Day 1 Severe Weather Outlook

Valid 021300Z – 031200Z


Severe storms are not expected across the U.S. mainland today.

As the synoptic trough off the Atlantic coast moves farther away
from the CONUS, a progressive upper-air pattern will continue. The
next substantial perturbation is apparent in moisture-channel
imagery offshore from the Pacific Northwest, with its height/
vorticity axes generally between 132W-135W. Satellite imagery shows
abundant glaciated convection over Pacific waters between the trough
and the coastline, indicating a broad field of favorable large-scale
ascent/destabilization aloft for supporting deep convection. With
the trough forecast to amplify as it approaches the coast, then
moves inland between 18-00Z, that ascent plume should at least
maintain its strength. By the end of the period, the trough should
extend from the northern Rockies south-southwestward across northern
NV and eastern CA.

…Coastal Pacific Northwest…
Isolated thunderstorms are possible, predominantly through the day
to about 00Z. This activity will be supported by marginal boundary-
layer theta-e accompanying the Pacific marine layer, as well as weak
but supportive buoyancy from that layer into areas of -20C and
colder temperatures aloft. Time series of near-coastal forecast
soundings prior to the passage of the 500-mb trough show steepening
low/middle-level lapse rates (compared to 12Z UIL RAOB) and little
or no CINH, from the Pacific marine layer upward to near a
tropopause located between 450-500 mb. Thereafter, the tropopause
will descend toward the -20C isotherm, concurrent with weakening of
lapse rates, thereby removing sufficient magnitude/depth of CAPE to
support thunder potential.

..Edwards/Kerr.. 02/02/2020


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