THE VERMONT WEATHER BOOK by David Ludlum (Vermont Historical Society, 1996)
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The front of the March battle zone often lies right over Vermont, creating much storminess and causing rapid changes from cold to warm and back to cold again. Temperature contrasts as great as 20 to 30 degrees may exist across the weather front, creating distinct thermal and precipitation zones. Rain may be falling on one side of the mountains while snowflakes are descending on the other side. Or the battleline may migrate north, then south, giving a locality periods of frozen or melted precipitation alternately. Often the combat zone has a vertical alignment: higher ground may receive a white covering while valleys experience a cold rain.
The main event in March is the beginning of astronomical spring at the vernal equinox, which falls on or about March 21. Having moved north to the equator, the sun rises directly in the east and sets in the west; hence night and day are about equal. The term equinox is derived from the Latin aequi (equal) and nox (night) (the words might just as well be aequi dies, or equal days). That the equinox has little to do with the daily weather led Dr. Henry Van Dyke to compose a warning about the spring climate: “The first day of spring is one thing, and the first spring day another. The difference between them is sometimes as great as a month.”
The principal jet stream in March enters the continent over Oregon and dips southeast to Missouri before heading directly east to follow the eastern part of the February track over Virginia. The southern jet, of such importance for storm making in January and February, gradually loses strength with the approach of spring and by the end of March has become a minor influence.
March is a transitional month, when storm tracks retain many of winter’s aspects yet at the same time start to exhibit some of the characteristics of spring. During March storms tend to form more often over the continent and less often over the ocean waters. Both principal storm tracks of February — down the St. Lawrence stormway and along the Atlantic seaboard — remain active, although they develop less frequently.
The daily progress of coastal disturbances along the Atlantic seaboard is influenced in March by the presence of blocking anticyclones over Quebec and the Atlantic provinces of Canada; their position slows the northeast movement of storm centers while at the same time increases their intensity and lifespan. Examples of severe storminess in March abound. Often the “Crown of Winter Storm” comes in early March and raises snow depths to the seasons’s high. The Great Blizzard of '88 is the supreme example of a stalled coastal storm keeping the precipitation process going about double the number of hours that an unfettered storm can and in so doing producing about twice the amount of snow.
Although the principal anticyclonic tracks during March retain most of the characteristics of the winter months, several typical spring features are introduced. Of importance to the Green Mountain region is the tendency of Canadian high-pressure areas to develop farther east, over central Canada, and to track east of the Great Lakes rather than west. The Hudson Bay High is often the parent of the blocking high-pressure areas over eastern Canada, mentioned above as having important influences on the duration and intensity of New England coastal storms.
With the increased elevation of the sun and the longer extent of daylight, mean temperatures take an upward jump of about 10 degrees during March. In the northeast, Newport averages 27.1°; Burlington, in the northwest, 29.2°; and both Vernon, in the southeast, and Bennington, in the southwest, just above 32°. Heat waves in March have driven the mercury as high as 84° at Bennington in 1945 and at Burlington in 1946, and cold waves have dropped readings as low as -37° at St. Albans in 1938.
March brings an increase in precipitation over the relative dryness of midwinter. Several mountain stations in the south average over four inches, topped by Searsburg with 4.69 inches. In the north increases are of smaller degree; some stations measure about two inches — Gilman 2.05 inches and Burlington 1.93 inches. Most stations at middle and low elevations report almost three inches. March can be a very wet month as the statewide average of 6.92 inches in 1980 demonstrated.
March brings the high rite of the Vermont spring — sugaring time. The metabolism of a maple tree is a most complex matter, and the stages of development are intimately tied to the prevailing weather conditions. Warm days in the 40s and cold nights in the 20s are basic requirements, and other considerations such as humidity, precipitation, cloud cover, wind direction, and solar intensity play a part. The annual spring contest between frost and sun is crucial. Scott Nearing, the author of many works on country living, first learned about the intricacies of sugaring from his own Vermont grove. His first boilings on the day of the initial tree tapping took place on dates ranging from February 23 to March 25 with the mean date falling on March 12-13. The length of the sugaring season averaged forty-one days. More sugar was made in April than in either March or May. The quality of the sap deteriorated rapidly in the absence of overnight freezes, and the run ceased altogether with the leafing of the trees. Increasing warmth was responsible for the commencement of the sap flow, and its continued increase also caused the ending of the sap run.
