The last two days have been a classic case of “Late Winter Slop” in the Pacific Northwest.  There has been a lot of snow in the Coast Range, Cascade foothills and High Cascades – and even low elevations have seen a tease of snow or sleet at times, especially in parts of NW Oregon and the Puget Sound.  This afternoon there was a wintry mix (rain, snow, sleet and graupel) at about 900 feet elevation on Sevenmile Hill, west of The Dalles.  But it hasn’t produced a classic midwinter-style snowstorm for the lowlands.  High temps at the lowest elevations are mainly in the low to mid 40s.

Probably a majority of years see at least a few days like this, but it’s more common at the end of La Nina winters (like this one was).  Occasionally I’ve seen these kind of near-snow teases happen as late as April, but only in the most extreme years.  Mid-February to Mid-March is the most typical timeframe.  The pattern is generally caused by cold, semi-arctic airmasses in the Gulf of Alaska sliding down from the north and over the top of us.

Of course, the lowlands CAN get a little bit of snow in this pattern if they’re lucky enough to see a really heavy shower.  Or if steady, moderate precip shows up at night or early morning.  Or if the airmass aloft is exceptionally cold (i.e. -8 or -9 C at the 850mb level). Unfortunately, the heaviest showers in this pattern typically come in the midday to afternoon, when convective energy from the powerful late-winter sun is at its strongest.  Then it’s too “warm” and unstable in the lowest elevations for snow to fall.  Sleet or graupel is quite common, however.

Right now, the models suggest we will have quite a few more late winter slop days in the first 2 weeks of March, with snow levels below 2,000 feet at times.  Of particular interest is this weekend, especially Saturday night into Sunday.  More on that in a moment.

HOWEVER….I’m quite confident there will be no more true arctic airmasses this season.  Nothing like that shows up on the models through the 9th or 10th of March – and arctic blasts simply don’t happen in the Gorge after that time.  Not even in the “old days.”  Early March is the absolute last chance we have for that, and it’s rare:  Only twice in DLS airport history, 1955 and 1989, did an arctic air event *begin* on or after March 1 (the 1960 cold blast actually began in the last few days of February).

We have a fairly quiet pattern for tomorrow through Thursday, but not quite dry and calm enough Wednesday to really qualify as a “lamb” start to March.  And with temps still struggling to get to 50 degrees, it sure won’t feel like a balmy spring day.  But Friday through Sunday things get stormy again as a powerful cold front pushes through.  This one is going to be a bit interesting because:  1) there’s bands of pretty heavy precip coming through with the front, and 2) it has a little bit of an “anafront” look, with quite a bit of shower activity continuing AFTER the colder air has moved in.  Depending on how the moisture and cold sector line up, this could produce another brief shot at snow pretty close to the lowlands.

Beyond that it still looks wet and cool…with no sign of 60-degree temps in sight.  In fact recent GFS maps suggest yet another shot at near-snow conditions around the 9th or 10th of March.  So our La Niña winter appears poised to limp along into March, fazed only slightly by the increasing sun angle.  Sorry, springtime lovers…..