LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1257 AM CDT Sun Jun 25 2023
Valid 251200Z - 261200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO TONIGHT ACROSS PARTS OF CENTRAL AND EASTERN INDIANA INTO
WESTERN OHIO...MUCH OF CENTRAL KENTUCKY...MIDDLE AND WESTERN
TENNESSEE...MUCH OF CENTRAL AND SOUTHERN ARKANSAS...NORTHERN
MISSISSIPPI AND ADJACENT PORTIONS OF NORTHWESTERN ALABAMA AND
NORTHEASTERN LOUISIANA...
...SUMMARY...
Strong to severe thunderstorms may become numerous late this
afternoon into tonight across parts of the southeastern Great Plains
and lower Mississippi Valley, into the lower Ohio Valley and
adjacent portions of the Great Lakes. This may include supercells
with a risk for tornadoes across parts of central and eastern
Indiana into western Ohio and central Kentucky.
...Synopsis...
Split flow across the eastern Pacific into western North America may
amplify a bit further today through tonight. While ridging within
the northern branch builds across the British Columbia vicinity, a
significant perturbation within larger-scale southern branch
troughing is forecast to progress inland across the central/southern
California coast. As this occurs, short wave ridging, extending to
the north of a prominent subtropical high centered over southwest
Texas, appears likely to build across the Rockies into the Great
Plains, while a significant downstream mid-level low digs southeast
of the Upper Midwest through the Great Lakes region. This will be
preceded by increasingly sheared mid-level troughing overspreading
the Atlantic Seaboard, including the remnants of a cyclonic
circulation turning northeastward across the northern Mid Atlantic
toward southern New England.
The prominent interior U.S mid-level low will be accompanied by a
broadening, occluded surface cyclone, trailed by a cold front
advancing southeast of the lower Missouri through lower Ohio
Valleys, with a segment farther southwest stalling and weakening
across the central into southern Great Plains. A corridor of
seasonably high boundary-layer moisture content (with lower/mid 70s
F dew points) along and southeast of this front likely will support
large CAPE (on the order of 2000-4000 J/kg), beneath a plume of
steep lapse rates associated with elevated mixed-layer air emanating
from the southern Great Plains. This plume will gradually become
suppressed southward and southwestward across the lower Ohio Valley
and Mid South, beneath flow transitioning from west-northwesterly to
northwesterly, to the southwest of the digging low. Closer to the
center of the low, it appears that a belt of 50-70 kt flow around
500 mb will nose across the lower Missouri through lower Ohio
Valleys.
...Southern Great Plains into Ohio Valley/Great Lakes...
The coverage and intensity of the severe weather threat for today
may be considerably impacted by sub-synoptic/mesoscale developments
which has been a source of sizable model spread.
However, it is appearing increasingly probable that forcing for
ascent downstream of the digging mid-level low and associated
troughing may be supporting an area of vigorous convection, mainly
rooted in a lower/mid-tropospheric warm advection regime, across the
western Kentucky/Tennessee vicinity at the outset of the period.
Convection allowing model output suggests varying subsequent
evolution. However, aided by rapid boundary-layer destabilization
with insolation to the south and southwest of this activity, it is
possible that associated outflow may gradually support increasing
new boundary-layer based thunderstorm development. There appears
sufficient shear to support an upscale growing cluster with
potential to produce strong wind gusts, with a tendency to propagate
south-southeastward then southward along the eastern periphery of
the better low-level moisture and instability, in the wake of the
Atlantic Seaboard mid-level trough.
Stabilization in the wake of this initial convective cluster results
in more uncertain convective potential across parts of the Tennessee
into lower Ohio Valleys. However, a narrow corridor of moderate to
strong pre-frontal destabilization across Indiana into southern
Michigan may provide another focus for strong thunderstorm
initiation by early this afternoon. Beneath increasingly difluent
and strengthening west-northwesterly mid/upper flow on the nose of
the digging jet, it appears that the environment could support
scattered discrete supercells, at least initially. Preceded by an
remnant effective warm frontal zone, associated with outflow from
early convection, it appears that this activity may be accompanied
by increasing tornadic potential potential, in addition to large
hail, while spreading across Indiana into western Ohio, with
additional storms perhaps developing southward into central Kentucky
through this evening.
Late this afternoon into this evening, if not a bit earlier, there
are indications that one or two perturbations (likely of subtropical
eastern Pacific origin) may contribute to thunderstorm initiation
along and ahead of the cold front across parts of northern Arkansas
into central Oklahoma. Beneath at least modest northwesterly
mid-level flow, in the presence of strong instability, the
environment appears conducive to consolidating and organizing
clusters, with southeastward propagation focused along the
northeastern periphery of the subtropical ridge.
...Northern Intermountain Region/Rockies...
A corridor of weak destabilization, along the track of a
northeastward migrating short wave perturbation may provide a focus
for vigorous thunderstorm development this afternoon and evening.
Deep-layer mean wind fields likely will be generally weak, but
relatively steep low-level lapse rates may contribute to potential
for small hail and perhaps brief, occasional gusts near severe
limits.
..Kerr/Lyons.. 06/25/2023
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