Winter Forecast 2017-2018

Winter is almost here and it’s looking like another one to keep the shovels handy.   The highlights include:

-Above normal precipitation and snowfall
-Warmer than normal temperatures
-Winter slow to let go in spring
-December icing event
-High probability of snow on the ground at Christmas

Maine averages between 4 feet of snow at the coast to around 10 feet near the Canadian border.

Snow lovers have been pretty happy over the past decade.

Average snowfall Portland is 61″

So what can we expect this winter?  A good way to forecast the winter is to look to the past.  Lets start with a change in the ocean water temperature over 3000 miles away called  ENSO (El Nino Southern Oscillation)  This winter is expected to include a weak La Nina.  Simply put, it’s an abnormal cooling of a portion of the the Eastern Pacific Ocean.

That change typically configures the jet stream in a way that provides New England with an active storm track.  It also usually results in plenty of cold air available in Canada and parts of the northern US.

I started my research by looking the expected ENSO index for the months of December, January, and February.   I came up with a range between -0.5 and -0.8.

I then went back to find all weak La Nina winters in that range for the months of December, January, and February.  They are.

Using climate normal’s 1981-2010  I focused in on Portland temperatures for the seven weak La Nina Winters over the 36 years. They resulted in 43% warmer than normal, 14% normal, and 43% colder than normal.  No winter temperature correlation was found for Portland. The US winter temperature anomalies look like this.

I then looked at winter snowfall for the 12 analog winters back to 1950.  Between the months of December and February 42% were snowier than average, 25% normal, and 33% below normal.  At best, you might be able to conclude,  the findings would suggest a 67% chance of normal or above normal snowfall. Here’s the breakdown on snow amounts for Portland based on ENSO. Portland’s record of 141.5″ in 1970/71 sticks out in a moderate La Nina winter.  Thanks @joshtimlin

Those same years and months were also analyzed for precipitation.  The findings show 83% chance of normal to above normal precipitation.  That would suggest to me wet snow holding lots of water, mix events, and even some rain or ice.

La Nina Winters are also known for ice storms, and particularly during the month of December.  The most recent is December 22nd,23rd 2013.

Ice Storm December 2013.
The 2008 December ice storm left NH with more power outages than the 1998 ice storm. I remember that one well because our family was without power for 4 days. CMP restored power on my street at 3:58PM and the Patriots kickoff was 4:00 PM.  Thanks CMP!  Both examples were La Nina Winters. Based on that, we’ll be looking for a higher than average probability if freezing rain events during the month of December.

The recent stretch of warm autumn weather can’t be ignored when forecasting the winter season. It’s well known, there’s a correlation between warm autumns and lots of snow during the winter months in Northern New England. September and October combined were the warmest on record in Portland.  Here are the top 10 prior to 2017 and following winter recorded snowfall.  70% showed above normal snowfall. And of those, in more than half, Portland recorded over 90″ for the winter season.

US Temperature and precipitation anomalies looked like this for the winter following Portland’s top 10 warmest September and October’s on record.

The correlation becomes even more interesting when you isolate the month of October. Here are the top 10 warmest (prior to this year) and their following winter snowfall.  90% showed above normal winter snowfall.

Our friends at Sugarloaf sent me their snow amounts over the past 15 years. The top 2 snowiest winters in that range occurred in La Nina winter’s. Both were preceded by the 2nd and 7th warmest September/October’s on record in Portland. Skiers and snowboarders should be happy with those stats.

The recent warm autumn was given lots of weight in this winter forecast for its strong correlation to above normal snowfall.

FORECAST MODELING

Lets look to a sample computer model guidance now.  Forecast seasonal modeling is hinting at a similar temperature scenario outlined above.  The US CSV2  suggests slightly warmer than normal temperature for the months of December, January, and February.


The Japanese Model is in a similar camp with warmer than normal temperatures for the northeast December through February.


Precipitation is only slightly above normal for the northeast.

SNOW FOR CHRISTMAS

Snow on Christmas… I know many that want it.  The odds of having at least 1″ of snow on the ground for the holiday breaks down like this.

Click here for your town or city.  Portland has a 53% chance of  having at least one inch of snow on the ground Christmas morning. The chances are higher this year.  Here are Portland’s percentages and stats for the past decade.

Our analog weak La Nina years above showed 75% had at least 1 inch of snow on the ground at Christmas.  Of the top ten warmest Septembers/Octobers on record, the following Christmas morning showed 70% of them had snow on the ground. For those reasons, we’re playing the numbers and going with a white Christmas for 2017.

My number one objective in this blog post is to highlight the winter months of December, January, and February.   It’s worth mentioning though, weak La Nina’s show a 67% chance of normal to above normal snow in March. Warm Octobers show an 80% chance of normal to above normal snow in March. That data researched is for the city of Portland.  Forecast modeling is also hinting at a winter that won’t let go in spring in the northeast.

So much like last spring, we may very well be talking about snow storms in March and temperatures slow to warm up.

Thanks for taking the time to read my blog.  On a personal level, I’m hoping for lots of snow this winter for fun outdoor activities.  My family and I enjoy skiing (both downhill and XCountry, snow shoeing, skating, and ice fishing.  Lets see what winter 2017/2018 brings.

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Charlie Lopresti

About Charlie Lopresti

Charlie makes up the "Weather Part" of CBS News 13s evening edition. A native New Englander, he grew up enjoying the area's exciting and sometimes wild weather.