Official 2012-2013 Winter Forecast Release Date

Mark your calendars!

The release date of The Weather Centre's Official 2012-2013 Winter Forecast will be Saturday, September 8, at 12:00 PM central time.

I will begin work on this forecast tomorrow. It may surpass the last forecast update in terms of amount of work put into it, but this will be an exciting forecast!

Andrew

Transformation into Positive PDO May Be Occurring

http://www.bom.gov.au/products/IDYOC059.shtml

A difference in temperature anomalies between June and July shows a cooling pattern now occurring in portions of the Northern Pacific, as well as a warming trend being observed on the Canadian and Alaskan coast, typical to what would be seen in a positive PDO.

http://jisao.washington.edu/pdo/

A warm phase, or positive PDO, is characterized by a cool North Pacific, as well as a warm coast of western Canada and southern Alaska. Also of interest is the warm anomalies in the Equatorial region and ENSO monitoring area. That said, it can be said that a positive PDO has a correlation with El Nino's. That does not mean that every El Nino has a positive PDO, but typically, they can occur together.
On the other hand, a cool phase of the PDO contains warm temperature anomalies spread across the North Pacific, as well as a cool Gulf of Alaska coast. Additionally, cool temperature anomalies are found in the ENSO monitoring area, showing a correlation between a negative PDO and La Nina.

A positive PDO typically brings about a warm and dry spell in the Northwest, which indicates a ridge of high pressure is in the area. Additionally, cool and wet conditions are found in the Southeast, showing that many disturbances move through the area during the October - March period.
You can find more effects in other areas in response to the PDO by clicking here.

Andrew

Great Lakes 4-8 Degrees Above Normal; Winter Lake-Effect Snows May Be Intense

Latest analysis of sea surface temperature anomalies in the Great Lakes show that the Lakes are 4 to 8 degrees (c) above normal, with some areas even warmer than that.

This winter will be composed of an El Nino, which should bring some variant temperatures across the Eastern US. If an arctic outbreak can come out of this winter, and keep hold for several days, the lake effect snow machine could go hard. Considering many areas get above 100 inches thanks to lake effect snow, I can see those same areas getting as much as another 7 feet or more, should a few arctic outbreaks pump those lake effect snows into action.

These snows could very well be helped if we see a repeat of the strong storm system we saw a few days ago in the Great Lakes region that produced gusty winds and dropped temperatures to unseasonably cool levels. If that happens again, the lake effect snows will only pile on more and more.

Andrew

East Atlantic About to Get Much More Active

The Eastern Atlantic is about to get much more active over the next several days.

Satellite imagery shows a couple clusters of intense convection in western Africa at this time. As these disturbances move west, they will certainly pose a tropical development risk as they move offshore. I have not seen clusters this strong this season in the time I have been monitoring the East Atlantic / West Africa.

The steering layer for the East Atlantic shows that these systems will likely start out their journey in the ocean by moving west. A big player in the track of each of these disturbances will be how far south they start when they move offshore. For instance, some disturbances will be too far north and end up swinging north into the middle of the ocean, whereas others will be far enough south to keep a westward track and possibly eye the Caribbean.

If I were to take a guess on the track of each of the two disturbances shown on the satellite image shown, I would say that the first cluster closest to the ocean will probably end up going out to sea, whether immediately after leaving Africa or just before entering the Caribbean.
I do believe that the second disturbance shown has a better threat to aim for the Caribbean, due to its dislocation to the south of the first disturbance.

Andrew

Tropical Development in Atlantic to Ramp Up

Additional tropical development in the Atlantic Ocean appears likely over the next couple of weeks as the Madden-Julian Oscillation (MJO) moves into Phases 8, 1 and 2 over the next several days.

The Madden-Julian Oscillation tracks anomalies of precipitation over the Equator. When these anomalies, dry or wet, are in certain parts of the MJO monitoring region, they are in different phases. When the MJO is in Phase 8, we typically see above normal precipitation anomalies over the Atlantic portion of the Equatorial region.
This above normal precipitation signals more convection than usual in the region, which can enhance tropical cyclone development. That is why, typically, when the MJO moves into Phases 8-2, you will see many forecasters become more optimistic on tropical cyclone development over the next few days.

This forecast of the MJO, from the ECMWF's Seasonal Ensembles, shows a very aggressive Phase 1 and Phase 2 in the forecast period, which is a very good sign for tropical development. Where this development occurs remains to be seen, but as of now, with Tropical Depression SEVEN dissipating and Invest 93 weakening, the Atlantic appears to not be prepared for significant development just yet, as the MJO is not favorable at the moment.

Andrew