CAPE

Euro Weeklies for the mid- late month period. Looks Okay. Certainly could be a lot worse.

My wag is it will take some time to get cold enough given how that massive trough out west is reluctant to weaken/retrograde, mostly Pacific jet related. Have been seeing some indications on the means of something closer to the 12th.

12z GEFS is wholly unimpressed with frozen chances for the 6-7th. Colder compared to the days prior, but not cold enough verbatim.

This was the set up a few days before- And here it is just prior to the event-

It was a well timed healthy wave moving along the boundary with some legit cold pressing in. There was also a bit of a bootleg -NAO. But yes there was plenty of intricate timing involved, and it came at the beginning of a pattern change as the western trough was shifting east and ridging along the east coast was breaking down.

6z GFS was absolutely a thread the needle deal, with that vorticity lobe rotating down over the southern tip of Hudson Bay at exactly the right time to enhance HP in a good spot. There is zero blocking and the antithesis of a 50-50 low, so any HP to the north will be on the move.

That's your WAR at work. Inland track with too much flow from the SE.

Wasn't much of anything wintry in 2014-15 prior to mid Feb iirc. Classic back loaded winter.

They had over 2" of rain just before the Arctic front. Going be some saturated soil.

For you friend.

Embrace the warmth. 6z GFS snows on us a few days later.

With a Bermuda high and a low tracking well NW, 70 is not out of the question Tuesday or Wed. Tough to see how the next wave for late next week is cold enough, but with an EPO ridge building colder air should be getting closer thereafter.

6z GFS is a pretty darn good run. Builds ridging into the EPO/WPO space, and wave breaking pinches off vortices sending them southward, while the trough off the west coast spins off pieces of energy eastward underneath.

A little hard to read the dates but it initialized on the 0z run on 28th- at that point it is shifted poleward and also quite extended, and moving forward in time it retracts some(also less poleward), which makes sense if you look at the jet stream level winds over the N Pacific (and the 500 mb heights) for the 0z run. eta- as for the magnitude of the jet extension and what constitutes 'too much' vs 'just enough' for our purposes, we have to consider other indices that interact. For example if there were a legitimate block downstream in the NAO space, that would slow/buckle the flow, and would have ramifications upstream as eastern ridging would be suppressed and replaced by the tendency for a trough- so for a given magnitude of Pac jet extension that was previously 'too much' with progressive flow, it may now not overwhelm and allow for a ridge in the PNA space or at least bring it to neutral.

That's a PowerPoint presentation(in pdf) based on the paper referenced in my post. Good overview.

EAMT absolutely plays a role. ENSO state has impacts on the jetstream configuration. Hadley cell expansion related to climate change..

Basically a jet extension (a) favors a ridge in the W US, a +PNA. A combo of extended and poleward shift (e) also favors a +PNA. A -PNA is mostly associated with jet retractions/equatorward shifts. Fig. 5. Composite mean 250-hPa wind speed (m s−1) is shaded in the fill pattern, 250-hPa geopotential height is contoured in black every 120 m, and 250-hPa geopotential height anomalies are contoured in solid red and dashed blue every 30 m for positive and negative values, respectively, 4 days following the initiation of (a) a jet extension, (c) a jet retraction, (e) a poleward shift, and (g) an equatorward shift regime. Composite anomalies of mean sea level pressure are contoured in solid and dashed black every 2 hPa for positive and negative values, respectively, and 850-hPa temperature anomalies are shaded in the fill pattern every 1 K, 4 days following the initiation of (b) a jet extension, (d) a jet retraction, (f) a poleward shift, and (h) an equatorward shift regime. The numbers in the bottom right of each panel indicate the number of cases included in each composite. Stippled areas represent locations where the 250-hPa geopotential height anomalies or 850-hPa temperature anomalies are statistically distinct from climatology at the 99% confidence level. Full paper- https://journals.ametsoc.org/view/journals/wefo/34/1/waf-d-18-0106_1.xml#fig5

It was generally extended, but not on steroids. We had a ridge along the west coast a couple days before Christmas iirc. Ofc we also had a massive EPO ridge at that point too. I will see if I can dig up the NPJ phase diagrams a bit later.

There are actually NPJ phase diagrams that define the different configurations- extended, retracted, more poleward and extended etc. Per those diagrams, the combo of extended and/or poleward favors a +PNA. But like I said, too extended causes the trough to be too far east and impinge on the west coast. Always a delicate balance. Getting snow is hard here lol.

Look at the EPS. At this point the NPJ is too extended- left exit region favors lower pressure below(towards the surface). In this case that's a trough in GoA, and digging south of there...no good. Towards the end of the run the Jet retracts some, and we get an improving look at h5 with a +PNA developing. Pretty quickly things look better downstream.

Pac jet is a problem regardless of ENSO, esp in recent winters. We want an extended Pac jet in general for a +PNA, but there is such a thing as too extended, which is what we are seeing now on guidance.

Generally agree, and still hints on the ens means although the most recent runs have been more meh for the potential around the 8-9th. Still think the window centered on the 12th could be interesting, assuming no more can kicking ofc. Really need to get the Pac jet to calm down a bit.

Probably just not at that level of desperation yet lol. I am sure certain hypsters on Twitter are all over it though.

We really need the NPJ to back off(retract) a bit, and/or shift a little more poleward. The location of the exit region of the jet core favors a trough in the GoA. It does appear to retract/weaken a bit towards the end of the run. Hopefully we see some relaxation over the next few model cycles.

Hard to believe, but your area has been betwixt and between a lot lately. Had 3 plowable events here last Jan alone.