Most weather fronts to the Northwest coast are generally weak.
There is only a small change in temperature, a small change in wind and a moderate change in humidity.
In stark contrast to the often powerful fronts in the central and eastern United States
The reason for our generally unexceptional fronts is twofold.
First, our coastal fronts are generally aging, with diminished shadowed fronts, compared with active, active fronts in the western Pacific. Cyclones and fronts are driven by large temperature gradients (temperature variation with distance) and strong jet streams, something that exists in the western Pacific, where cold air from Siberia meets the warm waters of Kuroshio line. Not true off our coast.
Front image produced by Dall-E Machine Learning
Second, temperature variations on our fronts are generally weak because they have traversed thousands of miles of temperate ocean, gradually warming cold air along the fronts (see sea surface temperature). Pacific Ocean below). The contrast in temperature weakens as a front crosses the Pacific, and conversely, the temperature contrasts with the pressure and the wind. Therefore, our front end has negligible changes in these parameters.
Result: weak front.
Tomorrow: A Special Front
But sometimes, the conditions make for a strong front, landing on the Northwest coast and that will happen tomorrow morning (Wednesday). I will show you.
A very strong front will reach the northwest coast early the next morning.
Below is the forecast radar image for 1 a.m. Wednesday. Do you see the narrow, undulating road off the coast (I hit the red arrow to help)? That’s the front. Meteorologists call this the narrow cold front rain band, and it has high rainfall and wind variability.
Three hours later, the front would be on the coast (see below).
This trough would be associated with a well-defined surface depression and the abrupt change in winds from southwest to northwest, as illustrated by forecast sea-level pressure and winds below at 1 am.
The front would ravage the coast and then weaken on the lee (east) side of the Olympics, making Puget Sound the worst.
But Puget Sound will pay the flute player later as strong winds pushing down the Channel create a torrential downpour of rain and another diverging wind will move into the Sound in the afternoon (see forecast radar image for 2pm inside). below). Thereafter, a Puget Sound convergence zone will be established around Seattle.
Why will this front be so powerful? Because an unusually strong jet of very cold air was rapidly pushed southeast out of Siberia and Alaska toward our region, pulled southward by a strong depression.
Here’s a map of the forecast for Wednesday morning temperatures and winds at about 10,000 feet (700 hPa pressure, blue and purple the coldest). You can actually see the cold arctic air push away from our shores. The North Pole is coming to visit us!
The uber cold air is clearly visible in the satellite image visible this afternoon (below). The speckled popcorn area signals cold air.
Interestingly, the temperature contrast with the front is stronger at 10,000 ft than at the surface–a true classical phenomenon around here due to the conditioning effects of temperate seawater.
Expect a wet/windy day tomorrow west of the Cascades, with temperatures dropping significantly. I may not cycle to UW….
