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.

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