March 20, 2013

Strong Spring Storm

A vigorous low pressure system and attendant front is now moving through the Northwest.
A 3-h forecast for 8 AM this morning shows a moderately deep low (985 hPa) crossing northern Vancouver Island and the surface occluded front now over western Washington (solid lines are isobars, colors are low-level temperatures, wind barbs as well--if you have good eyes).  Strong pressure differences exist west and south of the low and some of that will be moving into the region later this morning and during the afternoon.   So expect a major uptick in winds. Very strong pressure gradients and powerful winds west and south of low centers is very typical for oceanic cyclones...lots of names of this--bent-back trough, poisonous tail, and others.

Take a look at the 8:30 AM visible satellite image.....stunning picture showing the front over western Washington and the cold unstable air behind it. (click on it to get an enlarged view)

 Here is the forecast for this afternoon at 1  PM---you can see how the low has moved inland and large pressure gradients extend over western Washington and the coast.  Big pressure gradient cause strong winds.

 Of particular note, as the low moves past us, a very large pressure difference will be set up at low levels over the Strait, while aloft the winds will be aligned along the axis.  As a result, expect a strong surge of westerly winds down the Strait, with gusts reaching 40-60 mph.  Here is the sustained wind forecast for 2 PM this afternoon.  The green winds are sustained at 35 kts.

 The other major story with this system is snow---lots of it in the mountains.  For the first time this winter Mt Baker has reached 200 inches of snow depth with 203 inches reported at 6 AM PDT after 11 inches of new snow fell since late yesterday afternoon.  Normal snow depth for March 15 is 165 inches at Mt Baker.   And lots of new snow at Mt. is a view from Paradise this morning.

And congratulations...we are now officially into spring, which stated 4:02 AM this morning!


  1. FROPA through Downtown Portland in the last few minutes (apparently) with no marked increase in rain or wind, evidenced by the now complete lack of both and a clearing sky. Quite boring, actually.

    Just another typical mid-November-esque day, except we're on the wrong side of Christmas.

    Have fun up North, we got the shaft yet again down here.

  2. Cliff,
    It seems with these Low systems, the rain comes first, then the wind comes, Most of which the biggest intensity is after the rain. Thats also what I recall happening earlier in December when a similarly powerful storm hit us here in the northwest. You wrote about it here:

    is this a predictable occurance? It seems common, if so why is that?

    thanks for your insight and amazing work!

  3. Pretty windy right now in downtown Seattle. I am on one of the upper floors of the Wells Fargo building and the gusts are loud and constant. For the first time I can feel the building moving slightly in the heavier gusts.

  4. It seems we've been in the cloud doughnut hole rather than the convergence zone this last winter. Maybe the winds aloft haven't been strong enough fot a good convergence.

  5. The mountains aren't the only place with snow this morning! Just a dusting here in Clearview (on the hills between Woodinville and Snohomish).


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