Severe Thunderstorm Warning 20, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
749 PM CDT Mon Mar 19 2018

.UPDATE...
MESOSCALE UPDATE.

&&

.DISCUSSION...

...SEVERE WEATHER THREAT CONTINUES...

The environment remains favorable for severe thunderstorms with
wind shear continuing to increase across our northern and central
counties. Though storm development remains more isolated across
our southern and central counties, any activity that develops and
intensifies will have the opportunity to tap into favorable
instability and dynamics that will support all convective hazards
from very large hail to tornadoes to damaging winds. Currently,
the most favorable area for severe storms in where the best low
level convergence is from Double Springs to Oneonta to Helfin.
These storms will slowly move south and east the nest few hours.

An effective surface dryline extended from near Natural Bridge in
Winston County southwest to near Vernon in Lamar County. The
severe weather threat will end as the dryline progresses further
southeast.

We have launched special weather balloon soundings every 3 hours
since 18Z this afternoon and the trend over time has been
increasing wind shear across central Alabama while robust
instability has been maintained due to the solar heating much of
the area experienced for much of the afternoon along with
generally southerly winds that have helped maintain dew points
generally in the 60's across much of our forecast area.

A limiting factor in convective development has been the remnant
Elevated Mixed Layer (EML) that has persistently been present in
the observed soundings aloft this afternoon. This dry layer has
helped to promote the accumulation of convective available
potential energy while only permitting the strongest of updrafts
to break through the cap. This has resulted in the cap holding
strong across much of our south-central counties since mid
afternoon while earlier development across northeast Mississippi
and northwest Alabama have maintained their development and
further expanded in extent and intensity over the past few hours.

05/75

&&

.AVIATION...
00Z TAF Discussion.

Trend with this set of TAFs will be in a bit more optimistic
direction, as the higher coverage of convection thus far has
remained well to the north of central Alabama terminals. Will
maintain a VCTS for a couple of hours at most locations, although
it did push this back an hour or two from the previous forecast
(based on radar trends). Still quite a bit of uncertainty on how
far south the convection will get overnight. If radar trends over
the next couple hours show the storms eventually expanding in
area, then we can update the TAFs where necessary.

Winds will shift around to a more westerly direction overnight,
and start to increase and be more gusty after sunrise on Tuesday.
The models were giving me mixed signals on the development of
lower clouds after the rain/storm threat ends overnight. Given the
lack of clouds back to the west, I am inclined to believe the more
optimistic of the model solutions. But once the winds kick up
Tuesday, the cumulus field should start to fill in as well.

/61/

&&

.FIRE WEATHER...

After some storms tonight, light showers are possible Tuesday,
before dry conditions arrive by Wednesday. RH values will be
elevated the next couple days. There are no fire weather
concerns.

&&

.PREV DISCUSSION...
/Issued 649 PM CDT Mon Mar 19 2018/

Confidence has increased in the potential for explosive supercell
thunderstorm development late this afternoon into tonight
especially along and north of a line from Tuscaloosa to Calera to
Wedowee. A dangerous environment will also be in place south of
this line, but initiation of storms and storm coverage is
questionable.

Currently, surface winds have veered to the southwest across most
of the area following the passage of a warm front. Normally this
would yield lower dewpoints and overall moisture quality, but this
does not appear to be the case. Dewpoints are holding in the mid
to upper 60s upstream across MS. Moisture quality should not be an
issue as this event progresses.

This event will hinge on evolution of the surface to 850mb wind
fields in response to the approaching upper-level trough. We are
already seeing this response across the northern half of MS where
winds are south to southeast near Tupelo and Columbus. Hi-res
models appear to be getting a better handle on the mesoscale
features and are slowly trending more aggressive with surface
pressure troughing and backing of winds in the 23-03z time frame.
HRRR guidance suggests the potential for 0-1km shear to exceed
40kts. This amount of shear combined with SBCAPE of 2000-3000 J/kg,
supports a risk for a few long-track tornadoes. A violent tornado
cannot be ruled out. The best chance of these enhanced ingredients
coming together for long-track tornadoes appears to be from I-65
eastward and as far south as Shelby, Talladega, Clay, and Randolph
counties.

Balloon launches are planned for 330 PM, 6 PM, and 730 PM to sample
critical changes in the low-level wind environment.

87/Grantham

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     51  55  34  51  33 /  90  40  30   0   0
Anniston    53  56  35  53  33 /  90  40  30   0   0
Birmingham  49  54  37  56  36 /  80  40  20   0   0
Tuscaloosa  48  56  37  60  37 /  70  30  10   0   0
Calera      50  55  37  59  36 /  80  40  20   0   0
Auburn      56  59  38  58  36 /  70  20  20   0   0
Montgomery  57  60  39  62  38 /  60  20  10   0   0
Troy        55  62  41  62  37 /  50  20  10   0   0

&&

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

&&

Hazardous Weather Outlook...UPDATED
National Weather Service Birmingham AL
403 PM CDT Mon Mar 19 2018

ALZ011>015-017>050-210015-
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-
403 PM CDT Mon Mar 19 2018

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

.DAY ONE...Outlook Through Tonight.

Severe storms are expected late this afternoon into tonight These
storms will move from west to east, entering northwest Central
Alabama as early as 4 PM and exiting southeast Central Alabama as
late as 2 AM Tuesday morning. The greatest potential for strong
tornadoes is north of a line from Tuscaloosa to Calera to Wedowee.
However, tornadoes, very large large hail, and damaging winds are
possible area wide.

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

Cooler air moving in behind the system will result in the potential
for lows at or below freezing across parts of north central Alabama
Wednesday night into Thursday morning.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management will be
needed through early Tuesday morning.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
742 PM CDT MON MAR 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0726 PM     HAIL             2 N BLOUNTSVILLE        34.11N 86.58W
03/19/2018  E2.00 INCH       BLOUNT             AL   PUBLIC

            CORRECTS PREVIOUS HAIL REPORT FROM 2 N
            BLOUNTSVILLE. HAIL FROM PING BALL BALL TO
            EGG SIZE.

&&

MAL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
759 PM CDT MON MAR 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0758 PM     TSTM WND DMG     SNEAD                   34.12N 86.40W
03/19/2018                   BLOUNT             AL   EMERGENCY MNGR

            A FEW TREES WERE BLOWN DOWN NEAR SNEAD.

&&

MAL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
800 PM CDT MON MAR 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0759 PM     HAIL             1 NE SUSAN MOORE        34.08N 86.42W
03/19/2018  E1.75 INCH       BLOUNT             AL   EMERGENCY MNGR

&&

MAL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
803 PM CDT MON MAR 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0802 PM     TSTM WND DMG     3 E SARDIS CITY         34.17N 86.08W
03/19/2018                   ETOWAH             AL   EMERGENCY MNGR

            TREES WERE BLOWN DOWN ALONG LEATH GAP ROAD.

&&

MAL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
806 PM CDT MON MAR 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0805 PM     HAIL             2 NE HOWELTON           34.08N 86.16W
03/19/2018  E1.00 INCH       ETOWAH             AL   EMERGENCY MNGR

            QUARTER SIZE HAIL NEAR EGYPT.

&&

MAL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BIRMINGHAM AL
808 PM CDT MON MAR 19 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0807 PM     TSTM WND DMG     TRAFFORD                33.82N 86.74W
03/19/2018                   JEFFERSON          AL   EMERGENCY MNGR

            A FEW TREES WERE BLOWN DOWN NEAR TRAFFORD.

&&

MAL