Monday, November 12, 2012

Comparing Nov '11 to November So Far--Christmas Tree Lighting Forecast

So far so good....

The temperatures have been cooler over the last several weeks but no ultra cold air to drive lake effect snows....yet.  In fact, the stretch of cool that started Sunday October 28th and finished Thursday, November 8th was the longest stretch of temps below 50 this time of year since 1925! 

Most people fall victim to these bursts of cooler air as a harbinger of what might be lurking in the winter ahead. Yet as many amateur meteorologists on twitter remind me, and rightly so, that you can't use these short term trends or any other statistical tool as gospel in projecting future longer term winter trends. Yet by using these statistical similarities within the overall framework of the current and past atmospheric state (several days or weeks previous), patterns can be found which can lead to more accurate long term forecasts.

The most notable pattern so far this winter has been the Greenland Block which was one of the primary drivers of the Hurricane Sandy hybrid storm and the crippling Nor'easter a week later.

The North Atlantic Oscillation is a good predictor of the Greenland Block. When the NAO goes positive, the Block is less noticable. When the NAO goes negative, the Greenland Block becomes more apparent.

So far, this November, the NAO has been strongly negative. This helps drive Sandy to deepen and push inland. For comparison, FROM LAST NOVEMBER THROUGH VALENTINES DAY, THE NAO WAS NEGATIVE FOR ONLY 10 DAYS! You can see why the winter was so mild. No Greenland Block, you lose a big driver of cold air into northeastern Ohio.

The NAO seems to have rebounded a bit this past weekend. Some projections start to drive it back into negative territory.

Let's look back at last winter to see what the setup was in November just for continuity sake.

The ridge of high pressure and warmth was slowly developing over the eastern US and Ohio. By early December, the ridge was so strong that little lake effect snow took hold. Milder air across the eastern 1/3 of the US. November was the 4th warmest on record. December didn't crack the top 10 but it was close. Only 1.1 inches of snow fell in November; 7 inches in December.

What does all of this mean?

For one, I don't think the east coast ridge of high pressure will be a dominant feature this winter. It might come and go from time to time but it won't be a primary fixture. Notice the first week of November this year. 
We need to watch the behavior of the NAO for signs of blocking heading into the Thanksgiving holiday weekend. This could mean some snow for New England and colder air for Ohio!

Around Christmas time, the ice/snow cover over Canada will be a tell-tail sign on the depth of the preliminary cold. If the ice/snow cover is well ahead of schedule, the reservoir of cold would be enhanced by the snow/ice cover before it pushes south.

After the New Year, the focus will shift to the Arctic and the stratosphere. The dynamics are complicated and hard to visualize but in a nutshell, if rapid warming occurs in the stratosphere over the arctic, the potential for dramatic surges of cold increases. The warming will need to be watched.

All in all, the fox8 winter weather outlook remains as is. Near normal snowfall (65 inches for Cleveland; 35 for Akron, 120+ for the snowbelt)

No comments: