Severe Thunderstorm Warning 226, NWS Mobile, AL

Area Forecast Discussion
National Weather Service Mobile AL
640 PM CDT Thu Jul 21 2022

.AVIATION...
00Z issuance...VFR conditions prevail for the time being across
the region. An organizing complex of thunderstorms to the north
over central AL will continue to push south this evening affecting
much of interior southwestern into south-central AL. Expect
strong and variable wind gusts with this complex along with
reductions in ceilings and/or visibility to at or below IFR
category. Off and on scattered storms are anticipated elsewhere,
posing similar hazards although on a more localized scale. The
forecast becomes uncertain late overnight into the morning hours
Friday, although anticipate VFR conditions to prevail with some
locations continuing to experience reduced ceiling and visibility
due to thunderstorms across southeast MS, southwest AL, and the FL
panhandle. MM/25

&&

.PREV DISCUSSION... /issued 405 PM CDT Thu Jul 21 2022/

NEAR TERM UPDATE /Now Through Friday/...The near term forecast is a
rather complicated one, as the Southeast US remains situated
within an upper- level deformation zone, with upper ridging to the
west and east and upper troughing to the north and south. For our
region, upper-level flow is generally out of the north to
northeast as the upper ridge axis remains located just to our
north, across central AL/MS. Meanwhile, a subtle, embedded
shortwave is located over the Central US. Guidance suggests that
this shortwave will continue to push southeastward, within the
flow aloft, and approach our region from the north during the
evening hours as it rounds the eastern periphery of the ridge. By
Friday, the shortwave lingers over the northern Gulf of Mexico as
the upper ridge attempts to build eastward into our region. At the
surface, a frontal boundary is currently draped across western
Tennessee. This will continue to push southeastward before
stalling over the northern MS/AL region.

Currently across the local region, scattered showers and
thunderstorms are developing along the sea breeze boundary. With
ample moisture in place (PWATs around 1.9 to 2.1 inches) and plenty
of instability to work with (MLCAPEs around 2500 to 3500 J/kg),
storms are expected to continue popping up along the sea breeze
during the remainder of the afternoon and into the early evening as
it pushes inland. Looking to our north, a cluster of strong
thunderstorms are ongoing over the central AL/GA state line and are
slowly moving to the south and west. Additional storms are also
beginning to develop within the moist and highly unstable
environment over central AL (MLCAPEs in excess of 3500 J/kg). With
very steep low level lapse rates, as well as some dry air above
700mb, DCAPEs in that region are around 1000 to 1500 J/kg. This
will, in turn, help to produce outflow boundaries, which will act as
a focus for additional storms to develop, especially as the embedded
shortwave begins pushing into the MS/AL/TN region. Guidance suggests
that these storms may begin to coalesce during the early evening
hours and organize into an MCS (or similar type of feature), quickly
propagating southward through our area during the mid/late evening
and overnight hours. Although shear remains rather weak, the high
amounts of instability (even after the loss of daytime heating) and
high DCAPEs suggest that storms within this feature will have the
potential to become strong or even severe, with the primary hazards
being gusty to locally damaging winds, heavy rain, and small hail.
SPC currently has areas north of I-10 outlooked with a MARGINAL Risk
of severe storms for tonight and a SLIGHT Risk skirting the extreme
northern part of our area and then extending northward through
central AL. This feature will begin to decrease in intensity as it
approaches the coast due to lower instability values.

For Friday, convective coverage will likely depend on the timing of
the aforementioned feature, as well as how well the environment can
recover after it passes through. With the uncertainties in place,
reduced PoPs to 40 to 60 percent, with the best coverage over the
southern half of the region to account for sea breeze development.

Lows tonight will be in the mid to upper 70s, with low 80s along the
coast. Highs on Friday will be in the upper 80s to low 90s, with
heat indices remaining below Heat Advisory criteria (97 to 102
degrees). /96

SHORT TERM /Friday night Through Sunday night/...An upper level
ridge over the Plains states will begin to shift east and center
itself over the Tennessee Valley through the weekend. Mid level
heights rise over our forecaster as well which should help to
reduce overall convective coverage through the weekend.

Despite the increased heights aloft, there will still be daily
development of scattered showers and thunderstorms along a
developing sea breeze circulation near the coast spreading inland
each day. Kept pops near climatology with the increasing
subsidence aloft but continuation of deep moisture and the
presence of the low level forcing mechanism. Greatest coverage
will be near the coast with decreasing chances across the interior
portions of the forecast area.

The increasing ridging aloft and overall reduced storm coverage
will support rising temperatures. High temperatures will range
from the lower 90s along the immediate beaches, to the mid and
upper 90s across the interior both Saturday and Sunday. These
increasingly hot temperatures will combine with seasonably high
humidity values to force heat indices into the dangerous category,
ranging between 108 and 112 degrees during peak heating. Very warm
and humid overnight conditions will also persist with lows in the
middle 70s to around 80 degrees through the weekend. Heat
advisories will likely be needed for much of the forecast area
for the upcoming weekend. /JLH

EXTENDED TERM /Monday Through Thursday/...The upper ridge
gradually shifts east through the extended forecast period. A
series of shortwaves in developing easterly to southeasterly flow
aloft coincident with increasing deep tropical moisture from the
Caribbean will result in increasing coverage of showers and
thunderstorms into next week, especially by the end of the
extended forecast period. This is supported both by the
operational global models as well as the latest ensemble guidance
during this time period. Daily high temperatures should be a few
degrees lower as compared to the weekend with heat index values
falling back to near normal summertime levels through the extended
forecast period. /JLH

MARINE...A light to moderate southwesterly flow will persist
through Friday, becoming more southerly Friday night and through the
weekend. Isolated to scattered showers and thunderstorms can be
expected across the marine zones each day. Otherwise, no significant
impacts are anticipated. /96

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...None.
FL...None.
MS...None.
GM...None.
&&

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