Best Chance For Snow Yet!

January 25, 2008

Sure looks good for snow coming up the next few days, even down to the lowest elevations.  First, let’s talk about tomorrow though.
A nice clear night, at least through the next few hours, gives the entire region another freeze.  Then clouds move in around daybreak.  Models continue to produce moisture out of the cloud cover sometime during the 7-10am period.  We all know the cold air at the surface sure isn’t going to suddenly be swept out by a south wind, so most likely whatever falls before noon will be some sort of frozen precipitation.  As of the 4pm Salem sounding, we would see snow.  But I have no reason to doubt the strong warming shown overnight between 1,000-4,000′ on models.  So snow looks unlikely.  Far more likely is a spotty/messy mix of freezing rain or sleet (ice pellets).  I’ll talk more about that wintry mix around 10:45pm tonight.  I expect the combination of low level southerly flow, cloud cover, very light precip, and a nearly dead east wind by 10am to push temps into the 34-38 degree range through the early afternoon.

Then a strong cold front sweeps in from the northwest in the evening Saturday.  This will be the leading edge of arctic air that has poured out of SE Alaska out over the Pacific.    Our RPM model, and to a lesser extent the MM5-GFS, show the cold front enhancing and stalling over NW Oregon late Saturday night and Sunday morning.  I notice wind on both models is calm at the same time the steady precipitation is falling.  That’s why I went with a trace to 1" even in the city at that time.  There appears to be a break behind the front Sunday morning through early afternoon before the really cold showers surge inland in the evening.  (A brief break…I can’t believe I just saw a forecast for snow on another station right now with temps in the 40’s overhead!).  Okay, moving on…so then the coldest atmosphere moves over us later Sunday night and Monday morning.  Plenty of moisture too.  This is one of those situations where a heavy line of showers could dump 2-3" in one hour on one side of town, but nothing 10 miles away…That’s why I think forecasting a specific snow level (like 200 or 300′) is total crap in a pattern like this…just being honest!  Location and precipitation intensity will be far more important.

Next bit of excitement will be Monday night and Tuesday.  Depending on where the surface low tracks with that system, we either get rain with a 2,000′ snow level or a snowstorm down here in the city.  Too early to tell.  Enjoy the weekend.  I’ll be in Sunday evening and post again then…Mark Nelsen