SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0723 AM CDT Sat Sep 07 2024
Valid 071300Z - 081200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Organized severe thunderstorms are not forecast today, though a few
strong gusts could accompany the most robust convection.
...Synopsis/Discussion...
The mid/upper-level pattern will feature strong, progressive
troughing over the Great Lakes and vicinity, and ridging from the
Four Corners north-northwestward to the Canadian Rockies. The major
synoptic trough over the Great Lakes is anchored by a cyclone
initially centered over Lake Huron. The low should move erratically
eastward to northeastward across ON to southwestern QC by the end of
the period. As this occurs, strengthening cyclonic flow and height
falls will overspread the Northeast, while cyclonic flow remains
behind the low across the Great Lakes, Ohio Valley and central
Appalachians.
An associated surface cold front -- analyzed at 11Z from central NY
across northwestern VA, easternmost TN, northern MS, north TX, and
central NM -- should move eastward across NY to central/eastern New
England by 00Z, extending southward offshore from most of the Mid-
Atlantic Coast, and merging with a northeastward-moving surface
cyclone now located offshore from SC. A separate surface cyclone
(with mid/upper-level extension) now south of Nova Scotia will move
northward, with peripheral isallobaric effects limiting convergence
along the cold front for much of today. Still, a band of showers
and embedded thunderstorms may organize enough to produce strong
gusts for a couple hours this afternoon from the Hudson Valley
region into NJ, the NYC area and western Long Island. At this time,
weak lapse rates and low-level shear are still forecast, and
organized severe-gust potential appears too low and conditional for
an outlook.
In the West, a weak binary cyclone (with two apparent centers in
moisture-channel imagery) covers the coastal areas of OR and
northwestern CA, as well as adjoining Pacific waters. This feature
is devolving into an open-wave trough, and will continue to weaken
through the period as it slowly moves inland. Associated large-
scale ascent, overlapping diurnal/diabatic destabilization of higher
terrain, may contribute to thunder potential (including dry thunder
for fire-weather purposes) over portions of the interior Northwest.
Northwest flow aloft, east of the ridge, will overlie a well-
developed surface lee trough over eastern parts of CO/WY. Strong
veering with height is expected, but with weak low/middle-level
flow. Though ideally rich moisture will be well-removed from this
region, over the Gulf, enough residual/post-frontal moisture should
remain to support isolated to widely scattered, high-based
thunderstorms this afternoon over eastern WY/CO, and perhaps this
evening over southwestern NE near a strengthening LLJ. Forecast
soundings show a deep, well-mixed subcloud layer that may support
strong gusts from low-precip cells. However, with weak moisture and
strong mixing leading to limited buoyancy (MLCAPE less than 800
J/kg), severe potential appears isolated at best, with unconditional
areal probabilities remaining below 5% this outlook cycle.
..Edwards/Kerr.. 09/07/2024
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