9:15 PM Friday: With little change in the forecast shown below, the Friday night update has been postponed to Saturday morning. Check back for an update by 10 AM Saturday.
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No FastCast today…this blog is an update of Wednesday’s post about the dangerous fire weather ahead for the Pacific Northwest.
On Friday, the worst smoke of 2022 will begin impacting Western Washington. Most of Friday’s smoke will be from the Chilliwack Complex & NW Pasayten Fires in the North Cascades. The HRRR forecast for smoke aloft at 8 AM Friday is below.
Moderate concentrations of smoke aloft will be moving through the lowlands. By mid-morning, some surface smoke will be moving through the area as well, as seen below.
Surface smoke will have a hard time getting close to Puget Sound, as northerly winds will keep the air clean through Friday evening. Degraded air quality is possible, especially near the Cascade foothills and from Olympia southward, including the coast from Ocean Shores southward.
However, Saturday brings a much different picture. By Saturday morning, easterly offshore winds will have been blowing for over 12 hours, and smoke from Eastern Washington, Idaho, and Montana will be firmly entrenched over Western Washington.
Notice moderate concentrations of smoke aloft over the entirety of Western Washington. While smoke aloft will be heavier, the main impact will be much heavier and more widespread surface smoke, as seen below at 9 AM Saturday.
Moderate concentrations of surface smoke will degrade air quality across Western Washington most of Saturday. Conditions will be even worse in Oregon and from Ellensburg south in Eastern Washington.
As smoke first moves into the area on Friday, winds will begin increasing. The HRRR forecast for wind gusts at 6 PM Friday is below.
Northerly winds will be blowing down Puget Sound, while easterly gap winds will be ramping up in Northern Oregon. On Friday, expect northerly winds gusting 20-30 mph around the Puget Sound area, strongest in the afternoon & evening. Gusts near 40 mph are possible in Whatcom and San Juan Counties due to Fraser River outflow winds.
However, fire weather conditions will get worse as Friday night goes on. Overnight, winds will shift from northerly (down Puget Sound) to easterly (out of the Cascades). These easterly winds will substantially dry out the region and will be strongest in the Cascades and in areas downwind of gaps in the terrain. The NAM forecast for gusts at 5 AM Saturday is below.
At 5 AM Saturday, the NAM model shows winds gusting over 45 mph in the Cascades of Washington and Oregon, and in the Oregon Coast Range, with 30-45 mph gusts possible downwind of gaps in the terrain.
It is important to note that the NAM has been the most aggressive model with these winds. A more conservative estimate would be to expect winds in the mountains to peak at 40-50 mph, with areas downwind of the gaps reaching 25-40 mph. Peak winds will occur from early Saturday morning through early afternoon.
One more very important aspect of this upcoming event is the relative humidity. This is a measure of how much moisture is in the air at a given time. Northerly and easterly winds lower the humidity in Western Washington, and that will be very evident on Friday and Saturday. Northerly winds on Friday will drop humidity in Western Washington to 20-35%, which is very dry for our region.
However, by Saturday evening, conditions are much worse. The HRRR forecast is below.
Dark brown colors indicate very low relative humidity. Expect values to drop into the 5-15% range in the lowlands, an incredible feat. This will only elevate the risk of fire spread, combined with easterly winds and a hot day on Saturday.
The HRRR forecast for Saturday’s high temperatures is below. Note that smoke aloft and near the surface will likely decrease these temperatures by as much as 5 degrees.
Without the influence of smoke, highs in the lowlands would reach the mid 80s to low 90s, and the Willamette Valley would reach the low to mid 90s. However, smoke will make it hard for temperatures to climb to these levels. Expect lowland highs closer to the mid 80s. Offshore flow will bring abnormally warm temperatures to the WA & OR Coasts, likely in the upper 70s to low 80s.
This dangerous fire weather event won’t be limited to just Western Washington. Red Flag Warnings (magenta) stretch from Northern California to the Canadian border, covering the majority of Washington and Oregon.
Be sure to stay tuned. I will have another blog update by 10 PM Friday, and even more updates can be found by clicking the Twitter icon on the right side of the blog. Some helpful websites can also be found, including a link to current air quality.
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