Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 241152 CCA
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
639 AM CDT Thu May 24 2018

.UPDATE...
For 12Z Aviation.

&&

.SHORT TERM...
Today and Tonight.

The overall pattern has not changed much over the past 24 hours with
a low level circulation over central Georgia and a trof axis
extending westward into south Alabama. Light winds and minimal cloud
cover has produced conditions conducive for fog this morning. A few
places are already below one-half mile across west Alabama, and a
dense fog advisory may become necessary. Precipitable water values
are still above normal with values around 1.75 inches. The majority
of the convection today will be near and south of the low level trof
axis, but thunderstorms possible anywhere this afternoon due to
higher than normal PW`s and little or no capping inversion.
Convection will wane after the loss of daytime heating.

58/rose

.LONG TERM...
Friday through Wednesday.

Trailing vorticity from a shortwave moving through the Midwest
will result in falling 500mb heights on Friday as an upper-level
trough strengthens over the Gulf and adjacent states. A weak
frontal boundary will have dissipated, allowing moisture to return
northward. Cyclonic mid-level flow, daytime heating, and the moist
air mass will result in numerous showers and storms that will be
maximized during the afternoon hours.

Upper-level troughing over the region will be a persistent feature
of the forecast period due to a tilted omega block pattern at
500mb with ridging over the Plains flanked by the Gulf trough and
a closed low over the Great Basin. A developing surface low near
the Yucatan will be lifted northward by the trough. NHC indicates
that this low is likely to develop into a tropical or subtropical
depression. The GFS remains east of the guidance consensus but has
trended westward closer to the other model guidance. Will continue
to rely on the ECMWF which has support from the NAM and Canadian
as well as its ensembles. The ECMWF has trended slower in the last
couple of runs. Shear from the trough will prevent significant
strengthening, with the main impacts for the Gulf states
continuing to be heavy rainfall and flooding, as is often the
concern with slow-moving weak tropical systems. Saturday looks to
be the "least wet" day of the holiday weekend, as the low and
deep tropical moisture remain south of the area, but there will
still be enough forcing from the trough and moisture to warrant
likely PoPs for diurnally enhanced convection. By Sunday,
southerly flow aloft will over-run strengthening low-level
southeasterly flow likely resulting in more widespread/steady
tropical rains lifting up from the southeast. This will result in
cooler high temperatures, and will only mention a slight chance of
embedded thunder due to limited instability.

Sticking with the ECMWF solution, the low pressure system will
become vertically stacked and stall out somewhere just southwest
of the forecast area for the first half of next week. Continued
850mb moisture transport east of the low will result in wet
conditions continuing across the area, modulated by any patches of
dry air aloft that wrap around the system. Rainfall will likely
contract closer to the center at night while expanding in coverage
through the day. Greatest potential for flooding will be closest
to where the low stalls, but confidence is low exactly where that
will be. There will likely be some hefty rainfall totals somewhere
across the Gulf states and especially near the coast, but
confidence in placement is low. Will continue to highlight the
flooding potential in the HWO. More organized flooding chances
look to hold off until Sunday, but isolated flash flooding remains
possible Friday and Saturday due to the moist air mass and weak
flow through the column.

32/Davis


&&

.AVIATION...
12Z TAF Discussion.

Areas of LIFR conds due to cigs/fog will persist until 14z. Conds
will improve rapidly by 14z with VFR conds by 15z. A weak surface
trof across the southern counties of central Alabama will once
again act as the primary focus for diurnal convection. Activity
will be too isold north to include in northern TAF sites, with
VCTS at KMGM and KTOI. The convection will weaken considerably by
00z due to loss of daytime heating.

58/rose

&&

.FIRE WEATHER...

A moist pattern is expected over the next seven days and should
result in daily rain chances. Patchy fog and low clouds will be
possible each morning particularly where rainfall occurs during
the prior afternoon and evening.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     86  67  83  66  84 /  20  20  50  40  60
Anniston    85  68  83  66  84 /  30  20  60  40  60
Birmingham  87  69  85  69  85 /  30  20  60  40  60
Tuscaloosa  89  69  86  68  86 /  40  20  70  40  60
Calera      86  68  84  67  84 /  40  20  60  50  60
Auburn      82  68  81  67  81 /  50  50  60  50  60
Montgomery  86  69  86  68  85 /  60  40  70  50  60
Troy        85  68  85  68  84 /  60  50  70  50  60

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Dense Fog Advisory until 9 AM CDT this morning for the following
counties: Autauga...Barbour...Bibb...Blount...Bullock...
Calhoun...Chambers...Cherokee...Chilton...Clay...Cleburne...
Coosa...Dallas...Elmore...Etowah...Fayette...Greene...Hale...
Jefferson...Lamar...Lee...Lowndes...Macon...Marengo...Marion...
Montgomery...Perry...Pickens...Pike...Randolph...Russell...
Shelby...St. Clair...Sumter...Talladega...Tallapoosa...
Tuscaloosa...Walker...Winston.

&&

$$


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