Tuesday, October 13, 2015

Snow, and warm thoughts

Snow in the forecast, true winter cold isn't.

Snow, and warm thoughts


On a day when the temperature is heading into the '60s, computer models incongruously are hinting that some places near Philadelphia are going to wake up to a snow cover Thursday morning.

This should become clearer with model runs this evening, but right now it appears likely that at least some flakes are going to fall as the storm makes its exit.

After the storm passes, it will be moderately chilly, with below-normal daytime temperatures in the 40s into next week.

But the government's longer-term outlook sees above-normal temperatures throughout the East through the 19th, and as we've noted, the seasonal outlooks have been trending milder.

The North Atlantic blocking pattern that drove cold air into the East last year just hasn't developed, and a La Nina is cooling its heels in the tropical Pacific.

Judah Cohen, the Siberian snow specialist at Atmopsheric and Environmental Research, says that while the message from the Eurasian snow cover is mixed, he's seen enough elsewhere in the atmosphere to go with mild in the East for the winter.

Meteorologists who venture into long-range forecasting are wary of making seasonal snowfall predictions because the white stuff is so idiosyncratic.

Philadelphia's average is 22.1 inches, and one major snowstorm can put a winter in striking distance of that figure. Thust, temperature is a safer variable to forecast.

So we were somewhat surprised to find such a strong correlation between winter snow and average temperature during the meteorological winter -- December through February -- when looking at the seasonal data.

Winter temperatures averaged below the long-term mean, 34.4, in all of the 15 snowiest winters in Philadelphia.

In the 1982-83 season, No. 16 on the list, temperatures averaged 2 degrees above the average, and snowfall came in at 35.9 inches. But 21.3 of that, a season's worth, came in one February storm.

In the 63 winters in which the average winter temperature was above 34.4, the average seasonal snowfall was 16.1.

In the 65 winters that finished below 34.4 degrees, the average snowfall was 28.3.

We don't know what's to unfold in the next three months, but we do know that Philadelphia just experienced its fifth-warmest November on record.

We've observed that in the seasons coinciding with the 10-warmest Novembers before this one, snow was below average every season.

In short, if snow is on the ground Thursday, if you're a snow-lover it wouldn't hurt to savor it.

Inquirer Weather Columnist
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About this blog

Everyone talks about the weather, and here we write about it.

When we’re around and conditions warrant, we’ll keep you updated about what’s coming, but we will do our best always to discuss weather and climate developments in context and remind you that nothing in the atmosphere happens in a vacuum.

Tony Wood has been writing about the atmosphere for The Inquirer for 26 years.

Reach Tony at twood@phillynews.com.

Tony Wood Inquirer Weather Columnist
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