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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.



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