Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 211758
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1258 PM CDT Fri Jul 21 2017

.UPDATE...
This Afternoon through Saturday and 18Z Aviation.

&&

.SHORT TERM...

The combination of temperatures and humidity values were too
close to that danger zone and decided to go ahead an issue a Heat
Advisory through 7 pm. The morning BMX raob and model soundings
indicate some mixing will occur but that surface dew points will
generally stay 70-71 degrees for minimum levels, with a few
outliers in the 60s possible. Therefore, most heat indices will
reach the 105-106 degree range and generally last only a few hours
in the south and west. Please take the proper precautions when
conditions are so hot.

A combination of outflow boundaries from the north and south
kicked off some showers and thunderstorms over southwest areas
near Selma and Demopolis early this morning. This activity has
shifted south of the area at mid day. The clouds associated with
this activity have produced a differential heating boundary east
west generally from Livingston to Clanton to Alexander City.
Additionally, there is a low level convergence zone in the same
general area. The highest mean moisture and instability reside in
the Black Belt region which also closely co-located. Expect some
showers and storms to develop in this region and drift
southwestward into the evening hours. Elsewhere, activity will be
more isolated.

The mid to upper level ridge produces an easterly flow aloft and a
few subtle waves ride through the flow overnight. There could be
an isolated storm until midnight, and dont expect too much
thereafter. But with the low level moisture in place, will have to
monitor for activity that lingers or redevelops overnight.

For Saturday, a bit more moisture below 5k feet over Central
Alabama. This could mean more cloudiness. 1000-850mb thicknesses
also drop slightly. Therefore, high temperatures a degree or two
lower than today appear reasonable. With the slight increase in
the moisture, mixing as we move through the day will have a lesser
impact on surface dew points. So, we will be ever so close to the
Heat Advisory Criteria of 105-109 degrees again. This would be for
the same area outlined today with an emphasis on west central and
northwest areas. Will not issue an extension of the advisory at
this time, but we may need to by later this afternoon or tonight.
Rain chances for Saturday appear more randomly scattered.

75

Previous short-term discussion:Today and tonight.

Another hot summer day with convection expected once again this
afternoon with afternoon highs in the mid to approaching upper 90s
in the west and south. Focus for the afternoon convection will be
across the south as boundaries from yesterday will be in place
over the area. Storms could be on the stronger side as there will
be plenty of instability to deal with like yesterday.

Continued with isolated to scattered showers through Midnight as
outflows from the late afternoon storms will still interact with
some warmer air as they slide north and south. If we get the
overall coverage as expected we may see some patchy fog in the
south, so will add in for these areas after Midnight.

Outside of the scattered showers and thunderstorms we will flirt
with heat advisory criteria in the western and southern counties
once again. Not enough confidence to issue an advisory at this time
but will need to be re-evaluated this morning with the update to
see if we are going to mix out before the warmest temperatures
make it into the region. Will continue to mention in the HWO for a
low confidence.

16

.LONG TERM...
Saturday through Thursday.

Weak height falls will signal a gradual increase in daily
convective activity from Saturday into the upcoming week. The
highest rain chances could come on Monday/Tuesday with 50-60 POPs
areawide. Temperatures should accordingly trend downward to near
or just below normal for the heart of summer.

87/Grantham

&&


.AVIATION...
18Z TAF Discussion.

Terminal forecast take on the same flavor as the previous
forecast, except for rain chances. Took out the mention of
thunder for all northern terminals just because the actual chance
of rain is 35 percent or less. Will monitor this area and amend
for any isolated cells that develop near a specific terminal. For
MGM/TOI, it appears the rain chances will be near the 50 percent
mark and will leave the VCTS and tempo groups in and back them up
a few hours to 20-24z. Mentioned MVFR BR for a few hours right
near daybreak but no lower than 4sm at this time. Scattered
thunderstorms and SCT/BKN VFR ceilings on Saturday. Did not
mention any rain just yet. Winds remain on the light side
northwest to northeast today and swing around to southwest
Saturday.

75

&&

.FIRE WEATHER...

Isolated to scattered showers and thunderstorms are expected for
the next several days. There are no fire weather concerns at this
time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     73  92  73  89  72 /  20  40  20  50  40
Anniston    73  91  74  89  73 /  20  40  20  50  30
Birmingham  74  92  76  90  75 /  20  40  20  50  30
Tuscaloosa  75  94  75  92  75 /  20  40  20  50  30
Calera      74  91  74  90  75 /  20  40  20  50  30
Auburn      73  91  73  89  73 /  30  30  20  40  30
Montgomery  74  93  75  92  75 /  40  30  20  50  30
Troy        72  92  73  90  73 /  30  30  20  50  20

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Heat Advisory until 7 PM CDT this evening for the following
counties: Autauga...Barbour...Bibb...Bullock...Chilton...
Dallas...Elmore...Fayette...Greene...Hale...Jefferson...Lamar...
Lowndes...Macon...Marengo...Marion...Montgomery...Perry...
Pickens...Pike...Russell...Shelby...Sumter...Tuscaloosa...
Walker...Winston.

&&

$$



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