Interesting Change in Models Today

November 30, 2011

Of course the 12z GFS run caught my eye…showing the ridge moving just far enough west about a week from now to allow a major surge of cold arctic air into the Pacific Northwest.  It’s the first run of either the GFS or ECMWF to show such a thing, but oh, it is a beautiful sight!  For a reality check I had to head to the ensembles though and I “didn’t like what I found”:

The blue line is the actual GFS you see in the maps (operational run), the red is the average of all the ensembles.  And of course each line with its associated symbol is a unique ensemble member.  Note the operational one; the one we salivate over, is the coldest of them all.  There are several members that show nothing, but the majority do show SOME cooler air leaking south.  Clearly an indication the GFS wants to bring a trough down at least a bit closer to us on it’s way east.  We’ll see what future runs show. 

ECMWF will be finished in about 45 minutes and I’ll post it’s ensemble chart too so we can see if there’s any agreement.

3pm Update:  Here it is:

The 12z ECMWF Ensemble 850mb temp forecast chart has two items to note:

1.  The operational run…the maps we all see, shows no arctic blast of any sort as the Wednesday wave dives down out of Canada well to our east, unlike the GFS shoving it right down over us.  So the blue (operational) line shows no big plunge of cold air…makes sense.

2.  BUT, look at all those ensemble members that must be showing a sharper trough much like the GFS.  You see the huge plunge in temps during the same time the 12z GFS did.  This is where the ensemble forecast information comes in extremely handy.  Operational ECMWF says no cold spell coming, but many of it’s 51 “brothers” have suddenly decided it might happen. 

By the way, the 18z GFS had the cold air much farther east, but a mini blast of cold air at just 12 days away!

Get your model-riding chaps on folks!

Chief Meteorologist Mark Nelsen