Weather Synopsis for Thursday night through Saturday

Another deep low pressure positioned offshore will deepen rapidly tonight and produce a stormy conditions for our mountains.  Warm frontal precipitation will lift north overnight through OR and southern WA and spread precipitation toward the Canadian border around sunrise.  The low will briefly tap into subtropical moisture, aka an old atmospheric river boundary over inland NW and CA/OR, but significant moisture will be cut-off by Friday morning keeping this from being an exceptionally wet storm.  

E-SE winds will ramp up once again tonight with strong E-SE becoming strong S-SW on Friday morning in many areas.  Tonight through early Friday, the strongest E-SE will favor the central/southern WA Cascades and Passes, and then the post-frontal S-SW winds will be strongest over the Olympics and Mt Baker area Friday afternoon.

Unfortunately, this system will feature a warming trend with snow levels rising rapidly over Mt Hood tonight. Easterly flow through the Passes will help keep snow levels lower initially, but the WA Cascades will likely warm to 4500-5500' by Friday afternoon.  Precipitation totals will be highest along the east slopes of the Cascades with along the southern WA Cascades in general with storm WE totals of 1.00" or more.  Snow will transition to rain more quickly for Mt Hood and at mid-elevations along the west slopes of the Cascades south of I-90 Friday morning. As precipitation tapers Friday afternoon, we'll see a mix of sun and clouds for the latter half of the day. 

The same low pressure system will be like a house guest that just won't leave...hanging around offshore and continuing to send weak impulses (bands of showers) inland  on Saturday and making it difficult to pinpoint timing or cloud cover over the region. Plan for periods of wet weather and 3000-4000' snow levels, with the showers most likely to pepper the Olympic peninsula in this pattern.