Severe Thunderstorm Warning 227, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
100 PM CDT Sun Jun 25 2023

...New MESOSCALE UPDATE, AVIATION...

.MESOSCALE UPDATE FOR SEVERE STORM POTENTIAL...
Issued at 1215 PM CDT SUN JUN 25 2023

We continue to watch and wait for storms to blossom across Central
Alabama as we go into the afternoon hours. We already have our
first isolated convection developing across the northwest counties
within parameter space that continues to grow more volatile with
each hour that goes by. Due to the delay in the initial onset of
storms, we're going to realize our high temperatures of the day in
the lower 90s, especially along and west of the I-65 corridor and
across our far southern counties. RAP analysis is now indicating
SBCAPE values of 5000-6000 J/kg across Mississippi as surface
dewpoints have still not mixed in these areas. Unfortunately,
we'll have to issue a Heat Advisory as a result with Heat Index
values running between 103 and 106 across the western two tiers of
counties. A PWAT/MLCAPE gradient is currently bisecting Central
Alabama from north to south, ranging from 1.8 to 1.9 inches in the
west to 1.3 inches in the far east. We expect deeper moisture and
PWATS to continue to rise from west to east through the
afternoon, providing more fuel for severe storm development.

Based on initial development ongoing now and high-res guidance
trends this afternoon, we could be looking at isolated supercell
development first with large hail and damaging wind potential. As
widespread storms develop later on this afternoon, an MCS is then
expected to move southward or southwestward across Central
Alabama during the late afternoon and early evening hours.
Widespread damaging wind potential would accompany any MCS that
happens to develop as the cold pool rapidly advances with slab-
like lifting. Convective trends will continue to be monitored
through the afternoon, so stay tuned for future updates. PoPs were
adjusted back a few hours to account for the later initiation and
high temps were adjusted upward areawide.

&&

.SHORT TERM...
(Today through Monday)
Issued at 350 AM CDT SUN JUN 25 2023

So while the initial MCS, did not develop as expected overnight,
there are some pockets of clouds moving into middle TN, northwestern
AL that could produce a shower or two. through the morning. The next
shortwave is now sliding through the Ohio Valley and we are
beginning to see a piece break off and start its southeastward
motion toward our area. Models are really all over the place as for
timing as it works into the area. One model is as early as 10 AM,
where another model says 4 PM. The consensus says between 12 and 1
PM and then quickly sliding south through the afternoon and exiting
before 10 PM. This MCS is the biggest concern to our area. Also the
biggest headache to the forecast.

The current forecast brings in high PoPs generally at 1 PM.
Depending on the motion it could begin between 11 and 1 PM but had
go with an initial thought and best chances based on the consensus.
The MCS will quickly move through the area and will play havoc on
temperatures as it moves through. The northern counties highs will
be at Noon to 1 PM and then will drop into the 70s once the rain
starts. Areas in the far south and far west will likely hit the low
90s before the cloud cover/rain works in. In fact portions of the
far, far SW and SE may get close to the 95 mark. At 2 PM this
afternoon we potentially will see 75 in the northeast to 95 in the
southwest. Quite a gradient for the summer. This leads into 2 more
factors that we need to discuss. The first will be the chance of
excessive heat. With temperatures in the low to mid 90s this
afternoon and dewpoints in the the 70s, heat indices will be in the
100 to 104 range with isolated pockets of 105 to 106. With the lack
of coverage will not issue a heat advisory at this time. The second
factor will be the severe aspect. When the MCS was expected this
morning, we were not going to heat up as much, so the instabilities
were not going to be as robust, but now with a slower beginning, we
will warm up nicely before. Strong and severe storms certainly will
be possible this afternoon and into tonight before the MCS works
out. Damaging winds and hail will be the main threats. The best CAPE
will be over the northern counties with forecast over 2700 to 3500
J/KG. As the morning sounding comes in, we will see what the
modified soundings look like to get a better account for the
environment that the MCS would be working into.

As this MCS is working out of the area, a second MCS will move into
the far western counties. This will most likely develop along an
outflow from another MCS that will slide through western TN and
eastern AR this afternoon. The main concern here would be stronger
storms in the west through Midnight and heavy rain. There is a
chance that a severe storms may slide into the the western counties
as the airmass in MS this afternoon will be conducive. However the
MCS would be working into what should be an already worked over
airmass so the cold pool of the MCS should remain to our west.

After Midnight, the forecast is very uncertain as we work into
Monday. Some of the models redevelop a 4th or 5th MCS that would
work into the area close to sunrise Monday and push through the
east, while other models are content on the activity today and
keeps a meso high overhead through Monday. Giving ground to the
persistent forecast and location of boundaries from the left over
evening MCS, will continue with scattered showers and storms, with
the best coverage in the southeast by the afternoon. With that
said confidence is pretty low in the overall forecast after 10 PM
tonight. SPC did place the southeast in a marginal threat for
severe weather. Would consider it to be more a conditional
marginal as we will first need to see convection and I am not sold
on it for Monday. Much, much more on this over the next few
updates.

16

&&

.LONG TERM...
(Tuesday through Saturday)
Issued at 350 AM CDT SUN JUN 25 2023

An active weather pattern is expected to continue through much of
the week.

An amplified ridge persists across much of the Central CONUS with a
generally stationary trough along the East Coast. This synoptic
setup places Central AL under a northwesterly flow regime. Models
pick up on a few shortwave impulses sliding through the region, each
one supporting thunderstorm development. Given the MCS mode, any one
of these could lead to strong to severe storms (mainly wind).
However, model guidance really struggles with resolving the timing
and evolution of each wave, so confidence isn't there to include
severe storms in the forecast for any specific day at this time.

The low level ridge builds eastward over the Gulf States Thursday
into Friday, leading to a warming trend for the region. High
temperatures on both days will be in the upper 90s with many
locations nearing or hitting 100 degrees. Heat index values will be
in the 105-110+ degree range. However, the temperature forecast is
highly dependent on the timing and location of any convective
systems that may move through Central AL those days. The hot/humid
air mass continues into Saturday, so we may be looking at a
prolonged period of potentially dangerous heat with little overnight
recovery (lows in the upper 70s) , which could exacerbate the risk,
especially for vulnerable populations.

25/Owen

&&

.AVIATION...
(18Z TAFS)
Issued at 1215 PM CDT SUN JUN 25 2023

VFR conditions will continue through the afternoon followed by
deteriorating conditions between 20z and 02z areawide. Widespread
TSRA is expected to develop and have added in TEMPO TSRA with
variable stronger wind gusts for all terminals. Each TEMPO group
is timed according to when higher confidence exists in storm
development. Storms will initially form across northern terminals
then move southward and affect MGM and TOI after 00z this evening.
Rapid reductions in visibilities are expected as storms pass over
terminal locations, and at least VCTS could linger for an hour or
two after storms pass off to the south of a terminal later
tonight. Guidance continues to indicate MVFR ceilings developing
between 06z and 10z Monday morning, and have included that in the
planning period. Additional SHRA and TSRA are possible once again
during the day on Monday.

56/GDG

&&

.FIRE WEATHER...

Showers and storms are possible today into Monday with lower
chances on Tuesday as the associated front moves closer to the
immediate Gulf Coast. Minimum RH values will remain well above
critical thresholds. 20-foot winds should average from the
southwest on Sunday, west-southwest on Monday, and west-northwest
on Tuesday with speeds close to 10 knots at times, especially on
Tuesday based on the current forecast.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     68  91  67  92 /  20  30  10  10
Anniston    67  90  69  92 /  20  40  10  10
Birmingham  69  92  72  95 /  50  30  10  10
Tuscaloosa  70  93  72  95 /  60  30  20  20
Calera      69  91  72  94 /  60  40  20  20
Auburn      69  87  71  90 /  60  50  20  20
Montgomery  70  92  72  94 /  60  50  20  20
Troy        70  92  73  94 /  60  50  30  30

&&

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

SHORT TERM...56/GDG
LONG TERM....25
AVIATION...56/GDG

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Special Weather Statement
National Weather Service Birmingham AL
210 PM CDT Sun Jun 25 2023

ALZ013-015-252000-
Fayette AL-Walker AL-
210 PM CDT Sun Jun 25 2023

...A strong thunderstorm will impact portions of northwestern Walker
and northeastern Fayette Counties through 300 PM CDT...

At 210 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles southwest of Kansas, or 8 miles southwest of Carbon Hill,
moving east at 20 mph.

HAZARD...Winds in excess of 40 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...
Jasper, Carbon Hill, Berry, Oakman, Kansas, Cedrum Area, Fowlers
Crossroads, Holly Grove, Gamble, Corona, Townley and West Corona.

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 3372 8772 3391 8769 3390 8729 3364 8734
TIME...MOT...LOC 1910Z 278DEG 19KT 3381 8763

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH

87/Grantham

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