Today, while much of western Washington warmed and was hit by moderate rain associated with a warm front, Northwest Washington, stretching from Whatcom County to San Juans, experienced snow.
Why localized snow? Because of cool air jetting out of the Fraser River Valley northeast of Bellingham, as illustrated by this surface map at 10 AM today (Wednesday). The Fraser River Valley acts as a conduit of colder air from the interior of British Columbia and the approaching low pressure increased the pressure difference across the gap.
The warm front has brought dramatically warmer temperatures over our region. Check out the temperatures and winds above Seattle during the past 24 h using a time/height cross section (time is along the x axis, height is the y axis, see below). Huge warm up from roughly -6C to 3 C at 850 hPa pressure level (about 5000 ft). About 15F increase. The freezing level at Quillayuate along the WA coast rose to over 8000 ft this afternoon.
The warm southwesterly flow was associated with an atmospheric river, a current of large moisture values out of the tropics (see map of moisture values at 10 PM)
As this moisture ascended our terrain, moderate to heavy rain fell, as shown by the 24h values ending 8 PM. Particularly heavy rain was found over the southern WA and Oregon Cascades and over the coastal mountains (some places received more than 2 inches). That moisture is being added to rapidly melting snow at lower elevations.
But it doesn't stop there. Here is the precipitation total forecast for the next 48h from the UW WRF model. Wow....5-10 inches over the coastal mountains and the higher Cascades. California shares the fire hose of water as well.
All this precipitation (and a very high freezing level, rising to over 7000 ft), is causing the regional rivers to rapidly rise, with a number of them at or near flood stage (red dots).
And a combination of high astronomical tides and low pressure could cause coastal flooding.
Did I mention the potential for strong winds mid-day Friday as a strong trough of low pressure moves through our region?
Lots of activity to keep meteorologists busy...but remember, the start of meteorological spring in the NW is only a few weeks away: February 25th!
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Announcement
The Northwest Weather Workshop, the big annual weather gathering in the Northwest, will take place on March 3-4, 2017 in Seattle (NOAA Sand Point Facility). Everyone is welcome. For more information and to register, go to https://www.atmos.washington.edu/pnww/
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Why localized snow? Because of cool air jetting out of the Fraser River Valley northeast of Bellingham, as illustrated by this surface map at 10 AM today (Wednesday). The Fraser River Valley acts as a conduit of colder air from the interior of British Columbia and the approaching low pressure increased the pressure difference across the gap.
The warm southwesterly flow was associated with an atmospheric river, a current of large moisture values out of the tropics (see map of moisture values at 10 PM)
But it doesn't stop there. Here is the precipitation total forecast for the next 48h from the UW WRF model. Wow....5-10 inches over the coastal mountains and the higher Cascades. California shares the fire hose of water as well.
Did I mention the potential for strong winds mid-day Friday as a strong trough of low pressure moves through our region?
___________
Announcement
The Northwest Weather Workshop, the big annual weather gathering in the Northwest, will take place on March 3-4, 2017 in Seattle (NOAA Sand Point Facility). Everyone is welcome. For more information and to register, go to https://www.atmos.washington.edu/pnww/
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