SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0800 AM CDT Wed Jul 10 2024
Valid 101300Z - 111200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS
OF WESTERN AND CENTRAL NEW YORK...
...SUMMARY...
Tornadoes and damaging winds are possible over parts of
western/central New York.
...Synopsis...
In mid/upper levels, the pattern will continue to be characterized
by mean troughing over the Great Lakes and ridging in the west. An
anchoring anticyclone -- centered near LAS -- should remain
quasistationary over the Great Basin, lower Colorado River Valley,
Southeastern CA and much of AZ. In the Great Lakes regime, a
leading/strong shortwave trough is apparent in moisture-channel
imagery from Lake Michigan to the Mid-South, containing an
intermittently closed 700-500-mb circulation on the north end, over
Lake Michigan.
Associated cyclonic flow includes the increasingly diffuse midlevel
remains of Beryl, with a warm axis aloft still apparent in 700-
500-mb charts east/southeast of the shortwave perturbation's thermal
trough. This complex feature is forecast to eject northeastward by
00Z to the neck of ON, Lake Huron, southeastern Lower MI, and the
MIE area. Overnight, the trough should lose amplitude while
reaching southwestern QC and the Lower Great Lakes. Upstream, a
fairly prominent, compact, shortwave trough and PV anomaly were
located over MN and eastern SD. This feature should pivot
southeastward to IA by 00Z, then parts of northwestern IL and
northeastern MO by 12Z tomorrow.
At the surface, 11Z analysis showed a low over northwestern OH, with
cold front across eastern parts of KY/TN, to southern AL, becoming
quasistationary near the LA coastline. A slow-moving warm front was
drawn from the low across the western NY/PA line to near ALB, then
over central New England. By 00Z, the cold front should extend from
an occlusion triple point over (or just south of) Lake Ontario,
across west-central NY, central parts of PA/VA/NC, to southern GA,
becoming quasistationary and frontolytic over southern parts of
AL/MS/LA. The warm front should move slowly northward over western,
central and northern NY today, decelerating/stalling across the
higher terrain from the Adirondacks eastward across VT/NH/western
ME. The cold front also should decelerate as it shifts eastward
over the Atlantic Seaboard, extending by 12Z from a triple point
over northern parts of VT or NH across western New England, the
Mid-Atlantic Coast, and near-coastal NC, to a deepening low offshore
from MYR. A prefrontal trough should shift eastward today over
parts of NY/PA, while a post-frontal trough (with some mass-response
reinforcement by the northwest-flow shortwave trough) should move
southward over parts of IA, NE and northern IL.
...Northeastern CONUS...
Scattered thunderstorms are expected to develop along/ahead of the
cold front , especially near the prefrontal trough (with that
activity ultimately evolving upscale into a line. All severe
hazards will be possible from relatively discrete convection
(including potential for several supercells) from the early-stage,
pre-linear regime, and perhaps even in the warm sector to its east.
Tornado potential should be relatively maximized near the warm
front, where backed near-surface winds will contribute to enlarged
low-level hodographs and enhanced storm-relative flow in the
boundary layer. The corridor of greatest tornado probabilities is
narrow, and may need to be shifted around today as mesoscale trends
suggest (especially with regard to warm-frontal position). However,
at least marginally favorable low-level shear for embedded
supercellular or QLCS mesovortex tornado potential is possible as
far south as the western/upper Chesapeake Bay region.
Ample low-level moisture is in place, and will continue over the
area, with surface dewpoints commonly in the upper 60s to low 70s
along and south of the warm front. This will contribute to low LCL
and, in concert with diurnal heating that satellite imagery suggests
should be common, will yield peak/preconvective MLCAPE in the
1500-2000 J/kg range ahead of the main convective band. Activity
should weaken in and near eastern parts of the "slight" to
"marginal" probabilities this evening as it encounters a more-stable
boundary layer.
...NM and west TX...
Isolated to scattered thunderstorms should develop this afternoon --
preferentially over higher elevations as diurnal heating removes
MLCINH. Activity then should move generally southward over deeper,
straggly heated/mixed, yet favorably moist boundary layers to
sustain convective potential, and also, to support isolated severe
gusts from the most vigorous downdrafts. Forecast soundings show
mixed/subcloud layers extending well above 700 mb, yet still beneath
300-800 J/kg MLCAPE. Although strong veering with height is
expected over much of this area, very weak low/middle-level wind
speeds and lack of appreciable vertical shear will limit convective
organization and coverage of the severe threat overall.
...IA and vicinity...
Widely scattered to scattered thunderstorms are expected to develop
this afternoon, with isolated severe hail and a few damaging to
severe gusts possible. Activity should form in a weak-MLCINH
airmass near the surface trough, destabilizing through the
lower/middle troposphere via a combination of diurnal surface
heating, low-level warm/theta-e advection, and DCVA-forced cooling
aloft that precedes the shortwave trough. These factors, with
surface dewpoints generally remaining in the upper 50s to mid 60s F
through the boundary-layer heating/mixing cycle, should support a
meso-alpha scale patch of 1000-2000 J/kg MLCAPE, atop a well-mixed
subcloud layer. With weak low/middle-level winds and shear, the
main mode should be multicellular, with isolated pulse severe,
before evening boundary-layer cooling reduces instability and
convective coverage/intensity.
..Edwards/Bentley.. 07/10/2024
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