There was attention given to whether a major sudden stratospheric warming (SSW - defined as a reversal of the wind from westerly to easterly at 60N and 10 hPa) occurred in late November at the peak of the PV disruption. I of course framed it as an extreme stretched PV that I thought provided a better framework for temperature forecasts. And now that the whole event is winding down, I feel justified. However in the 1 Dec 2025 blog I did conceded it might be a hybrid of sorts. I was under the impression that it did not meet the criteria to be defined as a major SSW. However I did come across this LinkedIn post from Simon Lee demonstrating that according to ERA5, a major SSW did occur at the end of November.
I bring this up today because normally when wave reflection occurs it tends to clear out warm/positive polar cap geopotential height anomalies (PCHs) in the atmospheric column (both stratosphere and troposphere, regardless if an SSW occurs or not. As I have been documenting in the blog, we have had multiple wave reflection events and yet warm/positive PCHs persist. In fact, looking at Figure 11, it gives the appearance of the more classical dripping paint plot associated with absorbing SSW events in the polar stratosphere. I can’t recall something similar with wave reflecting events. This is mostly an academic exercise but something that I find curious. The latest GFS forecast suggests the warm/positive PCHs will disappear at the end of the month, but the GFS has predicted this for much of December only to reverse course. I can’t blame the GFS as we clearly have multiple wave reflection events, but it shows the models are really struggling predicting the atmospheric circulation correctly.
For the past three weeks, I have been doing my best Monty Hall from “Let’s Make a Deal” impression, and this week will be no different. However, I will keep it short this week. The three doors are: door number one - the reflective layer in the stratosphere that gave rise to the stretched PV also protects the PV from subsequent upwelling energy from the troposphere and allows the PV to strengthen. The second door is though there is short-term strengthening of the PV, high-latitude blocking resumes its assault on the PV and we see more stretched PVs and/or Canadian Warmings (that often transition to stretched PVs) until finally there is knockout punch and a true SSW either in January or February. And finally, the third scenario is that the stretched PVs just keep repeating for much of the winter punctuated or separated by a relatively strong PV and or Canadian warmings.
I have consistently favored door number three or what I like to call a “rinse, lather, repeat” PV and weather pattern for the foreseeable future. Basically, alternating stretched PVs and relaxation to a more circular PV and oscillating or alternating cold and mild periods for East Asia and or North America, that can feature some wild temperature swings. Eventually the pattern could transition to either door number one, persistently strong PV or door number two, a major SSW. For now, I see no evidence of either. For door number one/strong PV I would want to see a disappearance of high-latitude blocking or 180 degrees out of phase with the pattern that favors a weak PV or for door number two/SSW a much stronger and persistent Ural/Scandinavian blocking. So for now, I am continuing to ride the “rinse, lather, repeat” carousel as we saw last winter.