SPC AC 081932
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0232 PM CDT Wed May 08 2024
Valid 082000Z - 091200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM THE
MISSOURI OZARKS EASTWARD INTO SOUTH-CENTRAL KENTUCKY AND MIDDLE
TENNESSEE...
...SUMMARY...
Severe thunderstorms are 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.
...20z Update...
The ongoing forecast remains on track and no changes have been made
to the outlook with the 20z update. A broad area of severe
thunderstorm and tornado potential remains in place from parts of
the southern Plains to the OH/TN Valleys and the Carolinas. For
details regarding short term severe concerns see valid Watches
203-208 and Mesoscale Discussions 701, 702, and 704.
..Leitman.. 05/08/2024
.PREV DISCUSSION... /ISSUED 1145 AM CDT Wed May 08 2024/
...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.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
SPC AC 081735
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1235 PM CDT Wed May 08 2024
Valid 091200Z - 101200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EAST TEXAS
TO CENTRAL/SOUTHERN GEORGIA AND FAR SOUTHERN SOUTH CAROLINA...
...SUMMARY...
Very large hail with multiple supercells appears probable across
parts of central Texas into the ArkLaTex vicinity Thursday afternoon
and evening. A broader corridor of severe hail and damaging wind
potential will extend from east Texas into the lower Mississippi
Valley and Southeast.
...East TX to South Carolina...
Most guidance is in agreement that an MCS will be ongoing Thursday
morning in the vicinity of northeast AL into northern GA. The
expectation is that this MCS will develop southeast toward southeast
GA/far southern SC through the day. Maintenance of this system
should be supported by a shortwave impulse migrating across the
region with 40 kt of 850-700 mb southwesterly flow overspreading a
very moist airmass. Downstream destabilization ahead of the MCS
across central/southern GA and perhaps portions of eastern AL is
forecast, with MLCAPE to near 2500 J/kg expected. Both GFS and NAM
forecast soundings indicate steep low-level lapse rates develop amid
strong heating into the 80s F. Furthermore, midlevel lapse rates
around 7 C/km and elongated hodographs are present. Severe/damaging
wind potential will be the main concern given expected bowing
convective mode. However, should any more discrete convection
develop, a risk for large hail and a tornadoes also will be present
given an environment capable of supporting supercells.
Further east, a cluster of supercells is expected to develop across
north TX southward toward the Hill Country in the vicinity of the
intersecting dryline and cold front. Strong to extreme instability
(3500+ MLCAPE) is anticipated amid a plume of very steep midlevel
lapse rates. This will support intense updraft development amid 40+
kt effective shear magnitudes and elongated/straight hodographs.
Very large hail (2-3 inch diameter) will be possible with these
storms. Steep low-level lapse rates, large CAPE and water-loaded
downdrafts also will support damaging wind potential.
With time, the damaging wind risk will increase as clustering
occurs. Most guidance generates an eastward propagating MCS from
the east TX cluster, moving across northern LA into MS/AL during the
evening/nighttime hours. This activity is expected to move along the
gradient of strong to extreme instability across this region ahead
of the southeastward progressing cold front. Some potential will
exist for significant gusts (to near 75 mph).
...North Carolina to the Mid-Atlantic vicinity...
Some showers and thunderstorms may be ongoing across the Chesapeake
Bay vicinity southward to far eastern NC. Nevertheless, weak
destabilization/airmass recovery is forecast by afternoon. Isolated
to scattered thunderstorms are expected to develop from the Upper
Ohio Valley eastward across parts of VA/NC ahead of the
south/southeastward-advancing cold front. Locally strong gusts and
small hail will be possible with this activity.
..Leitman.. 05/08/2024
WUUS02 PTSDY2
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
SPC AC 080730
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Wed May 08 2024
Valid 101200Z - 111200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHEAST...
...SUMMARY...
Isolated strong to severe thunderstorms may occur Friday across
parts of the Southeast.
...Southeast...
An upper trough should dig southeastward across the TN Valley and
Southeast on Friday. A belt of strong (50-65 kt) westerly mid-level
flow should be present over much of the Southeast through the
period. A cold front is forecast to continue moving south-
southeastward across the Deep South and Carolinas through the day.
There is still considerable uncertainty regarding the placement and
intensity of a possible MCS/small bowing cluster at the start of the
period Friday morning across parts of AL/GA. This cluster would
impact the potential for moderate instability to develop ahead of
the front through the day, as indicated by the 00 NAM. Other
guidance shows less instability and a farther southward placement of
convective redevelopment Friday afternoon, mainly over parts of
north FL/southern GA.
Given these substantial uncertainties, have opted to include a
fairly broad Marginal Risk from southern MS/AL into north FL and
much of GA/SC. This should account for thunderstorms that may form
along the front in the afternoon and subsequently spread
south-southeastward, and for any lingering threat with the possible
morning cluster. Damaging winds appear to be the main threat with
primarily linear convection forecast. But, some hail could also
occur with any semi-discrete thunderstorms given strong-deep-layer
shear expected. Any severe threat should diminish through Friday
evening with southward extent into north FL, and as convection moves
offshore the GA/SC Coast.
..Gleason.. 05/08/2024
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z
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