Opinion

Is it climate averages or normals? It’s both

Climate averages are based on a 30-year period, which is recalculated every decade. Meteorologists presently use the 30-year period from 1981 to 2010. In 2021, the averages will be released for the period 1991-2020.

For any climate site, there are two timeframes to be aware of, the 30 year period, upon which the averages are calculated, and the period of record, which is simply the year they started keeping weather records, up to the present day. At Caribou, record-keeping commenced in 1939.

Before I continue, let me say that the word “average” is the same as the word “normal” when talking about climate data. For example, saying the average high is 32 for a given date is the same as saying the normal high is 32 for that same date.

If you are new to the area, and you think northern Maine winters are long, the snow stats support you. Based on 30-year averages, only three of our 12 months are snow-free — June, July and August. In September, Caribou averages 0.1 inches, 1.6 inches in October, 10.5 in November, 22.9 in December, 25.2 in January, 22.2 in February, 18.3 in March, 7.4 in April and 0.5 in May, for a seasonal average of 108.7 inches. (108 inches is 9 feet.)

A snow season runs from July 1 through June 30. This is done to ensure capture of any unusually early or unusually late snowfalls. Presque Isle saw 8 inches of snow on the Marston Road on May 16, 2016.

The snowiest March occurred in 1955 with nearly four feet at Caribou (47.1 inches), while the least snowy March was in 2006 with only 1.4 inches.

Sometimes, I run into people who have lived here their whole lives, and they speak of remembering weeks at a time where the temperature remained below zero. However, when you run the numbers, it tells a bit of a different tale, because the record for consecutive days where the high temperature at Caribou remained below zero is, perhaps surprisingly, only four days. The record for consecutive days where the low temperature fell below zero is 20 days, one day shy of three straight weeks of subzero overnight lows.d

Say, eight years ago, we were just getting started with the astonishing March melt of 2012, which, unfortunately, led to the Perth-Andover ice jam flood. From March 18 to March 22, the highs at Caribou went 64-53-73-75-73. The average high during that same period is 34-35-35-36-36. A local photographer took a five-day sequence of shots from the same location, and it is truly astonishing. I can send that along to anyone interested. Just email me at the address at the bottom of this column.

Unusual cold held sway five years later, when Caribou had its latest-on-record occurrence of a sub-zero daytime high on March 11, 2017, when the high was -1 F. That is one of only three subzero highs on record at Caribou, the others being a high of -1 on March 5, 1948, and a -3 F on March 8, 2007. That -3 F high temperature is the coldest March high temperature on record at Caribou.

A final note, and it has to do with forecasting. In our local forecast area, we have quite a bit of varied terrain, and it can and does make a big difference in the amount of snow or rain you get in a region-wide precipitation event.

If you live at a higher elevation and the wind is blowing up toward you, your snow or rain totals will be enhanced,

But on the other side, the “downslope” side, amounts will be reduced, as the air warms during the downglide, and the relative humidity, therefore, decreases.

To get a sense of our terrain, Google Map “Plaster Rock, New Brunswick.” Go to the upper left and add terrain, then zoom out a bit. 

A good upslope example is the higher terrain just west of Winterville. An easterly wind would glide up and deliver more snow on the windward side (the side the wind is coming from), and less on the leeward side, at lower elevations.

When listening to forecasts it’s always handy to know from which direction the wind will be blowing, as it will inform you whether you could have localized areas of more or less, depending on where you are, relative to the terrain.

Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.com.

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