Subj : DAY2SVR: Nws Storm Predic
To   : All
From : Mike Powell
Date : Tue Jul 18 2023 17:11:00

ACUS02 KWNS 181732
SWODY2
SPC AC 181730

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 PM CDT Tue Jul 18 2023

Valid 191200Z - 201200Z

....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS AND UPPER MIDWEST...

....SUMMARY...
Scattered severe thunderstorms capable of producing large to very
large hail and damaging winds appear possible Wednesday from the
central Plains into the Upper Midwest. Isolated strong to severe
thunderstorms may also occur from the Ozarks into the lower Ohio and
Tennessee Valleys, along with the Carolinas and Mid-Atlantic.

....Synopsis...
Upper ridging will remain confined to parts of the Northwest,
Southwest, and southern Plains on Wednesday. A mid/upper-level
trough/low is forecast to move from central Canada and the northern
Plains across the Upper Midwest and Great Lakes through the period.
A belt of enhanced (35-50+ kt) mid-level northwesterly flow should
persist across these regions, and into parts of the mid MS and OH
Valleys. A separate upper trough should progress over the eastern
U.S. through the day. Multiple low-amplitude, convectively enhanced
mid-level perturbations should advance generally east-southeastward
within the west-northwesterly flow regime that will remain over much
of the central/eastern CONUS.

....Northern/Central Plains into the Upper Midwest and Ozarks...
As the upper trough/low moves east-southeastward, isolated to
scattered thunderstorms will likely develop along and east/southeast
of a cold front. Diurnal heating of a moist low-level airmass will
foster the development of moderate to locally strong instability
from parts of MN into southeastern SD, NE, and northwestern IA.
Deep-layer shear of 40-50 kt will easily support supercells, with
associated threat for both large hail and severe wind gusts.
Isolated very large hail appears possible across parts of
central/eastern NE and eastern MN/western WI with this activity.
Based on consensus of latest guidance, have introduced a fairly
broad Slight Risk to account for this supercell potential. The
eastern extent of the severe risk should be modulated by the narrow
zone of greater low-level moisture return.

The southern extent of supercell potential into KS is rather
uncertain, as large-scale ascent becomes increasingly modest into
the central Plains. Still, there appears to be some risk for intense
convection to develop/spread southeastward from NE into at least
northern KS through Wednesday evening. Some potential also exists
for a cluster of thunderstorms producing severe/damaging winds to
spread from eastern CO into KS and perhaps eventually parts of MO
Wednesday evening/night.

....Carolinas into the Mid-Atlantic...
At least isolated thunderstorms may be ongoing Wednesday morning
across parts of the Carolinas and Mid-Atlantic. Cloud cover and poor
lapse rates may tend to limit the development of substantial
instability until late Wednesday afternoon. Still, at least moderate
instability should eventually develop and support robust updrafts.
Better chances for strong to severe convection appear to exist
along/east of a weak surface trough across eastern NC/VA/MD and
vicinity. Occasional damaging winds should be the main threat with
this activity, as deep-layer shear appears adequate for mainly
multicells and small clusters. But, some hail may also occur with
the strongest updrafts. Based on latest guidance, have expanded the
Marginal Risk across this region to include more of eastern NC/SC
and the Delmarva.

....Kentucky/Tennessee and Vicinity...
Isolated to scattered thunderstorms may be present at the start of
the period across this region. This activity may pose at least an
isolated threat for severe hail and damaging winds, as deep-layer
shear appears strong enough to support supercells. Most guidance
shows a weakening trend to this morning convection. The potential
for additional robust convective development in the wake of the
morning thunderstorms is highly uncertain. But, some chance exists
for renewed convection Wednesday afternoon/night along and south of
a weak front. The environment will conditionally support a threat
for all severe hazards, as enhanced northwesterly flow aloft appears
sufficient for supercells. Have opted to include a fairly broad
Marginal Risk across KY/TN and vicinity to account for potentially
multiple rounds of strong to severe thunderstorms through the
period.

...Gleason.. 07/18/2023

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