BIG TICKET COLD AND SNOW...

The United States is now in the grips of what's known as a positive TNH pattern. The +TNH reflects large-scale changes in both the location and eastward extent of the Pacific jet stream which in this case significantly limits the flow of mild Pacific air into North America. At the same time, it enhances the southward transport of cold Canadian air into the north-central United States.

In a nutshell, with a +TNH the axis of prominate ridges and troughs become aligned in such a way that a strong ridge develops along the west coast and a mean trough is established over the plains/Midwest (not the east). There's also a stable southeast ridge near Florida (which keeps the southeast mild).

The surface temperature departures for the +TNH in January are cold central and west.

The +TNH is aided and abetted by a strongly negative EPO (Eastern Pacific Oscillation) which strengthens and expands the west coast ridge.

The negative EPO teleconnects to the west coast ridge and large Arctic highs which deliver cold air intrusions.

Here's what the 500mb pattern is projected to look like February 1st. That is a text book +TNH

The ridge off the west coast and east coasts drives the trough and its cold air into the Midwest. We pay for that with the EURO indicating temperature departures of 30-35 below normal across Iowa and western Illinois February 2nd.