Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
226 AM CST Sat Jan 21 2017

.UPDATE...
MESOSCALE UPDATE.

&&

.DISCUSSION...

Low-level moisture advection is rapidly occurring across the
forecast area with dew points in the low 60s in many locations
and many mid 60s across southern Alabama and Mississippi.
Widespread convection across Mississippi and Louisiana continues
with a mix of supercells and line segments. Many rotating cells
have already been observed as well as hail cores. The main part of
the activity will will move into the forecast area around 10-11Z.
Will have to watch some additional activity lifting northward
across southwest AL which may arrive a bit before then. We will be
launching a special sounding at 9Z to sample the environment,
though some modifications to the surface temperatures/dew point
will have to be made to best analyze the severe potential matching
the conditions further southwest. The JAN 6Z sounding indicated
very impressive mid-level lapse rates of 7.8 C/km while the 6Z LIX
sounding is most representative of the environment. Not much
change in forecast thinking with tornadoes, large hail, and
damaging winds expected with this activity this morning. The
primary/elevated threat will be south of I-20. Will have to keep
an eye on instability trends after sunrise for areas south of I-85
as a strong tornado may be possible there around mid-morning.

This round will push east of the forecast area by noon, and the
afternoon will be dry as some lower dew points briefly mix down.
Round 2 is still on track mainly after 11 PM tonight through 6 AM
Sunday morning as another strong upper-level jet streak rounds
the base of the trough. Guidance now indicates another shortwave
ejecting out of the Southern Plains low this evening, with
additional thunderstorms developing across Arkansas/Louisiana and
moving northeastward across Mississippi and into our northwest
counties after 11 PM. Guidance now indicates a meso-low developing
over Arkansas ahead of the main surface low over Oklahoma, and a
pre- frontal trough features extending southeastward serving as a
focus for convection and also causing slight backing of the
surface winds. While the strongest low-level jet is still expected
to be across our southeast counties, guidance has come in stronger
with the LLJ areawide and especially with the meso-low feature.
Therefore some changes have been made to the impact graphics and
forecast. First, with stronger low-level shear there will be the
potential for isolated tornadoes areawide, with the highest chance
still being in the elevated threat area in the far southeast.
Also, CAMs are in good agreement on a line of convection moving
across our northwest counties in a cold core type setup. This
convection will be capable of producing large hail of golf ball
size or higher, damaging winds, and the potential for tornadoes.
With guidance indicating two favored areas for convection tonight,
one across the northwest and one across the southeast, two
elevated threat areas will be included in the impact graphics. A
relative minimum in convective coverage is expected in between,
but even in these areas a limited threat of hail, damaging winds,
and at least a brief tornado will be possible given the low-level
shear and instability present for any isolated convection that
develops.

32/Davis

&&

.AVIATION...
06Z TAF Discussion.

Main issues this TAF period continues to be timing out the storms
coming into the area later tonight into the morning hours. We are
expecting the possibility of strong to severe storms in the
morning. Shortwave will be coming in from the southwest and
spreading across Central Alabama late tonight into Saturday
morning with a low level jet to enhance it. We will be making
adjustments during the overnight as development begins to refine
TSRA start times. Before convection starts though, we have some
MVFR stratus/fog more IFR as you go south to start things off
tonight.

08

&&

.FIRE WEATHER...

Strong to severe storms can be expected Saturday and Sunday,
along with periods of heavy rainfall. Rainfall amounts through
Sunday will average 1 to 2 inches.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     67  55  63  45  53 /  80  70  80  70  20
Anniston    69  57  65  46  53 /  90  70  80  70  20
Birmingham  69  57  64  46  54 /  80  70  80  60  20
Tuscaloosa  71  56  65  46  56 /  80  70  80  50  20
Calera      70  57  64  46  55 /  80  70  80  60  20
Auburn      70  60  67  48  56 / 100  70  80  50  20
Montgomery  74  59  68  47  58 / 100  70  80  50  20
Troy        73  58  69  47  59 / 100  70  70  40  20

&&

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

&&

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Special Weather Statement
National Weather Service Birmingham AL
352 AM CST SAT JAN 21 2017

ALZ040-042-211030-
Dallas AL-Lowndes AL-
352 AM CST SAT JAN 21 2017

...SIGNIFICANT WEATHER ADVISORY FOR LOWNDES AND DALLAS COUNTIES UNTIL
430 AM CST...

At 352 AM CST, Doppler radar was tracking a strong thunderstorm near
Belknap, or 16 miles west of Mosses, moving northeast at 30 mph.

Nickel size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Selma, Valley Grande, Mosses, Hayneville, Selmont-West Selmont, White
Hall, Gordonville, Orrville, Lowndesboro, Benton, Bogue Chitto,
Memorial Stadium, Burnsville, Marion Junction, Paul M Grist State
Park, Dallas County Horse Arena, Dallas Lake, Old Cahaba Park,
Dannelly Reservoir and Gardner Island.

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 3205 8686 3205 8718 3214 8725 3221 8737
      3248 8731 3249 8711 3260 8704 3273 8702
      3266 8702 3266 8692 3231 8682 3231 8681
      3239 8678 3240 8673 3236 8671 3241 8662
      3236 8660 3234 8651 3196 8662 3196 8686
TIME...MOT...LOC 0952Z 212DEG 27KT 3212 8695

32/Davis