Category Archives: Meteorology

Was July a record wet month?

It seems likely that most of us would consider this month of July to be an exceptionally wet one and, in many ways, that is true.

First of all, we have received measurable rain on 11 days this month and a trace of rain on six other days. Thus, well over half of the days this month have involved precipitation. Continue reading

Category: Meteorology, Seasons

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Why does the sun melt ice on sidewalks even when the temperature is below freezing?

All objects exchange energy with their environment. They do this via conduction, advection, convection and radiation. If water is involved, a change in the water phase (liquid, solid or gas) also will involve an exchange of energy.

Conduction moves energy by physical contact. Convection results from hot air rising. Advection by the wind moves heat horizontally. Continue reading

Category: Meteorology, Seasons

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Is moist air lighter than dry air?

Yes. Our air is primarily composed of nitrogen and oxygen, but it always has some water molecules.

The weight of an individual atom is represented by its atomic weight. The (rounded) atomic weight of hydrogen (H) is 1, oxygen (O) is 16, nitrogen (N) is 14, and carbon (C) is 12. Continue reading

Category: Meteorology

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Can weather fan the flames of revolution?

July was the month of revolution in both America and France in the late 18th century as we declared independence from Britain on July 4, 1776, and the French Revolution began with the assault on the Bastille in Paris on July 14, 1789. It is interesting to examine the extent to which weather may have influenced the passions that led to these seismic events.

The author of our Declaration, Thomas Jefferson, was such an avid weather observer that he brought his instruments with him from Monticello to Philadelphia that summer. He recorded a mild day on July 4 with a high temperature of 76 degrees. Phineas Pemberton, a prominent citizen, independently recorded the same high temperature – nearly 10 degrees Fahrenheit below normal. Pemberton also noted a wind shift from northerly to southwesterly with a falling pressure as often accompanies passage of a surface high-pressure system. Thus, the great revolutionary act in America was birthed in benevolent weather conditions. Continue reading

Category: Meteorology, Severe Weather

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What causes a double rainbow?

The classic rainbow is a single, bright, colored arc. Red is the outermost color of this arc, and violet is always the innermost color.

On occasion, you may have seen two rainbows at once. The lower rainbow is the primary rainbow and the higher, fainter, colored arc is the secondary rainbow. The color sequence of the secondary rainbow is opposite to the primary; red is on the inside of the arc and violet on the outside. Continue reading

Category: Meteorology, Phenomena

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