Update 7:15 AM Wednesday: A Wind Advisory has been issued for the Puget Sound Lowlands, in effect from 5 AM to 8 PM, for winds gusting up to 45 mph. The alert is posted below.
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FastCast—Wednesday, May 18 to Sunday, May 22:
A significant May storm is approaching Western Washington, with impacts on Wednesday and Thursday. The biggest impact for most of the region will be winds. Expect gusts up to 30-40 mph on Wednesday, strongest in the morning. Locations near the water could experience gusts up to 45 mph. The coast, North Sound, and areas along the Strait of Juan de Fuca will gust 45-50 mph. Forecasts have also hinted at an area of stronger winds (40-45 mph) in Tacoma and vicinity. With leaves on most trees, there is a higher chance of power outages and tree damage. The lowlands won’t receive much rain with this storm, with 0.1-0.3 inches, except 0.4-0.5 inches south of Olympia and under the Convergence Zone, and up to 1.5 inches on the coast. Convergence Zone bands are expected late Wednesday through Thursday. These bands and cooler temperatures will bring mountain snow through Thursday. The Passes will receive up to 6 inches of snow (maybe less at Snoqualmie), and 1-3 feet will fall at higher elevations. However, good weather is finally on the way. High temperatures will increase from the upper 50s on Wednesday and Thursday to the upper 60s to low 70s on the weekend! Expect lows in the low 40s, except near 50 on the weekend.
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Continue reading the full blog below!
A significant May storm is heading for the Pacific Northwest, with main impacts on Wednesday and Thursday.
The biggest impact will be winds, especially on Wednesday morning. The HRRR high resolution forecast for gusts at 9 AM Wednesday is below.
Expect gusts of 30-40 mph around the lowlands, strongest from 7 AM to noon. Models have consistently been showing areas of higher winds, gusting near 45 mph, in the Tacoma area. Gusts of 45-50 mph are expected along the Strait of Juan de Fuca, in the North Sound, and on the coast.
With most trees fully loaded with leaves, the threat for power outages is higher with this storm than previous ones. Be prepared for outages and tree damage, as fully loaded trees create more drag and are more susceptible to breaking.
Before moving on to mountain snow, let’s take a look at another high resolution forecast. The NAM model forecast for gusts at 8 AM Wednesday is below.
The NAM and HRRR have good agreement in wind speeds for the lowlands, both showing a decent probability of 35-40 mph gusts (possibly higher). This is abnormal for May, and if these predictions are indeed correct, there will likely be tree damage.
This storm will also bring mountain snow, both on Wednesday and in Convergence Zone bands on Thursday. The HRRR forecast for snow through Thursday evening is below.
Although it is quite rare, it will snow at the passes in mid-May. The snow level will drop to near 3,000 feet by Thursday evening, and most passes will receive 4-6 inches of snow, with the most expected at Stevens. This snow is not enough to cause major impacts, but rapidly lowering snow levels with heavy snow in Convergence Zone bands can temporarily worsen road conditions, even at this time of year. Higher elevations will receive 1-3 feet of snow, adding to our already above average snowpack.
Lowland rain with this system will not be that impressive. The HRRR forecast for rain through Thursday evening is below.
Generally, expect 0.1-0.4 inches in the lowlands, potentially more under Convergence Zone bands on Thursday. Areas south of Olympia and on the coast will receive 0.5-1 inch, with the most in the Olympic Mountains (1-3 inches).
In short, a storm reminiscent of winter or early spring will impact Western Washington on Wednesday. The main impact for the lowlands will be abnormally gusty winds, potentially near or above 40 mph at their peak on Wednesday morning.
Stay tuned for details about the warm (upper 60s to low 70s) and sunny weather possible this weekend!
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