First, we had an unusual cold, then a freezing cold snowstorm, then heavy rain, and then unusual warmth.
But the weather gods are not through with us.
A powerful storm could form off our coast on Tuesday.
In such cases in ancient times, people would wonder why the gods were angry and asked their priests to intervene with an appropriate prayer or sacrifice. Today, our modern weather priests often blame such storms on carbon emissions and predict doom without an appropriate response.
Human nature has not changed. But in this blog, let’s stick to the science.
A profound change in atmospheric circulation
Let me show you a higher level weather map (500 hPa, about 18,000 ft) from three days ago (Wednesday at 10 a.m.) and yesterday at the same time.
A profound change. On Wednesday, a trough was deep inland while another was offshore, leading to a strong stream of cold air from the northwest.
Wednesday
By yesterday, the trough had moved inland and south, while the depression had amplified over the Gulf of Alaska. The result is a strong, warm, and humid current from the southwest.
We will be in this model for quite a long time.
Saturday
The resulting variation in temperatures west of Washington was remarkable (see SEATAC temperatures below, purple the normal high, cyan the normal low). We are generally cooler than usual until December 21 and then bottom out. And then yesterday we warmed up above normal.
This warming is accompanied by very heavy rains that lead to localized flooding in the streets. Rainfall over the past 36 hours has been remarkable (see below), with some locations reaching over 5 inches. Over an inch above the Puget Sound lowland.
Poor gang doesn’t stand a chance. At least airports can resume normal operations. And many of our rivers are full.
The storm is approaching
Both the US and European models show a large low-pressure system that will develop off our coast on Tuesday morning, with very low pressure.
This is the UW model’s prediction for sea level pressure at 10 a.m. Tuesday. A deep low of 971 hPa is off the coast of WA, with a sharp change in pressure (slope) along the Oregon Coast. That means strong winds.
The European Central model also has a low of 970 hPa in a slightly different position. There will be a big low off our coast. The question is where will it go.
Now I’m confident that the Oregon coast will get a good blow.
The storm will then move east and north, but there is still considerable uncertainty about its impact on inland western Washington. But 20-40 knots around Puget Sound is not unreasonable.
I’ll leave that analysis for another blog tomorrow, so stay tuned. But you might consider making offerings in your holiday fireplace.
