Looking For Snow

February 25, 2009

Snapshot Here's something to think about in relation to tomorrow's possible snow.  This is the output from our RPM model from 12z today.  It's the precipitation output from 4am-1pm tomorrow.  Can you say orographic???  I'll post sometime this evening…Mark Nelsen


9:30pm Update:  Looks like things are working out pretty well this evening.  Cold air is moving in nicely with temps down into the 30s everywhere north and west of Portland.  Our 1900' tower temp is down to 31 degrees, which means over downtown Portland the snow level must be around 1200' or lower in the heavier showers.  As you go north and west the snow level is much lower, around 500 feet or even a bit lower based on reports from Longview, Vernonia, Battle Ground and Yamhill.  Keep those comments coming down below!  In situations like this I do try to read the comments to see who's getting a mix or all snow.  You can't get that off of official observations.  Too bad we can't pull out the Jim Bosley phone board and talk to you anymore…that would be so…1980s.  How many of you remember that?

00z Models have come in even drier for tomorrow.  Our RPM has a total of .07" precip from 4am-4pm tomorrow.  I have a gut feeling based in the IR imagery and models that after this inital surge of moisture the next few hours, we'll just see very light snow showers through midday tomorrow here in the valleys, and partly to mostly sunny skies by sunset (42 degree high due to that).  Weak showers and a Coast Range to our west in westerly flow have been bad news in the past couple of winters.  We have a cold enough atmosphere to get a good snowfall here in Portland, but I just think the moisture is lacking.  I HAVE noticed the nice surge of cold dry modified arctic air down into northwest Washington as far south as about a Hoquiam to Seattle line.  It would be nice if it would move down over us, but the surface low sliding down the Coast moves inland towards Olympia tonight and then dissolves into a trough that stays to our north tomorrow.  So we never lose our onshore flow the next 24 hours. 

We are done with the showers soon after midday tomorrow, then it's on to a rapidly warming atmosphere late Friday through the weekend.  A deep upper-level low forms well offshore, which pumps up the mild southerly flow.  March will come in with seasonal temps in the 50s Sunday…Mark Nelsen