A Change in the Forecast for Next Week

In my previous blog, I noted that it looked like high pressure would dominate our area next week, bringing us dry and cold weather.  But recently the computers have slightly adjusted this forecast, and it looks to have some impacts on our area.

First, the snow forecast for tonight is still pretty much in line with what I had talked about in the previous blog.  Snow will spread into the area this evening (Saturday evening).  Amounts will generally be light.  Look for about an inch in most valley locations.  In fact, our low temperature tonight may hold above freezing, which would further limit snow accumulation. The snow will change to rain and temperatures will warm to the mid 40s on Sunday, so the snow won't stick around long.

The change in the forecast has to do with the placement of the forecast high pressure next week.  Instead of being located directly over us, it is now expected to be a little to our east. (This image is compliments of the website Tropical Tidbits).

This will allow a rather large area of low pressure to our west send a warm front into our area by Wednesday morning.  The set up is fairly classic.  Cold, dry air will move into our area on Monday and Tuesday ahead of the warm front.  So precipitation type isn't a difficult forecast.  The problem is that the computers are still trying to adjust to this new forecast.  There are some hints that the offshore low will be too far offshore, limiting the amount of snow east of the Cascades.  

Here is the European model forecast for snowfall.  It's actually not that different from the snowfall we expect from tonight's event.

And similar to tonight's storm, the precipitation type will change to rain late Wednesday and continue off and on through the end of the week as temperatures warm back into the 40s.  The Blue line (snow probability) is higher than the Green line (rain probability) at the start of the event on Tuesday night, but then they switch places for the rest of the week.

So again, I caution you on getting to drilled in to a specific snowfall forecast for Wednesday.  At this point there are a wide range of solutions, so we'll just have to wait another day or two before a better consensus is reached.  There are some forecasts out there for a really heavy dump of snow, and they might turn out to be correct.  While others keep the snow mostly confined to the Cascade east slopes (Wenatchee, Methow valley) as we as the US/BC border area.

What does seem likely is that the previously mentioned high pressure will be too far east to shut the storm door, so to speak.  As such, the latter half of next week should be milder and wetter than previously thought.