October starts cold and wet with unusually early snow

October’s weather was more fitting for November than during our typical leaf-peeping season throughout New Hampshire.

Cloudiness, periods of wet weather and even some unseasonably early snow made it feel more like Thanksgiving than Halloween.

New Hampshire and a large portion of the U.S. and Canada shared cooler than normal temperatures last month. North America’s large-scale cold weather pattern during October was because of a strong mean trough across the central and eastern part of the continent.

This chilly pattern peaked during the middle of October when some record cold occurred through the central U.S. For our area, temperatures were cool, but no records were set.

The growing season came to a close right about on schedule, with Nashua’s first frost on Oct. 11 and first killing freeze on Oct. 15, two days later than the average.

Snowfall was observed in the area twice during October. Flakes were noted in the air early on the morning of Oct. 16, followed by some heavier snow during the afternoon of Oct. 18 that featured some huge, wet flakes.

The second event produced some slushy accumulation on grassy areas, with elevation playing an important role with respect to amounts. While little more than a dusting was noted at lower elevations closer to the Merrimack River, including at the official Nashua recording site at Pennichuck Water Works, amounts of an inch or two were measured on some of the hilltops around the area.

Enough snow stuck to leaves to pull down tree branches and limbs in some areas. A snow total of 2.4 inches was measured at an elevation of 570 feet in Pelham. Anyone who tuned in to the New England Patriots game may have thought it was a replay of playoff games of past years when snow was falling during January.

So, just how unusual is snow during October? Snow observed in the air isn’t that unusual, but accumulation on the ground is rare. For the Nashua area, this year’s snow was just the sixth time that a measurable amount has been observed from reliable local records back to 1884.

The snow that fell Oct. 18 was the second-earliest measurable amount during that same period. The earliest came Oct. 10, 1979, when an inch fell. As recently as 2002, we saw 0.5 inches, and in 1962, 1.5 inches was recorded.

Flakes of snow in the air have been observed 23 other years during Nashua’s weather history. So, we would expect that every five or six years, at least a few flakes of snow will fall across the lower Merrimack Valley.

Does an October snowfall have any impact on the upcoming winter and its snow total? During winters following an October snow, there was almost an even split, with 12 having above-average snowfall and 11 totaling less than average snowfall.

It appears that early snow means little as to what the upcoming winter’s snowfall will be. It should be noted that following the October 1979 snow, Nashua saw its least snowy season, with only 18.4 inches. On the other end of the spectrum, 1992-93 and 2000-01 were followed by amounts exceeding 90 inches.

A check of temperatures during the winters following October snowfall showed 10 were milder than normal and 13 were colder than normal. Other factors certainly affect how a season’s temperatures and snowfall will tally up.

The current moderate El Nino and the extremely low solar activity, along with numerous other long- and short-term cycles, have some effect on how a season’s weather will turn out.

October’s temperatures were rather persistent at staying cooler than normal, with a period of very cold weather at midmonth. Nashua’s average temperature of 47.1 degrees was 2.0 degrees below normal. Last month was the coolest October since 1993 and ranked as the 18th coolest since 1885.

Temperatures reached 70 only once, which is a considerably low number for the middle month of fall. Several hard freezes occurred from mid to late month, with readings falling to the mid and upper 20s around the area.

Rainfall tallied 5.03 inches, with much of the rain falling during five significant weather events. Nashua’s total ranked as the 20th-wettest October since 1884 and saw a surplus of 1.10 inches.

While October is generally one of the sunnier months, we saw cloudiness dominate this year.

At Blue Hill Observatory in Massachusetts, 41 percent of the possible sun was observed, making it the ninth-cloudiest October on record.

November normally will bring us increasing cold, more storminess and more threats for some snow. Periods of winter-like weather can start even before the official beginning of meteorological winter on Dec. 1.

November 1950 saw temperatures reach the low 80s, while subzero cold was recorded on the day after Thanksgiving in 1989.

Keep in mind that the days start getting longer in only six weeks. Of course, there is the old Yankee saying, “As the days lengthen, the cold strengthens.”

Weather & Climate appears the first or second Saturday of each month, depending on when final weather data are available. Doug Webster of Hudson is senior meteorologist at Meteorlogix in Woburn, Mass.