11:30pm…Wrapping Things Up

November 22, 2010

What a long day…it’s been 12 hours and time to drive home (slowly).  Not much to talk about for the next 24-36 hours.  We’ll see about the Wednesday snow possibilities tomorrow.  Not a lot of moisture and none on some models.

Then it’s on to a quick switch to southerly wind Thanksgiving Day.  That can warm us up quickly.  Remember in the middle of the 2008 cold spell when a low pressure are formed to the north?  We went from teens at 10pm one night to 39 by noon the next day with a breezy southwest wind.  It does happen.  Especially since we have no cold Gorge wind to keep us cool this time around.

Chief Meteorologist Mark Nelsen

9:30pm Update: Snow Showers Continue

November 22, 2010

Some real nice bursts of snow showers this evening as the colder air has moved in.  Speaking of cold air moving in…models just nailed it.  I would have never thought I would see a gusty west to northwest wind and a temperature of 31 here at our station in Beaverton.  Arctic air always comes in from the east (through the Gorge) here in Portland…well, apparently not always.

No change in thoughts about a Trace to 1″ for most areas.  Of course more up in Kelso/Longview since you folks already had snow coming down all day long.  Some snow now also in the Valley with a dusting in Keizer, Salem, Dallas, Monmouth etc…  Once again, anyone can get some light accumulation.  Even the north Coast is getting in on the snow action. 

Edge of the dry arctic air (the arctic front) passed reaching Longview/Kelso about 1/2 hour ago.  Dewpoint dropped from 27 to 21 in ten minutes as the wind went from gusty west to gusty north.  That should reach a good chunk of the Metro area by 11pm to midnight.  That’s when everything freezes solid.  Watch out if you’re driving around after 11pm!

I know there are a lot of new people reading the blog tonight…since we’ve had 70,000 visits today.  That’s far more than any other day in the 5 year history of the blog.  Welcome to you folks!  This is a place to discuss weather (really the only one in Portland), and notice the archives go all the way back to 2005.  Feel free to check it out the “past issues” if you get snowbound by our mega 1″ snowstorm…

Chief Meteorologist Mark Nelsen

6:00 PM Update: Cold Air Arriving

November 22, 2010

The good news?  Cold air is definitely moving in from the northwest.  The bad news?  Radar is definitely drying out.

Take a look at some of the “upstream” obs.  Snow at Astoria with a strong west wind…down to 34 degrees now.  Tidewater RAWS, just inland from Astoria at 2,000′?  Dropped from 31 to 27 the last couple of hours, and I assume it’s even colder now at 6pm.  That air advects right over us in the next two hours…so a 30 degree temp at the top of the West Hills is likely by 8pm.  Note the dramatic drop in dewpoints too.  All a good indication that the much advertised sudden cooling in the upper-atmosphere is now coming south out of Washington.  And it’s getting even colder up there.  I see Hurricane Ridge at 5,000′ is down to +1 degree!  That very cold upper-level air is dropping south.

At the surface, all of Puget Sound has gusty northerly wind now at temps well down into the 20s.  Arctic front passed Olympia and appears to be somewhere between there and Chehalis.

So will moisture stick around?  I still would be surprised if we don’t get a dusting this evening at some point.  But that one inch might be a stretch!  We’ll see.

Still expect freezing temps by the time we get to 10pm or so.  Watch out on roads that are still wet.

Chief Meteorologist Mark Nelsen

1:30pm Update: Wet Through 6pm

November 22, 2010

Here’s the latest:

1.  No freezing/snow issues in the lowlands from Portland south through at least 6pm.  After that time things could change quickly, but more likely 8-10pm.

2. Will it snow in the lowest elevations around the Metro Area?  Still a definite possiblity.  I would be VERY surprised if there is not at least a dusting most areas by 10pm.  I would also be surprised to see more than one inch.

Quite a bit more precipitation than expected today, that’s due to a stronger-than-expected area of low pressure developing right around Forks, WA this afternoon.  Pressures down around 1000 millibars instead of the 1005 models were showing.  Check out Tatoosh Island…northeast wind gust to 45 mph, while just 30 miles south a buoy is gusting from the west over 40 mph!  That’s some great meteorological stuff.

That low should race SE and be near Pendleton by late this evening…opening the door for something very unusual here:  a big surge of arctic air from the north/northwest WHILE a west wind is increasing through the Gorge.  Almost every arrival of arctic air here in the Metro area is accompanied by that gusty east wind blowing out of the Gorge.  That’s not happening this time around.

So the obvious question is…where is the cold air going to come from?  Regardless of the depth and position of the low…ALL models show the big cold surge from the north this evening.  Look at these numbers…2,000′ temp over PDX @ 4pm = 32 degrees (accounts for snow level a little over 1,000′ this afternoon).  But by 10pm it’s down to 20 degrees @ the same elevation!  So where is the cold air coming from again?  Check out temps up around the Olympic Peninsula.  The RAWS sites are that cold (or colder) at that elevation, they’ve been cooling all day.  So once the low passes to the east, the cold air should whip around the back side of it.  This is an incredibly cold airmass moving south in the upper-atmosphere, and a good chunk of that is moving in at the surface too.  Should be fun to watch….let’s just hope there is still moisture around to generate SOME snow.

A side note:  Don’t want to sound cranky, but I don’t have any tolerance for bad behavior here today.  Especially with 50,000+ hits to this blog.  I haven’t read comments yet, but I know some will get very upset and lash out when their big snowstorm doesn’t materialize, but you know what?  That’s what forecasting weather is about.  Sometimes it doesn’t turn out like you expect.  Move on…

Chief Meteorologist Mark Nelsen

10:00 am Update: No Snow During the Day

November 22, 2010

Apparently the NAM is correct so far…low pressure is developing off the Washington Coast, pulling back the dreaded south and southwest wind up the Valley and over the Coast Range.  The arctic boundary (front) appears to be in a line from around Hoquiam to Chehalis to Mt. Adams west of the Cascades.  Areas to the south of that are getting a mild south wind (including metro area), to the north it’s cold and snowy.  Until the low pressure passes by late this afternoon, we stay in the “warm” airmass.

All models show the arctic air surging south behind the low this evening, supported by the incredibly cold upper-level trough dropping south.  THAT is our last chance for snow…with the arctic front.  We’re talking after dark.  Now obviously models have trouble with the small-scale details…for example once again there is more precipitation than expected today (just too warm!).  So we should get at least a dusting as the precipitation ends, maybe an inch or so if we get REALLY lucky.  Unfortunately the UW-WRFGFS decided to fail it’s morning run today (too cold?), but our RPM shows a brief burst of snow right along the arctic boundary; supposedly around 7pm.  We’ll see.  I will say that is the one feature our model has been very consistent on, regardless of where the low presssure system was expected to be today.

Disappointing for the snow lovers (I mean people that love snow, not lovers hanging out in the snow of course).  But it IS weather and half the excitement is the anticipation.  Plus, we still have the coldest November airmass in a generation descending on us tonight!

So here’s my latest forecast:

Portland Metro:  Rain/snow showers today…streets remain wet until at least sunset.  Then a Trace to 1″ of snow sometime after 5pm.  Clearing and freezing up by 10pm.

Salem:  Mainly rain showers today, then a mix or all snow showers briefly sometime between 7-10pm.  Could get a dusting then…freezing up after midnight.