SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0302 PM CDT Sat May 13 2023
Valid 132000Z - 141200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM IOWA INTO
CENTRAL ILLINOIS...
...SUMMARY...
Thunderstorms associated with a few tornadoes, wind damage and large
hail remain possible this afternoon and evening from Iowa into
central Illinois. Isolated strong to severe storms are also possible
across southern Oklahoma and East Texas as well as the eastern
Virginia/North Carolina border vicinity.
...IA into the mid MS Valley...
The Slight Risk across IA has been expanded slightly to the west and
trimmed from the northeast, based on the location of ongoing
convection and an outflow-reinforced surface boundary that is
expected to move little during the rest of the afternoon. The
environment remains only marginally favorable for supercells, but
storms near the boundary may continue to pose a threat for at least
brief tornadoes, in addition to isolated hail and gusty winds.
Farther south, a storm cluster is ongoing from near St. Louis into
parts of central IL. This cluster may continue to pose a threat for
isolated severe hail/wind and possibly a brief tornado as it moves
eastward this afternoon, and the Slight Risk has been expanded
slightly southeastward. Renewed development along the remnant
outflow cannot be ruled out back into east-central/northeast MO,
which could also pose at least an isolated severe threat later this
afternoon into the evening.
...Central/southern OK...ArkLaTex...East TX...
2% tornado probabilities have been confined to parts of
southwest/central OK and north TX, in closer proximity to ambient
surface vorticity near an MCV and associated weak surface low.
Otherwise, no changes have been made to the Marginal Risk. See the
previous discussion below.
...VA Tidewater into northern NC...
No changes have been made to this area, see the previous discussion
below for more information.
..Dean.. 05/13/2023
.PREV DISCUSSION... /ISSUED 1115 AM CDT Sat May 13 2023/
...IA into the Mid MS Valley...
Recent surface analysis places a low about 30 miles northwest of OFK
in far northeast NE. A cold front extends southward from this low
through central KS and then back southwestward from north-central
trough southwest OK. Surface pattern east of the low is a bit more
complex, with a warm front extending from the low southeastward
across southwest IA and into north-central MO. This warm front
intersects a residual stationary boundary near DSM, with this
stationary boundary continuing eastward across the OH Valley.
The surface low is forecast to make modest eastward progress
throughout the day, with the warm front continuing to move northward
as well. However, the presence of the stationary boundary may
impeded the northern progression of the warm front somewhat.
Expectation is a corridor or mid to upper 60s dewpoints to extend
from east-central MO/southern IL northwestward through central IA.
This corridor will likely be south of the warm front, but east of
dryline-like boundary that is expected to mix eastward with time.
Moderate buoyancy is anticipated within this corridor as well,
contributing to likely thunderstorm development as the boundary
moves eastward.
Southeasterly surface winds will beneath modest westerlies will
contribute to moderate deep-layer vertical shear and the potential
for more organized storm structures capable of all severe hazards
across IA. Strong low-level buoyancy (i.e. 0-3 km MLCAPE greater
than 150 J/kg) and low-level vorticity throughout the corridor of
southeasterly winds could increase what would otherwise be a low
probability tornado risk given anticipated shear magnitudes. Farther
south, surface winds will be weaker with a more outflow-dominant
storm structure anticipated. Here, some clustering is also possible,
with storms then forward-propagating into west-central IL.
...Central/Southern OK...Arklatex...East TX...
Widespread thunderstorm development is anticipated this afternoon
from central OK eastward into the Arklatex and East TX amid the
tropical air mass in place. Vertical shear is weak, limiting storm
organization and the overall severe potential. Even so, a few
water-loaded downbursts and maybe even a tornado or two remain
possible. This low-probability tornado threat appears maximized
across southern OK, where greater low-level vorticity is expected.
...VA Tidewater...Northeast NC...
An upper trough is rotating quickly southeastward into New England,
with a cold front sagging southward across WV/VA. This boundary
will move into a relatively moist airmass over southern VA this
afternoon, resulting in thunderstorm development. Strengthening
westerly flow aloft and relatively steep boundary-layer lapse rates
may result in a few strong wind gusts in the more intense cells.
Activity will move into northern NC this evening before weakening.
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