Severe Thunderstorm Warning 9, NWS Birmingham, AL

645 
WWUS54 KBMX 282131
SVSBMX

Severe Weather Statement
National Weather Service Birmingham AL
331 PM CST WED FEB 28 2018

ALC133-282141-
/O.CAN.KBMX.SV.W.0009.000000T0000Z-180228T2145Z/
Winston AL-
331 PM CST WED FEB 28 2018

...THE SEVERE THUNDERSTORM WARNING FOR NORTHWESTERN WINSTON COUNTY IS
CANCELLED...
        
The storm which prompted the warning has weakened below severe
limits, and has exited the warned area. Therefore, the warning has
been cancelled.  However gusty winds are still possible with this
thunderstorm.

LAT...LON 3430 8729 3417 8725 3415 8761 3429 8761
      3431 8754
TIME...MOT...LOC 2130Z 251DEG 22KT 3428 8730 

$$

25/Owen

Area Forecast Discussion
National Weather Service Birmingham AL
1217 PM CST Wed Feb 28 2018

.UPDATE...
For 18Z Aviation.

&&

.SHORT TERM...
Today through Thursday.

An large area of light rain continues to lift northeastward across
northern and eastern portions of Central Alabama at this hour.
This activity is associated with a lead shortwave and located
north of a warm front which is currently located along a Greenwood
MS to Meridian to Pensacola line. A weak wave of low pressure is
currently located over Arkansas. Dew points are in the 50s on the
cool side of the boundary, and in the mid to upper 60s on the
warm side. The initial area of rain will lift north of the area by
mid-morning. Main focus for precipitation will then shift to the
warm front. After the weak meso-low lifts to the north, the warm
front will slow/stall as the low-level flow veers to westerly,
parallel to the front. The warm front will be located roughly
along/just north of our northern CWA border through the day.
Isentropic lift/warm air advection interacting with the moisture
axis along the frontal zone will cause multiple rounds of
showers/storms to train along this area. Models still disagree on
exactly where this will be, but our northern row of counties (the
Highway 278 corridor) could see around 1-2 inches of rain with
locally higher amounts. Rainfall amounts will be much, much lower
along the I-20 corridor and associated metro areas. Flash flood
guidance is fairly high along the Highway 278 corridor, around 2.5
inches in 3 hours and 3+ inches in 6 hours. So widespread
flooding in this area looks unlikely, and therefore a flash flood
watch will not be issued, but localized flooding will be possible.
Meanwhile, rain chances across the southern two-thirds of the
area will be much more isolated due to drier air aloft. Some
breaks in the clouds in the warm sector will allow highs to reach
the upper 70s to low 80s in the southern/southwestern counties.

CAMs indicate that 500-1000 J/kg of CAPE may develop across our
far northwest counties by afternoon with around 50 kts of westerly
0-6km bulk shear. So a few strong storms with gusty winds/perhaps
some small hail will be possible, and an isolated severe storm
can't be ruled out. However, potential will be limited by profiles
becoming saturated and competition between multiple updrafts, and
the flow aloft will be a bit anticyclonic due to ridging over the
Gulf implying a lack of upper-level support. Given the presence
of a warm front in the vicinity, it will be prudent to monitor
storms for rotation. As stated in previous discussions, the
threat for a brief tornado in the far northwest counties will be
non-zero. As would be expected, the highest SRH will be on the
cool side of the front with surface-based instability confined to
the warm side. Taking a look at HRRR forecast soundings, by the
time appreciable instability works in during the afternoon, SRH
weakens below 200 m2/s2 and hodographs become fairly straight
rather than curved due to veering low-level flow behind the meso-
low. Better instability looks to remain further west in MS. So
will not include a low confidence tornado threat at this time but
mesoscale trends will continue to be monitored just in case.

Tonight, low-level flow backs to the southwest ahead of the main
shortwave ejecting into the southern Plains. This should give the
warm front a small push northward, causing the bulk of the rain
to shift just north of the area, with the main flash flooding
threat area being across the Tennessee Valley region of Alabama
and Tennessee. Meanwhile, the loss of daytime heating will result
in a loss of instability over the area. Also, 700 mb southwest
winds will advect a very warm and dry air mass in that level,
associated with an EML, that will serve as a cap for convective
development. A few light rain showers/patchy drizzle will be
possible given onshore flow.

Meanwhile, a pre-frontal QLCS will develop over the Lower
Mississippi Valley. This will begin to move into the northwest
counties after sunrise. The fast motion of the system will limit
the potential for heavy rainfall. Models continue to indicate
that the associated southern stream shortwave will not phase with
the northern stream shortwave, and therefore will remain
positively tilted/sheared out. This results in a anafrontal
precipitation structure. Strong shear will be present with this
QLCS, but will be mainly uni-directional with veered low-level
flow, and the primary upper-level forcing will lag behind the
front. The EML will remain ahead of the line, capping any pre-
frontal development, with mid-level lapse rates becoming much
weaker along the line. Will continue to monitor for a brief
tornado threat, but it looks like the gust front should quickly
undercut updrafts and CAM reflectivities look unimpressive, so
this potential looks very low at this time. Instability will be
very weak initially, but will increase over the southeast
counties with daytime heating. A marginal damaging wind threat
could develop in these areas with some DCAPE and inverted V
soundings, which will continue to be monitored depending on the
strength of the convection. Also of note, strong gradient winds
will be present ahead of the line as one surface low deepens over
Indiana/Ohio and a new low develops in the lee of the
Appalachians, and 925 mb winds will be around 40 kts. This will
result in sustained 15-18kt winds and wind gusts to around 30 kts
(wind advisory criteria). Will therefore add a mention of gradient
winds to the HWO for Thursday.

32/Davis

.LONG TERM...
Thursday Night through Tuesday.

The main bulk of rain will be exiting the area shortly after sunset
on Thursday. There may be some lingering showers just behind the
front as well as across the northeastern counties with the upper
level feature sliding through so continued to mention a slight
chance of light showers through 9 pm.

We will then really dry out Friday and remain dry through the
weekend. The next system will begin to work into the area late
Monday afternoon as a warm front lifts northward and then a cold
front will move through the region on Tuesday. Will need to continue
to monitor this system as it gets closer as March is now here but
at this point the best lift to support stronger storms remains north
of the area. Stay tuned over the next few runs to see if anything
changes.

As for temperatures during the period, look for more seasonable
temperatures with highs in the 60s to low 70s. Lows will generally
be in the 40s through the period, with the coldest nights on Friday
and Saturday nights, where low to upper 30s are possible. In fact we
may actually see another freeze across a good portion of the the
north on Saturday morning, with isolated spots on sunday morning.
With the frost/freeze program still officially inactive through
March 15th, will not mention in the HWO at this time.

16

&&

.AVIATION...
18Z TAF Discussion.

MVFR cigs will continue for many for much of the afternoon. During
the latter part of the afternoon and early evening we may go VFR
with cigs around 4-5KFT. Lower MVFR cigs are expected to return
again during the late evening in advance of our storm system. A
few sites may see IFR as well toward sunrise/early am. While a
few light rain showers my scrape the northern TAFs this afternoon,
most of the activity should hold off until during the day
Thursday as the front approaches. A few thunderstorms are
possible, but will leave out mention at this time. Conditions
will be windy overall in and out of rain areas.

08

&&

.FIRE WEATHER...

Rain chances will be focused along the far northern counties of
Central Alabama today, with more isolated chances further south. A
line of showers and embedded thunderstorms will move through on
Thursday. Drier and cooler weather will move in Friday and continue
into the weekend. Relative humidity values are not expected to reach
critical levels, and no fire weather concerns are expected through
the forecast period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     69  62  68  39  59 /  70  80 100  20   0
Anniston    70  62  69  40  61 /  70  30 100  10   0
Birmingham  73  64  69  41  61 /  40  20 100  10   0
Tuscaloosa  77  65  69  42  63 /  30  20 100  10   0
Calera      74  64  71  42  62 /  30  10 100  10   0
Auburn      72  65  76  44  63 /  40  20 100  20   0
Montgomery  79  66  78  45  66 /  20  10 100  10   0
Troy        77  66  80  47  66 /  20  20  90  20   0

&&

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

&&

32/16/08

Hazardous Weather Outlook
National Weather Service Birmingham AL
250 PM CST Wed Feb 28 2018

ALZ011>015-017>050-020000-
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-
250 PM CST Wed Feb 28 2018

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

.DAY ONE...Outlook through Tonight.

A few strong to severe storms will be possible through 7 pm across
the northwest counties of Central Alabama through 7 pm. Main
threats will be isolated damaging winds up to 60 mph, but a brief
tornado cannot be ruled out. Locations include along and north of a
line from Millport to Cordova.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

A few strong to severe storms will be possible on Thursday generally
across the eastern counties of Central Alabama between 11 am and 4
pm. Main threats will be isolated damaging winds up to 60 mph, but a
brief tornado cannot be ruled out. Locations include along and east
of a line from Anniston, Talladega, Rockford, and Auburn.

In addition, outside of storms, breezy conditions are expected on
Thursday ahead of a cold front. Sustained gradient winds of 15 to 20
mph with gusts of 35 mph will be possible.

Minor river flooding is expected to redevelop along the Tombigbee
River in Southwestern Alabama Thursday night into the weekend. See
river flood warnings and flood statements for the latest
information.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management may be
necessary on both this afternoon and on Thursday.

08

Special Weather Statement
National Weather Service Birmingham AL
157 PM CST WED FEB 28 2018

ALZ011-282030-
Marion AL-
157 PM CST WED FEB 28 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN MARION COUNTY UNTIL
230 PM CST...

At 157 PM CST, Doppler radar was tracking a strong thunderstorm near
Weston, or 8 miles northwest of Hamilton, moving east at 30 mph.

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

Locations impacted include...
Hamilton, Weston, Pigeye, Shottsville and Bexar.

This storm 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.

LAT...LON 3431 8789 3412 8789 3413 8819 3421 8819
      3426 8818 3427 8815
TIME...MOT...LOC 1957Z 269DEG 26KT 3419 8812

25/Owen

Special Weather Statement
National Weather Service Birmingham AL
237 PM CST WED FEB 28 2018

ALZ011-014-282115-
Winston AL-Marion AL-
237 PM CST WED FEB 28 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN MARION AND
NORTHWESTERN WINSTON COUNTIES UNTIL 315 PM CST...

At 236 PM CST, Doppler radar was tracking a strong thunderstorm over
Brinn, or 10 miles northeast of Hamilton, moving east at 25 mph.

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

Locations impacted include...
Haleyville, Needmore, Brinn, Bear Creek, Weiss, Posey Field Airport,
Tessner, Delmar, Pebble and Upper Bear Creek Reservoir.

LAT...LON 3430 8749 3414 8749 3416 8783 3431 8782
TIME...MOT...LOC 2036Z 269DEG 23KT 3420 8781

25/Owen

Special Weather Statement
National Weather Service Birmingham AL
249 PM CST WED FEB 28 2018

ALZ013-282115-
Fayette AL-
249 PM CST WED FEB 28 2018

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN FAYETTE COUNTY UNTIL
315 PM CST...

At 248 PM CST, Doppler radar was tracking a strong thunderstorm near
Fayette, moving east at 25 mph.

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

Locations impacted include...
Fayette, Berry, Bevill State College Fayette, Hubbertville, Fowlers
Crossroads and Richard Arthur Field.

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 3389 8764 3369 8760 3369 8794 3372 8795
      3378 8795
TIME...MOT...LOC 2048Z 257DEG 23KT 3373 8789

75