Mountain Lakes does not have a weather monitoring station of its own.  The Jersey City Water Commission takes daily weather observations at its reservoir in Boonton. This station, being in close proximity to and of approximately the same elevation as Mountain Lakes, serves as a good basis for describing our local climate.

Mountain Lakes lies in the humid continental climate zone. This zone is noted for its changeable weather, because it is in the conflict zone between warm, humid air masses from the south and cooler, drier air masses from the north.

Winds in Mountain Lakes can blow from any direction; however, in winter, cold northwest winds predominate, and summer winds are most often hot and humid out of the southwest.

The amount of insolation (incoming solar radiation) received in a given day reflects the angle at which the sun’s rays are striking the earth (the more nearly this approaches 90°, the greater the intensity) and the number of hours during which the sun is shining.

The declination of the sun during June and December is shown in Figure 1.

Local cloud cover and haze caused by pollution tend to diminish the amount of sunshine received.  Normally, in Mountain Lakes, the sunshine is slightly over one-half the possible amount, with the greatest number of sunny days occurring in October and the least in February.  The average summer temperatures, for the hottest months of July and August, are in the low 70°F’s.  The average winter temperatures for the coldest months of January and February are in the high 20°F’s as shown in Figure 2.  These, however, are monthly averages and do not show the great variation that sometimes occurs.  The record high temperature of 104°F was recorded in the summer of 1953, and the record low of -20°F occurred in the winter of 1934.

Monthly Mean Temperatures and Precipitation

The last killing frost in the spring generally occurs between May 5th and 10th and the first killing frost in the fall generally occurs between October 5th and 10th.

Precipitation is generally well distributed throughout the year but with a slight increase during the summer months due to local thunderstorms, of which the area receives between 25 and 30 per year. The precipitation averages about 45 inches a year with the monthly distribution shown in Figure 2.

Even in the wintertime more of the precipitation falls as rain than as snow. Figures on the exact amount of snow that falls are difficult to obtain because they are affected markedly by variations in local conditions, such as elevation. The Army Corps of Engineers reports that the average annual snowfall over the Passaic River Basin is about 34 inches with a water equivalent of about 4 inches. Snow falls of more than 10 inches in a single storm occur occasionally.

In the 21st century, according to C. Rosenweig and W.D. Solecki, global climate models indicate that the New York metropolitan area will experience warmer year round temperatures, hotter heat waves in the summer, more severe storms, and increased drought and flooding.