What caused Western Washington's spring storms

The last day of March had some pretty wild weather across the Northwest, everything from heavy rain to lightning, thunder, and hail -- even heavy snow in the Cascades.

The main culprit for these thunderstorms was a batch of cold air aloft that helped to destabilize the atmosphere. A few sunbreaks warming the surface added to the instability. The analogy would be like letting a beach ball go underwater, it promotes that bubbly, rising motion that creates widespread showers.

Hail storms moved over northern Seattle neighborhoods on Tuesday dropping a coating so thick it looked more like snow. A tree in Washington Arboretum Park was splintered by lightning. The view from the roof of my apartment looking at the hail shaft as it crossed Interstate 5 around 4:30 p.m.

With the unstable air in place, we also had what's called a convergence zone develop. This typically forms behind cold frontal passages, like we had earlier in the day. Winds shift from the west, flow around the Olympic Mountains, and meet back up near Puget Sound -- much like a river flowing around a rock island.

When the air meets, it creates a small scale front that is forced to rise and generates a persistent band of rain. Or in some cases, like yesterday, snow.

The convergence zone generated a band of snow that dumped specifically on Snoqualmie Pass. By the morning, 15 inches of new snow had fallen and chains were required to drive the summit.

Unfortunately, the ski season for Snoqualmie is done. Areas where they may still open if the opportunity presented itself, such as Stevens Pass, would've loved that snow. However, Stevens only got 2-3 inches.

On another funny note, April 1st is the first day Washington and Oregon drivers cannot drive with studded tires. Mother Nature played her own April Fools joke.

The good news: a persistently low snow level through the weekend should allow the mountains to gain some ground in their snow deficit.

Wednesday another disturbance took a similar path to Tuesday's, and brought more afternoon thunder showers around the region.


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