SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Wed Sep 07 2022
Valid 072000Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE INTERIOR NORTHWEST AND NORTHERN ROCKIES/HIGH PLAINS...
...SUMMARY...
Scattered thunderstorms may yield some severe wind gusts, a few of
which could be significant, across parts of the interior Northwest
and northern Rockies/High Plains this afternoon and early evening.
...20Z Update...
No changes have been made to the Slight Risks across the interior
Northwest and northern Rockies/High Plains. Latest surface
observations show substantial warming/mixing of the boundary layer
has occurred from eastern OR into ID and MT. Instability is expected
to remain quite limited owing to the meager low-level moisture.
Still, high-based thunderstorms spreading quickly east-northeastward
across these areas should be capable of producing some severe
downdraft winds given the deeply mixed boundary layer.
The Marginal Risk across parts of south-central/southeast TX into
southwest LA has been expanded to include more of central LA and far
southwestern MS. See Mesoscale Discussion 1767 for more information
on the near-term threat for isolated hail/wind with thunderstorms
occurring across these areas.
..Gleason.. 09/07/2022
.PREV DISCUSSION... /ISSUED 1134 AM CDT Wed Sep 07 2022/
...Interior Northwest/northern Rockies...
A high-impact to extreme fire weather day is anticipated this
afternoon into the evening. Please see the latest Day 1 Fire Weather
Outlook for details on all hazards.
Upper ridge will break down over the region as a vigorous shortwave
trough over British Columbia amplifies and shifts east-southeastward
toward the Canadian Rockies. Mid-level height falls accompanying
this wave will overspread the interior Northwest as a belt of 50-kt
500-mb westerlies becomes centered from northeast Oregon/eastern
Washington across northern Montana into southern Saskatchewan.
Modest moisture along with record warmth will yield very deeply
mixed boundary layers, especially east of the Rockies in Montana and
across the Idaho Snake River Valley into southeast Oregon.
Dry thunderstorms will increase in coverage this afternoon as both
the boundary layer deepens and large-scale forcing for ascent
strengthens. While buoyancy will be quite meager with MLCAPE of 300
J/kg or less, the extreme lapse rate profiles to 500 mb will support
dry downbursts mixing to the surface from high-based/low-topped
convection. Latest convection-allowing guidance are consistent in
suggesting severe wind gusts will be prevalent within this
fast-moving, skeletal activity. The eastern extent of this threat
may include amalgamating convective outflows which could maintain
severe gusts into eastern Montana despite diminishing lightning
flashes this evening.
...Southeast/south-central Texas and southwest Louisiana...
A minor mid-level impulse evident in water vapor imagery over the
Ark-La-Tex will gradually move south-southwest into south Texas by
this evening. A pocket of relatively cooler mid-level temperatures
and steeper lapse rates attendant to this impulse should support a
plume of moderate to large MLCAPE of 1500-3000 J/kg. While
deep-layer shear will be modest and generally offset west of the
greater instability/buoyancy, isolated marginally severe hail and
strong to localized severe wind gusts will be possible as scattered
thunderstorms develop this afternoon.
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