Next Round of Gap Winds Ahead

 FastCast--Friday, Feb. 16 to Tuesday, Feb. 20:

After a complex system that produced areas of snow and gusty gap winds, another round of strong easterly offshore winds is ahead across the region. Near the foothills, especially around North Bend, Enumclaw, and Gold Bar, expect gusts of 45-55 mph. Isolated areas, mainly on backcountry ridgetops, could reach 60+ mph. Lowland locations from the King/Pierce County line north to the Everett area, and then north of Bellingham, will have gusts of 30-40 mph. These winds will likely be strongest between Federal Way and Seattle, extending west toward Bainbridge Island and east to the foothills. Coastal areas will also be impacted by offshore winds gusting 40-50 mph, strongest around the Willapa Bay area. Outside of wind impacts, expect a chilly morning on Friday, with the lowlands dropping to the upper 20s to low 30s. After peaking on Friday evening, gap winds will ease on Saturday. Expect off-and-on light rain from late Saturday through Tuesday. Additionally, expect highs in the low to mid 50s, with lows in the upper 30s to low 40s. Conditions through Tuesday will be partly to mostly cloudy.

----------------------------------------------------------------------

Continue reading the full blog below!

Another round of gap winds is ahead for Western Washington, and this round will be stronger than the winds on Wednesday night and Thursday morning. Let's take a look at the forecast! (Cold temperatures statewide on Friday morning...forecast at bottom!)

First, we'll take a look at the NAM high-resolution forecast, showing peak wind gusts through Saturday.

This forecast shows very strong gusts over the Cascades and in the immediate foothills, with 45-55 mph gusts possible for North Bend, Enumclaw, and Gold Bar, with gusts over 60 mph for remote ridgetops. This forecast also shows gusts of 40-50 mph from Kent to Shoreline, with an area of 50-55 mph gusts from Renton to Issaquah. Lesser areas of gap winds are found around Chehalis (gusts up to 35-40 mph) and north of Bellingham (35-40 mph). The coast will have offshore winds gusting 40-50 mph, with isolated areas of stronger gusts possible in Pacific County.

This forecast is on the higher side of what's possible, but is definitely within the realm of possibility. One thing to note is that there is usually a sharp cutoff on the southern edge of gap winds in the Puget Sound area.

Let's compare this to the HRRR high-resolution forecast, seen below.

This forecast shows slightly lesser winds, with the foothills (such as North Bend, Enumclaw, and Gold Bar) gusting 45-55 mph, and gusts from roughly Kent to Everett reaching 35-40 mph. Areas from Renton eastward could reach 40-45 mph. Additionally, expect gusts of 40-50 mph on the coast, strongest in Pacific County.

Gap winds frequently cause power outages in the Cascade foothills and areas between I-5 and the foothill region. Whenever gap winds could reach 40+ mph, be prepared for tree damage and power outages.

So, what is causing these gap winds? The answer can be found below, in the NAM high-resolution forecast for surface pressure.

Notice how pressure is higher (darker red/brown) east of the Cascades, and lower (lighter orange/red) west of the Cascades. A strong cross-Cascade pressure gradient is what fuels gap winds. On Friday evening, the gradient between Seattle and Wenatchee (a key measurement for gap winds) will be approaching 8-12 millibars, a decent gradient that is a sign of potentially strong gap winds.

Finally, let's take a look at the forecast low temperatures across Washington on Friday morning. With relatively clear skies and a somewhat colder airmass, temperatures will get below freezing for most of the state. The European model forecast for Friday morning's lows is seen below.

Expect lows in the mid 20s to low 30s for the lowlands (colder in areas sheltered from easterly winds). The coast and Willamette Valley will only drop to the mid 30s. In Eastern Washington, expect lows in the upper teens to mid 20s, with mountain towns dropping to the upper single digits to mid teens. 

Stay safe and stay warm!