Friday, November 16, 2012

November Snowfall: 1970s vs Present

Cleveland Plain Dealer - Shoreway Near East 55th
Those late 70s winter were brutal. I remember driving to Fairview Park Hospital for the birth of my sister in 1978 in my dad's 1977 Buick on the Ohio Turnpike. The snow was unlike anything I had EVER seen. The winds were unbearable. It was the poster child of a typical winter back in the late 1970s in northern Ohio.

After last winter, our perceptions have become twisted. We hadn't had a winter with little snow (38.5"; 62" is the average) and mild temperatures like 2011-2012 in a while. Using the National Climate Data Center temperature data for all of northeastern Ohio, the December-February period in the winters of 2001-02, 1997-98 (El Nino), 1982-83 (El Nino), 1948-49 & 1931-32 were the only winters milder than last.

So when I show an 8day forecast that features temperatures trending slooowly back to normal or slightly above into Thanksgiving week, we immediately think of last winter. We remember how lackluster the snow was. We try to paint a similar picture now since we've had little to no snow this month. I bet if I surveyed 1000 people on the street, most would say that this winter will be similar to last winter. The RECENCY EFFECT (our instinctive ability of placing too much significance on more recent experiences or events) is a very powerful cognitive bias.

How about those 1970s snowfalls specifically in November. Were they extraordinary? Here are the November snowtotals from 1975 to 1983. Surprisingly, nothing out of the ordinary.

What about the DECEMBER and JANUARY snowtotals that followed compared to our last 9 winters? It seems that DECEMBER-JANUARY snow totals since 2004 have outpaced the same months in the late 1970s and early 1980s.

What should we take from the numbers? NEVER fall victim to thinking that a snowless November will always lead to a winter will less than normal snowfall. It happens of course. It happened last year. It didn't happen during the 2004-05 season which ended up as the SNOWIEST WINTER EVER!

It didn't happen in the 1970s and it probably won't happen this year. Next post, I'll take a look at the temperatures for the same period.

Wednesday, November 14, 2012

What Are The Teleconnections Telling Us?

We Didn't See Much of This Last Winter
I don't want to harp too much about the connections between the oceans and atmosphere and their influence on our long range outlooks. As I mentioned earlier in the week, teleconnections like El Nino or La Nina or the North Atlantic Oscillation, which has received alot of media attention since Hurricane Sandy rarely provide a straight forword, hard-and-fast forecast commandment to follow. If they did, long range outlooks would be as easy as looking out the window and saying whether it was sunny or cloudy.

Last winter gave us a great laboratory environment by which to view the atmosphere, like a fly on a wall, react to several teleconnections abrupt shift to levels that feature a lack of arctic drivers. This was a wake up call for all of us after a few very cold winters in 2009 and 2010. As a scientist, it was nice to see the other end of the spectrum at work in nature. Let's look at the late 2011 teleconnection levels:

The North Atlantic Oscillation, The Arctic Oscillation and the Pacific North American Index (Click on the link here for a detailed description)

Each one is more influential on weather patterns in the winter. The more POSITIVE the NAO and AO; the more NEGATIVE the PNA, the "colder" pattern shuts down. Conversely, the more NEGATIVE the NAO and AO; the more POSITIVE the PNA, the "colder" pattern becomes stronger and stronger.

North Atlantic Oscillation/Arctic Oscillation/Pacific North American Index charts from late 2011. Notice the perpetual POSITIVE levels. The PNA forecast for December 2011 was barely in positive (colder) territory.

 Now compare late 2011 to late 2010 and late 2009. Notice the levels were opposite.

How are the levels currently as we approach Thanksgiving 2012? They are no where as "mild" as last year and not as "cold" as 2010 or 2009. The NAO and AO are showing signs of more frequent negative turns. Yet the PNA still shows the western ridge or warmth hasn't developed into something steady and strong which would ultimately drive a trough/colder pattern more in the east and Ohio.

I still do not think this winter will be a repeat of last winter. The index levels are reflect a pattern that features a higher frequency of colder air episodes. The wild card will be whether or not the WESTERN RIDGE strengthens and STAYS WEST. Keep an eye on the PNA INDEX. If this happens in December coincident with INCREASED SNOW COVER in CANADA along with a few other factors over the arctic and Siberia, expect more cold this winter than last.

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)