Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 241218

Area Forecast Discussion
National Weather Service Birmingham AL
718 AM CDT Tue Apr 24 2018

For 12Z Aviation.


Today and Tonight.

Currently this AM, a surface low extends from C TN into N GA. The
upper low is currently over TN/KY and is expected to progress
eastward through tonight into NC. A few light rain showers may be
noted across Central Alabama as a result today and this evening.
Overall chances are low, but the best chances will remain across the
northern counties closer to the low. Mainly, we should see extra
cloud cover and a little lower temperatures as a result. Late
tonight, as the low moves away, we should see clouds clear some from
the southwest as well as surface pressure gradients relax some over
LA/MS into the western half of AL with weak ridging building over
LA/AR/MS. Have added in some patchy fog southwest for late tonight.


Wednesday through Monday.

Upper-level flow will becomes westerly on Wednesday as the upper
low finally reaches the Mid-Atlantic coastline, and a potent
shortwave in the northwest flow digs into Oklahoma. Low-level flow
will remain northerly behind the departing low pressure system,
preventing a significant warm-up. Morning low clouds will
gradually lift, lingering the longest in the northeast counties.
Highs will be in the 70s, except in the northeast where more
cloudcover will keep highs in the 60s. Mid and high level clouds
will begin to increase from the west. Couldn`t rule out a few rain
drops reaching the ground late in the afternoon in Marion/Winston
Counties ahead of a mid-level speed max, but most should remain
dry during the day.

An initially diffuse cold front will sink into the area Wednesday
night and stall out. Low-level moisture is initially very limited
along the front, due to offshore/northwest winds ahead of it. But
models are coming into agreement that a wave of low pressure will
develop along the front over the ArkLaMiss due to strong synoptic
forcing via the potent shortwave. Strengthening moist isentropic
lift will cause rain to move in from the west late Wednesday
night. The GFS is often too slow to saturate during these
situations, so the wetter ECMWF/European ensemble mean/Canadian
was favored during this period. Widespread precipitation is
expected across the area Thursday due to strong lift from the
shortwave and the surface low moving through and sufficient
moisture. Raised PoPs to categorical across much of the area
given a wet signal in the European ensembles. Southerly winds
developing ahead of the surface low may allow dew points to reach
60 degrees across our southern counties. Cold temperatures aloft
will help compensate for lower dew points to allow some
instability to be present, and added in a slight chance of thunder
areawide. It`s not out of the question that some stronger storms
could develop across our southern counties or even an isolated
severe storm, as 500mb temperatures drop to -18 to -20C, with a
main threat of gusty winds/hail. Severe potential is still much
too low to mention in the HWO. Rainfall amounts look to generally
be a half inch to an inch, preventing much in the way of flooding
concerns. Added in some small PoPs in our eastern counties
Thursday night given uncertainty regarding the speed of the

Dry air moves in behind this system, but another dynamic shortwave
follows closely on its heels Friday with another cold front.
Moisture return in the wake of Thursday`s system is very
questionable, and latest deterministic models are dry for most of
the area. But some of the European ensemble members are wetter, so
will keep in some slight chance PoPs for Friday/Friday night. A
pattern change is still expected to begin Saturday through the
rest of the extended forecast period, with the current western
ridge/eastern trough upper-level pattern switching to a western
trough/eastern ridge. At low-levels a Bermuda high looks to set up
early next week. Rain-free conditions are expected for the weekend
and the first part of next week. Highs will be in the low to mid
70s behind the front Saturday, warming to the upper 70s to low 80s
Sunday and Monday.



12Z TAF Discussion.

MVFR and in some spots IFR cigs evident on satellite and obs this
AM circling around from the northwest and west into Central
Alabama as the upper low moves across TN/KY toward NC. Some patchy
drizzle and light showers are possible today associated with the
low. As it moves away this evening, we should see a decrease in
cloud cover. Low cigs are expected to build in tonight, but from
the northeast toward and after midnight. With clearing in the
southwest part of the state with lighter winds could see some
patchy fog develop, but think that for tonight it should remain
south and west of C AL TAFs.




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


Gadsden     68  52  68  51  64 /  40  20  10  40  80
Anniston    68  53  70  51  66 /  40  20  10  30  80
Birmingham  69  54  72  54  66 /  30  20  10  50  80
Tuscaloosa  70  54  74  55  67 /  20  10  10  60  80
Calera      69  54  71  53  66 /  30  10  10  50  80
Auburn      71  54  71  53  70 /  20  10   0  10  80
Montgomery  71  54  75  54  70 /  20  10   0  30  80
Troy        72  54  74  54  73 /  20  10   0  10  60





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