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November 2014

More Shadows

Posted: November 24th, 2014


This morning's High Resulotion Rapid Refresh model showing another big rain shadow over the city, while the mountains get hit.

This morning’s High Resolution Rapid Refresh model showing a lunging warm front and another big rain shadow over the city (while the mountains get hit).


The weather pattern looks to remain active this week and beyond, with rainy-but-not-too-wet systems passing through about once every three days. It’ll also get relatively warm and humid with lows temperatures near 50°F Tuesday through Thursday.


Not-too-wet certainly described this past weekend when strong rain shadowing provided lots of sun to the lowlands. Three-day city-wide rainfall totals ranged from 0.95″ (SODO) to 1.27″ (Haller Lake). The maximum intensity recorded by an SPU rain gauge was 0.42″ (Magnuson Park) in one hour on Sunday morning. Maximum recreational intensity was undoubtedly recorded later in the day.


First up this week is a robust warm front associated with a large low pressure system well offshore. Rather than drifting northward up the coast, this front and its moisture plume will lunge at us from the west. That flow will once again place Seattle in the rain shadow while surrounding mountains get drenched tonight and tomorrow. The National Weather Service has issued a Flood Watch for King County.


After a lull on Wednesday, the above system’s cold front will finally reach us late on Thursday and provide the next shot of rain. The flow is expected to nudge the rain shadow north a bit, so Friday city-wide rainfall totals—especially south end totals—should be higher than they’ve been in weeks. Beyond Friday models suggest quiet weather, though the atmosphere is moving too quickly to inspire much confidence.


Also of note: predicted tides will be somewhat high this week; fortunately air pressure is not forecast to exacerbate the issue. Coastal impacts are therefore not likely, regardless of rainfall amounts.



The latest National Weather Service forecast for Seattle indicates 0.59″ of rainfall before midnight tonight, followed by 0.45″ tomorrow, 0.06″ Wednesday, 0.43″ Thursday, 0.68″ Friday, and 0.04″ both Saturday and Sunday. Southerly winds will be occasionally gusty, but will likely remain below advisory levels.


Over SPU’s mountain reservoirs, the latest NWS forecast shows around 4″ of rainfall tonight through tomorrow, followed by another 1-2″ late Thursday into Friday. With the warm frontal passage, snow levels will sadly climb to over 8000′. By Friday they should drop back under 5000′ at which point a little white may return. Like the lowlands, southerly winds will be occasionally gusty throughout the period, but not damaging.


NWS Area Forecast Discussion
NWS Forecast Table Interface—Seattle
NWS Forecast Table Interface—Tolt Reservoir
NWS Forecast Table Interface—Chester Morse Lake