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Weather Wise: August Singularity

A recurring weather phenomenon specific to the Northern Rockies.
August 1992 snow in Great Falls
Posted at 6:12 AM, Aug 29, 2022
and last updated 2022-08-29 08:12:53-04

Longer-term residents of the northern Rockies may recall a significant cold spell frequently taking place around the third week in August - most notably in 1992, when the temperature fell to near freezing five times and the earliest snow on record blanketed Great Falls - more than eight inches.

Research from 2008 found that a long-standing folklore among Montana fire officials is actually a legitimate meteorological phenomenon. It is known as the "August singularity" and it can have implications for wildfire season.

The American Meteorological Society's glossary defines a singularity as "A characteristic meteorological condition that tends to occur on or near a specific date more frequently than chance would indicate."

The most commonly known singularity in the western United States is the southwest monsoonal season.

National Weather Service Great Falls incident meteorologist Bob Hoenisch points out another commonly known singularity: "The most popular, widely known singularity is the January thaw that you hear about in the northeast United States. It is similar in that way, in that it's the opposite of what you would normally see at that time of year."

The study, by North Carolina professors Peter Soulé and Paul Knapp, found a significant deviation in temperatures around the third week in August - sometimes as much as 40 degrees below seasonable normals.

In 2021, on August 18th the temperature climbed to just 48 degrees and Great Falls experienced more than an inch and a half of precipitation throughout a two-day period. The normal high temperature for August 18th is 83 degrees.

As seen in recent years, the fire season extends well into fall. The August singularity can be a huge help to firefighters but it is not the end-all, be-all to fire season. "It happens a little too early to be a season-ending type of weather event. It's more of just a slowing of the season," explains Bob Hoenisch.