Climatologist explains warm April sun

04/16/08 7:34AM By Nina Keck
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(Host) Many of us are getting our first real taste of spring this week with sunshine and temperatures in the 60s, and even 70s, across much of the state.

Climatologists say there's a reason the sun feels warmer at this time of year - and gardeners should take advantage of it.  

VPR's Nina Keck has more.

(Keck)   Dr. Alan Betts is an atmospheric researcher who lives in Pittsford.

(Betts) "I do research on weather and climate - I study how the climate system works, how weather works."

(Keck)  As we walk across his backyard, which is soggy from snow melt, he explains why the sun feels so intense at this time of year.

(Betts) "The reason it feels warmer is because we've gone from a very strong transition - from having snow on the ground and the snow reflecting a lot of the sun's heat - to the snow melting, the ground melting. And now for the first time the ground is warming up so it feels very warm."

(Keck) The fact that the ground can absorb sunlight is one reason for higher temperatures.   But Betts says the lack of humidity at this time of year is also important.

(Betts) "Even though the landscape is very wet - we have floods at the moment at the valley here in front of me - the air is actually very dry."   

(Keck)   Plants and forests give off huge amounts of water vapor, making the air more humid.   But Betts says that cooling evaporation won't begin until leaves pop out on trees.   

(Betts) "So there's a two-week window now until the leaves burst open when all the sun's heat is heating up the ground and going back into the atmosphere basically as hot air."

(Keck) Betts says the farther north you go, the more extreme this phenomenon becomes. Here at home, he says, this climate shift is important to understand - especially if you're a gardener.

(Betts) "This is the week - the next two weeks - is the time to plant the peas and your really cold-hardy crops. They'll like the warming ground and they're not bothered by frosts."

(Keck) So go ahead and plant your broccoli, beets, cabbages and brussels sprouts.    But Betts says wait until mid May to plant tomatoes, peppers, basil and other more delicate crops. 

(Betts) "Traditionally Vermonters used to not plant until Memorial Day, but now many warm weather crops you can plant by the middle of  May because the spring melt and warm up that we are seeing this week, has come on average at least a week earlier than say 30 years ago.''  

(Keck) While global warming has lots of negative connotations, for gardeners in Vermont, Betts says, there's an upside: A growing season that's two or even three weeks longer.   

For VPR News, I'm Nina Keck in Pittsford.  

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