TOI and
tempo it at MGM.

MVFR ceilings are expected by 15-16z with some decrease in
coverage and rise after 19z. Scattered showers are possible again
on Tuesday and may be near ASN/ANB and will address in the next




A moist air mass will remain in place the next few days. Scattered
light showers and patchy drizzle are expected through Tuesday
due to a slow moving low pressure system. A cold front moving
through late Wednesday night and Thursday will bring additional
rain chances. Afternoon minimum relative humidity values will
remain above 50 percent through Thursday. Critical fire weather
conditions are not expected to be met.


Gadsden     53  69  53  69  51 /  30  50  20  20  30
Anniston    54  69  53  70  52 /  20  50  20  10  30
Birmingham  55  69  54  71  53 /  30  50  20  10  50
Tuscaloosa  55  70  54  74  54 /  30  40  10  10  60
Calera      55  69  54  72  53 /  20  40  10  10  50
Auburn      54  69  53  70  53 /  10  50  10  10  30
Montgomery  54  72  54  75  55 /  10  20  10  10  30
Troy        54  72  54  75  54 /  10  10  10   0  30




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