Today, parts of Montana, including the Great Falls area, were blanketed by up to 6 inches (15.2 cm) of snow according to the National Weather Service's Public Information Statement (PNS).


Public Information Statement


Yellowstone National Park

Before any suggestions are made that this event has any bearing on the observed ongoing warming of the global climate, it should be noted that this event is largely a product of a synoptic pattern that has occasionally occurred during negative Pacific Decadal Oscillation periods and in the wake of a strong La Niña event.

A similar snowstorm occurred on June 7-8, 1950. With respect to that event, the June 9, 1950 edition of The New York Times reported, "Four inches of snow piled up at Great Falls, Mont., where the mercury dived to 31, a record low for the date [June 8]."

June 1950 vs. June 2008: Pacific Decadal Oscillation and La Niña
Spring 1949-50 occurred in the midst of a negative Pacific Decadal Oscillation (PDO) regime. Late last fall, it appeared that the transition from the long positive PDO event that commenced in 1976 toward a new negative regime had been completed late last year.

In addition, both Winter 1949-50 and Winter 2007-08 featured a strong La Niña that persisted through the spring. The 1949-50 La Niña finally came to an end in summer 1951. Winter 2007-08 featured a strong La Niña, as well. Cool anomalies have persisted into the first week of June with ENSO Region 3.4 maintaining an anomaly of -0.3°C.

June 1950 vs. June 2008: Synoptic Patterns:
If one examines the upper air (500 mb) patterns for June 8, 1950 and June 10, 2008, one finds some similarities:

• Much above normal height anomalies in the vicinity of the Gulf of Alaska
• Much below height anomalies over the northwestern quarter of the United States
• Above normal height anomalies across eastern North America


June 8, 1950


June 10, 2008

The on-the-ground weather was also similar in both circumstances. While the stage was being set for unseasonable cold and snow at locations such as Great Falls, eastern North America was experiencing unseasonable warmth.

The June 9, 1950 edition of The New York Times reported, "While the eastern half of the nation sweltered in summer's first heat wave today [June 8] northwest householders shoeveled snow off their sidewalks. The June 11, 2008 issue of The New York Times reported, "For a second consecutive day, the 96-degree heat and electricity use set records as residents cranked up their air conditioners to get through the unusual four-day June heat wave... The thermometer hit 96 in Central Park, one degree above the record for June 10, set in 1984. Temperatures at La Guardia and Newark Liberty International Airports also reached new peaks."

June 6-10, 1950:
New York City: High temperatures ranged from 86°-89°
Richmond: High temperatures ranged from 87° to 92°
Toronto: High temperatures ranged from 82°-90° (27.8°C-32.2°C)

Great Falls (maximum and minimum temperatures):
6/6 63°-43°
6/7 48°-31° 0.8" (2.0 cm) snow
6/8 39°-31° 3.1" (7.9 cm) snow

June 6-10, 2008:
New York City: High temperatures ranged from 74°-96° (June 7-10 saw readings reach or exceed 90° on each day)
Richmond: High temperatures ranged from 91°-101° (June 7-8 experienced the earliest consecutive 100° readings on record by more than two weeks)
Toronto: High temperatures ranged from 75°-93° (23.8°C-34.1°C)

Great Falls (maximum and minimum temperatures):
6/9 64°-36°
6/10 59°-33° Trace of snow
6/11 Low temperature so far this morning: 32° 6.0" (15.2 cm) snow per PNS

Conclusion:
The synoptic pattern, which has occasionally occurred during similar states of the Pacific Decadal Oscillation and El Niño Southern Oscillation, is responsible for the late-season snowfall that blanketed Montana today.