MD 0434 CONCERNING SEVERE POTENTIAL…WATCH UNLIKELY FOR PORTIONS OF EXTREME NORTHERN CALIFORNIA INTO CENTRAL OREGON
Mesoscale Discussion 0434
NWS Storm Prediction Center Norman OK
0325 PM CDT Sat Apr 13 2024
Areas affected…portions of extreme northern California into
central Oregon
Concerning…Severe potential…Watch unlikely
Valid 132025Z – 132300Z
Probability of Watch Issuance…20 percent
SUMMARY…Thunderstorms are expected to gradually increase in both
coverage and intensity through the afternoon. Hail and strong wind
gusts will be the main threats, though a brief tornado cannot be
completely ruled out. The severe threat should remain isolated and a
WW issuance is not expected.
DISCUSSION…Despite limited surface heating, increasing deep-layer
ascent, driven by the approach of a mid-level jet streak, is
contributing to a gradual increase in thunderstorm coverage across
parts of southern OR/northern CA. Temperatures are warming into the
mid 50s F, with dewpoints near 40 F in place, supporting around 1000
J/kg SBCAPE, but under 500 J/kg of MLCAPE. Given widespread clouds
in place, the boundary layer remains moist, but also cool, with the
aforementioned CAPE constrained to short and narrow profiles (per
19Z RAP forecast soundings) despite steep tropospheric lapse rates
in place. Shear profiles favor some severe potential, with forecast
soundings showing curved and elongated hodographs, with up to 50 kts
of effective bulk shear in place. As such, multicells and supercells
should be the primary mode of convection, with gusty winds and hail
the main threats.
A brief tornado also cannot be ruled out, especially to the
immediate lee of the southern Cascades, where 20Z mesoanalysis
depicts a local maxima in low-level vertical vorticity coinciding
with over 100 J/kg of 0-3 km CAPE. Any supercell that manages to
develop and traverse this local corridor may stretch the vorticity
and spawn a brief landspout/supercell hybrid tornado, though this
scenario remains highly conditional. Furthermore, the overall severe
threat is expected to remain isolated and a WW issuance is not
anticipated.
..Squitieri/Leitman.. 04/13/2024
…Please see www.spc.noaa.gov for graphic product…
ATTN…WFO…BOI…PDT…MFR…PQR…
LAT…LON 41392088 41442137 41572172 41962219 42292234 43162272
43782296 44272288 44682207 44752089 44592016 44331969
44191956 43271975 42671993 42022009 41532055 41392088
