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Cold Weather Threatens Certain Local Crops

By Terry Eliasen, WBZ-TV Executive Weather Producer
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BOSTON (CBS) – Since when is a freeze a big story in the month of March? Just another example of how abnormal our weather has been as of late. March is currently running over 10 degrees above normal, a pace that would make this the mildest March on record if it were to continue. We had five record high temperatures in Boston in the last two weeks and have not come close to the freezing mark in even longer! The last time Boston dipped below 32 was March 11th, and we only went down to 30 briefly. Our last “hard freeze” was way back on March 6th when temperatures fell to 20 degrees overnight.

You won’t hear any freeze warnings issued for tonight because the official growing season is still several weeks away. However, the early onset of summer-like conditions has kick started the growth of vegetation nearly everywhere. Farm owners tell us that their fruit trees are about 3-4 weeks ahead of schedule and are absolutely in danger tonight of losing some of their crop.

Temperatures will be critical overnight take a look at this chart, many apple trees are now in the half inch green phase or even slightly more advanced. That means there could be as much as a 10% kill if temperatures were to drop to 23 degrees and a 90% kill at 15 degrees. The current forecast for much of Southern New England in the low 20s with some upper teens in Southern New Hampshire and far northwestern suburbs of Boston.

So what can our local farms do to protect their crops? Unfortunately the answer is not much. Homeowners can take precautions such as bringing their tender vegetation indoors or covering it to keep in the heat. Farmers do not have this luxury and are at the mercy of mother nature in cases like tonight.

Many farmers use irrigation (water) to prevent crop damage when temps drop below 32. It may seem counter-intuitive to water your fruit trees with below freezing conditions but under the right circumstances it really works. When temperatures are between 24-32 degrees you can use the energy that the water releases when it freezes to heat the vegetation! As long as you keep the ice wet, the temperature should stay right around 32. Unfortunately this will not work tonight because of the wind. Wind speeds overnight will remain high, in the range of 10-25mph. Therefore irrigation will not be effective and actually could prove to be detrimental to the trees and plants.

There is some good news regarding the wind tonight however. The wind will work to keep the air-mass well mixed and prevent radiational cooling to drop temperatures even lower. With no wind tonight, since the air is so dry (dew-points in the single digits), temperatures would have cooled much lower approaching the dew-point value in areas that radiate heat rapidly.

Thankfully the wind will prevent that from happening. This will not be the case Tuesday night. Winds will be nearly calm Tomorrow night and early on Wednesday, thus allowing temperatures to drop to nearly their full capacity, causing frost to form and creating another sleepless night for local growers.

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