Some snippets from a very detailed AFD from Mount Holly this afternoon-
As ridging builds over the Pacific Northwest and southwest Canada, a strong +PNA will develop. This begins over the weekend, then strengthens early to mid next week as an even stronger ridge builds in over the Northwest. This will force a downstream trough over the eastern and southeastern US beginning late in the weekend and likely continuing through most or all of next week, driving colder air into the southern US. Notably, this pattern is very counter to what would normally be expected in a moderate to strong La Nina. But a good reminder that other aspects of intraseasonal forcing can sometimes overcome the dominant global pattern driver. It is also usually an active, stormy pattern for the East Coast.
Sunday night-Wednesday... As mentioned above, active weather is likely for this period. It will be a highly complex evolution as the new pattern takes shape. We will be watching two systems which are likely to begin interacting late in the weekend. One is a Canadian clipper low dropping towards the northern Great Lakes. The other is a robust southern stream wave propagating out of the desert Southwest, supported by an anomalously strong subtropical jet. Guidance has given strong indications for days that these systems are likely to phase over the East. However, as is usually the case, this interaction is likely to be complex, and while the general signal between models is fairly consistent, there are significant differences in details and timing.
By the middle to end of next week, additional unsettled weather is possible as trailing shortwave disturbances rotate into the broader longwave trough in the East. With colder air in place, wintry outcomes may be more favored with time, but given the uncertainty associated with the early week system, changes are likely.