Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 260452

Area Forecast Discussion
National Weather Service Birmingham AL
1152 PM CDT Tue Apr 25 2017

For 06Z Aviation.


Through Wednesday night.

The departing surface low along the east coast, and resultant
surface ridging along the Gulf coast, will help keep conditions
dry in the short term. A small bump up in upper level heights will
also allow the warming trend to continue through Wednesday as

Our next good chance of rain still appears to be on track for
Wednesday night into early Thursday. A rather strong shortwave
trough is forecast to round the base of the longwave trough, and
12z models have this feature swinging across the Ohio and TN
valleys in the 00z to 12z Thursday time frame. Looks like the
associated surface cold front should get to the western counties
of central Alabama around midnight Wednesday night, and reach the
I-65 corridor by 12z.

Based on latest model output, will maintain the low confidence
mention of severe storms in the HWO for both late Wednesday into
Thursday, associated with this system. Time of day factors a lot
into the lower confidence in this case, as the predawn to early
daylight hours are typically not the most conducive times for
severe weather (from a climo standpoint). As one would expect,
instability levels are forecast to wane from the higher values the
lower MS valley will likely get Saturday afternoon, by the time
the line of showers/storms gets here. Regardless of severity,
high POPs certainly seem justified as this system quickly pushes

NOTE: based on 12z model runs, we also added a low confidence (1)
mention of a tornado threat for Sunday.


Thursday through Tuesday.

The cold front stalls across Central AL towards the end of the day
Thursday and into Friday before being lifted northward as a warm
front in the afternoon on Friday. This could produce some scattered
thunderstorms during peak heating on Friday in our northern
counties. Another longwave trough digs into the Central US Friday
as a surface low develops over the Southern Plains and tracks
northeastward into the Upper Midwest over the weekend. Models have
been going back and forth on the timing as a cold front stretches
down through the Mississippi River Valley and pushes eastward
across Central AL. Current runs have front pushing through Sunday
afternoon into Sunday night. The GFS has a shortwave pulse coming
out of the base of the trough, resulting in more shear. However,
the ECMWF doesn`t have as much shear across Central AL.

Low level ridging builds in behind the frontal passage Monday night
into Tuesday, resulting in clearing skies, dry weather, and near-
normal temperatures.



06Z TAF Discussion.

Currently we have VFR TAFs. After the fog Tuesday morning, we had
ample sunshine to aide the drying process. We are expecting clear
skies and light winds for tonight, we are not expecting as much
overall boundary layer moisture. I have included only tempos at
ASN/ANB/TOI for MVFR visibility toward morning. Any patchy fog
should clear up quickly as surface pressure gradients are expected
to tighten on Wednesday with higher winds and some gusts as a
surface front approaches from the west. Rain should hold off until
after TAF forecast period.




High pressure will keep conditions dry through Wednesday. An
approaching cold front will bring a round of showers and
thunderstorms to Central Alabama Wednesday night into Thursday.


Gadsden     53  84  62  81  60 /   0   0  50  60  10
Anniston    56  83  62  81  63 /   0   0  40  60  10
Birmingham  58  85  65  81  65 /   0   0  50  60  10
Tuscaloosa  55  85  63  82  63 /   0   0  70  40  10
Calera      56  84  64  82  65 /   0   0  50  60  10
Auburn      57  82  63  80  67 /   0   0  20  60  10
Montgomery  57  86  66  85  68 /   0   0  40  60  10
Troy        56  84  65  82  68 /   0   0  30  60  10





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