When it comes to the possibility of reinforcing cold surges... and any possible disturbance that may draw moisture into that cold, much of that has to do with the current extension of the jet stream over the open North Pacific, which has been and will continue to wiggle about like a sprung door stopper, sending out various troughs and ridges out into western Canada and the Pacific Northwest, which thanks to the extension of the PV over central Canada will tumble over the Rockies into our area. There are certainly many planes over the North Pacific from trans-Pacific air travel, but they're not capturing a very considerable depth of the atmosphere. At this range, it is too far out to predict with reasonable accuracy the specifics of smaller shortwave kinks in the broader pattern originating from such data-sparse areas.
The deterministic guidance can be enticing to follow closely, because they give neat, singular snapshots, but right now,
the ensembles (and trends in said ensembles) are your friend. The initial surge of cold air, being more larger scale, is in the realm of reasonable predictability. It's tricky to predict exactly how cold it'll be, but the usual wisdom is that these strong blasts of cold air that run down the Plains against the Rockies tend to come in faster than synoptic guidance... an artifact of the lower resolution of those models. That airmass is the gift of the broader, larger-scale (maybe even planetary scale) troughing pattern, which is why the general sketch of anomalous cold is easier to predict, why those CPC probabilities went up so quickly, and why "colder than the last cold snap" can seem like a very reasonable, perhaps even likely take. What is less certain is any followup bursts of cold that ride down the larger trough, because those are more likely to be driven by smaller-scale features which have yet to be well-sampled. The staying power of the cold will hinge on those smaller perturbations, and the path those perturbations themselves take determine how effective moisture moves into the region. Too weak, and too little moisture gets dredged up from the Pacific/Gulf for much precipitation to happen. Too late, and the cold air warms up just enough to allow the moisture pull to be a little too overwhelming, spoiling the cold air with warmth.
What is nice about the deterministic guidance at this range is they help you spot failure modes, or success modes, depending on if you're wxman57 or not. For example, the 18z GFS fails to amplify a shortwave over the Rockies Monday/Tuesday, opting to instead reel a spaghetifying bit of vorticity obliquely around a longwave. The result -- Texas takes a more glancing blow from the cold air, ridging is able to reestablish behind the trough (which wouldn't happen if the shortwave amplified!), southerly flow comes back, and poof, the cold air gets replaced by a miserable cold rain. The 18z GEFS mean is more cautious than the GFS. Those ensembles have been warmer than their Canadian and European counterparts, but still show considerably
more vorticity (a la stronger shortwave) over the SW US than
the deterministic GFS. Is the GFS a canary in the coalmine or being a ruse? Well, wait till those possible disturbances responsible for reinforcing cold or wintry precip get better sampled, or better yet, even exist in the first place.
Source: TropicalTidbits
The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or 
that was 4 days out from us getting 6 inches of snow(which was the snowiest day at the airport in 14 years) how could it be so wrong
