Sunday Night Extra…A Big Freeze Coming?

November 29, 2009

     Steve Pierce here with a “special guest blog post” tonight. Had to swing by Fox 12 tonight to take care of some business. I guess I picked a good night to swing in. Why? By now you have all likely viewed the 0z GFS model run showing the Pacific Northwest going from “cool” to downright “frigid” this coming weekend. Not that this is a “lock” at this point in time, but the changes on tonight’s GFS are pretty dramatic, wouldn’t you say? Most obvious change is the colder 850mb temps, along with reinforcing shot of cold air again early next week. A quick check of historical data (stored mostly in my brain) leads me to think, if verified, that this would be the coldest air this early in the season since 1985. There is plenty of time for future model runs to change things one way or the other, but a trend to much colder sure looks better tonight than it did last night. Could it be the “09/10 Cycle” that I spoke of at the fall AMS meeting? Only time will tell! Stay tuned! ~ Steve Pierce – Oregon AMS

So what Steve really meant to say is “Mark allowed me to geek out all evening but is about to kick me out”.  Actually Steve behaved pretty well.

The image above is the 6-10 day 500mb. height deviation from normal.  It shows a huge 500mb height anomaly (positive) over SE Alaska.  That allows cold air to stream down the eastern side of the high as Steve has already pointed out.  The trend is definitely faster with the arrival of cold air on both the GFS and GEM (Canadian Model).  They also don’t have moisture of any kind for snow or rain through early next week.  The 12z ECMWF was much slower and not nearly as cold, but had plenty of moisture in here by Monday.

Of course it’s Sunday evening, and we’re talking about something 6 days away.  I won’t get really jazzed up about a big arctic outbreak until another 24 hours of cold on the GFS and the ECMWF needs to come around as well.  That’s why I didn’t go crazy with high temps in the upper 20s or 30.  I figure a forecast high of 35 on Sunday when all other forecasts are 45-50 is wild enough for now.  Wait…I was almost shoving Steve out the door but he just told me the 00z ECMWF would be out by 11pm.

Chief Meteorologist Mark Nelsen