Special Weather Statement, NWS Mobile, AL

Area Forecast Discussion
National Weather Service Mobile AL
414 PM CDT Wed Aug 17 2022

.MESOSCALE UPDATE /Now Through Tonight/...The atmosphere has
become strongly unstable across much of southeast Mississippi into
coastal counties of southwest Alabama. Latest SPC mesoanalysis
suggests that MLCAPES are around 3500j/kg as of 19z. Overall, the
greatest instability remains displaced to the south of the best
analyzed 0-3km shear, which appears maximized between 30-40 kts
per latest SPC mesoanalysis and local VAD profilers in that area.
This suggests that much of the convection will remain loosely
organized along any developing cold pool/gust fronts.

Numerous storms have developed across portions of southeast
Mississippi into coastal Alabama as of 20z. Some of the strongest
cells have approached severe limits already with strong cores
developing near the favorable -20C height. A subtle mid level
shortwave noted in low/mid level water vapor over the Arklamiss
will continue to advance southeast and support further storm
development and intensification through the remainder of this
afternoon and into this evening.

Regional 12z soundings suggested an enhanced wet microburst
potential as plenty of mid level dry air was noted above
approximately 5km with very moist air below and through the
boundary layer. In addition, lapse rates below roughly 5km were
sufficiently steep around 7.0C/km. This all supports a localized
damaging wind potential with any of the storms that reach severe
limits. Marginally severe hail between nickle and quarter size
also will be possible but not the primary threat.

Considering the very moist airmass below 5 km, with overall PWATs
exceeding 2.0 inches per latest GOES 16 TPW and the potential for
storms to regenerate and move repeatedly over the same areas,
flash flooding will be a concern as well. This is especially the
case in a corridor from southeast Mississippi into southwest
Alabama and portions of the western Florida Panhandle, where
latest model guidance suggests the potential for several inches of
rainfall. Antecedent conditions remain wet with lowered flash
flood guidance around 2 to 2.5 inches per hour, and around 3
inches per 3 hours. This may support areas of flash flooding in
areas where storms train. Remember, never drive into areas where
water covers the roadway.

Numerous storms should persist in the evening with the heavy
rainfall threat continuing. This activity will persist until the
shortwave departs to the southeast later tonight. Please continue
to monitor our social media channels for the latest information
and updates through late this evening and be prepared to take
cover if a severe thunderstorm warning is issued for your
location. /JLH

&

.PREVIOUS NEAR TERM /Now Through Thursday/...An upper level
trough over continues to remain rooted across the eastern CONUS,
expanding west and digging somewhat into Thursday as another
shortwave digs into the west side of the trough. The
aforementioned shortwave is going to be a driver for weather
conditions Thursday, and a more subtle series of shortwaves this
afternoon through tonight will be responsible for scattered to
numerous showers and thunderstorms. At the surface, a relatively
stationary boundary is situated across interior portions of
southeastern MS into southwestern AL, serving as a present foci
for a few showers and isolated thunderstorms.

As we move forward in time this afternoon, expect a substantial
uptick in convective coverage for the region from west to east as
the first shortwave tracks into the area. Scattered to numerous
showers and thunderstorms can be expected. The environment is
overall primed for wet microbursts with high PWATs over 2", large
DCAPE of 1,000 to 1,400j/kg, MLCAPE values over 3,000j/kg, and
very steep low level lapse rates over 8 to 8.5C/km. Storms may
have a better time organizing today with the presence of stronger
sfc-3km shear on the order of 20 to 25kts, so loosely organized
multicell clusters and perhaps an eventual MCS may develop out of
the storms today as they track from northwest to southeast. Main
hazards with storms today will be frequent lightning, torrential
rainfall, strong to locally damaging wind gusts, and perhaps some
small hail up to around nickel size. A weaker thermodynamic
environment overnight tonight into tomorrow should preclude much
of a damaging wind or hail threat.

There is increasing concern for heavy rainfall and potential flash
flooding this evening into Thursday. With several shortwaves
tracking across the area there will be multiple rounds of heavy
thunderstorms resulting in training of heavy rainfall over some
areas. The greatest threat for this presently appears to be across
southeastern MS into southwestern AL. CAMs remain somewhat
divergent on solutions of where the heaviest axis of rain sets up,
but a general 1 to 2" of rainfall can be expected over these
areas. Locally, where the best training of storms sets up, some
spots could see upwards of 5" through Thursday considering
thunderstorms will have rainfall rates of 2 to 4" per hour. At
this time given the uncertainty on positioning and relatively more
confined area of flash flood potential, have held off on issuing
a Flash Flood Watch. However, if confidence increases in a more
widespread heavy rain event, one may become necessary for tonight
into Thursday.

In regards to temperatures, highs are reaching the middle 90's
today for most locations. Lows tonight will dip into the lower to
middle 70's, warmest nearer the coast. Highs Thursday are tricky
and will depend on convective coverage. For now have stuck with
the NBM for highs in the middle to upper 80's, but can see this
being too warm if some of the more bullish CAMs verify on
convective coverage overnight tonight into tomorrow afternoon. MM/25

&&

.SHORT TERM /Thursday night Through Saturday night/...Increased
rain chances will continue into the weekend. Broad upper level
troughing will be in place across the Southeastern States Thursday
night and into Friday while a shortwave pivots within the broader
flow. This shortwave will deepen the trough on Friday as it digs
over the area and takes on somewhat of a negative tilt. Upper
level flow will turn from westerly Thursday night to more
southwesterly on Friday as a result. Down at the surface, a weak
boundary will linger over the area before slowly lifting north on
Friday as the shortwave lifts out of the area. Moisture will be
abundant across the area Friday morning with precipitable water
values around 2 to 2.3 inches. This moisture combined with the
synoptic boundary will support the development of numerous to
widespread showers and storms Friday morning and continuing into
the afternoon hours. Convection may be too widespread would likely
limit any strong to severe storms as surface temperatures will
struggle to reach their convective temperatures. However, if areas
can break out into sun then some stronger storms/clusters with
damaging wind potential could be possible given some level of
DCAPE and modest shear. Heavy rainfall will continue be the bigger
threat given the overall saturated grounds from the days prior
and heavy rainfall rates.

The upper shortwave will quickly lift away from the area Friday
night and into Saturday. The surface boundary will move further
north in response with deep layer moisture (precipitable water
values around 2 inches or just below) remaining across much of
the Northern Gulf Coast. Another upper trough will begin to dive
out of the Upper and Middle Mississippi Valley later on Saturday
afternoon. This pattern will continue to support showers and
storms throughout the day with coverage generally peaking in the
afternoon and evening hours.

The increased rain chances will keep high temperatures in the
middle to upper 80s on Friday. By Saturday, temperatures warm into
the upper 80s across most of the area as rain chances decrease
slightly. Overnight lows will remain in the lower 70s inland with
middle to upper 70s along the immediate coast. /14

&&

.EXTENDED TERM /Sunday Through Wednesday/...Upper level ridging
attempts to build in from the western Atlantic on Sunday which
will result in some drying across the area. However it won't last
for long as an upper trough deepens into a closed low and
gradually slides over the Ohio Valley and Midwestern States
through early next week. The weak surface boundary mentioned in
the short term will move back into the area as the base of the
upper trough digs into the Tennessee Valley and northern portions
of the Southeast. As we approach the middle of next week, the
upper trough will begin to broaden out with the surface boundary
likely lingering over much of the area. Moisture will remain
plentiful in this pattern and with the proximity to the upper
trough will see the increased rain chances continue through much
of next week. Locally heavy rainfall may continue to be a concern
especially into the middle of next week as the moisture and
enhanced deep layer moisture returns to the area. Temperatures
will be below seasonal normals given the increased cloud and storm
coverage. /14

&&

.MARINE...No impacts are expected for the marine area other than
higher winds and waves in and around showers and thunderstorms. A
light to moderate westerly flow is expected to prevail through early
Friday. Winds turn mainly southwesterly Friday afternoon through
early next week. Afternoon thunderstorms will generally be sliding
into the marine zones from the north over the next day or two. /22

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Heat Advisory until 6 PM CDT this evening for ALZ261>266.

FL...Heat Advisory until 6 PM CDT this evening for FLZ201>204.

MS...Heat Advisory until 6 PM CDT this evening for MSZ075-076-078-079.

GM...None.
&&

This product is also available on the web at:
www.weather.gov/mob

Special Weather Statement
National Weather Service Mobile AL
327 PM CDT Wed Aug 17 2022

MSZ067-172130-
Wayne MS-
327 PM CDT Wed Aug 17 2022

...A strong thunderstorm will impact portions of central Wayne County
through 430 PM CDT...

At 327 PM CDT, National Weather Service doppler radar indicated a
strong thunderstorm 5 miles south of Goodwater, or 16 miles northwest
of Waynesboro, moving southeast at 15 mph.

HAZARD...Wind gusts up to 50 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Waynesboro and Clara.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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 3182 8894 3183 8876 3185 8867 3171 8847
      3148 8884 3171 8895
TIME...MOT...LOC 2027Z 324DEG 12KT 3183 8886

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

MM

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