833
ACUS01 KWNS 081647
SWODY1
SPC AC 081645

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1145 AM CDT Wed May 08 2024

Valid 081630Z - 091200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM THE
MISSOURI OZARKS EASTWARD INTO SOUTH-CENTRAL KENTUCKY AND MIDDLE
TENNESSEE...

...SUMMARY...
Severe thunderstorms appear likely from parts of the mid
Mississippi, Ohio, and Tennessee Valleys into the southern Plains.
All severe hazards, including tornadoes, very large to giant hail,
and potentially significant damaging winds are possible.  Some
tornadoes may be strong.

...Ozarks to Mid Mississippi, lower Ohio and Tennessee Valleys...
A complex, partially mesoscale-driven forecast is apparent for the
Ozarks eastward into the lower OH/TN Valleys.  A morning
thunderstorm complex over TN has draped an outflow boundary
--western portion of it advancing northward-- across the lower TN/OH
Valleys.  A very moist/unstable airmass is located along and south
of the boundary across the MS Valley, with surface dewpoints in the
upper 60s to lower 70s contributing to a very unstable airmass
(2500-4000 J/kg MLCAPE).  A strong belt of southwesterly 500-mb flow
extending through the base of a mid-upper level low over the
north-central High Plains, will remain overhead from the southern
Great Plains east-northeast into the Mid South/OH Valley.

Ongoing severe storm cluster late this morning will likely expand in
convective coverage over eastern MO into western TN/KY through the
mid afternoon.  Supercells potentially capable of tornadoes, a few
of which may be strong, and large to very large hail and significant
severe gusts are possible with this activity.  Have adjusted
(lowered) severe probabilities on the northern periphery of the risk
area given expected concentration of thunderstorms and associated
severe to favor the corridor in the vicinity of the boundary.
Eventual upscale growth is expected later today into tonight as this
activity moves east-southeast with an accompanying swath of wind
damage.

...Eastern OK to AR, Mid-South and central TX...
Thunderstorms should develop by mid-late afternoon near the front
and dryline, as a combination of lift along those boundaries and
strong surface heating combine with very rich low-level moisture to
erode the cap.  Once storms initiate, rapid evolution to supercells
is expected.  Forecast soundings in the OK/AR/MO border area show
very large CAPE and elongated hodographs.  Large to giant hail and
tornadoes will be the primary hazards early in the convective life
cycle.  Have extended the 10-percent significant tornado
probabilities into far southwest MO, northwest AR, and far eastern
OK.  There is some signal for upscale growth to occur this evening
across AR with an MCS moving east across the Mid South.  Have
adjusted severe-wind probabilities farther south to account for this
potential scenario.

Farther southwest, lower storm coverage is expected across the
TX/Arklatex.  However, steep lapse rates and 70s dewpoints will
contribute to extreme MLCAPE.  Although near-surface flow generally
will be 10 kt or less, limiting lowest-km hodographs/shear,
effective-shear magnitudes in the 40-55-kt range indicate supercells
will be possible.  These will be capable of very large/destructive
hail exceeding 3 inches in diameter.  Clusters or upscale mergers of
convection also may offer deep, precip-loaded, hail-cooled
downdrafts with locally severe gusts.  Cell mergers and interactions
with boundaries will factor into tornado potential on the storm
scale, since the environmental low-level shear appears on the
margins.

...Southern Appalachians/Cumberland Plateau into Carolinas...
Ongoing strong to severe thunderstorm cluster over the eastern TN
will likely continue to develop to the east-southeast during the
afternoon.  The airmass will continue to destabilize downstream
across the western Carolinas.  Scattered strong to severe gusts
(55-70 mph) will be capable of wind damage.  A few of the stronger
cells may also pose a large hail threat.  Additional storms are
possible east over the Piedmont and into portions of the coastal
plain this afternoon into the early evening.  An attendant severe
risk may accompany the stronger storms.  Later tonight, an MCS or
several smaller-scale bows are forecast to move east-southeast along
the instability gradient forecast to remain draped across the Mid
South.  Moist/unstable conditions will support a continued risk for
damaging gusts moving into northern AL/southern Middle TN into
northern GA late tonight.

...Northeastern CONUS...
Widely scattered to scattered thunderstorms may develop this
afternoon over parts of eastern NY and New England.  A diurnally
destabilizing airmass will become weakly unstable (500-1000 J/kg
MLCAPE) along/ahead of a prefrontal surface trough.  Ample
deep-layer shear attendant to a Northeast U.S. shortwave trough,
will act to organize updrafts.  A mix of multicell and modest
supercell characteristics are forecast before activity moves over
more-stable air and/or offshore, and weakens by early evening.
Isolated hail/damaging gusts are the primary expected hazards.

...Eastern SD to eastern IA and vicinity...
Widely scattered to scattered thunderstorms are possible from early
afternoon in western parts to evening closer to the Mississippi
River, with isolated damaging gusts, large hail and possibly a
tornado or two.  Activity should form in an area of deep-layer lift
(including low-level convergence/mass response) related to a
vorticity lobe in the southeastern part of the mid/upper-level
cyclone.  Associated cooling aloft will combine with residual
low-level moisture (dewpoints mid 40s to mid 50s F) to yield pockets
of around 500-1000 J/kg MLCAPE.  Backed low-level winds will aid
convergence and storm-relative low-level flow, and may contribute to
locally enlarged hodographs.

..Smith/Jewell.. 05/08/2024

$$