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000
ACUS01 KWNS 131939
SWODY1
SPC AC 131938

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0238 PM CDT Sat Apr 13 2024

Valid 132000Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF OREGON AND ADJACENT NORTHEASTERN CALIFORNIA...

...SUMMARY...
Thunderstorms with isolated severe hail and strong wind gusts remain
possible this afternoon and early evening across parts of Oregon.

...Discussion...
Current forecast reasoning, and the MRGL risk area across parts of
the Oregon vicinity, appear to remain valid at this time, and thus
no changes are being implemented in this forecast update.  The most
appreciable change has been to remove the small thunder areas from
the central U.S., as any lightning should remain sparse at best, and
to add a small thunder area over northern Maine where sporadic
lightning is ongoing, and may continue for a couple of hours.

..Goss.. 04/13/2024

.PREV DISCUSSION... /ISSUED 1106 AM CDT Sat Apr 13 2024/

...Far Northeast California into Oregon...

An upper low off the northern/central CA coast will continue to
slowly migrate east through tonight. Deep-layer south/southeasterly
flow on the northeast periphery of this cyclone will advect a plume
of midlevel moisture and steep lapse rates over the area. Heating
through broken cloud cover will allow temperatures to warm into the
60s F by mid-afternoon and MLCAPE around 500-1000 J/kg is forecast.
Moderate deep shear, with 0-6km effective shear magnitudes near 35
kt will support organized clusters, or perhaps a supercell,
developing in the 20-22z time frame. Isolated large hail around 1 to
1.5 inches in diameter will be possible with the strongest cells
given steep lapse rates and favorable shear in the 4-6 km layer. In
addition to hail, a deeply-mixed sub-cloud layer will result in
inverted-v thermodynamic profiles, and isolated strong gusts may
occur.

While low-level moisture will remain a limiting factor for tornado
potential, a brief spin-up can not be ruled out. Enlarged low-level
hodographs are evident in forecast soundings and effective SRH will
increase to 100-200 m2/s2 by 22-00z amid 0-3km MLCAPE near 100 J/kg.
Have added a 2 percent tornado probability to reflect this low, but
non-zero potential.

Uncertainty in storm coverage will preclude an upgrade to Slight
risk at this time.

...Great Lakes...

A low-amplitude shortwave trough migrating through large-scale
northwesterly flow regime will foster elevated thunderstorm
development during the evening/overnight. Weak instability (MUCAPE
generally less than 500 J/kg) will limit storm intensity, though
steep midlevel lapse rates and cool temperatures aloft may be
sufficient for a few instances of small hail.

$$