Transition Day

The temperatures in nearly all of western Washington are now in the 40s and warmer southwesterly flow has removed the persistent cold air. Take a look at the Seattle profiler winds and temperatures for the last day. 24h ago there was weak SE low-level winds and temps around 0C (32F) in the lower atmosphere...now there is fairly strong SW flow and temps of 6-7C. The melt-out has begun in earnest. Many primary and secondary roads are passable, with a little slush in places.

A cold front is now making landfall on our coast...you can see that by the switch to NW flow on the coast (see map). General precipitation will drop back in the lowlands...although it looks like a Puget Sound convergence zone will form north of Seattle this afternoon (that usually occurs with NW winds on the coast). However, this is an ideal pattern to get big snow in the mountains. In fact, the heaviest snows often fall there after cold front passage when winds are more westerly. Why? Winds from the west have a stronger wind component up the mountains then prefrontal winds from the south. Also the air behind our cold fronts are cold and unstable...with lots of cumulus-type clouds. Such instability clouds really blossom as they are forced to rise by terrain.
The next several days promises one wet system after another and more seasonal temperatures. The media has been pushing the flooding issue, but I don't think that lowland flooding will be a serious threat this time...assuming everyone clears their drains. Behind the cold front, temperatures will fall and the melt off will be much slower than in 1996..the last major melt-off flood event.