Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
1229 PM CDT Wed Aug 8 2018

.UPDATE...
For 18Z Aviation.

&&

.SHORT TERM...
Today and Tonight.

Overnight synoptic observations continued to show an upper-level
trough axis extending from Lake Superior down through the
Mississippi River Valley. This trough has been gradually
deteriorating the upper ridge over the southeastern CONUS as the
stronger ridge in the west continues amplification northward, though
remnant anticyclonic flow aloft lingers over central Alabama per
GOES-16 water vapor imagery. Obs also showed ongoing convective
activity, possibly enhanced by a 30kt LLJ, along a rather diffuse
surface front positioned across the Ohio Valley with a general east
to southeast trend. This frontal boundary should continue slow
forward progress but will remain to our north throughout the day.
Outflow from more vigorous thunderstorms ahead of a H7 shortwave
trough in Arkansas can be observed moving eastward across western
TN, with its southern extent gradually approaching our northwestern
CWA by morning. MGM and other locations measuring rainfall yesterday
should see any fog clearing shortly after day break this morning.

Overall expectations for today will focus on thunderstorm
development along and ahead of the outflow/shortwave to our
northwest. With the frontal boundary lagging behind, OFBs/mesoscale
differential heating axes will dictate development of thunderstorms
as we remain south and downstream of the upper-level trough. This
being said, afternoon SBCAPE values should range from ~2,000-3,000
J/kg given observed soundings from the past couple of days and the
fact our overall low-level thermodynamics remain in place. Exact
thunderstorm timing/placement will depend on how convection behaves
once initiation occurs in the early afternoon and into peak diurnal
heating. Best confidence in showers and thunderstorms will remain in
the northern half of the CWA where better forcing/deep-layer
moisture will extend along and ahead of the frontal boundary where
PWs could approach 2.0". Though some merging could take place, as
well as stronger areas of convection developing cold pools,
thunderstorms are expected to remain sub-severe as mid-level lapse
rates range ~5.5 C/km and better wind shear resides farther north in
the Ohio Valley. Anticipating heavy rain, lightning, and high precip
rates as the biggest threats. Given what mid-level flow we have
(~15 kts at 500mb), convection should gradually propagate
southeastward from the northwest. With higher PoPs and general
cloud cover today, have gone with highs in the upper 80s/lower 90s
with the warmest temperatures in our southern counties where more
isolated precip is expected. As we head into the overnight hours,
thunderstorm re-development could take place in the northwest as
forcing associated with the front/upper trough remains.

40/Sizemore

.LONG TERM...
Thursday through Tuesday.

High rain chances will be the story for Thursday and Friday as an
upper-level trough moves eastward across the Lower Mississippi
Valley. Height falls and increasing upper-level support, coupled
with PWAT values around 2 inches, should result in several rounds
of convection that may continue into the overnight hours. Coverage
could become rather widespread, and rain chances have been
increased to around 70 percent for most of the forecast area.

Model agreement worsens on Saturday regarding the evolution of the
upper-level shortwave. There is the possibility of stronger
subsidence occurring in the wake of the trough, which may reduce
rain chances across the northern part of the CWA. Our forecast
currently indicates slightly higher rain chances across the
southern counties.

Models generally agree that a trough axis will develop from the
Ohio Valley southwestward into Texas for Sunday and Monday. A
series of small shortwaves may move across the Deep South, leading
to a continuation of above normal rain chances.

87/Grantham

&&

.AVIATION...
18Z TAF Discussion.

VFR conditions are prevailing at all sites early this afternoon
with only scattered cu developing in most locations. Scattered to
perhaps numerous showers and storms will continue to develop later
this afternoon and into the early evening across the northern half
of Central Alabama. Therefore, have added VCTS in for BHM, EET,
and TCL. With TSRA chances lower at MGM and TOI, have only gone
with VCSH at those sites through the rest of the day. Confidence
is high that we will not see much in the way of low cloud or fog
development overnight except in a few isolated spots. Surface
winds will remain light between 5 and 10 knots mainly from the
southwest.

56/GDG

&&

.FIRE WEATHER...

High relative humidity values will continue. Increasing rain
chances are expected through Friday. Morning fog and low clouds
will be possible in locations that receive afternoon and evening
rainfall. There are no fire weather concerns at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     71  87  71  86  69 /  50  70  50  70  40
Anniston    72  88  71  87  70 /  50  70  50  70  40
Birmingham  73  89  73  87  72 /  50  70  50  70  40
Tuscaloosa  74  90  73  89  72 /  50  70  50  70  40
Calera      71  88  71  86  70 /  50  70  50  70  40
Auburn      72  88  72  87  72 /  50  50  40  70  40
Montgomery  74  91  74  89  73 /  40  60  40  70  40
Troy        73  91  73  89  73 /  30  50  30  70  40

&&

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

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
431 AM CDT Wed Aug 8 2018

ALZ011>015-017>050-091245-
Marion-Lamar-Fayette-Winston-Walker-Blount-Etowah-Calhoun-Cherokee-
Cleburne-Pickens-Tuscaloosa-Jefferson-Shelby-St. Clair-Talladega-
Clay-Randolph-Sumter-Greene-Hale-Perry-Bibb-Chilton-Coosa-Tallapoosa-
Chambers-Marengo-Dallas-Autauga-Lowndes-Elmore-Montgomery-Macon-
Bullock-Lee-Russell-Pike-Barbour-
431 AM CDT Wed Aug 8 2018

This Hazardous Weather Outlook is for the counties served by the
National Weather Service office in Birmingham.

.DAY ONE...Outlook through Tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management is not
expected at this time.

Special Weather Statement
National Weather Service Birmingham AL
305 PM CDT WED AUG 8 2018

ALZ020-082030-
Cherokee AL-
305 PM CDT WED AUG 8 2018

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL CHEROKEE COUNTY UNTIL 330
PM CDT...

At 304 PM CDT, Doppler radar was tracking a cluster of strong
thunderstorms near Sand Rock, or 8 miles northwest of Centre, moving
east at 25 mph.

Wind gusts up to 50 mph will be possible with these storms.

Locations impacted include...
Centre, Cedar Bluff, Little River Canyon National Preserve, Leesburg,
Sand Rock, Gaylesville, Cherokee Rock Village, Cornwall Furnace Park,
Western Weiss Lake, Blanche, Eastern Weiss Lake, Little River Falls,
Weiss Dam, Fullerton, New Moon, Yellow Creek Falls, Chesnut Bay
Resort, Broomtown, Waterhouse and Chesterfield.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If on or near Lake Weiss, get out of the water and move indoors or
inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.

&&

LAT...LON 3445 8550 3420 8545 3413 8583 3424 8583
      3424 8581 3426 8581 3426 8577 3436 8566
      3437 8563 3439 8562 3440 8563 3440 8561
      3444 8558 3450 8556 3450 8555 3453 8552
TIME...MOT...LOC 2004Z 251DEG 22KT 3425 8575