Strong storm off the Pacific Northwest coast

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

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Nighttime images  of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) data (above) showed an occluded extratropical cyclone off the coast of the Pacific Northwest at 1050 UTC or 3:50 AM local time on 13 November 2017. This system was producing storm force winds offshore.

A GOES-16 Mesoscale Sector had been positioned over that region, providing imagery at 1-minute intervals — the structure and evolution of the storm could be seen using Lower-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor imagery (below).

GOES-16 Lower-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play MP4 animation]

GOES-16 Lower-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play MP4 animation]

A more detailed view was provided by GOES-16 “Red” Visible (0.64 µm) images (below), with hourly wind gusts plotted in yellow. Peak wind gusts as high as 89 mph were reported within the Seattle and Portland County Warning Areas.

GOES-16 Visible (0.64 µm) images, with hourly wind gusts plotted in yellow [click yo play MP4 animation]

GOES-16 Visible (0.64 µm) images, with hourly wind gusts plotted in yellow [click yo play MP4 animation]

A comparison of Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 2038 UTC or 1:38 PM local time (below) showed a curved cloud band with embedded convective elements moving inland over western Washington and Vancouver Island. Note that the VIIRS instrument will also fly on the JPSS series of satellites.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Wind Storm Update

The first...and lesser act...of today's wind event took place this morning, the passage of an occluded front associated with the offshore low.  But the main act is still in the cards, and folks should be prepared.

The infrared satellite image at 6 AM shows the swirl of clouds around the low center, located southeast of Vancouver Island.  The occluded front is indicated by the roughly north-south band of cloud over the Cascades at that time.


Heavy rain accompanied the occluded front (see radar at 2 AM), and after its passage winds surged.


The maximum winds during the last 24 hr (ending 6 AM), which pretty much happened during the past 6 hours, are impressive: several over 40 mph in the central Puget Sound, with some on the Kitsap Peninsula reaching 50-60 mph.  Even stronger winds on the coast.


 Power outages have already occurred over Seattle
 And Puget Sound Energy has about 25,000 customers blacked out, including large areas over the Kitsap.

The winds above Seattle-Tacoma Airport show the movement of strong winds aloft, some of which have reached the surface in gusts.  This chart shows sustained winds from the surface to 10,000 ft (700 hPa pressure in this figure), with time increasing to the right (in UTC, 13/12 is 4 AM this morning).  The solid triangles indicate 50 knot sustained winds.  Strong winds came in aloft overnight, and intensified with the occluded front.  Temperatures area cooling as well (think snow in the mountains).

We are now in the break before the main act.   You will even notice the rain has backed off and there will be sun breaks. Absolutely typical.  We must wait until late morning/early afternoon when the low approaches and the winds will increase again, probably exceeding what we experienced last night.

The UW has developed the Seattle WindWatch site (sponsored by Seattle City Light) to assist City Light in preparing for and managing wind outages.  One of its capabilities is to present the latest High Resolution Rapid Refresh forecast from the National Weather Service.   This system forecasts very strong winds along the coast at 11 AM (blue indicates gusts about 50 mph), with lesser, but still problematic winds (40-50 mph gusts) over the Seattle, with stronger gusts from Everett westward.
 By 4 PM, winds will accelerate further over central and southern Puget Sound.  With many leaves still on the trees and new branches untested by strong winds, expect more power outages.
Be prepared for the increasing gusts and avoid places with a lot of trees.  No biking to the UW on the Burke Gilman trail for me today!  And if you have trees around your home, expect lots of leaves down.

Überströmungs Cyclogenesis!

A classic example of Alpine lee cyclogenesis of the "Überströmungs-type" is bringing heavy snowfall to portions of the Alps and southern Europe.

Alpine lee cyclogenesis is the birth of a cyclone in the lee (downstream side) of the Alps.  Überströmungs-type Alpine lee cyclones form in northwesterly large-scale flow as cold air is blocked and flows cyclonically to the west of the Alps, while the upper-level trough continues to move downstream, inciting cyclone development in the western Mediterranean region.  Terrain impacts are especially pronounced in cyclones that form in this fashion.

The satellite and sea level pressure loop below shows the situation from 1200 UTC 11 November through 1200 UTC 13 November.  The system begins as a surface trough that plunges southeastward across the British Isles, France, and Germany.  The cold air plunges southward through the low elevation region between the Alps and Pyrenees (note faint rope cloud in the loop), and strong cyclogenesis occurs over northern Italy.


@severe-weather.EU is the feed to monitor this morning as they are tweeting out some wonderful images from across the region.  Here are a few.

 Enjoy the look at the fresh snow.  Let's hope we can join the party later this week.