Heavy Mountain Rain, River Flooding, and Then a Major Cool-down
There will be plenty of action during the next week---more than I can possibly describe in this blog.
We start with a modest atmospheric river--a plume of enhanced low-level moisture--aimed at our area on Friday and early Saturday (see below), bringing substantial rain to the Olympics and north Cascades.
This atmospheric river will result in substantial rain over the next 48h, as shown by the figure below (accumulated precipitation through 4 PM Saturday). Over 5 inches over the upper windward slopes of the Olympics and north Cascades. Much less rain in the lowlands, with a dramatic rainshadow centered south of Port Townsend. This is not a record-breaking rain event, but typical of the stronger ones we have several times a winter.
This rain is falling on saturated ground and flowing into rivers that are already high. The past 72 hr have been quite wet over the southwest Olympics, mountains of Vancouver Island, and the north Cascades (see below), with many of these regions receiving 3-5 inches.
With wet ground, high river levels, and substantial rain, some flooding is inevitable, particularly since warm air and strong winds will accompany the heavy rain. Such warmth will melt some of the lower-elevation snow, contributing to rising rivers.
The latest forecasts of the Portland River Forecast Center predictions project major flooding (purple diamonds) on several rivers draining off the central and northern Cascades, and moderate or nominal flooding on several others (see below).
To further illustrate the flooding potential , here is the predicted river levels for the Snoqualmie River at Carnation. A very rapid rise on Friday and Saturday to a peak level of roughly 58 ft, roughly ten feet above normal. Followed by a rapid fall.
On late Saturday, cold air will flood into the region. Trust me, you will notice it. Not quite as cold as last time, but cold enough to bring large amounts of snow to the mountains, and a chance of lowland snow in some areas (particularly if a Puget Sound Convergence Zone forms on that day).
I will leave the snow and cold analysis to Saturday, when I can provide a more accurate forecast. And that gives me enough time to pick up milk, eggs, and bread. 😊
We start with a modest atmospheric river--a plume of enhanced low-level moisture--aimed at our area on Friday and early Saturday (see below), bringing substantial rain to the Olympics and north Cascades.
Atmospheric moisture early Friday evening, reds and white indicate high values--the
atmospheric river
This atmospheric river will result in substantial rain over the next 48h, as shown by the figure below (accumulated precipitation through 4 PM Saturday). Over 5 inches over the upper windward slopes of the Olympics and north Cascades. Much less rain in the lowlands, with a dramatic rainshadow centered south of Port Townsend. This is not a record-breaking rain event, but typical of the stronger ones we have several times a winter.
This rain is falling on saturated ground and flowing into rivers that are already high. The past 72 hr have been quite wet over the southwest Olympics, mountains of Vancouver Island, and the north Cascades (see below), with many of these regions receiving 3-5 inches.
With wet ground, high river levels, and substantial rain, some flooding is inevitable, particularly since warm air and strong winds will accompany the heavy rain. Such warmth will melt some of the lower-elevation snow, contributing to rising rivers.
The latest forecasts of the Portland River Forecast Center predictions project major flooding (purple diamonds) on several rivers draining off the central and northern Cascades, and moderate or nominal flooding on several others (see below).
To further illustrate the flooding potential , here is the predicted river levels for the Snoqualmie River at Carnation. A very rapid rise on Friday and Saturday to a peak level of roughly 58 ft, roughly ten feet above normal. Followed by a rapid fall.
On late Saturday, cold air will flood into the region. Trust me, you will notice it. Not quite as cold as last time, but cold enough to bring large amounts of snow to the mountains, and a chance of lowland snow in some areas (particularly if a Puget Sound Convergence Zone forms on that day).
I will leave the snow and cold analysis to Saturday, when I can provide a more accurate forecast. And that gives me enough time to pick up milk, eggs, and bread. 😊
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