Posted: 8:18 am Friday, September 29th, 2017
By Kirk Mellish
Last winter had a combination of La Nina and El Nino like weather patterns and an unexpectedly strong and persistent Pacific Jet Stream. This winter is not expected to have that combo.
I’ve already covered the “typical La Nina” winter in a prior post.
As I pointed out in that post there is more to what will influence a winter than just El Nino or La Nina, or the sunspot cycle or any other single thing. Here’s just a partial list of things we look at:
And it all flexes over time.
The type and timing and strength of the La Nina matters, an east/central based event is more favorable for a colder winter east of Rockies compared with a modoki type more western based event.
A stronger La Nina signal usually means a more vigorous Southeast U.S. ridge.
But any seasonal forecast for the winter that is based upon La Nina right now is based upon a projection of an event which is still developing. This makes any EARLY winter forecast very difficult. For example the American CFS model shows a moderate La Nina in place by January but most of the other climate models including the European and the Japanese show a weak La Nina in place. This obviously has major implications for the overall winter patterns over the central and eastern portions of the country.
“Lower heights” usually equates to lower temperatures.
Those favor more blocking of the jet stream allowing for southward moving air out of the North Pole.
CPC researchers 27 years ago found the southeast ride in a La Nina was stronger in years when the QBO is positive/west (like last winter). The ridge in the SE is flatter when the QBO is negative/east (expected this winter):
As we moved through summer it was worth noting:
So we may be heading for a weak to moderate La Nina, in a low solar cycle, with a negative easterly -QBO. That would favor a healthy winter for the northern plains and Midwest.:
There are also other, longer cycles of the sun.
TEMPS LEFT PRECIP RIGHT:
Keep in mind that while we are in a low sunspot cycle we are not yet at the bottom, we may have to wait a couple years or so for full impact with the SOLAR MINIMUM expected somewhere about 2021.
Recent winters approaching but not at the sunspot trough such as 1985-86 and 1995-96 have favored ridge west east trough +PNA type winters.
Past weak La Nina winters with a -QBO had sudden stratospheric warming (SSW) events with blocking of jet stream and a weakened polar vortex (strong ones can bottle-up arctic air), a stronger Polar/Pacific Jet Stream and a weaker Sub-Tropical Jet Stream. So we may get a polar vortex pattern similar to last winter but not exact. This raises an eyebrow for ice concerns in the Tennessee Valley rather than snow.
Last year was LOW SOLAR, but the QBO was very strongly positive +QBO. A screaming strong and persistent Pacific Jet Stream often flooded the nation with mild air.
The water has warmed in the North Atlantic over the past couple months, if it continues to do so, with an easterly QBO, increase odds of a return of the –NAO and –AO this winter:
La Nina by itself:
You can see from the above La Nina is usually not a southern snow lovers friend… on its own. It’s possible other factors yet TBD will mitigate the La Nina flavor of the coming winter.
MODEL ENSO PROJECTIONS:
Considerable agreement on a La Nina.
SEA-SURFACE PATTERNS ARE IMPORTANT AROUND THE GLOBE
GLAAM (Global atmospheric angular momentum) or just AAM also known as GWO (Global wind oscillation) is another factor we monitor for medium and long-range weather outlooks.
Atmospheric Angular Momentum (AAM), a measure of how fast the atmosphere is spinning relative to the Earth’s rotation, is a complex variable that can offer insight to particular flow configurations within the atmosphere. It’s related to mountain torques among other things. Google if interested in more.
The colder than normal far north, warmer far south pattern shows in the projected AAM ABOVE IF it doesn’t change, this is just the current look. It may not hold.
We look for matches to this year from the past for analog years. Models are rather similar:
MODELS AND ANALOG 500mb JET STREAM PATTERN FOR WINTER:
Except for the ECMWF seasonal look there is considerable agreement on the mean 500mb pattern above.
MODELS BY MONTH…
SNOWFALL ANOMALY MODEL:
Purple shading above normal, yellow-orange below normal.
EARLY PARTIAL ANALOG LIST TEMPERATURES WINTER MEAN:
EARLY PARTIAL ANALOG LIST PRECIPITATION WINTER MEAN:
Remember, all this represents modeling and data RESEARCH looking for CLUES (drivers) in the form of analogs that represent similar ocean-earth-atmosphere-stratosphere-cyrosphere conditions to some years in the past as a sign post to the future.
It’s NOT YET A FORECAST.
PROBABLY GONNA TURN OUT BADLY, if ya know what I mean.
FOLLOW ME on Twitter @MellishMeterWSB