Area Forecast Discussion
Issued by NWS Birmingham, AL

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861
FXUS64 KBMX 230504
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1204 AM CDT Wed Aug 23 2017

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...

Overall the forecast remains on track but applied minor updates
to the forecast today for rain and thunderstorm chances this
afternoon. Surface analysis depicts a cold front extending from
northwest Texas across west Oklahoma and into southeast Kansas and
extending northeast across central Missouri and Illinois while
surface pressures are falling across the Mid South area along what
appears to be a pre-frontal trough. Satellite imagery late this
morning shows a band of taller cumulus clouds developing from
northeast Mississippi through central Tennessee. Expect this
feature to help encourage further cumulus development over the
next hour or so with shower and thunderstorm chances increasing
across our northern counties.

Across our central and eastern counties, cumulus development is
most pronounced across north-central Tuscaloosa County and into
west-central Jefferson County. Additional noted development is
witnessed across portions of Clay, Cleburne and Randolph
Counties, some of which appears to be influenced by terrain
effects.

Across our southern counties the cumulus field is more isolated
with some development now across northern Barbour and into
portions of Russell County. Some mid level thicker clouds are
affecting portions of Sumter and Marengo Counties and are helping
to delay cumulus field development in the short term.

Expect the northern and central counties to see developing shower
with possible thunderstorm activity emerging within the next few
hours while southern counties are expected to see shower and
thunderstorm activity toward mid to late afternoon, influenced
potentially by outflows from ongoing convection near the Alabama
and Florida coastline earlier this morning.

JH/05

Previous short-term discussion:Today and tonight.

The only interruption in the sun heating up the area today will be
the clouds and scattered showers/storms that will likely develop
this afternoon. More coverage is expected today as we will have
prime heating this afternoon in addition to a front beginning to
approach the area. Models are hinting at 2 main areas of
concentration and trended the forecast that way. The first being in
the southeast and the continued gulf moisture in place. Several
boundaries from yesterday are still around here. A second area is
really highlighted by the ARW and hinted at in the NMM this
afternoon and that would be right along the I-20/I-59 corridor as a
possibly a prefrontal trough or area of convergence sets up later
this afternoon. Much of this activity dissipates by early evening.

As we see the front begin to approach even more overnight there will
be an increase in showers/storms in the far northwest. Will also
need to watch the area south of the I-20/I-59 corridor where the
rain is forecast to be today as a couple of the models generate
activity by sunrise there as well. This has been the case over the
past few months as we have remained in a wet pattern so can not
totally rule that out for now.

16

.LONG TERM...
Wednesday through Monday.

The cold front and a 500mb vorticity lobe will move into the
forecast area on Wednesday as a trough continues to amplify over
the eastern CONUS. Scattered activity will be possible during the
morning hours, with CAMs indicating a broken line forming in the
vicinity of the I-20 corridor by early afternoon along a pre-
frontal trough. Additional scattered development will be possible
ahead of this line in far southeastern portions of the area in a
a moisture axis. A couple strong storms with wind gusts up to 40
mph will be possible, but weak lapse rates/shear should prevent
anything from approaching severe criteria. Isolated heavy rainfall
will be possible as well. Scattered activity should continue into
the evening across the south while drier air begins to filter in
from the north.

Rain chances will be confined to the far southern counties on
Thursday and Friday as the front stalls, while less humid
conditions are expected across the north under dry northwest flow.
Easterly low-level flow looks to develop by Saturday as a CAD
wedge begins to develop along the East Coast. This is due to a
large surface high over the eastern CONUS, and a surface low that
potentially develops in the Atlantic as Invest 92L interacts with
the stalled front. This will initially bring in some additional
moisture and small rain chances, followed by a drier and
relatively cooler air mass. Meanwhile, NHC now indicates a 90
percent chance that the remnants of Harvey will re-generate into a
tropical system as it moves through the southwestern Gulf towards
the vicinity of the mouth of the Rio Grande. Don`t want to get
too hung up on deterministic model solutions yet, but latest
trends in models and ensembles is for low pressure to eventually
move northeastward somewhere in the vicinity of the Texas coast
and eventually inland towards the Lower Mississippi Valley. The
GFS looks be a fast outlier currently compared to the ECMWF and
the EC ensemble mean, which keep this system well west of the
forecast area through the 7 day forecast period. It`s far too
early to speculate what impacts, if any, Central Alabama could see
from this system.

32/Davis


&&

.AVIATION...
06Z TAF Discussion.

Have some MVFR fog mentioned area wide beginning as early as
08-09z. We had some show up last night and the model soundings
indicate another round tonight. Only have 4-6 miles at this time,
except for areas near BHM/EET where most of the rain fell on
Tuesday.

A cold front and a pre-frontal trough will into Central Alabama in
the next 12 hours or so. Added mention of showers north and chance
of thunder by 16-17z. The outflow boundary is slightly farther
south than anticipated, so where the thunder fires up will have to
be monitored the next forecast cycle. Mentioned VCTS for the
northern terminals and prob30 for MGM/TOI at this time. Will
narrow timing down somewhat and mention at all locations in next
forecast. Winds will generally be light overnight and swing to the
west northwest and 7kts or below as the pre-frontal trough moves
by and then northerly late in the day north behind the front.

75

&&

.FIRE WEATHER...

Moisture and chances rain increase gradually ahead of a cold
front that will move through the area Wednesday. Drier air returns
to the area for the end of the week. There are no fire weather
concerns at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     88  67  85  63  86 /  50  20  10  10  10
Anniston    88  70  86  66  88 /  60  20  10  10  10
Birmingham  89  70  87  67  88 /  60  30  10  10  10
Tuscaloosa  91  71  89  67  90 /  60  30  10  10  10
Calera      89  71  87  68  88 /  60  40  10  10  10
Auburn      89  72  88  70  87 /  50  40  30  10  20
Montgomery  93  74  91  72  91 /  50  40  40  20  20
Troy        90  72  90  71  89 /  40  30  50  30  30

&&

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

&&

$$



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