



These snow showers are associated with an approaching upper level trough of lower pressure that is providing upward motion that is leading to a band of clouds and weak snow showers (the satellite picture at the same time is shown below).









Close in to a major weather event, I like to look at the NOAA/NWS High Resolution Rapid Refresh Model--in which a new high resolution forecast is made each hour. Below shows the accumulating snow in time.





There is some light snow reaching Seattle around 11 AM....but this is stage 1 stuff.









Today's snow event will be in two acts, with the first one already begun. Very light snow is now falling over Northwest Washington (locations such as Bellingham and Orcas Island)--something that is confirmed by the 8:30 AM weather radar (see below)That will occur as the upper trough spawns a tight low pressure center in the lower atmosphere, as illustrated in the surface pressure forecast for 7 PM tonight. An absolutely classical pressure pattern for a snow event over Puget Sound. The low pressure draws in cold air form the north (note the large north-south pressure change) over Puget Sound and pushes moist air from off the Pacific above the low-level cool flow.The snow extends south by 4 PM at which time the amounts are just starting to increase. Stage 2 is beginning as the low center develops along our coast.By 10 PM tonight, there is a lot of snow as stage 2 revs up ...4-6 inches around Seattle and more to the east.And by 1 AM, there is a bit more around Puget Sound, but much more over northwest Oregon.The essential point in all this, is that things should not be too bad before roughly 2-3 PM, but by rush hour, the situation should be declining rapidly. The UW is closing around 12:30 PM, which is wise, since it allows folks to be home by mid-afternoon.Later today I will talk about the next big snow threats... late Sunday/Monday for SW Washington and Oregon and Tuesday for Washington. Today is just a "warm up" as cold air remains in place for most of the week. And no, I won't give a name to the upcoming snow events (but the picture below is a hint)