ZCZC SPCSWOMCD ALL ACUS11 KWNS 162331 SPC MCD 162331 WAZ000-ORZ000-170400- 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 NNNN