Last night there was a weak push of marine air into western Washington that will take the edge off the heat today. Related to my earlier blog, the thermal trough has moved into eastern Washington, easterly flow over the mountains has ceased, and there is an onshore pressure gradient, pushing marine air inland. This was not a strong marine push and temps will remain at or a bit above normal today.
But something else is going on...a weak upper trough is moving northward through the region, and with relatively unstable air above, we are seeing a line of mid-level convection pass northward across the area. Here is the radar image around 10 AM... the radar is seeing precipitation, but as we shall see, most of it is not reaching the ground. Not much lighting..just a single hit in the last hour in eastern WA.
What is causing this line of clouds and showers? An upper level trough moving northward--here is the model simulation for 11 AM...the red color is vorticity, a measure of the sharpness of the trough...red is more.
Most of the showers are associated with mid-level convection...and much of the limited precipitation is not reaching the ground...evaporated on the way down (see image from UW webcam). This