Monday, September 10, 2012

Long Range Arctic Oscillation Pointing Negative

Courtesy Kyle MacRitchie
A long range forecast for the Arctic Oscillation, an index commonly used to distinguish potentials of cold weather, is dipping into negative territory. As shown above, ensemble forecasts of the AO are bringing the index well into negative territory beginning in October and into the winter months.

A continuity of such a negative Arctic Oscillation would enhance cold weather potential over the nation. A negative AO also enhances the chances for a negative NAO, seeing as how close the two indices are. This does not necessarily mean that they will both go negative, but, because they are so close in how they function, they can move together.

This is still very long out and subject to major change, so take this and use it at your own risk.


Winter's On The Way: First Cold Outbreak On The Horizon

Hour 192 of the 12z ECMWF
The first real cold outbreak of the season appears to be on the horizon, signaling winter is peeking around the corner.

The ECMWF is forecasting a strong disturbance to drop down into the northern Plains in mid-September, as depicted above. The 540 line on the upper right image is dipping down into the Northern Plains. The 540 line is commonly referred to as the rain/snow line, with snow being north of the 540 line. That said, if precipitation were ongoing in the northern Plains and this verified, some very early snow may fall in North Dakota/Minnesota.

After the system dips into the US, it will become closed off, and its cold pool will rotate around the western side of the storm. As it closes off, it will rapidly strengthen over south central Canada. This will likely produce some windy weather in the southern Canada and northern Plains regions, and cool air should continue to flow around the regions mentioned.

This is just one of a few signs being seen that show winter is inching closer to our region.