In estimating the weather for a coming season we look at a very long list of indicators. Like predicting the economy or the stock market well in advance, signals are often mixed. No two winters, even ones that have a lot of ocean-atmosphere markers in common are ever the same. Similar but not the same. We forecast based on what such past signals have brought, but they are the average or mean of many variations. Since a picture is worth a thousand words, take a look at what things like a +PNA or a -NAO mean. We can not predict these but days to weeks in advance. So we look at other signals to get an idea of what the "mean state" of these might be in the season ahead. For example certain states of the oceans and sea ice and early season snow cover Poleward are related to the QBO as is the solar cycle/sun spots which in turn are related to stratospheric warming events and blocking patterns. We are in a deep long-term down solar cycle but are past the minimum, recent sun spot activity has picked up.

We are in a 40 day period where new weather cycle patterns develop that erase the summer and early fall pattern, which in turn point toward the winter, the new pattern usually locks in around Thanksgiving.

MODERATE TO STRONG LA NINA WINTERS OFTEN HAVE A NEGATIVE PACIFIC DECADAL OSCILLATION SIGNAL (or the other way around) WHICH MEANS THE WARMEST WATERS RELATIVE TO NORMAL ARE IN THE WESTERN PACIFIC OCEAN. THIS SET-UP FAVORS RIDGING OVER THE CENTRAL OR EASTERN PACIFIC OCEAN VS WESTERN NORTH AMERICA. THIS MEANS THE ARCTIC INTRUSIONS ENTER THE CENTRAL TO WESTERN UNITED STATES FIRST. MODERATE TO STRONG LA NINAS TEND TO FAVOR SLIGHTLY MILDER THAN NORMAL WINTERS IN THE NE/MID ATLANTIC AND WARM FOR THE SE US.

Note I said FAVOR, not always. That is because a season’s weather is determined not by El Nino OR La Nina alone, but by many factors working in conjunction. The map diagrams will help show this is true. The problem is if you get just one little thing wrong then your long-range forecast can be a bust even if you get most of the index signals correct. See the diagram maps for examples of the different flavors of winter patterns.

This coming winter the La Nina is forecast to be in the weak to moderate category. There are of course climate models showing other outcomes!

A BIG RANDOM ELEMENT OR WILD CARD IN OUR WINTERS IS ALWAYS THE NORTH ATLANTIC. AS THE WINTER OF 2009-10 SHOWED, A STRONGLY NEGATIVE NORTH ATLANTIC OSCILLATION CAN EVEN HOLD A STRONG EL NINO AT BAY giving much different weather than a strong El Nino normally would. We saw this again last winter 2010-11 when this this time a moderate to strong LA NINA signal was held at bay by a strongly negative AO/NAO, resulting in atypical La Nina winter weather.

UNFORTUNATELY FORECASTING SKILL OF THIS FEATURE IS NOT EASY AND IS BEST ONLY A FEW WEEKS IN ADVANCE, and low for months or seasons in advance, this is also true for the EPO and QBO.

RESEARCH ARTICLES INDICATE WHEN THE QBO IS NEGATIVE, THE TENDENCY FOR BLOCKING AROUND THE POLES (AND THUS THE STORMIER, COLDER AND MORE NEGATIVE NAO) INCREASES AND WHEN IT IS POSITIVE THERE TENDS TO BE LESS BLOCKING.

LAST WINTER WAS A RECORD BREAKING NEGATIVE AO/NAO WINTER, BUT STRONGLY NEGATIVE NAO WINTERS DO NOT OFTEN OCCUR IN PAIRS. ABOUT EIGHTY PERCENT OF THE TIME, THE SIGN SWITCHES. STILL SOMEONE SHOULD TELL MOTHER NATURE THIS BECAUSE THE WINTER PRIOR ALSO SAW A STRONG NEGATIVE AO/NAO!

So far there are conflicting signals for this winter, but that is more often the case than not, and why making a forecast for a coming season is so difficult. If you Google the terms I use here, such as PNA, QBO, EPO, MJO etc. and click "images" you can see for yourself many fine examples of each since a picture is worth a thousand words as they say.

Preliminary indications are that we will have less blocking (lesser -AO/-NAO) this coming winter than the past two, allowing a more typical La Nina pattern to evolve over the course of the November to March time frame, particularly December through February.

So take a look so you have the background needed to understand the winter outlook when it's issued. I know its complex and can give the brain a headache. But it's kind of like boiling down complex macroeconomics or foreign policy matters to bumper sticker slogans. It's fun and easy but lazy and represents small thinking and possibly low IQ. If only life was easy and simplistic. If only weather was, too.

CLICK ON THE FIRST MAP then you can "scroll" through all the maps added, NOT ALL the maps show up with the text so you have to do this to see them all. Quirk of the publishing tool I guess. Thanks.