THE VERMONT WEATHER BOOK by David Ludlum (Vermont Historical Society, 1996)
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The path of the undulating jet stream across the eastern United States reflects the changing season. The increasing influence of the Bermuda-Azores high-pressure area becomes evident with the northward shift of the jet stream’s location, whose central core now flows northeast from the Ohio Valley, over southern Pennsylvania, to the vicinity of Long Island south of New England. However, this is the mean course of the jet stream, which actually shifts its position north and south many times as it undulates eastward, from day to day and from week to week.
The speed of cyclonic disturbances crossing the United States and Canada slows and their intensity diminishes in May. The path from the interior of the continent now traverses Ontario and southern Quebec to the north of the St. Lawrence Valley, though their fronts still extend southward over Vermont and bring frequent weather changes. The track along the Atlantic seaboard practically disappears as a weather-making factor for interior New England.
The Bermuda-Azores high grows larger and stronger. Its lateral axis now lies along 40°N latitude and the north-south dimensions expand. The influence of the Hudson Bay High gradually lessens as the month progresses, but occasional blocking of the normal movement of storm centers still remains a factor to be reckoned by the forecaster.
The isotherms, or lines of equal temperature, continue their northward progress as in April. All of Vermont except the high elevations have means above 50°, ranging from 53.1° at Newport in the northeast to 56.5° at Bennington, a smaller difference between north and south than in the winter months. During May the thermometer has ranged up to 95° at Bloomfield and Cornwall in 1929 and Bellows Falls in 1962, and down to 14° at Bloomfield in 1946. The anomaly of having the highest temperature in the state registered at the most northerly station may be explained by the fact that air in May moves over heated land, and the station with the longest overland trajectory for southwest winds therefore will have the highest temperatures.
All sections of the state show increases in precipitation over April: the northeast by 17 percent, the west by 13 percent, and the southeast by 6 percent. The greatest amounts fall in the mountains where monthly catches range up to 4.53 inches at Searsburg Station in Bennington County. Totals are less in the north: Newport has 3.22 inches and Burlington 2.96 inches. Most of the increases result from more frequent thunderstorm activity; three are expected in the month of may in the Burlington area, whereas in the two previous months only one is the norm.
May usually witnesses the last killing frost of the season, generally coming between the 15th and 25th, but varying according to location. Injurious frosts have been recorded at many stations in June. The latest of record was at Bloomfield on June 30 and at Chelsea on July 1. The weather station at the latter is located in a frost hollow notorious for low temperatures and may not be representative of the surrounding countryside. The normal growing season ranges from a maximum of 162 days at Burlington in the Champlain lowland to a minimum of 110 days at Cavendish in the hills of Windsor County and 111 days at Bloomfield in the Northeast Kingdom.
May opens with a folklore holiday and closes with a national holiday of remembrance. Both are closely connected with nature’s calendar. The first of May was celebrated as a spring rite in England. The community went into the woods early in the morning to gather May flowers and then spent the rest of the day in feasting and celebrating the arrival of the new season. Since the 1880s, either May 30 or the Monday of the last weekend in May has been set aside to honor those who gave their lives for their country by placing flowers on their graves. One normally finds few flowers in bloom in Vermont on May 1, but the end of the month usually brings an assurance of a bountiful supply. Still, Vermont weather has many quirks. In 1903 a complete drought existed throughout May to wither nature’s products, and on May 30, 1884, the day was made doubly memorable by a general snowstorm and freeze.
