Mid-spring is a very volatile time for the atmosphere over the Pacific Northwest.
What does unstable mean? That means upwards displaced air masses will tend to accelerate skyward for a while, leading to the creation of cumulus clouds… and even thunderstorms (see the images. below was taken on Tuesday in Seattle to see what this looks like).
Instability is related to a decrease in temperature with altitude, with a larger temperature drop with altitude creating a more unstable atmosphere. Spring, when the surface is warmed by a rapidly stronger sun while the upper atmosphere remains cooler than winter, is the time of greatest uncertainty.
The atmosphere has begun to fill this morning with small cumulus clouds forming around Puget Sound (see Seattle PanoCam below)
And a satellite image visible early this morning shows some dramatic calcareous/cumulative growth approaching the northern Oregon coast:
This volatility is being “fueled” by an approaching bottom that provides upward movement that helps release instability (see upper map forecast for 5pm below).
My team forecasts the model and identifies where the lightning threat is. Forecasts at 3pm suggest that much of the area (red shade) could experience lightning.
Here at UW we also run very high resolution models that are able to directly simulate strong convection (product activity). The simulated clouds forecast at 5 p.m. today predicts the existence of large cumulus/cumulonimbus bands developing in the area (look for small ovals in the infrared satellite images). burn below)
So be prepared for some showers and even some booms this afternoon. Certainly not like the Kansas thunderstorms, but a reminder of how spring can bring the legendary showers and sunshine to the Pacific Northwest.
