LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Thu Aug 24 2023
Valid 241200Z - 251200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE GREAT LAKES REGION...
...SUMMARY...
Scattered severe thunderstorms producing damaging winds, large hail,
and perhaps a tornado should occur from mainly late this afternoon
through tonight across parts of the southern Great Lakes region into
the central Appalachians. Some of these winds could be significant
(75+ mph).
...Synopsis...
A large upper-level anticyclone will remain dominant today over much
of the southern/central Plains and lower/mid MS Valley. A weak
mid-level perturbation is forecast to round the apex of the upper
ridge over the central CONUS and move east-southeastward across
parts of the Upper Midwest and Great Lakes through the day. A
separate and more amplified shortwave trough will dig
east-southeastward along the U.S./Canadian border through tonight.
At the surface, a convectively reinforced front should extend across
parts of the southern Great Lakes region into the central
Appalachians, with a very rich/moist low-level airmass present to
its southwest.
...Great Lakes/Ohio Valley into the Mid-Atlantic...
Mainly elevated thunderstorms will probably be ongoing at the start
of the period this morning across parts of Lower MI into OH. This
convection will be tied to modest low-level warm/moist advection and
related large-scale ascent. While an isolated threat for hail/gusty
winds may exist with this activity through the morning hours, it is
forecast to generally weaken through the day as the low-level warm
advection slowly weakens and capping becomes reestablished over the
warm sector. In the wake of these morning thunderstorms, most
guidance shows strong to locally extreme instability (MLCAPE
3000-5000+ J/kg) developing along/south of a weak front from
southern WI/northern IL into Lower MI and much of the OH Valley.
This very favorable thermodynamic environment will be aided by the
presence of mid 70s to perhaps low 80s surface dewpoints, steep
mid-level lapse rates emanating from an EML over the Plains, and
robust daytime heating.
Warm mid-level temperatures (700 mb around 10-14C) across the warm
sector will likely inhibit thunderstorm development for much of the
day. Still, modest ascent associated with a weak mid-level impulse
may be enough to breach the cap by late afternoon (around 21-22Z or
later) across parts of Lower MI and vicinity. Most 00Z
convection-allowing model guidance is in general agreement with this
plausible scenario. If thunderstorms can initiate, they would likely
become severe and pose an initial threat for both large hail and
damaging winds across Lower MI given around 30-40 kt of deep-layer
shear and very strong instability. Upscale growth into an intense
bowing cluster appears likely along/south of a warm front, and the
risk for severe/damaging winds would likely increase once an MCS
develops. Given the potential for extreme instability, some threat
for isolated 75+ mph winds may also exist across parts of southern
Lower MI into northern OH when the MCS matures. With ample
instability and some low-level shear present, a tornado or two also
appears possible with the cluster. The severe wind threat should
continue through the evening into parts of the OH Valley and central
Appalachians before convection eventually weakens.
...Northern/Central Plains...
Ascent associated with a shortwave trough along the international
border, along with modest low-level convergence along a weak front,
should encourage convection to develop late this afternoon across
parts of ND. Weak to moderate instability and strong deep-layer
shear should support organized updrafts, with multicells and perhaps
a supercell or two possible. Isolated hail and severe wind gusts
should be the main threat with these thunderstorms as they move
eastward into parts of northwestern MN through this evening.
Confidence in greater coverage of severe convection across ND
remains too low to include higher severe hail/wind probabilities at
this time.
A somewhat separate area of convection should form this afternoon
from the Black Hills vicinity of SD into parts of western/northern
NE along/near a weak front. While deep-layer shear should be weaker
with southward extent across this area, it may still be sufficient
for loosely organized multicells, and perhaps a marginal supercell,
posing an isolated hail/wind threat through the early evening.
..Gleason/Weinman.. 08/24/2023
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