More thoughts on December and the coming winter | Weather
Here are a few more thoughts relative to the longer range outlook:
We in the weather office have been doing some research over the past few days, trying to better assess where we are heading this winter…a winter of conflicting data in the global indicators.
We were inspired by a recent research that showed that the AO was so strongly positive in November so as to rank among the top two on record.
With that kind of powerful signal we decided to start there and then look at some of the other trends in global teleconnectors to see if a relationship could be found.
What we discovered, using data points with strongly positive AO’s, negative PDO’s and weak La Nina’s was one season really stood out: the winter of 1994-95.
To test our findings, we pulled Rochester data to see if there were local congruities. Here is what we found: November of 1994 had an average temperature of 45.8 degrees which was 5 degrees above normal. November of 2011 had an average temperature of 45.8 degrees (yes, identical which is eye-catching). November of 1994 had a snowfall of 2.8 inches compared to a normal of 7 inches. November of 2011 had a snowfall of 0.3 inches.
To further test our findings and to further represent the Great Lakes, we pulled Chicago data to again see if there were local congruities. Here is what we found: November of 1994 had an average temperature of 44.4 degrees, compared to a normal of 40.3 degrees. November of 2011 had an average temperature of 44.9 degrees. November of 1994 had a trace of snowfall compared to a normal of 1.2 inches. November of 2011 had a trace of snowfall. Hmmm…
Do you get the feeling that we may be on to something here?
Oh, and one more thing: harsher (more typical) winter weather conditions at both sites were skewed toward February and March. This could be attributed to the +AO, which is related to intensely cold air above the arctic circle, finally going negative as the “dam breaks” and the cold air floods lower latitudes…something that could conceivably happen this year.
Of course, no two seasons are identical. And if forecasting the weather were as simple as finding a similar month in the past I would be out of a job.
Furthermore, there are other teleconnectors to consider, some that do not fit neatly into this little hypothesis. But even at that, some do fit such as the recent increase in solar activity and the recent decrease in higher latitude volcanism.
So, an obvious question might be given these significant linkages: “How did those Decembers and winter seasons turn out in 1994-95?”
In Chicago, with an average temperature of 34.9 degrees, December of 1994 ended up the 17th warmest in more than 100 years of record keeping. The total seasonal snowfall was 24.1 inches which was the second lowest total since the winter of 1957-58 and two-thirds of the normal.
In Rochester, with an average temperature of 34.8 degrees, December of 1994 ended up 5.4 degrees warmer than normal and there was just 7.6 inches of snowfall, a third of the normal. Total seasonal snowfall was just 56. 2 inches compared to a normal of 100 inches.
Now, I caution you to not draw direct links from one season, no two seasons are identical. And remember, if the AO and its subset the NAO, suddenly tank, conditions can turn in a hurry and forecast revisions may be necessitated.
But for Rochester, here are some of our projections: This winter will bear little resemblance to last winter (consistent cold, lots of snow, no really big storms). In fact, it will be much different with “inconsistent” cold, near to below normal snowfall and a higher probability of a big storm or two (but with Great Lakes-centered storms favored over east-coastals). Additionally, December will have a couple of arctic incursions complete with wind and lake snows, but will likely still average above normal in temperatures and below normal in snowfall. The late January to February to early March period will be coldest (relative to normal) and the snowiest in absolute terms and will turn harsh if the AO/NAO couplet goes strongly negative.