Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
101 PM CDT Mon Jun 25 2018

.UPDATE...
For 18Z Aviation.

&&

.SHORT TERM...
Today and Tonight.

We continue with lots of low level moisture with Atlantic ridging
and onshore southerly flow into Alabama around the ridge. In the
upper levels, we have flat ridging across the Southeast U.S. This
would tend to suppress the extent of our convection. However, with
very hot afternoon temperatures, some scattered heat induced
activity is expected to occur. With precipitable H2O values from 1.7
to 2.0 possible across Central Alabama today, depending on model of
choice, we have plenty of available moisture with afternoon heating
for some activity. Not expecting any severe today, but storms should
develop.

The other story for today though is the heat. With highs a tad
higher today and dew points in the middle 70s, we need to issue a
heat advisory for this afternoon for much of the area except for
extreme east-northeast counties.

08

.LONG TERM...
Tuesday through Monday.

Hot and humid weather will be the main story through the extended
forecast. Ridging remains in place across the Southeast US on
Tuesday as a trough moves through the Upper Midwest and into the
Great Lakes Region. The best lift associated with this trough should
remain north of our area, though the GFS and ECMWF do bring some
showers/storms into our eastern counties thanks to a shortwave
moving through the Central Appalachians earlier Tuesday morning.
The NAM picks up on a few storms in the east, so have kept chance
PoPs in the forecast for the far east, clearing out by the evening
hours. Afternoon high temps on Tuesday will be similar to today,
so a heat advisory isn't out of the question, but will hold off
for now to see how models trend with that trough. If the trough is
deeper, it could lead to higher coverage of showers/storms, or
cloud cover at the least, which will limit our afternoon high
temps.

Beginning Wednesday afternoon, the trough has generally moved over
the East Coast and upper level ridging builds in across much of the
Central and Southern CONUS. The GFS tries to slide the southern
extent of the trough axis through our area Wednesday night into
Thursday morning, which would lead to some increased rain coverage;
however, the ECMWF doesn't have near as deep of a trough axis, so
the ridge is able to build in quicker and clear out the rain
chances. I've kept mention for slight chance to chance PoPs for
Thursday, but this could be lower if the GFS starts to trend more
towards the ECMWF. Models are in pretty good agreement with 1000-
850mb thickness values increasing to 1436-1444m by Thursday
afternoon. This could support afternoon high temperatures reaching
the mid to upper 90s; however, the GFS still develops decent
coverage of afternoon storms, which could limit heating. I've edged
high temps up slightly to lean more towards the ECMWF, but haven't
gone too extreme. It will likely be difficult to reach upper 90s
with dewpoints being as high as they are. NAEFs highlights temps and
geopotential heights in the 90th percentile, so a hedge warmer than
the usual blends seems reasonable, which incidentally aligns fairly
well with the National Blend Model. PWATs for much of the extended
are nearing the top of the climatological values, so I'm keeping
dewpoints in the mid to upper 70s for most locations in Central AL.
Combining both of those factors, heat indices exceeding 105 is
certainly a possibility; therefore, will increase the confidence in
the HWO for heat impacts, especially on Thursday. The one
uncertainty in all this is how much, or if any, convection develops
in the afternoons.

Thickness values decrease Friday and into the weekend as the
center of the high pressure lifts northward into the Northeast US.
Flow around the high will bring more southeasterly to southerly
winds to Central AL, and both the GFS and ECMWF begin to develop
the more typical diurnal pattern of thunderstorms for the weekend
and into the first of next week. While heat indices will remain
high, the higher rain coverage will add more uncertainty in
regards to heat impacts. Therefore, will add a low confidence
mention of heat into the HWO for Friday and wait to re-evaluate
the weekend in coming days.

25/Owen

&&

.AVIATION...
18Z TAF Discussion.

Scattered showers and storms have developed, with most of the
activity east of the I-65 corridor. Main terminals to be impacted
over the next few hours will be BHM, ASN, and ANB. Activity at other
terminals cannot be ruled out. Thunderstorms will produce frequent
lightning, reduced vis, and gusty winds. Outisde of thunderstorm
activity, winds will be from the west to northwest at 8-12kts.

Activity is diurnally driven and will dissipate with sunset, with
winds becoming calm.

14

&&

.FIRE WEATHER...

A ridge aloft will develop across the area today, but some
isolated to scattered mainly afternoon storms are possible with
heating. Very warm temperatures with triple digit heat indices
will be the biggest issue for crews. Humidity values remain high,
and there are no fire weather concerns at this time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     92  72  92  72  92 /  40  20  20  10  40
Anniston    91  73  93  72  92 /  40  20  30  10  40
Birmingham  93  74  94  75  94 /  40  20  20  10  30
Tuscaloosa  96  75  96  75  96 /  30  10  20  10  20
Calera      92  74  93  73  93 /  40  10  20  10  30
Auburn      92  74  91  73  91 /  30  20  30  20  40
Montgomery  94  76  94  75  95 /  30  20  30  10  40
Troy        94  75  93  73  94 /  30  20  40  20  40

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Heat Advisory from noon today to 7 PM CDT this evening for the
following counties: Autauga...Barbour...Bibb...Blount...
Bullock...Chambers...Chilton...Coosa...Dallas...Elmore...
Fayette...Greene...Hale...Jefferson...Lamar...Lee...Lowndes...
Macon...Marengo...Marion...Montgomery...Perry...Pickens...Pike...
Russell...Shelby...St. Clair...Sumter...Talladega...Tallapoosa...
Tuscaloosa...Walker...Winston.

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
424 AM CDT Mon Jun 25 2018

ALZ011>015-017>050-261230-
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-
424 AM CDT Mon Jun 25 2018

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

.DAY ONE...Today and Tonight.

Heat indices will reach or exceed 105 degrees for many locations in
Central Alabama this afternoon; therefore, a heat advisory is in
place from noon to 7pm this afternoon. Plan to limit outdoor
activities and drink plenty of water during the afternoon hours.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Heat indices will approach or reach 105 degrees for many locations
in Central Alabama each afternoon Tuesday through Friday. Plan to
limit outdoor activities and drink plenty of water.

.SPOTTER INFORMATION STATEMENT...

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

Special Weather Statement
National Weather Service Birmingham AL
121 PM CDT MON JUN 25 2018

ALZ026-251845-
St. Clair AL-
121 PM CDT MON JUN 25 2018

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL ST. CLAIR COUNTY UNTIL
145 PM CDT...

At 121 PM CDT, Doppler radar was tracking a strong thunderstorm over
Branchville, or near Odenville, moving east at 10 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Pell City, Moody, Odenville, Margaret, Argo, Riverside, Ragland, Bald
Rock, Branchville, Logan Martin Lake, Wattsville and Chula Vista.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3381 8611 3373 8611 3371 8613 3371 8614
      3368 8614 3367 8616 3370 8618 3369 8620
      3368 8620 3366 8617 3362 8617 3361 8620
      3359 8619 3359 8622 3357 8621 3357 8649
      3368 8650
TIME...MOT...LOC 1821Z 265DEG 11KT 3364 8643

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