Tuesday, February 10, 2009

Snow



We are going to see snow today in the western Washington lowlands. The Pacific warm front is now moving in and precipitation is now entering the western Puget Sound lowlands (see radar). Central and north coast stations are now reporting snow as is Shelton. The air mass in place is cold enough to support snow, as indicated by the latest profiler data (see graphic). Offshore flow has not developed yet, and without it, the drying and warming that would have lessened the snow threat over the eastern Sound will not be in place. However, SE flow should develop as the system approaches, producing a large E-W snow gradient across the Sound..lighter on the Cascade western slopes and heavier towards the Olympics. Between now and 9 AM the snow shield should progressively move into area. SW Washington will also see light snow (up to a few inches).

The big question is how fast the temperatures will warm up aloft and whether the precipitation will be heavy enough to delay the transition to rain into the afternoon.

31 comments:

Anonymous said...

How much snow are we looking at then?

Anonymous said...

31 degrees and light to moderate snow in Olympia. Starting to stick to the road.

Joseph Ratliff said...

A light snow in Lacey...sticking but not piling up...

Anonymous said...

Moderate SNOW in West Seattle. Sticking everywhere at 30 degrees.

Anonymous said...

Hooray for Olympia snow! But tiny flakes here near the Capitol, falling fast (for a minute there) - almost rain. Is there a vocabulary for different types of snowflakes that reflect different atmospheric conditions? We'd have a different assortment here in W WA than in the Far North, I'd guess.

Brian said...

Why is an east wind bringing in warm air? Normally, whenever we have an east wind, it brings in cooler air because Eastern Washington is colder then Western Washington.

I don't get it.

Cliff Mass Weather Blog said...

Brian...sinking on the western slopes compresses the air and warms and drys it...

Anonymous said...

Olalla: At 7:15, a faint dusting of snow on roofs, lawns, and cars, but not the concrete driveway. That tells what the overnight temperature was, close to but not below freezing. Overcast but no pptn now. I'm expecting to see more snow later in the morning.

- Pete

Josh-B said...

so far dry in Bellingham

azure said...

Cliff, could you explain those charts with the blue arrows and red lines again?

I don't know how to interpret them at all.

Thanks,
Sandy

andycottle said...

Light snow here in Woodinville here on Hollywood hill. Temp is 32 with dp of 29. No new accumulation over night or this morning so far.

Jessica said...

A dusting (still coming down right now) compared to Monday a.m.s 1/2 inch or more of wet snowcover.

A few systems of hail and maybe frozen rain thru early last night hours. Anyone; what is difference btw hail & freezing rain? Thanks -

Eastlake/Lk Union

Michael said...

Actually had a thunderclap and lightning last night here in Ravenna before the hail intensified ( around 6:30pm)

andycottle said...

Jessica...

Hail is actual frozen water droplets that grow in size when being forced upward into the updrafts. And with each pass, the hail/ice pellet gets another thin coating of ice. This will continue as long as the updraft can keep it aloft before it gets to heavy and falls to earth.

Freezing rain on the other hand is supper cooled rain drops that freeze on contact with already cold surfaces. The precip starts out as snow high aloft, and then hits a thin layer of slightly warmer air(33, 34) and melting into rain. This rain then encounters a thin layer of cold air just above the surface, and thus, supper cooled(below freezing), and when it comes in contact with a cold surface, it instantly freezes on contact.

Anonymous said...

Teresa in Sammamish: We still have a bit of snow on the ground from yesterday, but I've only seen a flake or two today.

Where's my snow! (just kidding, if I never see a snowflake again this year, I'll be happy).

JewelyaZ said...

34.3 at Phantom Lake (Bellevue) and not a flake in sight. Bummer.

Josh-B said...
This comment has been removed by the author.
Scrantz said...

Report from NE Portland, Alameda ridge - elev ~200 ft - Snowing, roads still black. Daffodils slightly sad.

Josh-B said...

Professor Mass,
I know you are a busy man so you can skip over this if you want. I was wondering if anybody else can answer something for me? Or if there is an answer? I was interested if there is data that shows how model forecasting is doing? Or what the percentage of accuracy is. Have there been studies or postpartum followups after a set period of time? How has the UW Ensemble been doing? What about other models (ETA, GFS and ENSO) We know computers are getting faster and increasing in memory and storage and meteorologist and climatologist are finding new ways to model the atmosphere. But is the Atmosphere getting more chaotic? Has there been a net increase in forecast prediction? Or do we keep making new antibiotics while bacteria keeps throwing us new curve balls keeping us at a net neutral (little analogy). If there is data are some people afraid that the general population will interoperate it wrong, IE, yes model forecasting has increased in accuracy but you need to look beyond the cold data on the surface that might show otherwise? Maybe someone has been keeping tabs of forecast discussions and doing followups on them. Even Professor Mass has mentioned that beyond 5 days the forecast get a little more fuzzy. Though 24hr can be little off as well. Just some thoughts. Thank you

ps Andy
Keep writing your post I like them contrary to what other people say

Anonymous said...

The NWS just extended their watches and warnings for the lowlands until 6 p.m. Should one surmise that the warm up is taking longer than expected and that we may have frozen precip for most of the day?

Anonymous said...

Please could you give rather more coverage of longer range forecasting rather than the TV weatherman "it's snowing lightly in our parking lot right now" type stuff.

Anonymous said...

Olalla: It has been snowing lightly for more than an hour, but the light dusting that we got this morning has mostly melted, and the present pptn. isn't sticking.

- Pete

Anonymous said...

The NAM shows 2" of snow for Seattle between noon and 4 p.m. This event has hardly begun!

Anonymous said...

Why did the NWS issue winter weather advisories?? There's hardly anything falling, and nothing accumulating partly because it's above freezing. From what I've heard or seen, it's not any different elsewhere. Anyone have any idea?

Then you go to the NWS point and click forecast and it gives a forecast of rain for late morning and afternoon today. With a winter weather advisory out.

?

Anonymous said...

200 feet above Chehalis, upwards of one inch, enough to almost whiten grassy areas, temp - 33F

RobLL

Anonymous said...

We are at 500 feet elevation just above Hood Canal in the Union area and as of 11:40am have just under 4" of snow with more falling heavily. Temp is steady at 32--it looks like a pretty significant event for us!

Anonymous said...

Olalla: It is now snowing heavily enough to cause snow to accumulate faster than it is melting. Still no accumulation on the driveway though.

- Pete

WeatherNerd said...

I'm down in Lacey today and it is snowing hard and piling up. The roads are getting slush, some places worse than others of course. A couple inches so far...

WeatherNerd said...

Anonymous
Advisory means conditions exist that COULD produce snow. And from what the radar shows the snow is heading north from where I am at in Lacey. Hang tight.

climo man said...

A comment on last night`s hail: I think most of us experienced snow pellets, not hail.The difference is that snow pellets are softer and can be easily crushed ( if you squeeze them), often bursting on impact with the ground, while hail and ice pellets are hard, opaque, pieces of ice that bounce upon impact( except when they hit your car windshield in Oklahoma.)

I`m a bit curious why the NWS is still predicting accumulating snow for the Seattle Metro Area this afternoon.Historically, when we get a low pressure moving south along the coast,a relatively warm southerly flow kicks in, and rain results.I can`t see this not happening once again today--maybe I`m missing something, if anyone will clue me in.

Justin said...

"Advisory means conditions exist that COULD produce snow. And from what the radar shows the snow is heading north from where I am at in Lacey. Hang tight."

Well, actually if it was only something that COULD produce snow, they wouldn't issue an advisory. They would have to be confident on the chance of snow.
Source? I have worked for the National Weather Service in the past.