SPC Mar 26, 2025 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1246 AM CDT Wed Mar 26 2025

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE PACIFIC NORTHWEST...

...SUMMARY...
Severe thunderstorms are forecast across parts of the Pacific
Northwest this afternoon and evening. Supercells are expected west
of the Cascades across Oregon into Washington. These may produce
large hail, perhaps a brief tornado, and locally strong gusts.

...Pacific Northwest...

Seasonally strong upper low off the Pacific Northwest Coast will
shift east today as a 100+kt 500mb speed max translates toward the
OR Coast by late afternoon. Strong 12hr height falls will spread
across this region and the associated synoptic cold front should arc
from off the WA Coast-south along the OR Coast by 27/00z. 

Upper ridging has permitted boundary-layer moisture to increase/hold
across both the interior Northwest, and west of the Cascades where
surface dew points are currently in the mid 50s. While PW values are
not forecast to be particularly high across this region, large-scale
forcing will contribute to moistening profiles and PW values may
approach 1 inch prior to convective initiation. Of particular
concern are the cold mid-level temperatures, and the steep lapse
rate plume that will overspread this region. Forecast soundings
suggest convective temperatures should be breached by 21-22z west of
the Cascades, and surface-based CAPE should approach 1000 J/kg
within a favorably sheared environment for organized, rotating
updrafts.

Latest thinking is isolated-scattered robust convection will develop
by 21-22z across western OR, immediately ahead of the strong
forcing. This activity should grow upscale and lift north-northeast
ahead of the approaching speed max. Profiles favor supercell
development and latest HREF guidance supports this scenario. Hail
should be common with this activity and the strongest updrafts may
generate quite large stones, possibly exceeding golf ball size, or
even larger with the strongest storms. While a brief tornado can not
be ruled out, low-level shear does not look particularly favorable
for more than an isolated report. Damaging winds are also possible
with any of these supercells. Strongest storms should spread into WA
during the early evening as the short wave ejects northeast.

...Lower Rio Grande River Valley...

Water vapor imagery depicts a substantial sub-tropical cirrus plume
from the southern Baja Peninsula, across Mexico toward the lower Rio
Grande Valley. Latest model guidance suggests a weak disturbance
will approach the international border by mid day and this will draw
a substantial moisture plume into south TX. Forecast soundings
exhibit modest lapse rates despite the moistening profiles. While
forecast shear is not particularly strong, some organization is
possible and this activity could generate gusty winds or perhaps
some hail. Otherwise, a considerable amount of convection/precip is
expected across this region which may disrupt/limit organizational
potential.

..Darrow/Lyons.. 03/26/2025

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