Viva la Zone

Noodler on Monday, September 7, 2020 – 08:09 am

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Portland NWS offices 4am

Portland NWS offices 4am discussion;

<<.SHORT TERM...Today through Wednesday...Forecast appears to be very well on track this morning, with strong east to northeast winds expected to develop across much of the forecast area later today. As such, we only made minor changes on this shift. The synoptic features models have been portraying for days are becoming evident on satellite and surface observations. High pressure is indeed strong over northern British Columbia at nearly 1040 mb. Meanwhile, 3.9 um thermal satellite imagery clearly shows very warm conditions along/near the Oregon Coast south of Cape Blanco, maintaining a thermal trough of low pressure there. North Bend to Spokane MSLP gradients remain weakly onshore, but that will be changing soon - and rapidly - as the strong B.C. high pushes south into the Interior Northwest. In other words, all the ingredients are coming together as expected for a potent and likely historic September East Wind event in our forecast area.

The strongest east winds still appear to focus through the gap in the high Cascades between Mt Adams and Mt Hood (sort of the broader Columbia Gorge area) across western portions of the Columbia Gorge, Portland/Vancouver metro area, north Oregon Coast and Coast Range. While high resolution guidance has generally backed off ever so slightly with the magnitude of this event, 00z NAEFS and EPS means continue to show the type of event that only occurs a couple times a century in September. 00z NAM/GFS are still forecasting Spokane to North Bend MSLP gradients of 21 to 23 mb late tonight and early Tuesday morning, with 900 mb east winds of 65-75 kt over Portland. Any weakening in the models` projections for this event has only put the expected wind speeds down into the ranges we`re forecasting - if they had remained in the 23 to 26 mb range with 75-85 kt 900 mb winds over Portland, we would have had to increase our forecast. As such, confidence is only increasing that 40 to 60 mph east wind gusts will develop through the corridor mentioned at the beginning of this paragraph, with gusts 60 to 80 mph expected on exposed ridges. In other words, the High Wind Warnings currently in place look to be in great shape, and no changes were made on this shift.

The existing Red Flag Warnings also look to be in good shape. We are on track for an extremely dangerous period of fire weather beginning this afternoon, as discussed below by the evening shift. The rare combination of an easterly downslope windstorm and extremely low relative humidities have led the Storm Prediction Center to put the area mentioned above into a rare "Extremely Critical" category in their Day 1 Fire Weather Outlook.

We will be issuing a Heat Advisory starting 4 PM this afternoon until 10 PM Tuesday for the coast Tillamook southward and the central Coast Range of Oregon, where high temperatures in the 90s will be common once the east winds arrive. The timing of this advisory is a bit tricky, as some portions of Oregon`s Central Coast may remain cool and cloudy today until the east winds arrive sometime this afternoon or evening. It`s entirely possible many coastal locations south of Lincoln City will see their temperatures rise tonight as offshore winds develop. Offshore winds will persist through the day Tuesday, holding off any sea breeze which could cool off the immediate coast.

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Oregon ~ Portland Wind and Fire Sept. 2020

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