Unstable Air Today with Potential Thunderstorms

Middle spring is a very unstable time for the atmosphere over the Pacific Northwest.

What do we mean by unstable?    It means that parcels of air displaced upwards will tend to accelerate skyward for a time, resulting in the production of cumulus clouds...and even thunderstorms (see pictures below taken on Tuesday in Seattle to see what this looks like).

Instability is related to the decline in temperature with height, with larger temperature decreases with height producing a more unstable atmosphere.  Spring, when the surface is being warmed by a rapidly stronger sun while the atmosphere above is still cool from winter, is the time of largest instability.

The atmosphere is already starting to percolate this morning with small cumulus clouds forming around Puget Sound (see Seattle PanoCam below)

Middle spring is a very unstable time for the atmosphere over the Pacific Northwest Unstable Air Today with Potential Thunderstorms

And a visible satellite image earlier this morning shows some impressive cumulus/cumulonimbus development approaching the northern Oregon coast:


This instability is being "juiced up" by an approaching upper-level trough that provides upward motion that helps release the instability (see upper-level map forecast below for 5 PM).


My group takes in the model forecasts and determines where a threat of lightning exists.  The prediction for 3 PM afternoon shows much of the area (red shading) could experience lightning.


Here at the UW we also run very high-resolution models capable of directly simulating strong convection (cumulus activity).  The forecast of simulated clouds for 5 PM today predicts the existence of bands of large cumulus/cumulonimbus developing over the region (look for the small oval shapes in the simulated infrared satellite image below)


So be prepared for some showers and even some boomers this afternoon.  Not like Kansas thunderstorms for sure, but a reminder of how spring can bring the fabled showers and sunbreaks to the Pacific Northwest.


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