Lightning in the Cascade Foothills and Snow in the Mountains

Yesterday evening, western Washington had the visual treat of a magnificent lightning display along the western foothills of the Cascades.   A stunning picture by Sigma Sreedharan, illustrated the active thunderstorms that hit the region after roughly 5 PM


And the lightning strike map over the 24-h ending 1 AM today (Wednesday) shows the hundreds of lightning strikes west of the Cascade crest.

 Theses thunderstorms were associated with huge towering cumulonimbus clouds as illustrated by this wonderful cloud shot by Dr. Peter Benda, looking east from Bellevue.  Virtually mountains in the sky.


The huge cumulonimbus clouds were associated with the approach of an upper-level trough (low pressure), which caused upward motion (which helps initiate thunderstorms) and cooler air aloft (which helps to promote a large decline in temperature aloft, which in turn produces instability). Low level westerly winds pushed the unstable air up the western side of the Cascades, releasing the convection.

500 hPa (about 18,000 ft) heights, winds, and temperature (color shaded).

The visible satellite image at 7:01 PM clearly shows the bubbling thunderstorms on both sides of Seattle (the Kitsap had a storm as well).


Lots of lightning...but what about snow?

A fairly strong front (white arrow pointing to it) was lurking offshore yesterday afternoon (see visible image around 5 PM).  Behind the front was much cooler air, something made evident by the popcorn-looking instability clouds behind it (they are produced by cool air moving over warmer water).


Behind the front, the freezing level dropped to around 5000 ft (snow level around 4000 ft), but snow in the central Cascades got supercharged by the development of a Puget Sound convergence zone (which formed as the winds behind the front veered into a westerly direction).  The radar imagery this morning around 9 AM shows the convergence zone extending from Seattle eastward towards the Cascades--providing lots of precipitation and helping to drop the freezing level further (melting snow cools the air below).


The scene at Steven Pass at 10 AM this morning was, well, wintry and beautiful.


The cold air will soon be history and dry conditions, with temperatures zooming up into the lower 80s will be enjoyed by western WA residents this weekend.

Comments

Post a Comment

Popular posts from this blog

Why so little lightning in the Pacific Northwest? And a very nice weekend ahead.

Image
During the past 24-hours, there have been a few lightning strokes over the region (see below) but nothing to write home about (see below). It turns out that the Pacific Northwest and the remainder of the West Coast have some of the lowest frequencies of thunderstorms in the entire country (see below). But why?    My podcast provides the answer. And I also give the weekend forecast....and I think most will like what I have to say. To listen to my podcast, use the link below or access it through your favorite podcast service. Some major podcast servers:     Like the podcast? Support on Patreon 
Read more

The Time of Year You Can See the Air Move

Image
  Most of the time, you can not see the air move.   You can feel it, but the complex, turbulent motions are invisible to you, except when it interacts with leaves and branches on trees and plants. But for a few weeks of the year, the sky is full of small, cotton-like tuffs that like a natural MRI machine reveals the complex three-dimensional motions of the atmosphere.   Cottonwood season.  And we right in the middle of it.   Being cottonwood aware is of particular value this year.  It reveals the active dispersion and movement of air that makes the outdoors essentially COVID safe, and thus should be of some comfort for those nervous about transmission outside. Cottonwood seeds are embedded in small cotton-like fibers.   A million seeds weigh about 3 pounds.  Yes, each seed and tuff weights about .000003 pounds.   And that fact, plus the cottonwood tuff, means that these seeds fall VERY, VERY, VERY slowly.   So slowly that they are excellent markers for the three-dimensional flow of the
Read more

A Much Colder Than Normal April: But How Unusual?

Image
  April was a chilly month over the Northwest, but how chilly?     It turns out the answer depends on where you are located. The difference between this April's temperatures from normal across Washington State (below) shows that the entire state was well below normal.  The eastern side of the state was particularly frigid:  some areas were more than 6 degrees below normal.   Considering the west side of the state, the April mean temperatures at SeaTac Airport are plotted below.   This April was the coolest since 2011. April 2020 was in 15th place for the coolest April since the mid-1940s and was a bit more than 4F below normal.  So if you felt that you were cheated out of normal spring warmth...you are right. But if you really wanted to experience extraordinary April cold you had to be east of the Cascade crest. Consider Yakima.  Wow.  It had the third coldest April temperature since the mid-1940s.   And the all-time record in 1955 was only slightly colder. If you want a longer-te
Read more