Flash Flood Warning 53, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
649 AM CDT Mon Oct 4 2021

.UPDATE...
For 12Z Aviation.

&&

.SHORT TERM...
/Updated at 0340 AM CDT Mon Oct 04 2021/

Today, Tonight, and Tomorrow.

There's a lot of weather to talk about across Central Alabama for
the next few days.

Currently, a positively tilted upper-level trough is situated across
much of the eastern CONUS, and an associated surface front is now
draped across Central Alabama. This front has become somewhat
diffuse and hard to analyze, though it can be seen through out the 0-
1 km layer as a zone of southwesterly confluent flow. Nonetheless,
skies have cleared to the north of the front overnight (generally
along and north of the Black Warrior) and dense fog has developed
in the wake of earlier convection. A Dense Fog Advisory is in
effect for these areas through 9 AM.

Looking at water vapor imagery and mesoanalysis, it is clear to see
a couple shortwave troughs/vorticity maxima diving south through the
Mississippi River Valley and portions of the Plains. These
disturbances ride along the western edge of the parent synoptic
trough and will make their way into our region throughout the next
24 hours or so. As they dig south, our westerly 30 kt 500 mb flow
will become more southwesterly and nearly parallel the surface
front and axis of low-level confluence, which expected to be near
the I-85 corridor later today. This general zone will also see
modest instability (MLCAPE <1,500 J/kg) and PWs in the 1.7-1.9"
range. Periods of heavy rainfall are expected as a result.
Additionally, embedded thunderstorms could persist over the same
areas at times. Given rainfall rates in the 2-4" per hour range,
flash flooding is possible. Thus, a Flash Flood Watch has been
issued for these areas through Tuesday night.

Throughout tonight, the upper-level disturbance to our northwest is
expected to become more prominent as it establishes near the
ArkLaMiss. By then the disturbance will become more of a cutoff low
and the trough axis will begin to swing toward a more neutral tilt.
Stronger forcing for ascent will subsequently overspread the Deep
South by Tuesday morning. A 30 kt low-level jet is progged to advect
warm, moist air northward toward the Tennessee Valley and into the
occluding low. With the aid of anomalously high PWs and modest
instability, periods of heavy rainfall will be possible throughout
the day and could persist through tomorrow night across much of
the area. It's for these reasons the Flash Flood Watch covers the
majority of Central Alabama today despite the fact that many areas
along the I-20/59 corridors may not see heavy rainfall until
tomorrow.

40/Sizemore

.LONG TERM...
/Updated at 0340 AM CDT Mon Oct 04 2021/

Wednesday through Sunday.

The presence of the upper-level low will still be felt across the
region on Wednesday. In fact, additional heavy rainfall is
possible across areas east of I-65. The Flash Flood Watch may end
up being extended in time for these areas, but we'll allow time to
reassess for now. By then the primary vort max/occluded low will
have begun to retrograde to the northwest, and overall forcing is
expected to be not as strong. Nonetheless, PoPs remain quite high
for the eastern two-thirds of the area. Overall rainfall activity
will slowly depart to the east as the low-level jet weakens and
spreads northeast along the Appalachians. Drier air should then
begin to work into the area from the west on Thursday with
transition to westerly flow. PoPs have been reduced as a result.
Northwesterly flow should subsequently work into the region by
Friday, and a drier/warmer trend is forecast toward the weekend.

40/Sizemore

&&

.AVIATION...
12Z TAF Discussion.

Rain, low ceilings, and fog continues this morning. Seeing a
little break in the heavier activity but passing showers to
continue. Ceilings remain low through mid day then we get some
sun briefly then followed by more periods of showers and a few
storms. Ceilings lowering again at the end of the cycle.

16

&&

.FIRE WEATHER...

A weak surface front is draped across the area today and a mix of
clouds and fog will continue throughout this morning. Winds will
remain light and variable, though should favor a southerly
direction south of the boundary, and a northerly direction north
of the boundary. Nonetheless, elevated rain chances are forecast
for areas south of I-20 today. Rainfall could be heavy at times,
and flash flooding is possible. Rainfall becomes more widespread
on Tuesday with additional heavy rainfall possible farther north.
Drier and warmer conditions aren't expected until later this
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     78  63  74  64  77 /  50  70  90  80  90
Anniston    78  65  75  66  78 /  70  80  90  80  90
Birmingham  78  65  74  65  77 /  50  70  90  70  80
Tuscaloosa  80  66  75  65  78 /  50  50  90  50  60
Calera      77  66  74  66  77 /  60  80  90  70  80
Auburn      77  65  73  65  77 /  80  90  90  70  90
Montgomery  79  67  76  67  79 /  80  90  90  70  90
Troy        80  67  77  66  79 /  80  80  90  70  90

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Flash Flood Watch through late Tuesday night for the following
counties: Autauga...Bibb...Blount...Bullock...Calhoun...
Chambers...Cherokee...Chilton...Clay...Cleburne...Coosa...
Dallas...Elmore...Etowah...Hale...Jefferson...Lee...Lowndes...
Macon...Marengo...Montgomery...Perry...Pike...Randolph...
Russell...Shelby...St. Clair...Talladega...Tallapoosa...
Tuscaloosa...Walker...Winston.

Dense Fog Advisory until 9 AM CDT this morning for the following
counties: Blount...Fayette...Lamar...Marion...Pickens...
Tuscaloosa...Walker...Winston.

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
903 AM CDT Mon Oct 4 2021

ALZ011>015-017>050-051715-
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-
903 AM CDT Mon Oct 4 2021

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

.DAY ONE...Outlook through Tonight.

Periods of heavy rainfall are possible across portions of Central
Alabama through tonight. This could lead to flash flooding of low
lying or poor drainage areas.

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

Additional heavy rainfall is possible across much of Central Alabama
Tuesday and Wednesday. This could lead to flash flooding of low
lying or poor drainage areas.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management may be needed
through Wednesday.