SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0734 AM CDT Mon Aug 01 2022
Valid 011300Z - 021200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH LATE
EVENING FOR THE OH VALLEY...AND FROM THIS EVENING INTO EARLY TONIGHT
ACROSS NORTH/NORTHEAST NE...
...SUMMARY...
Scattered severe thunderstorms, mainly capable of damaging gusts,
are possible today across parts of Ohio, Indiana and Kentucky.
Isolated strong to severe storms also are possible across the
broader Midwest vicinity as well as parts of Nebraska.
...OH Valley area later this afternoon through late evening...
A midlevel shortwave trough now from northern IL to Lake MI will
continue east-southeastward over the OH Valley and lower Great Lakes
by tonight, accompanied by a weak surface cold front. Some slightly
elevated convection has persisted overnight in the zone of ascent
and low-level warm advection immediately preceding the midlevel
trough and surface front. This convection may persist through at
least midday/early afternoon with an isolated strong-severe gusts
threat given the somewhat organized cold pool and weak-moderate
buoyancy with only small convective inhibition ahead of the storms
across IN. In the wake of this morning convection, strong surface
heating and warm/moist advection from the mid MS Valley eastward to
the OH Valley will contributed to destabilization, with MLCAPE
increasing into the 2000-3500 J/kg range with minimal convective
inhibition by mid-late afternoon.
Additional thunderstorm development is anticipated after 21z along
the surface wind shift. The individual storms will move toward the
southeast, though there will be a tendency for upstream development
toward the west through the evening. Forecast hodographs show
sufficient vertical shear for clusters and some supercell
structures, given effective bulk shear near 35 kt with the
moderate-strong buoyancy. Supercell longevity will tend to be
limited somewhat by forecast weaknesses in the midlevel flow by
evening. Damaging winds and marginally severe hail will be the main
threats, though an isolated tornado or two could occur with embedded
supercells based on sufficient low-level moisture (boundary-layer
dewpoints in the low 70s) and hodograph curvature (effective SRH
near 200 m2/s2).
...North/northeast NE late this afternoon into early tonight...
A surface cold front is in the process of stalling across east
central and central NE, and this boundary is expected to move some
to the north as a warm front this afternoon. Strong surface heating
and deep mixing could support thunderstorm development by this
evening across north central NE, where low-level ascent will be
strongest at the intersection of the warm front and a more
north-south lee trough. Steep low-midlevel lapse rates and
boundary-layer dewpoints in the 60s will support large MLCAPE near
3000 J/kg, and deep-layer vertical shear will be sufficient for
supercells. The steep lapse rates and large buoyancy with DCAPE in
excess of 1200 J/kg will favor occasional severe outflow gusts,
whereas any supercells will be capable of producing isolated large
hail from this evening into early tonight as storms spread generally
eastward.
...ND this afternoon into tonight...
The richer low-level moisture is confined to along and south of a
front across NE/southern IA, but residual boundary-layer dewpoints
of 55-60 F remain across ND this morning. Strong surface heating
beneath steep midlevel lapse rates will result in destabilization
during the day, but some convective inhibition is likely to remain
through the afternoon. There will be some chance for deep
convection to form on the north/northeast edge of the deepest mixing
near a weak surface lee cyclone in southwest ND by mid-late
afternoon. If storms do form, thermodynamic and wind profiles will
support high-based supercells capable of producing isolated
strong-severe outflow gusts and some hail. Otherwise, some elevated
convection may form tonight across northeast ND in a zone of 850-700
mb warm advection, though the magnitude of buoyancy and the threat
for large hail are unclear. Given the conditionality and/or
uncertainty in both scenarios, will not add any severe wind/hail
probabilities.
..Thompson/Kerr.. 08/01/2022
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