Posted: 4:39 am Monday, February 19th, 2018
By Kirk Mellish
March madness may not be restricted to basketball this year.
March and April are “transition” months in the weather and so often produce extreme changes as aging winter tries to fend off the advance of youthful spring.
March and to a lesser extent April are also known in weather circles as “bowling ball” season. That’s a nickname for closed low pressure systems aloft because they look that way on our weather charts. They often bring spring snowstorms and severe thunderstorms.
This happens thanks to the seasonal weakening of jet stream speeds, allowing shorter wave lengths that can “bundle energy” into the bowling balls.
The closed circles in blue are examples of “bowling ball” lows aloft:
I’ll discuss bowling ball season further if it becomes relevant in the future.
If you follow my blog posts regularly and follow me on Twitter then you know I alerted you to this warm spell coming well in advance, but also warned of distant signals hinting at a return to a more winter-like jet stream in the U.S. to follow.
Forecasters looking for long-range trends don’t look at APPS, websites or just computer model printouts. We have a host of tools to diagnose the atmosphere and prognosticate trends if not specifics. I will cover some of them in this blog post as I’ve covered so many others over the years.
The SSW or sudden stratospheric warming above the North Pole was one of those signals and it has occurred as the models suggested. Remember the stratosphere is ABOVE the atmosphere where we live. Now we await to see how the troposphere (where weather occurs) will respond and if the models can detect it. The time lag is typically on the order of weeks.
Like anything else in weather, no two SSW or its impacts are alike.
This SSW is at historic levels at about a +4 sigma amplitude. But so far its impact is colder and snowier than usual for much of Eurasia and Europe.
SSW researcher Cohen says:
- The temp pulse is resulting in a significant polar vortex (PV) disruption. One PV center previously over the Canadian Arctic archipelagos has begun to split into two sister vortices with the dominant/primary PV center over Northern Canada and the secondary PV center over northwestern Eurasia.
- A significant PV disruption is often followed by widespread cold temperatures across northern Eurasia and the Eastern US. However the cold is more certain across northern Eurasia following these type of PV disruptions.
- The poleward heat flux into the polar stratosphere is an all time record. The reversal of the zonal wind is predicted to be a daily record and near an all time record with unusually strong easterly winds. Finally polar stratospheric temperatures I believe are predicted to be near record highs.
- As far as the sensible weather an important question is will the extreme event in the stratosphere translate into an extreme event in the weather? I think it is possible but not necessarily and I can recall other extreme events in the stratosphere that produced less than extreme weather.
- Though there is ample precedent for the cold air to take a long time reaching the Eastern Seaboard even on the timescale of months and not weeks. Also given the uniqueness of the event, historical precedent could be misleading and may be more an example of the “exception proving the rule.”
So we are in uncharted territory here and it remains to be seen whether orthodoxy will hold in this case.
Around 19 MILES high about a 50 degree spike in air temperature over a short period of time has occurred;
(Chart: Judah Cohen)
We are in a weak La Nina to near neutral Nada condition with a -QBO and low solar cycle.
La Nina and Neutral Pacific Ocean ENSO conditions are often the most variable as shown by this Dr. Dew Point chart:
The NAO has not been negative since November.
SSW events often result in a negative AO and/or negative NAO which often signal colder weather in the East third of the U.S. 1-3 weeks later, occasionally over a month. The GFS Ensemble is projecting a negative:
There is cross model agreement in a -NAO by the end of February.
This is how the indices correlate to temperature patterns (+/neutral/-):
We are sort of in-between the two phases below with a La Nina tilt to the left panel:
The GWO (aka GLAAM or AAM) Global Wind Oscillation Global Atmospheric Angular momentum (torque) has been HIGH for quite a stretch now, preventing small disturbances in the jet stream flow from consolidating into larger stronger long-wave disturbances (mid-latitude cyclones) and preventing jet stream amplitude or big north south swings because the Pacific jet is so strong/fast. Or put another way, +AAM favors fast zonal west to east jet and -AAM favors a slowing PAC jet and high latitude jet stream blocking.
It is projected to go LOW:
The NAO forecast is similar to what happened in January to March of 1962:
However, the PNA index is forecast negative to near neutral, which is a warm signal for the Southeast U.S. (a +PNA is a cold sign for SE, and often a snow/ice sign) so it is a contradictory signal thus far [but trending up]:
So thus far the Pacific Pattern West Coast pattern does NOT support the change to cold in March while the other signals do.
Researchers at WeatherBell and elsewhere have noted similarities to projected patterns coming up with March of 1962. I wrote about it in my previous blog post.
That year had a cold March after a warm February:
Similar blocking was seen in March of 1984, a year that had March snow in Northern Alabama and Georgia and points North.
No guarantees this happens but food for thought.
The research has also found similarity to SSW event patterns of 2008-2009. The match is striking to my eyes:
This is NOT a forecast.
Weather is chaotic, and similar patterns can result in different specific outcomes. It does let us know what can happen because it’s happened in the past. That is what “analogs” are all about. Also, it would not have to happen on the exact dates either.
There’s something about the potential pattern that has my gut twitching about ice rather than snow, but of course that’s not science just a nagging feeling.
Data on ice is sparse in these parts I am afraid. My not so great long-term memory says significant ice in March or later is very rare based on personal experience here 30+ years, but without data I don’t know.
As Dr. Cohen points out, the uniqueness and extreme nature of this SSW event means we don’t have anything like it for comparison so there’s no telling how this one will impact actual weather in America.
As blocking moves from the Barents Sea to the Davis Strait Pacific Jet Stream retraction gets underway (graphic from NewYorkmetroweather):
As of now the models do not show a change to cold and show no snow or ice. Or they show cold one run and take it away on the very next 12 hours later. This is why I am looking BEYOND models for clues.
SSW events disrupt the atmosphere and make it more chaotic so I would expect the models to struggle. They have already struggled this year more than normal thanks to the weird warm and cool ocean pool configuration around the planet.
A SSW does not guarantee a polar air mass. Odds of more winter in any given year go down quickly after March 10th or so anyway.
However, the Greenland-Canadian blocking projected would normally result in an East Coast trough to replace the strong ridge, eventually.
On the other hand I think SSW events are more rigorously tied to our weather in mid winter, so the lateness of the season gives me pause to wonder if the impact will be muted by the date.
Of course, mother nature no longer seems to respect what has been normal.
It’s interesting that such NH blocking has been absent for quite a few consecutive winters.
I have not studied stratospheric warming in the scientific literature enough to know what the false alarm ratio is, but knowing this weather history lets us know not to let down our guard and to watch models for any signs something like this might be coming.
Follow me on Twitter @MellishMeterWSB.