Canadian trough

The next ten days will be all about the long wave trough anchored over Canada. As a review from the last post, in the few days we have witnessed Pacific Jet energy dump into western North America and amplify over the northern Plains. Meanwhile, ridging originally suppressed south of the jet has exploded poleward over Alaska. This has formed a very strong block upstream of the continent. Downstream of the block, disturbances dive south and amplify. 

The first in a series of these disturbances is responsible for the shot of unseasonably cold air into the southern Plains and the early season snowstorm across North Dakota and Minnesota yesterday. More of these disturbances are poised to dive south into the CONUS over the next week. This cycle of shortwaves act to carve out a broad trough extending from northern Canada into the northern Plains.

What does this mean for you?

Expect much below normal temperatures to continue across the Midwest, Great Lakes, and Northeast through October 15th. Disturbances in the trough will also bring stormier conditions to Mid Atlantic and Northeast. There will be at least a couple of *cold rain* events in New England; the first coming this Sunday-Sunday night, and another possible at the end of next week.

What about beyond next weekend? Looking ahead, the block over the Gulf of Alaska does eventually break down, and the Canadian trough starts to lift northeast. New England stays on the cooler side but the rest of the nation should be warming up by next weekend.

GEFS projected upper level pattern by next weekend

My next point of interest is what happens once the block breaks down. The configuration of this block (which evolved from an omega to rex formation) includes a disturbance locked south of the massive ridge. Once the block erodes, this disturbance is ejected eastward into the southwest U.S.

At the same time we must consider the Canadian trough again and the strong upper level confluence upstream of the trough, over the northern Plains and Midwest. This confluence prevents the southwest U.S. disturbance from amplifying much and breaking northward. Instead, it slides eastward toward the southern Plains. In addition, with the block gone, the doors open to more shortwaves taking a similar track into the southwest and southern Plains.

What does this mean for you?

We could be looking at a period of enhanced storminess in the southern Plains including thunderstorms and severe weather, beginning next weekend and continuing through the following week.