You can see the changes in the sky. Clouds moved in overhead accompanying warming aloft.
An interesting observation...temperatures warmed a bit in the middle of the night as the cloud spread overhead. The temps at Seattle-Tacoma Airport show this:
Nothing changed at the surface. Why? The reason is that clouds emit infrared radiation better than the clear air, so when clouds came in aloft there was more infrared radiation directed down to the surface...and thus warming.
There has been some snow flurries with the clouds aloft (you can see the light stuff in the radar below)
Ok, lets talk about the forecast. This is a MUCH easier forecast than Monday--fairly straightforward system coming off the Pacific without the coastal troughing/low generation that made the Monday forecast so uncertain.
First, what we are SURE about? It will warm up tomorrow afternoon. The ice and snow will rapidly melt late tomorrow and Friday. And rain is coming back.
So lets talk it through, including where the uncertainties lie.
Today the temps will stay in the 20s, and with little sun roads will not improve much. Keep in mind that ice is much less slippery in the lower 20s than in the upper 20s or near freezing. So in some sense conditions are much better now than on late Monday or what will occur as melting starts. And here in Seattle most of the major streets are in good condition.
Tonight the air will begin warming more rapidly aloft, but it will take time to scour out the cold dense air near the surface. Our computer models tend to mix the cool air out to quickly...and we know that. Anyway, warm- frontal precipitation should enter the region between 6 AM and 10 AM. It could well start as light snow. But by noon or early afternoon it should switch to rain and decrease in intensity. Good chance the precip will stop in the later afternoon and early evening. The main cold front comes in Friday morning.
There should be very strong winds over NW Washington and along the coast later on Thursday and Friday morning.
So the bottom line:
today...what you see is what you get.
tomorrow morning will have the potential for some light am snow and increasingly slippery conditions of melting ice.
By late Thursday the warming should improve conditions substantially.
Friday we will transition back to normal with rain,typical conditions, and wind in the normal locations.
Just in time to go shopping for black Friday. Hopefully METRO will turn its bus-tracker website back on (much more that in a future blog!)
Post a Comment