Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
1247 AM CDT Thu Jun 20 2019

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...

A convective line of strong/severe storms are currently moving
eastward across Mississippi at ~60 mph, on track to enter western
portions of Central Alabama shortly after midnight. Severe
characteristics have been maintained by the MCS thus far with
damaging straight-line winds the primary threat. 04 Z RAP
mesoanalysis depicts a broad region of MLCAPE upwards of 2,000 J/kg
with ~40 kts eff. bulk shear as the MCS moves eastward in
association with the convectively induced shortwave. 50-60 kts of
westerly flow at 500 mb was also analyzed, with 1,100-1,200 J/kg
DCAPE already in place up to the I-59 corridor. 925-850 mb
southwesterly flow of ~30 kts appears to be aiding in replenishment
of instability and moisture to the system, though there is a CAPE
and moisture deficit in front of the line which may act to weaken it
as it moves eastward, as well as an eastward weakening trend in mid-
level lapse rates.

Regardless, a buoyant lower-troposphere and active low-level jet
suggests the MCS will pose a severe threat as it moves into portions
of the forecast area given lightning and remote sensing trends
showing a relatively healthy system as of 0430 Z. Uncertainties
remain as to when the line weakens below severe limits tonight, and
where the resultant boundary develops for severe potential again on
Thursday afternoon. Best forecast thinking as of now suggest severe
threats remain generally along and west of I-65 and north of I-59 in
the coming hours, areas outlined by Severe Thunderstorm Watch #406.

40/Sizemore

Previous short-term discussion:

Have removed the chance of any strong storm over Central Alabama
this evening. An exiting short wave trough has produced some
subsidence in its wake and much of the cloud cover has dissipated
north. Some convection still exist along a localized boundary in
south central Alabama, but this activity was rather limited.

Convection has begun in earnest near the Ark-La-Tex early this
evening. This is the beginning of the system that will affect
Central Alabama later tonight in one fashion or another. Models
are still split in whether the convection holds together as strong
to severe as the activity moves in after 1am. It certainly appears
there will be a chance this activity keeps some strength,
especially northwest as it moves in. Therefore, have held the
severe weather outlooks in place with an ever so slightly drop
south and east of the slight risk zone. As mentioned previously,
the discussions below due handle the conditional situation quite
well.

75

.LONG TERM...
/Issued at 430 AM CDT/

* A Slight Risk for severe weather on Thursday.

* Heat indices of 100-105 F possible Friday through Sunday.

Thursday.

The advertised shortwave moving across the Southern/Central Plains
eastward into the eastern CONUS will bring two possible rounds of
severe weather to Central Alabama on Thursday.

The first possible threat window opens ~1 AM Thursday morning
with a potential ongoing MCS advancing eastward across northern
Mississippi and into northern Alabama. This particular threat will
carry the chance for damaging straight-line winds up to 60 mph as
it moves into the forecast area. This scenario remains at low
confidence at this time as the system could very well weaken
before it arrives here, though MLCAPE ~2,000 J/kg and 30-40 kts
eff. bulk shear across its inflow region suggest maintenance of
strong to severe characteristics if the system doesn't become too
outflow dominate overnight. Nocturnal 925-850 mb winds ~30-40 kts
also suggest the convective system will be actively replenished
throughout its journey into our area. As a result, a Slight Risk
has been placed across our northwest forecast area as a damaging
straight-line wind threat may manifest in the early morning hours
Thursday.

Thereafter, effects from the possible early-morning MCS will have
implications for the second round of potential severe weather in the
afternoon & evening. As the overall synoptic shortwave amplifies
with eastward progression, height falls & cooling temperatures
aloft will overspread our area with a remnant outflow/theta-e
gradient across Central Alabama. Wherever this gradient
establishes will generally determine the spatial area favorable for
convective development in the afternoon. Convergence along this axis
will need to be sufficient enough to overcome unfavorable synoptic
scale subsidence as confluent flow aloft establishes behind the
shortwave trough axis. If lift is sufficient, guidance has certainly
maintained favorable thermodynamic variables (MLCAPE upwards of
3,500 J/kg and ~7 C/km mid-level lapse rates) with deep-layer shear
~30-40 kts for severe thunderstorm organization. Thunderstorms will
be capable of large hail and damaging convective downbursts
considering DCAPE 1,100-1,300 J/kg & 500 mb temperatures -9 to -10
C. As the shortwave continues eastward into Georgia and the
Carolinas, flow aloft will veer more northwesterly as upstream
ridging amplifies. Because of varying scenarios of how severe
threats may manifest in the next 24-48 hours, forecast confidence
remains low with a Marginal Risk being maintained for Thursday
afternoon & evening in our graphical products. Stay tuned for
future forecast updates.

Friday through Tuesday.

In wake of the exiting shortwave Friday morning, the mid/upper-level
pattern will transition to a longwave trough building across the
Intermountain West with resultant ridging developing along the
Mississippi River Valley. This ridge will continue to
strengthen/amplify into the weekend as hot temperatures develop in
the afternoons. To make matters worse, a humid, Gulf airmass will
linger across the Southeast. As such, heat indices are expected to
increase to the 100-105 F range on the afternoons of Fri/Sat/Sun. It
appears the hottest afternoons will be Fri/Sat with some locations
likely approaching criteria for a Heat Advisory. With this
possibility now likely, will be mentioning in the HWO and monitoring
trends in temperatures & dewpoints in the next day or so. Looking
ahead in to next week shows a relatively active pattern for this time
of year to continue with the ridge axis now approaching the East
Coast. Rain chances will be on the increase with the upstream trough
and associated surface frontal boundary moving in from the northwest.

40/Sizemore

&&

.AVIATION...
06Z TAF Discussion.

VFR conditions were present at all terminals at 05z. A line of
showers/storms was approaching the Mississippi Alabama state line
line and was encountering an atmosphere that was limiting its
further development. Therefore, the line has weakened the last
hour but still has a good push behind it. Went ahead and tracked
the motion and added prevailing thunder at TCL/BHM/EET around
07-08z with some wind gusts. Have lesser confidence in areas
east and south with convection. ANB/ASN did get a tempo group as
some thunder will be possible. Much lesser idea of how the area
will set up near MGM/TOI and have little mention. Due to the
increased wind, and mixing with the convective line, took out
mention of the MVFR ceilings outside convection at all but TOI at
this time. The convection will eventually diminish and southwest
winds will increase to around 10-12kts. The storms should set up a
boundary and where this boundary ends up will play a role in where
storms develop Thursday afternoon. At this time, left mention of
PROB30 thunder at all locations. This may eventually be shifted to
southern sites only and may push out of the area all together.

75

&&

.FIRE WEATHER...

Rain and thunderstorm chances remain high through Thursday with
an active upper-level pattern. Southerly flow and tropical air
will keep relative humidity values at or above 60% percent with
further recovery after peak heating subsides. KBDI values remain
high, but increased low-level moisture & recent rainfall will keep
us from reaching critical fire weather criteria. Drier weather
with hot afternoon temperatures are expected Friday through Sunday
with heat indices likely exceeding 100 degrees.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     87  68  91  70  91 /  70  30  30  20  20
Anniston    89  70  92  72  92 /  60  40  30  20  20
Birmingham  90  72  93  74  94 /  60  40  30  20  20
Tuscaloosa  92  73  95  75  95 /  50  40  30  10  10
Calera      90  71  92  72  92 /  50  40  30  10  20
Auburn      89  72  91  73  91 /  40  40  30  10  20
Montgomery  93  73  95  74  95 /  40  40  30  10  20
Troy        92  72  93  73  94 /  40  40  30  10  20

&&

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

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
316 AM CDT Thu Jun 20 2019

ALZ011>015-017>050-201600-
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-
316 AM CDT Thu Jun 20 2019

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

.DAY ONE...Overnight.

There is a Marginal to Slight Risk of severe storms through 7 AM,
for the northwest two thirds of Central Alabama. Damaging, straight
line winds and large hail are possible. The storms will be near the
Interstate 65 corridor by 4 AM.

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

A Marginal to Slight Risk for severe weather exists across a
majority of Central Alabama for the remainder of Thursday. Primary
threats with storms that redevelop are large hail up to golf ball
size and damaging winds up to 60 mph. The strongest storms are
expected as early as Noon and may continue through around 11 PM.

Heat index values of 100 to 105 degrees are possible during the
afternoon Friday through Sunday, with some locations possibly
exceeding 105 degrees. Anyone with plans for outdoor activities
should take action to reduce over-exposure and dehydration.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management may be needed
overnight and Thursday.

Special Weather Statement
National Weather Service Birmingham AL
118 AM CDT Thu Jun 20 2019

ALZ011-014-200715-
Winston AL-Marion AL-
118 AM CDT Thu Jun 20 2019

...SIGNIFICANT WEATHER ADVISORY FOR MARION AND WESTERN WINSTON
COUNTIES UNTIL 215 AM CDT...

At 117 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Sandy Springs to 6 miles southwest of Detroit
to near Bedford. Movement was east at 50 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Hamilton, Winfield, Haleyville, Guin, Hackleburg, Brilliant, Glen
Allen, Gu-
Win, Weston, Brinn, Lake Buttahatchee, Bear Creek, Twin, Natural
Bridge, Tucker, Rankin Fite Airport, Upper Bear Creek Reservoir,
Delmar, Marion County Public Lake and Piney Grove.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Birmingham.

&&

LAT...LON 3431 8760 3400 8760 3400 8764 3391 8764
      3392 8795 3402 8795 3402 8799 3405 8799
      3406 8821 3432 8818
TIME...MOT...LOC 0617Z 267DEG 44KT 3444 8838 3397 8826 3383 8825

40/Sizemore

Special Weather Statement
National Weather Service Birmingham AL
144 AM CDT Thu Jun 20 2019

ALZ018-020-200715-
Etowah AL-Cherokee AL-
144 AM CDT Thu Jun 20 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN ETOWAH AND WEST
CENTRAL CHEROKEE COUNTIES UNTIL 215 AM CDT...

At 143 AM CDT, Doppler radar was tracking a strong thunderstorm over
Sardis City, or near Boaz, moving northeast at 55 mph.

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

Locations impacted include...
Sardis City, Leesburg, Reece City, Sand Rock, Tabor Road, Cherokee
Rock Village, Aurora, Western Weiss Lake, Crudup, Yellow Creek Falls,
Mountainboro, Keener, Rockledge, Chesnut Bay Resort and Black Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Birmingham.

&&

LAT...LON 3420 8567 3404 8615 3416 8623 3418 8619
      3419 8611 3420 8610 3420 8584 3424 8584
      3424 8581 3426 8581 3426 8577 3428 8575
TIME...MOT...LOC 0643Z 238DEG 46KT 3414 8610

40/Sizemore

Special Weather Statement
National Weather Service Birmingham AL
306 AM CDT Thu Jun 20 2019

ALZ035-040-041-200900-
Chilton AL-Autauga AL-Dallas AL-
306 AM CDT Thu Jun 20 2019

...SIGNIFICANT WEATHER ADVISORY FOR AUTAUGA...CHILTON AND CENTRAL
DALLAS COUNTIES UNTIL 400 AM CDT...

At 305 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from American Village to near Talladega National
Forest to Vaiden. Movement was east at 50 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Prattville, Selma, Millbrook, Calera, Clanton, Valley Grande,
Jemison, Selmont-West Selmont, Thorsby, Deatsville, Autaugaville,
Maplesville, Billingsley, Gap Of The Mountain, Parnell, Autauga
County Airport, Verbena, Mulberry, Marbury and Mitchell Lake.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Birmingham.

&&

LAT...LON 3240 8684 3239 8742 3248 8742 3249 8711
      3260 8704 3284 8702 3284 8688 3307 8688
      3307 8661 3306 8662 3302 8652 3282 8646
      3275 8638 3241 8641 3234 8649 3241 8662
      3235 8668 3240 8672 3239 8678 3231 8681
TIME...MOT...LOC 0805Z 280DEG 44KT 3316 8682 3281 8703 3251 8738

40/Sizemore

Special Weather Statement
National Weather Service Birmingham AL
321 AM CDT Thu Jun 20 2019

ALZ018-019-025>027-200915-
Calhoun AL-Etowah AL-Shelby AL-Talladega AL-St. Clair AL-
321 AM CDT Thu Jun 20 2019

...SIGNIFICANT WEATHER ADVISORY FOR TALLADEGA...CALHOUN...EASTERN
SHELBY...ETOWAH AND ST. CLAIR COUNTIES UNTIL 415 AM CDT...

At 321 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from Arab to near Vandiver to near Calera. Movement
was east at 50 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Gadsden, Anniston, Oxford, Talladega, Sylacauga, Pell City,
Jacksonville, Leeds, Moody, Rainbow City, Attalla, Childersburg,
Hokes Bluff, Columbiana, Springville, Odenville, Wilsonville,
Talladega Springs, Cobb Town and Fort McClellan.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Birmingham.

&&

LAT...LON 3411 8584 3412 8579 3397 8573 3356 8578
      3350 8590 3330 8598 3329 8612 3311 8618
      3310 8649 3302 8655 3307 8666 3331 8654
      3372 8653 3380 8658 3382 8643 3389 8634
      3394 8637 3407 8632 3418 8619 3420 8584
TIME...MOT...LOC 0821Z 258DEG 42KT 3433 8648 3348 8657 3314 8670

40/Sizemore