An RGB computed using the GOES-16 Cirrus Channel

Cloud Type RGB at 1502 UTC on 3 November 2017 (Click to enlarge)

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

Red-Green-Blue (RGB) Composite Images are a handy way of showing information from multiple satellite bands (or band differences) at once. The image above shows an RGB created by NOAA Scientist Andy Heidinger that uses the GOES-16 Visible Band (0.64 µm) as the green component, Snow-Ice Band (1.61 µm) as the blue component and Cirrus Band (1.38 µm) as the red component to tease out information about Cloud Type.  The Cirrus Channel (unique to GOES-16 as far as Geostationary Satellites are concerned) is a handy channel to use in an RGB because it discriminates very well between high clouds and low clouds.  In a moist environment, low clouds are not apparent at all in the Cirrus Band.  The toggle below shows the Visible, Snow/Ice and Cirrus Channels at 1502 UTC.  Low clouds over Kansas have no signal in the Cirrus channel — there are other differences as well, of course.

In the RGB, Thin cirrus clouds (for example, the contrails over Illinois) are red, opaque ice clouds (over the western Atlantic) are yellow (having a contribution from both Red and Green Components), Low Clouds (over the southern Plains) are Cyan (having a contribution from Blue and Green), snow is Green, and lofted water clouds are white (having a contribution from all three). As the atmosphere dries, the amount of lofting necessary for the Cirrus channel to view a cloud composed of water droplets (and therefore white in the RGB) decreases.

GOES-16 Imagery at 1502 UTC on 3 November 2017: Snow/Ice (1.61 µm), Visible (0.64 µm) and Cirrus Channels (1.38 µm) (Click to enlarge)

The Day Land Cloud RGB (sometimes called ‘Natural Color’) can also be used to estimate cloud type. The toggle below shows how the Cloud Type RGB has more gradations between ice cloud type because of the use of the Cirrus Channel.  The Cloud Type RGB also highlights the contrails and thin cirrus more effectively, again because of the use of the Cirrus Channel

Cloud Type RGB (1.38 µm, 0.64 µm, 1.61 µm) and Day/Land/Cloud RGB (1.61 µm, 0.86 µm, 0.64 µm), 1502 UTC on 3 November 2017 (Click to enlarge)

 

Three toggles below show the Snow/Ice and Visible and Cirrus channels zoomed in over Illinois (where contrails are present), over the western Atlantic (where strong convection is occurring) and over the southwestern United States.

GOES-16 Imagery at 1502 UTC on 3 November 2017: Cirrus Channel (1.38 µm), Visible (0.64 µm) and Snow/Ice (1.61 µm) (Click to enlarge)

GOES-16 Imagery at 1502 UTC on 3 November 2017: Cirrus Channel (1.38 µm), Visible (0.64 µm) and Snow/Ice (1.61 µm) (Click to enlarge)

GOES-16 Imagery at 1502 UTC on 3 November 2017: Cirrus Channel (1.38 µm), Visible (0.64 µm) and Snow/Ice (1.61 µm) (Click to enlarge)

GOES-16 also has a Baseline Product that shows Cloud Type. That is shown below. The 1502 UTC Image was incomplete, so the 1507 UTC image is shown.

GOES-16 Cloud Phase, Baseline Product, 1507 UTC on 3 November 2017 (Click to enlarge)

Light Snow Reaches the Lowlands of Western Washington

Snow revved up in the mountains yesterday, but this morning the snow level fell to near sea level over several locations of western Washington.

About an inch at 1300 ft in Bellevue (picture courtesy of Peter Benda)

The upper-level flow pattern was a classic for western Washington snow with high pressure offshore and a sharp trough of low pressure reaching the Northwest coast (see upper level map at 5 AM).    This pattern brings both upward motion (which produces precipitation and clouds) and helps push cold air into the region.

If this was a month or two later, we would have been worrying about a major lowland snow event.

Cooler air and higher pressure first moved into British Columbia yesterday, and as a result cool winds started blowing in the Fraser River Valley northeast of Bellingham, where northeasterly winds revved up yesterday (see below).  Winds gusted to 39 knots (45 mph) there, and temperatures plummeted from the upper 40s to 31F.  And yes, it is snowing there.


The is cool, but not super cold---still very early in the fall/winter season, of course.  The cool air pushed south overnight, with northerly flow ascending  the northern Olympics, enhancing snow in places like Port Angeles and Sequim (see map at 6 AM).  No rain shadow for these weather-spoiled folks.
Snowy Sequim

The freezing level (the height where the temperature falls to freezing) dropped all day yesterday, and the latest observations at Sea-Tac airport suggest it is at about 1300 ft (950 hPa pressure)--see the time-height cross section below (red lines are temperature, x-axis is time, y-axis is height in pressure).

Heavy precipitation showers can push the freezing and snow levels (the lowest level of snow) down to near sea level, and we do have unstable air and showers over the region (see radar at 7:04 AM)


The model forecasts had suggested this snow interlude.  Here is the 24-h snow amount ending 5 PM today from last nigh's run.  Not bad!  And the mountains are going to be hit hard today.  Note the substantial upslope snow on the north side of the Olympics.


Today the lowland precipitation will quickly end as the area of showers moves through.  So Seattle and other lowland mayors can rest easy.  Furthermore, road surfaces are relatively warm. 

But the snow fun is not over.    Another upper trough and associated low moves in Saturday night and Sunday, with some significant lowland snow, particularly south of Seattle (see forecast below).  Olympia gets hit hard. Lots of uncertainty with this...so keep tuned.


This is a La Nina winter and this situation is classic for a La Nina year.  The Cascades will have a good start to a winter base for skiing and other snow fun.  I mean several feet above 5000 ft.
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NWS Snow Reports

Public Information Statement
National Weather Service Seattle WA
1056 AM PDT Fri Nov 3 2017

..Updated Snowfall Reports...

Location Amount Time/Date Elevation (ft.)

..Washington...

..Clallam County...
3 SW Port Angeles 10.0 in 0700 AM 11/03 0
3 WSW Agnew 5.0 in 0700 AM 11/03 0
5 SW Sequim 4.0 in 0830 AM 11/03 0
1 SSE Port Angeles 2.8 in 0700 AM 11/03 0
1 SE Sequim 2.0 in 0700 AM 11/03 0
Port Angeles 1.6 in 0700 AM 11/03 0
1 W Port Angeles 1.5 in 0800 AM 11/03 0
4 ESE Port Angeles 1.3 in 0700 AM 11/03 0

..Jefferson County...
1 SW Chimacum 0.5 in 0700 AM 11/03 0
4 W Port Ludlow 0.4 in 0800 AM 11/03 0

..King County...
1 NW Snoqualmie Pass 1.4 in 1000 AM 11/03 3100
6 WNW Greenwater 1.0 in 0400 AM 11/03 3900
Tolt South Fork Reservoir 1.0 in 0815 AM 11/03 2000
Eastgate 0.4 in 0600 AM 11/03 0
1 ESE Woodinville 0.4 in 0800 AM 11/03 0
1 ESE Woodinville 0.4 in 0925 AM 11/03 0
1 NNE Redmond 0.3 in 0800 AM 11/03 0
2 WSW Mercer Island 0.2 in 0700 AM 11/03 0
2 ENE White Center 0.1 in 0830 AM 11/03 0
1 ENE Seattle 0.1 in 0800 AM 11/03 0

..Kitsap County...
1 SW Bainbridge Island 0.1 in 0859 AM 11/03 0

..Lewis County...
Paradise 14.0 in 0800 AM 11/03 5130
7 S Longmire 1.0 in 0900 AM 11/03 3770

..Pierce County...
Rainier Paradise Ranger Stn 10.0 in 1000 AM 11/03 5427
Longmire 2.0 in 0745 AM 11/03 2762
6 W Crystal Mountain 1.3 in 1000 AM 11/03 6410
10 WNW Mount Rainier 1.0 in 0900 AM 11/03 3160
4 SSW Crystal Mountain 1.0 in 0900 AM 11/03 5240

..San Juan County...
8 SE Eastsound 1.3 in 0800 AM 11/03 0
4 SSW Friday Harbor 1.0 in 0800 AM 11/03 0
5 E Friday Harbor 0.5 in 0605 AM 11/03 0
6 ESE Friday Harbor 0.5 in 0700 AM 11/03 0

..Skagit County...
18 W Mazama 2.0 in 0200 AM 11/03 3930
5 N Sedro-woolley 1.5 in 0800 AM 11/03 0
Concrete Ppl Fish Stn 1.3 in 0640 AM 11/03 195
14 SE Diablo 1.0 in 0900 AM 11/03 4320
1 E Mount Vernon 0.5 in 0715 AM 11/03 0
Mount Vernon 0.3 in 0800 AM 11/03 0

..Snohomish County...
Brier 0.2 in 0640 AM 11/03 0

..Whatcom County...
Wells Creek Snotel 17.0 in 0800 AM 11/03 4030
7 S Mount Baker 14.0 in 0700 AM 11/03 3520
12 NNE Hamilton 13.0 in 0800 AM 11/03 3040
4 SSE Glacier 12.0 in 0900 AM 11/03 4970
12 NW Diablo 7.0 in 0700 AM 11/03 3630
1 E Maple Falls 4.5 in 0700 AM 11/03 0
3 SE Bellingham 4.5 in 0700 AM 11/03 0
2 SW Bellingham 4.3 in 0700 AM 11/03 0
Glacier 4.1 in 0725 AM 11/03 0
2 S Bellingham 4.0 in 0700 AM 11/03 0
Mount Baker 3.3 in 1000 AM 11/03 4210
3 NNW Sudden Valley 2.8 in 0700 AM 11/03 0
4 ESE Blaine 2.5 in 0700 AM 11/03 0
8 NNE Concrete 2.0 in 0600 AM 11/03 689
1 W Lawrence 2.0 in 0600 AM 11/03 0
4 ENE Deming 1.8 in 0700 AM 11/03 0
1 SSE Lawrence 1.7 in 0925 AM 11/03 0
2 WNW Ferndale 0.7 in 0700 AM 11/03 0
Lynden 0.3 in 0800 AM 11/03 0
Point Roberts 0.3 in 0700 AM 11/03 0

No Skiing This Weekend

Between now and late Monday, we are in this sort of bits and pieces pattern, one in which there is strong southwesterly to westerly flow at crest level, but the main moisture plume is to our north.  The Tetons are in the cross hairs and we're on the fringe. 

As a result, we will see some periods of snow and snow showers at upper elevations through Monday afternoon.  These snow and snow showers will add up some, with the average water equivalent produced at Alta-Collins by our downscaled SREF product reaching just over 1.5 inches by Monday afternoon (07/00Z). 

Most members are between about 0.5 and 2.0 inches of water, which would probably be anywhere from 5 to 20 inches of snow at these temperatures.  There's an outside chance that we'd do better if the orographics kick in or the plume drifts a bit further south than currently predicted, but my view is that there won't be any skiing this weekend. 

It's worth taking a look at the broader regional picture.  Note in particular that the highest water equivalents forecast by our downscaled SREF product through Friday afternoon are found in the mountains of eastern Idaho and western Montana, including the Tetons and Wind Rivers. 

The plume diagram for Rendezvous Bowl at Jackson Hole Mountain Resort is tightly clustered, with a range of accumulations of about 1.5 to 3 inches from midnight last night through the forecast period.  Much of this precipitation falls by late tomorrow afternoon.   
A break is likely after Monday.  There are hints of the potential for more action later next week, but it's too far out to waste energy on at this time.