Sunday, November 21, 2010

How much snow?

First, here are the snow reports from the Seattle NWS office:

PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE SEATTLE WA
610 PM PDT SUN NOV 21 2010 ..
SNOWFALL TOTALS THROUGH SUNDAY AFTERNOON...

KING COUNTY SNOWFALL(IN) TYPE

ENUMCLAW 6(MILES)NNE 3.5 SPOTTER
PIERCE COUNTY SNOWFALL TYPE
EATONVILLE 3.0 SPOTTER
PUYALLUP 5 WSW 1.1 SPOTTER

PUYALLUP 4 SSE 1.0 SPOTTER
LEWIS COUNTY SNOWFALL TYPE

ETHEL 4 SW 1.5 SPOTTER
THURSTON COUNTY SNOWFALL TYPE

GRAND MOUND 5 NNW 1.8 SPOTTER
CLALLAM COUNTY SNOWFALL TYPE

FORKS 2.0 CO-OP
PORT ANGELES 4W 1.9 SPOTTER

Most of region had a few flurries or some drizzle, with the heaviest snow concentrated near or just west of the foothills southwest of Seattle. Puyallup and Federal Way had some sticking light snow. Also some snow in the Shelton area and the northern Coast.

The weather service is going for a 70% chance of snow tomorrow...with 1-3 inches.
Seattle DOT is applying anti-icing substances on the roads tonight (a good precaution) and Metro is putting its vehicles on snow routes tomorrow morning (commendable perhaps but probably unnecessary).

The latest model runs are in and here it is (24h total ending 4 PM tomorrow).

Bottom line...NO ACCUMULATING SNOW in Seattle, but white stuff over SW Washington and Oregon. We could get a few flurries like today.

and here is the latest probcast probability of precipitation based on ensembles and statistics. Same story. Very low probability of precipitation in Seattle. Again, no accumulating snow.


The weather channel...which computes an independent forecast... is going for scattered snow showers and snow of less than an inch in Seattle.

Again, my conclusion....no accumulating snow in or north of Seattle. But if you are driving south, particularly south of Olympia, the chances go way up. Also snow in the mountains and foothills and along the coast. SDOT and Metro can probably rest easy.

But it will be cold..tonight the temps will dip into the 20s in many locations and the winds will pick up. Really strong NE winds over NW WA and northerlies pushing down the Sound. Temperatures dropping into the low 20s and teens on the west side of the State on Tuesday AM...it will be brutal. And east of the Cascades them combination of strong wind and temperatures in the single digits will produce extreme, dangerous conditions on Tuesday.

Finally, for users of probcast...it has a problem with minimum temperatures that will be fixed soon...don't take crazy low temps seriously (unless you work for some TV station weather hype dept!).

20 comments:

John said...

I've really got to rant a little about Probcast; It's performance during last December's cold spell was horrible.... and they *still* haven't fixed it?
Also, I don't think I've ever seen the chance of precip under 10%, even when they were predicting clear, sunny skies.
They really should take that thing off-line until they get it working.

Katy said...

My poor kids. They've been hobbling around with their toes crossed all day to no avail.

willowbasketmaker.com said...

Thanks for mentioning the problem with the minimum temps on probcast. I was wondering about the huge difference between it and NWS.

orcmid said...

Uh, would someone who creates those weather advisories please notice that we haven't been in PDT for some time now.

Not momentous, but, um, it helps to demonstrate attention to detail.

JayNorth said...

Was just at the movies at Bellis Fair and the wind is outrageous in northern part of Bellingham tonight. Back at our house on Alabama Hill in eastern Bellingham we can hear the wind to the north, but it is much lower speed here.

Michael said...

Models are saying no snow yet the NWS is saying 1-3", is there any specific reason for this?

Experience with lows and the interactions and arctic air masses maybe?

Modified Arctic Boundary?

paintlover said...

3.5 inches in Enumclaw.....ummmmm try 5 inches off my back porch in town....I don't know where they get their measurements, but remeasure please....still light flurries and just got the call that Enumclaw schools are closed!

MicroMethow said...

It seems the Probcast program does not have the ability to forecast below zero degrees. Here in the Methow Valley NOAA is forecasting a low of -8 on Monday, -21 on Tuesday and -6 on Wednesday (real temps - no wind chill or anything) but the probcast just says -0.

I was thinking about defrosting our 30 lb turkey in a bucket of water outside like I did last year, but I guess that's not going to happen...

Kevin Purcell said...

Michael said "Models are saying no snow yet the NWS is saying 1-3", is there any specific reason for this?"

It's explained in the 345PM SUN AFD ... the NWS forecasters think the models underestimate the precip in this sort of situation.

Why an advisory?

AS FAR AS WHAT OFTEN CAN BECOME A HODGE PODGE OF ADVISORIES...I FOUND THE SIMPLEST WAY TO DEAL WITH MISC SPOTTER REPORTS TODAY OF AN INCH OR TWO HERE AND THERE WAS TO GET A WINTER WEATHER ADVISORY UP. THE WEBCAMS WERE MORE WINTERY AT 11AM THAN THEY ARE AT 3PM...BUT WHERE THERE WAS PRECIP TODAY IT COULD GET SLICK OVERNIGHT. I MAINLY NEED TO HAVE SOMETHING UP THRU MONDAY AS THE NEXT SHORTWAVE DROPS SOUTH OVER THE AREA.

and

Why the 1" to 3" comments?

AT THE UPPER LEVELS THIS NEXT NEXT SYSTEM DEVELOPS INTO MORE OF AN UPPER LOW...MORE CYCLONIC FLOW WITH A BETTER VORTICITY FIELD AND SUCH. AT THE SURFACE THE MODELS STILL KEEP THE MAIN BOUNDARY AND SFC LOW PRES DEVELOPMENT ON THE MODIFIED ARCTIC FRONT...WHICH RUNS FROM THE COASTAL WATERS THRU SW WA. THE SFC LOW DEVELOPMENT IN THE NAM SORT OF TRACKS SIMILARLY FROM THE CENTRAL WA COAST TO THE SOUTH CASCADES DURING THE DAY MONDAY...PRESSURES FELL ABOUT 2MB/3HRS THIS AFTERNOON ON THE CENTRAL COAST AND THEN SW WA WITH THIS IMPULSE...I WOULD WANT TO KEEP A CLOSE EYE ON PRES FALLS MONDAY. THAT SAID THE NAM ONLY HAS A 1006MB LOW JUST NW OF GRAYS HARBOR AT DAYBREAK MONDAY...ONLY DROPPING IT A FEW MILLIBARS BY THE TIME IT MOVES TO THE SOUTH CASCADES AFTERNOON. THAT IS NOT THE SORT OF SYSTEM ONE WOULD PUT OUT A WINTER STORM WATCH OR WARNING FOR. HERE IS THE 18Z NAM SLP FCST AND 3HR PCPN ENDING 10AM (image) AND A 500MB HEIGHT FCST WITH THE COLD AIR ALOFT (image). THE FCST IS A BALANCE BETWEEN THE MODELS...WHICH ARE NOT ESPECIALLY WET...AND THE EXPERIENCE OF SEEING UPPER LOWS DROP OVER WRN WA AND TRIGGER MORE PRECIP THAN IS SOMETIMES FCST BY THE SIMULATIONS. THERE IS AN OUTSIDE CHANCE THAT THE UPPER LOW TRIGGERS A MORE CONVECTIVE TYPE OF PCPN MONDAY WHICH GIVES MORE UNPREDICTABLE AND BRIEF BUT MORE INTENSE SNOWFALL.

And they get shot less for overestimation than underestimation, I think :-)

Mike McFarland said...

orcmid--I checked over all the products sent out today and everything I checked on the NWS WFO Seattle website is correctly stamped with PST.

Mattias said...

For some reason the mesoscale models (MM5 and WRF) are showing significantly less precipitation than the operationals (NAM and GFS.) 6z NAM is the snowiest yet and shows 0.25" of liquid precip all the way to Everett. Is this a case of the mesoscale models picking up on something the operationals can't see due to their lower resolution or are they overestimating some moisture limiting factor? Hard to tell but seems to me like a compromise is in order. I think Seattle will be near the Norhtern edge of the significant precip but it won't be as far South as the MM5 and probcasts show it. I'm sticking with a 1-2" forecast for Seattle but we'll see. Really impossible to tell at this point. It all hinges on exactly how strong and thus how far North the low will be and it hasn't even formed yet.

Nancy said...

Thx for your snow predictions. In years past you have criticized school district closure decisions when the actual weather didn’t warrant closure. I request you refrain from doing so. Those officials are making a forecast + safety decision, and need to err on the side of caution. As you know, forecasting is just that, a statistical prediction. We don’t know for sure until the weather happens. Your criticism of public officials during those embarrassing situations only undermines our faith in government, and we have too much of that these days. Math curriculum, yes, but too much caution….let it go. I remember when students were trapped at our local school and teachers went around the neighborhood looking for sleeping bags and other supplies for the kids. Finding supplies was easy and an adventure here in N Seattle, but perhaps not so easy in other neighborhoods.

Upupaepops said...

Thanks for the mention of the probability service UW.

I saw those single digits and was looking for devils on the streets!

Heading out to Neah Bay for Thanksgiving... oping for a good strong storm event while there.

kosmo said...

Fun to read the progression and hesitation to forecast any chance of snow since last Monday from CM. That was the infamous post throwing the local media under the forecasting bus - as CM is find of doing - for daring to anticipate some intriguing weather on the horizon. A little egg on the face here is fun to see. We'll see if it leads to a shift from hating on the media to joining in the fun and appreciating that having fun with a weather message is important. Hi Cliff! Thanks!

superdeluxe said...

Looked like it was accumlating snow on I-5 on the way in from the south (On the side of I-5..saw accumlating snow), around Southcenter

Donna & Chris said...

WE had wicked wind and we have some snow (not much but it is sticking given it is 27 degrees) at Woodland Park.

Justin Sweet said...

So I guess this is what you would call a "bust" forecast Cliff? Sure looks like accumulating snow in Seattle to me!

Shannon said...

Well, my kids are thrilled. We have half an inch on the ground in North Seattle. Its enough for a slushy snowball!

Teresa said...

Sammamish, snowing respectably and sticking to the roads in places where they haven't put de-ice....

7:35am Monday

Indy Falconheads said...

Accumulating snow in Shoreline. Less than an inch but definitely sticking.

Prettier than rain!