MD 0076 CONCERNING FREEZING RAIN FOR PORTIONS OF NORTHWEST OR INTO FAR SOUTHWEST WA
Mesoscale Discussion 0076
NWS Storm Prediction Center Norman OK
0531 PM CST Tue Jan 16 2024
Areas affected…Portions of northwest OR into far southwest WA
Concerning…Freezing rain
Valid 162331Z – 170400Z
SUMMARY…Freezing rain will increase in both intensity and coverage
across much of the Willamette Valley, the Oregon Coast Range, and
the far southern Chehalis River Valley during the next 1-2 hours and
persist through around 04Z.
DISCUSSION…Latest water vapor imagery depicts a compact midlevel
cyclone tracking eastward toward the Pacific Northwest. Strong DCVA
preceding the cyclone should overspread coastal OR over the next 1-2
hours, supporting an increase in precipitation intensity and
coverage across the region. The 12Z SLE observed sounding and more
recent Portland ACARS soundings showed lingering dry air in the
1-5-km layer, though persistent precipitation (and related
wet-bulbing) along with increasing moisture ahead of the
aforementioned cyclone are likely contributing to a deep saturated
layer which will further support increasing precipitation rates. In
fact, freezing rain is beginning to increase in coverage across
coastal OR per the latest surface observations.
Low to mid 20s surface wet bulb temperatures beneath a 3-4 deg C
warm nose as low as 925 mb in the Willamette Valley into the Oregon
Coast Range will support complete hydrometeor melting and
re-freezing at the surface, suggesting that freezing rain will be
the predominant precipitation type (with pockets of sleet also
possible). And, given the strengthening large-scale ascent amid a
deeply saturated thermodynamic profile, freezing rain rates could
exceed 0.1 inch/hour. These conditions will likely persist through
around 04Z, before surface temperatures begin to warm and the dry
conveyor belt accompanying the midlevel cyclone impinges on the
area.
..Weinman.. 01/16/2024
…Please see www.spc.noaa.gov for graphic product…
ATTN…WFO…MFR…SEW…PQR…
LAT…LON 44262371 44892370 44992384 45192392 45342363 45682358
46122370 46472335 46522282 45892250 45412222 45042253
44372277 44022285 43742309 43792355 44262371
