Although the weather over the next few days should be somewhat benign, us weather folk usually try to find something to look forward to in the future as far as a serious weather threat or storm system. In this case, we have a significant lack of those, but no lack of long range pattern interest as it seems that at least for a brief period, the anomalous above normal pattern will take a hiatus across our region. In a previous post a few days ago we discussed the importance of the Alaskan vortex retrograding to the Aleutians. With forecast guidance agreeing on that occurrence, the effects can be seen immediately in the pattern forecast by the GFS OP and individual GFS Ensembles this afternoon. As a result of the retrograding vortex, almost all of them forecast a +PNA west coast ridge to develop, as well as a large trough engulfing much of the Central and Eastern US.

The question then becomes: what's the quality of the air source in this air mass change? The answer is above normal, but still well below normal for our area. Much of Canada is well above normal departures at this time, owing to the aforementioned anomalous above normal pattern. That said, the airmass will still be below normal for our region which is a big change based on what we've been seeing lately (70 F + today in some areas, wow). Though it may be initially modified, any semblance of blocking or sustainability of the +PNA ridge would mean increased chances at additional intrusions of negative departure/below normal air. For those harping on well below/anomalously cold departures, look for the Siberian airmass feed (pretty rare this time of year), snow cover in Eurasia is running well above normal with an anomalously cold pattern in place.

Over the next few days or the immediate future, all this banter doesn't add up to all that much. But we will certainly be keeping our eyes on the guidance as our first shot at below normal departures approaches, and as we head into the fiasco that can so often be meteorological winter in New York City.

John