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Lake Effect Snow on Fort Peck Lake - December 4th, 2002

How does it form?
Basically there are a couple of main ingredients that you need to produce lake effect snow. The first is a relatively warm body of water (aka Fort Peck Lake). The second ingredient is a source of cold air. In the United States, that source comes from the high latitudes of North America where arctic airmasses often "spill southward" over those warm bodies of water. Heat and moisture from the warm lakes rises into the "modified" arctic air where it then cools and condenses into snow clouds. The prevailing wind direction through the depth of the snow clouds (third ingredient!!) determines where the snow will occur. Click on the image below for a full size picture: (narrative adapted from the NWS office in Buffalo, NY... home of lake effect snow.)

How Lake Effect Snow Forms

Does it really happen here?
The following pictures should cause even the most pessimistic of attitudes to agree that lake effect snow does indeed fall in northeast Montana.
Looking toward Fort Peck Lake approximately 10 miles south of Glasgow on Highway 24. Looking toward Fort Peck Lake from the parking lot of Lakeridge
highway 24 lakeridge
Looking north down the main street in the Town of Fort Peck. Looking south down East Kansas street.
main street
east kansas
Looking at the Fort Peck Hotel from across the parade field. Looking at the Corps of Engineers building from across the parade field.
fort peck hotel corps building
Looking east toward the Interpretive Center and Power Houses. Glasgow NWS radar image shortly after sunrise.
power houses radar

Does it bring much moisture?
At 32 degrees Fahrenheit, most snow has a ratio of 10:1. This means that for every 10 inches of snow, the water equivalent would be 1 inch of precipitation. As the air temperature drops, the ratio goes up. Lake effect snow typically has a ratio of 20:1 or 30:1. In northeast Montana, lake effect snow will usually only occur under a very cold airmass. Temperature readings from the Fort Peck Lake area for this event were around 0 (zero) degrees Fahrenheit. For this event, we estimated only .05 inches of liquid which would give a 40:1 ratio. Some lake effect events have had ratios as high as 50:1! The good thing about dry snow is that it is easy to remove... as this NWS employee demonstrates:
snow removal
 

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