MD 2067 CONCERNING FREEZING RAIN FOR PORTIONS OF NORTHWEST OREGON INTO WESTERN WASHINGTON
Mesoscale Discussion 2067
NWS Storm Prediction Center Norman OK
1047 PM CST Thu Dec 22 2022
Areas affected...Portions of northwest Oregon into western
Washington
Concerning...Freezing rain
Valid 230447Z - 231015Z
SUMMARY...Freezing rain is expected to increase this evening and
into Friday morning across northwest Oregon into parts of western
Washington.
DISCUSSION...Dry low-level air was present on the observed 00Z
soundings from SLE and UIL. Surface observations have continued to
indicate that light precipitation has been reaching the ground in
northwest Oregon. Due to influx of cold air through the Columbia
Gorge and some diabatic cooling from precipitation, the low-level
air cold airmass remains deep enough to support a mix of freezing
rain and some sleet. A shortwave trough evident on water vapor
imagery is currently approaching the region. As this occurs, warm
advection at 850 mb will increase. At the same time, the offshore
pressure gradient should also weaken towards Friday morning. These
processes should lead to the low-level cold layer becoming more
shallow and support primarily freezing rain. Given the cold
temperatures already present in the region, ice accretion should be
relatively efficient. Portions of the Willamette Valley, having
already nearly saturated the low-levels, are more likely to see
greater accretions than areas to the north.
..Wendt.. 12/23/2022
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...SEW...PQR...
LAT...LON 44672271 44302292 44082308 44032345 44672354 45472346
46202343 46702349 47142350 47462306 47422237 46312210
45552203 45302214 45132234 45102251 44672271
