MIL-OSI USA: SPC Jul 9, 2021 0600 UTC Day 1 Convective Outlook

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Source: US National Oceanic and Atmospheric Administration

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Jul 9, 2021 0600 UTC Day 1 Convective Outlook
Click to see valid 1Z – 12Z Day 1 Convective Outlook
Updated: Fri Jul 9 05:07:14 UTC 2021 (Print Version |   |  )
Probabilistic to Categorical Outlook Conversion Table

 Forecast Discussion

SPC AC 090507

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1207 AM CDT Fri Jul 09 2021

Valid 091200Z – 101200Z

…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LOWER MISSOURI
VALLEY…

…SUMMARY…
Thunderstorms, some with potentially significant severe weather, are
expected this afternoon into tonight across parts of the lower
Missouri Valley westward into the parts of the north-central High
Plains.

…Lower Missouri Valley…
A cluster of strong thunderstorms may be ongoing this morning near
the nose of a LLJ over IA. Warm air advection is forecast to weaken
during the morning with thunderstorm outflow and differential
heating providing a focus for additional thunderstorm development
during the afternoon. As a mid-level speed max moves from SD to the
IA/MO border by late afternoon, initial storms will likely develop
on the cool side of a warm frontal zone draped over the region.
Surface-based storms will likely develop farther west over southern
IA/northern MO during the late afternoon/early evening within a very
unstable airmass (3000+ J/kg MLCAPE). A strongly veering and
strengthening flow with height will favor supercells with the
stronger and more discrete updrafts. Upscale growth into a cluster
of high-precipitation supercells and subsequently into a squall line
will favor swaths of severe gusts over the lower MO Valley during
the evening. Some of the stronger gusts may be hurricane force in
localized areas. As this activity moves east into less-buoyant air
over IL, a weakening and/or lessening in severe coverage is
expected. Storms may develop over southeast NE/northeast KS during
the evening as a LLJ intensifies over the central Great Plains.
Hail/wind will be the primary severe hazards with this activity
during the evening.

…Central Plains…
Upslope flow regime is expected to evolve north of stalled front
across the central plains. Models are consistent in showing a
corridor of mid 50s to near 60 F dewpoints beneath steep lapse rates
and contributing to moderate instability with up to 2000 J/kg MLCAPE
as the boundary layer destabilizes. A mid-level shortwave trough
initially over eastern ID will move into the north-central High
Plains by late afternoon and contribute to 50+ kt effective shear.
Supercells will be the preferred storm type before one or more
clusters evolves during the evening. Large to very large hail and
severe gusts will accompany the stronger storms.

…Southern New England to the Delmarva…
T.C. Elsa will continue to progress northeast moving beyond the
coast of southern New England by the early afternoon. A conditional
risk for a weak/brief tornado may exist near the immediate coast in
association with an environment characterized as weak buoyancy and
enlarging hodographs. During the afternoon, isolated to scattered
storms are likely to develop. A few of the stronger storms may
yield a localized wind-damage risk.

..Smith/Wendt.. 07/09/2021

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