TODAY: We will start off with mostly cloudy skies and temperatures just above freezing in the mid-30s with light winds out of the East at 5 to 10 MPH as showers chances climb back up to 70% for isolated showers off and on. As we move through the day we will see the daytime high of mid to low 40s right around noon then temperatures will fall in the afternoon as cold arctic air filters into the region from the North. This will take temps back into the mid-30s and lower the freezing line to around 750 to 1,000 Ft. However with Dewpoints in the low 30s by this time we do have a threat of “Wet Bulb effect.” This means we could see snow mixed in with any showers that come through even if we are only in the mid to upper 30s but would not stick to the ground or would only last an hour or two before melting. Best chance to see this happen will be in the evening and overnight hours of Wednesday & Thursday.
LATE WEEK: The region is under a fairly complex upper pattern with this morning`s low having already moved across eastern Oregon earlier today with a compact and filling secondary low currently crossing the central Oregon Cascades. A deformation zone currently stretches from about Corvallis northeast to Mt. Hood. The band is becoming more diffuse although a trailing burst of rain in the last hour has brought a new month of February record to the Portland Airport. The monthly total is at 10.04 inches as of about 215 pm which breaks the record of 10.03 inches from February, 1996. Accumulating snow levels are currently around 4000 feet to the south and about 3000 feet to the north they will lower back to around 3500 feet to the south and 2500 feet to the north as a pseudo front begins to push southeast over the region behind the primary deformation band. Will leave the snow advisories in place as planned with the North Oregon Cascades ending at 6 pm and the Lane County Cascades ending at 10 pm tonight. A large scale upper trough will continue to shift southeast to cover the entire Pacific Northwest by this time tomorrow. The colder and drier air mass is becoming apparent at the coastal sites with dew points lowering into the mid-30s. As the trough digs south, another reinforcing and smaller scale closed low will slide down the western periphery of the parent trough tomorrow. This will bring a brief period of particularly unstable air over the region and possible thunderstorms to the Coast Range westward. This pattern could be the first shot of low elevation snow mixing in with the rain showers. The upper trough will linger over the broad region through Friday and models do show a fairly vigorous closed low dropping offshore to the west on Friday. So far, it seems far enough west the southerly flow will bring slightly warmer air along the coast where the best threat of precipitation could clip our area. Temperatures will be noticeably cooler the next several days, however, an overall lack of modest easterly flow will keep the best chances for accumulating snow above 1000 feet. That said, all of the showers over the next few days will not likely bring more than a couple inches of snow over any given 12-hour period. That would remain below advisory amounts of snow to the foothills. It`s even more unlikely to get more than 6 inches for the Cascades. The lowest elevations, including the Willamette Valley and the Coast, will likely see periods where snow mixes into the showers...particularly during the late overnight and early morning hours. Any accumulating snow at the lowest terrain will occur under a particularly heavy shower but would be unlikely to stay frozen on the ground for more than 1-2 hours.