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Frost advisory for many, chilly for all

Posted by David Epstein  April 25, 2012 07:27 PM

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Tonight will turn mostly clear and quite chilly as any evening showers and clouds disappear. The day Thursday will dawn bright, sunny and cold with many places into the 30s. We have a weak weather system that will move just to our north Thursday night and bring with it a few showers.

The clouds of today will melt away overnight as we lose the heating from the sun. It was the sun that caused all the clouds and even a few showers, late this afternoon. While the sun is usually a welcome site, today, the sun caused clouds to form in the afternoon. Tonight, with the lift gone, and dry air over us, temperatures will fall rapidly after sunset. There is a frost advisory up for many places away from the coast for early Thursday morning. If you have tender plants outside, I would bring them in or cover them with a sheet or some burlap.

What is lift?
When the sun heats the earth, the air above the ground starts to rise. This process is much like a hot air balloon rising. Once the sun sets, as each hour passes this evening, the ground will cool and skies will clear. Whenever you see clouds, rain, snow, etc. the air at the ground somehow had to get lifted high enough to produce the clouds and/or precipitation. Air can get lifted from sea breezes, air hitting mountains, low pressure and yes, even the sun. lift.jpg Wednesday's lift was primarily solar based. Lift is one of the most important aspects of meteorology and something we always try to understand.

More rain for Thursday PM
On Thursday warmer air will be moving towards our area from the south. As the warm air hits the cool air over us, it will be lifted. This type of lift is called overrunning. overruning.jpg Overrunning also causes clouds and precipitation. In winter, overrunning can cause snow, sleet, freezing rain, and rain. This time of the year, we will get rain.

On the weather map for Thursday (image below) we see an area of rain that will move through New England during the afternoon and first part of the overnight. This area, though not large, should produce up to a quarter of an inch of rainfall by the early morning Friday. As the storm passes, skies will clear and leave us with a very nice, though breezy and chilly Friday. I don't expect temperatures to hit 60F for the weekend. Speaking of the weekend, right now, it looks like the next system of rain will stay to our south. This means clear and cool conditions both Saturday and Sunday. If things change I will let you know. Stay tuned.

Thursday 26th.jpg

Gardening tip of the week
This week I am sharing with you a video that shows how raised beds can be used to create usable space for a garden. The beds you will see in the video are part of a project at the Massachusetts Horticultural Society. They have the luxury of a lot of space,but you could try this on almost any scale.

Follow me on Twitter at @growingwisdom and check out my latest videos at

This blog is not written or edited by or the Boston Globe.
The author is solely responsible for the content.

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About the author

David Epstein has been a professional meteorologist and horticulturalist for three decades. David spent 16 years at WCVB in Boston and currently freelances for WGME in Portland, ME. In 2006, More »
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