The snowfall during the Tuesday morning commute hours was quick-hitting, wet and not well-predicted by forecast models from Monday night.

However, in the pre-dawn hours, a little feature spinning down out of the Strait of Georgia became visible on radar.  (Watch video explanation at left; radar video without commentary below.)

Created by the ebb and flow of air currents around our Northwest topography, and embedded in the northwest flow around a trough of low pressure was a meso-low.

It was a small, but very-apparent eddy in the larger-scale main air flow.  

Spinning counter-clockwise as it moved south, it produced positive vorticity advection; simply put, the feature enhanced uplift and that rising air was able to produce snow showers in the cold airmass.

http://link.brightcove.com/services/player/bcpid836564316001?bckey=AQ~~,AAAAR_p154k~,Ay3i1IziTki8aMdGaY0jFtvV8ga6DiJN&bctid=1492193804001

These very small features are often very poorly represented or not at all resolved by forecast models.    

Our hope is that as our forecast modeling becomes better and resolution becomes finer, we'll see these small features more accurately.

One great such innovation has been the high-resolution 1.33km WRF model from the University of Washington.

And, while the timing was a little off, the very fine detail given by this model did indeed detect an eddy moving southeast during the overnight hours (at 850 millibar level).  

However, it predicted the snow associated with the eddy missing the central Sound and moving into the Cascades well before dawn.  

So while the model didn't quite get it right, the fact that a forecast model is resolving features this small is a triumph for numerical weather prediction.   The UW's 1.33km WRF model is certainly one of the highest-resolution operational forecast models in the U.S. and probably the world.

Snow totals from around Western Washington

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE SEATTLE WA
1045 AM PST TUE MAR 6 2012

...SNOW REPORTS FROM ACROSS WESTERN WASHINGTON...

SNOWFALL REPORTS GATHERED FROM SPOTTERS AND COCORAHS OBSERVERS.
LOCATION                    SNOWFALL(INCHES)
KING
BOTHELL                            0.8
NORTH BEND 5.4 ESE                 4.2
NORTH BEND 2.8 SE                  3.0 
BELLEVUE 2.3 SSE                   2.0
EASTGATE 1.1 SW                    2.0      
FALL CITY 0.4 SW                   1.8
BELLEVUE 0.8 S                     1.3
ISSAQUAH 3.1 SW                    1.3
CARNATION 3.3 N                    1.2
RENTON 3.2 E                       0.8
WOODINVILLE 1.7 SE                 0.7
ISSAQUAH 3.0 SSE                   0.6
DUVALL 0.8 WNW                     0.5
BELLEVUE 1.8 W                     0.4
SAMMAMISH 1.7 NNE                  0.2
LAKELAND NORTH 0.5 ENE             0.2

SNOHOMISH
MARYSVILLE 4 N                     2.0 
LAKE STEVENS 0.9 NW                3.0
STANWOOD 3.7 S                     1.5
EVERETT 1.0 S                      1.2
STANWOOD 0.7 N                     0.8
BOTHELL 4.9 NNW                    0.4
BRIER 0.7 WSW                      0.2
RENTON 3.6 SSE                     0.2
SHORELINE 1.7 NW                   0.2
KENT 1.7 SSE                       0.2
SEATTLE 3.0 WNW                    0.1

PIERCE
GIG HARBOR 4.4 NNE                 1.5
TACOMA 3.1 NW                      1.0
PARKLAND 0.9 NE                    1.0
TACOMA 1.1 NW                      1.1
SOUTH HILL 3.3 WSW                 0.2

THURSTON
ROCHESTER 1.3 NNE                  0.1

LEWIS
ETHEL 4 SW                         0.8
ONALASKA 2.8 NE                    0.5
CURTIS 1.3 SW                      0.5
MINERAL 0.2 S                      0.4
CHEHALIS 1.4 SSE                   0.2

GRAYS HARBOR
MONTESANO 5.8 WNW                  0.2

JEFFERSON
PORT TOWNSEND 1 NNW                2.4
PORT TOWNSEND 2.2 W                0.7
CHIMACUM 5.1 S                     0.5
BRINNON 1.7 WSW                    0.2
PORT LUDLOW 1.1 SSE                0.1

CLALLAM
PORT ANGELES 8.1 SSW               0.3
PORT ANGELES 2.5 SSW               0.2

KITSAP
BREMERTON 1.8 NE                   2.5
OLALLA 2.2 NW                      1.5
BREMERTON 2.9 NNE                  0.2
POULSBO 3.2 NNW                    0.1

SAN JUAN
LOPEZ ISLAND 2.2 WSW               1.0
STUART ISLAND 0.2 SW               0.7
LOPEZ ISLAND 3.9 NNE               0.2

ISLAND
GREENBANK 0.8 W                    4.0
LANGLEY 4.1 W                      4.0 
FREELAND 1.2 ESE                   1.8
CAMANO ISLAND 3.8 N                1.3
CAMANO ISLAND 2.3 ENE              1.0
OAK HARBOR 1.1 NNW                 0.5
OAK HARBOR 2.1 NE                  0.5

SKAGIT
MOUNT VERNON 1.1 E                 1.7
MOUNT VERNON 0.8 SW                1.6
MOUNT VERNON 1.8 SW                1.4
ANACORTES 4.9 S                    0.5
ROCKPORT 6.5 E                     0.5
CONCRETE 4.9 ESE                   0.3
ANACORTES 4.7 SSW                  0.1

WHATCOM
BELLINGHAM 2.0 ENE                 1.5
CUSTER 3.0 NNW                     1.5
LYNDEN 0.8 ENE                     1.4  
BELLINGHAM 1.5 SW                  1.0
FERNDALE 1.1 NNW                   0.7
LYNDEN 1.0 SW                      0.6

Nicer weather for remainder of the week

As the large-scale trough of low pressure moves east, high pressure is quickly building in and will give us much nicer weather for the rest of the week with highs near 60 as soon as Thursday.