The Carlisle Mosquito Online

Friday, August 24, 2007


How's the weather?

It's Carlisle in August and the town seems deserted. Lots of town folk have packed up and rushed away to enjoy the last few weeks of beautiful weather before school begins and storms start. But Carlisle isn't really empty; there are plenty of folks whose idea of a perfect vacation is to stay home and enjoy the slow pace in our small town. Carlisle is lovely no matter what the weather, but rain, snow and storms are never far away. Here are some weather questions Carlisle "homies" might be thinking of as they picnic at Center Park in the heart of town.

Why does it always seem to rain on the weekends?

Weekends do get their share of rain. According to a study done at the Arizona State University and published in the August 1998 issue of Nature Magazine, we're almost 25% more likely have rain on Saturdays than on Mondays. After reviewing historic weather data, the researchers concluded that air pollution from commuters, truckers, power plants, and industries act as microscopic "seeds" in clouds. Pollution builds up and levels are highest at the end of the week. When too much moisture attaches to the "seeds," a rainstorm results. So skip work on Monday for the perfect vacation day.

Why does Carlisle seem to miss the violent storms?

This summer in particular has been a lucky one. We have had numerous hazardous weather warnings, almost daily. If you are a radar watcher, you've seen the dark yellow and red blobs on the screen, indicators of a severe storm, and sliding north and south of Carlisle on their way to Nashua or following Route 2. Does Carlisle have some magical protection like the village in "Brigadoon"? Further evidence can be found on the National Weather Service's five-year Lightning Density Map. ( Close examination of eastern Massachusetts shows the area around Carlisle receives fewer lightning hits than areas inside Route 128 or outside of Route 495. Weather systems seem to follow major roads, which are usually built in valley paths. To this date we couldn't find a scientific study to explain our luck.

If I hear thunder, how much time do I have before I should run

for cover?

Most people are hit by lightning before the storm is on top of them or after it seems to have passed. A recommended plan is the "30/30" rule. If there is a delay of 30 seconds or less from flash to the rumble of thunder, find shelter in a safe environment (covered on all sides) such as a car or building. Carports, tents, or porches are not considered safe. After the storm passes, continue to follow the 30/30 rule. While inside, stay away from the bathtub, telephone (cell phones are okay), kitchen sink, and computer. The charge from lightning can enter the home through buried or overhead wires even if the "hit" is further away.

Why did houses and barns once have lightning rods and they no longer do?

Ben Franklin, credited as the inventor of the lightning rod after his famous experiment in 1752, would be surprised to hear not every house in Carlisle has a lightning protection system. According to the December 9, 2001, issue of the Boston Globe, barn fires became such a concern after the Civil War that insurance companies required lightning rods be installed when barns were constructed. Some newer Carlisle homes have lightning protection systems built into the home, with only around 10" of a rod showing out the roof. But the majority of homes don't have lightning protection. Should they?

Modern homes contain more metal than homes of the 1700s and 1800s. Besides the metal in the cement and siding, we have pipes, cable and computer lines. In addition, each home has underground pipes leading to a well. All are good conductors of electrical charges. But 200 years ago there were fewer tall trees around homes and barns. How often does Carlisle get hit? The National Weather Service's five-year Lightning Density Map ( shows the average lightning per square kilometer per year, based on lightning activity from 1996 to 2000. Carlisle is in the second-to-lowest bracket, .25 to .5 hits per square kilometer. New England is generally on the low end of the scale. The southern states have the highest strikes, with some spots in Florida rated 16 hits per square kilometer per year and higher. But, of course, if your house is hit averages don't matter.

Why do storms from all over the US seem to arrive in

New England?

Weather watchers know to look to the west for a change in weather, unless a nor'easter is forecast (in which case look to the northeast). The flow of weather systems is generally from west to east, following known "storm tracks" across the United States. The storm tracks move toward the "Icelandic Low," a consistent low pressure system in the northern Atlantic. Most of the storm tracks flow north of, south of or through New England.

The Alberta ("Alberta Clipper"), North Pacific, North Rocky Mountain and Colorado storm tracks bring low pressure systems from the northwestern U.S. to north of Carlisle. The Texas storm track brings storms through western Massachusetts, while the South Pacific and East Gulf storm tracks flow up the coast south and east of Carlisle. Storms that arrive via the East Gulf track bring warm, moist air up the coast, setting up collisions with the cooler northern air. Many of our nor'easters are formed this way.

Does an abundance of acorns or stripes on a wooly bear caterpillar predict a harsh winter?

Scientists aren't sure what oak trees or wooly bears know. Folklore says the orange band in the middle of the caterpillar will be small if a harsh winter is in store. Wooly bears aren't worried about winters, though. Their strategy is to hide under leaves and freeze during the winter, thaw in the spring, and eventually become a fuzzy-headed Isabella tiger moth.

Wooly bear caterpillar. (Photo by Kay Fairweather)

However, there is a tool weather forecasters use to make short-term predictions. Forecasters watch data on the North Atlantic Oscillation (NAO), which describes the relationship between the Icelandic Low pressure in the north Atlantic and the Bermuda-Azores High pressure in the mid-southern Atlantic. The difference between the two pressures (low or high) affects position of the jet stream, which is an atmospheric current of air that flows across the US from west to east. When the Icelandic and Bermuda-Azores pressure areas are strong ("positive mode") the jet stream flows from northwest to northeast in a relatively straight path. Last year's winter was an example of a positive mode: we had a cool, mild winter with less than 30 inches of snowfall. The average snowfall is around 41 inches. When the pressures are weak ("negative mode"), the jet stream's path is variable. It can dip south, allowing moist air to ride up the coast, bringing us our famous nor'easters.

But back to acorns. Carlisle's oak trees produced bumper crops of acorns in 2003 and 2004, but a scarcity of nuts in 2005. Scientists haven't determined a pattern but think it has more to do with stress on the trees (drought or mice) than a prediction for a harsh winter. Carlisle has many types of oak trees which produce acorns in cycles from two to seven years. No clear pattern can be found. Scientists in Missouri studied the acorn cycles, wondering if bumper crops of acorns would predict an increase in Lyme disease. Mice and deer eat acorns, so more mice and deer, perhaps more Lyme disease. The first year of the study show a connection between acorn and production in three states, but not in four other states participating in the study. Moreover, the mouse population actually decreased during the time of acorn abundance. Acorns are not ready to be taken seriously.

Was there a drought period when Carlisle wells dried up?

Carlisle has had dry periods, with some wells drying up and brush fires during those times. From approximately 1903 to 1930 we consistently received a third less than the average precipitation. A second dry spell, from around 1962 to 1975, was shorter but severe. Carlisle's population had changed significantly since 1930, so the demand on water was greater. Former Fire Chief Waldo Wilson warned during the dry spell of 1974 that Carlisle's wells were extremely low, with some running dry. A more recent record dry spell occurred in 1995, causing crops to fail and streams to run at their lowest. A three-acre brush fire was put down on the Conant Land. Precipitation levels were 9 inches below normal in August 1995 and fire danger went from "high" to "extreme" during September. Former Fire Chief Robert Koning noted the fire ponds were the driest he had seen in 30 years. But rain returned by October 7, unfortunately the first day of the 1995 Pig & Pepper event.

Is Carlisle getting warmer

and wetter?

A report by the United States Geological Survey states ground level water levels in Carlisle were "generally normal" for June 2007. We had roughly three inches of rain in June which was, according to the NOAA, "-0.51 inches less than the 1901-2000 average, the 58th driest such month on record." But the trend for precipitation shows an increase of 0.11 inches per decade. June was the 50th warmest June in 113 years, with a temperature increase trend of 0.1 degrees Fahrenheit per decade.

No chance of an earthquake during my week off, is there?

There's always a chance, but the vast majority of earthquakes in the region are too small to be felt. The most recent Massachusetts earthquake was on March 26, 2007, on the New York — Massachusetts border, registering just 1.8 on the Richter scale. Any rumbling you may feel may be due instead to music emulating from teenagers' cars parked at Ferns.

What will the temperature be next August?

That's not a crazy question, though weather predictions are subject to, well, the weather. The National Weather Forecast Service offers a "three-month temperature outlook" which, in some areas, is extended to a year ( According to their predictions, the months of July, August, and September 2008, have around a 53% chance of having above-normal temperature — a good time to enjoy a cool drink at Center Park.

2007 The Carlisle Mosquito