I am a meteorologist from New York who has been studying and forecasting the local weather for years. I especially enjoy tracking winter storms.
By: NYCvort, 7:03 PM GMT on December 30, 2011
It’s looking more and more like the first week and half or so of January will in fact be a temporary pattern change. The MJO is throwing us a bone and supporting a persistent trough in the east during this time period. If we can’t get a big storm, could we squeeze out a light isentropic lifting snow event on the way out of this pattern? Maybe. But I continue to highlight that we really need to get something to happen in the beginning of January because after that it looks like we will be entering back into the same unfavorable pattern. The latest CFS and JMA weeklies both show retrogression of the ridge over the western US during week 1 back into the eastern Pacific by week 3. This will result in a trough dropping into the west and a ridge returning in the east.
The MJO, which will be edging close to more favorable phases during roughly the first week and a half of January, is forecast to turn and race toward an unfavorable state once again by mid-January.
This will accordingly adjust the hemispheric pattern resulting in a negative PNA developing once again.
The ensembles do show the NAO falling to near neutral or slightly negative by the end of the two week forecast, but I still don’t see any real high latitude blocking on any of the forecast maps which continues to make me very skeptical of such a change. The cold sea surface temperature anomalies around Greenland as well as this year’s trend for lack of blocking remain against this idea. The one force that I could see changing this would be the stratospheric warming currently underway, but I still don’t see enough downward propogation of this warming at the top layers to effect the blocking situation as of yet.
So all I can say is let’s hope we can at least squeeze a little something out of this pattern because otherwise we may have to wait until February for our next best shot.
By: NYCvort, 9:20 PM GMT on December 27, 2011
The models have been suggesting the possibility of a strong positive PNA ridge forming over western North America late this coming weekend into early next week.
If this occurs, we could see a storm ride up the eastern seaboard and drive in some much colder air.
While the ECMWF is going all in, the GFS is not so quick to jump on the bandwagon and remains much flatter and more progressive. I am a little suspect on the idea of such a strong PNA ridge forming. In favor of the PNA ridge would be the MJO orbiting into phase 7, as being forecasting by some of the models like this one:
Here are the corresponding 500mb anomaly composites for a phase 7 MJO in January (courtesy of Allan Huffman):
Note the anomalous trough in the eastern Pacific, western North America ridge, and trough in the east, roughly similar to that being forecasted by the ECMWF. As I mentioned in my winter forecast, the MJO is the biggest factor capable of temporarily reversing the PNA into a positive state during La Nina.
Continued positive (though improving) AO—will cause any storm that should develop to be lacking in cold air to tap into overall:
Continued positive NAO—lack of overall blocking:
So the potential storm would be driven solely by the changes in the PNA and the associated phase. This is something that is much too early to call, but it is the first time period of the official winter season worth keeping an eye on. My best guess at this point would be that if a storm should form, the most likely areas for accumulating snowfall would be the interior north/west of I-95, based on the lack of blocking in the pattern. But right now we need to continue to monitor how the models trend on the PNA ridge and the phase.