Morning Update: Major Windstorm Expected, Impacts Likely

Update 8:00 AM Tuesday: It is likely that a significant windstorm will impact Western Washington on Tuesday. Strong gusts will bring a likelihood of widespread power outages and widespread tree damage. Low pressure, king tides, and strong winds will bring tidal overflow in Puget Sound and damaging high surf on the WA & OR Coasts. Continue reading below for an explanation of the impacts.

Let's start with the forecast. Below is Monday night's run of the high-resolution HRRR model. Forecasters have noted that this model seems to be accurately predicting the dynamics of the winds for the Seattle area. 

The HRRR shows peak winds around the lowlands around 4 PM Tuesday, with peak wind gusts of 55-65 mph. Earlier, the coast will peak at 60-70 mph, and around this time, Eastern Washington will reach 50-65 mph, and the Eastern Strait of Juan de Fuca will be gusting 50-65 mph with a very strong westerly surge.

Below is a wind gust graphic from NWS Seattle, showing expected peak wind gusts around the region on Tuesday.

NWS Seattle is calling for gusts of 50-60 mph for all areas from Everett south and along the Eastern Strait.

Finally, the high-resolution NAM model forecast.

This forecast underscores the still-present uncertainty regarding the windstorm forecast, showing a lower & later peak winds (around 8 PM, 40-50 mph) for the Sound. It still shows 60-70 mph on the Coast, 50-65 mph in Eastern WA, and 50-60 mph along the Eastern Strait. Additionally, the NAM shows peak winds of 55-65 mph for the Portland area around 3 PM.

Regardless of the exact wind speed, any gusts over 45 mph can be problematic in Western Washington, with scattered power outages and tree damage possible. However, when gusts go over 50-60 mph, much more widespread power outages and tree damage is expected. Saturated soils from recent rain & snow will make it easier for trees to fall. Included below is the High Wind Warning for the Seattle area from NWS Seattle. It is in effect from 1 PM Tuesday to 1 AM Wednesday, for SW winds of 30-40 mph, gusting to 55 mph. It is good practice to read the warnings and see what impacts are expected in the storm.

Below is a 7:45 AM satellite image, showing the storm offshore.

The area outlined in red is what we have to worry about. It is called the bent-back occlusion, sting jet, or scorpion's tail. This brings the strongest winds up the lowlands in a sudden surge, with gusts going from 20-30 mph to 45-65 mph in minutes. Be prepared for this sudden wind surge between 1 PM and 3 PM Tuesday.

Below is the UW forecast showing the strong pressure gradient that will cause the strong wind surge. This forecast is for 7 PM Tuesday, a bit later than the rest of the models.

The UW model shows the peak pressure gradient around 7 PM, later than other forecasts but showing the uncertainty that still exists with this setup.

Finally, due to very low pressure and king tides, coastal flooding/tidal overflow is expected around Puget Sound, and dangerous surf conditions are expected along the coast, with the combination strong winds, low pressure, king tides, and high surf creating dangerous conditions. Below is a NWS Portland graphic showing expected surf heights on Tuesday.

Maximum wave heights of 30-40 feet are expected for the WA & OR Coasts. This will likely run up most beaches at high tide and create areas of coastal flooding. Tidal overflow is also expected in bays and estuaries.

Stay tuned as this storm is ongoing. The best places to stay updated are Twitter (link on top right of blog), NWS Seattle, and Pacific Northwest Weather Watch on YouTube, where Michael Snyder makes a very informative briefing each day.

Stay safe and be prepared for power outages. Charge your cell phone and have a flashlight ready!