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This is Edan Lindaman with the National Weather Service in Reno presenting an online informational
weather briefing on the lake effect snow event that occurred on November 9th-10th, 2012.
Lake effect snow is most common in the fall or late spring when lake water temperatures
are warm, relative to the air temperature. It typically occurs after the passage of a
cold front and when cold, northerly or westerly flow remains. The image above shows a cold
low pressure system across northeastern California and northwestern Nevada. The cold front pushed
through the region Thursday, leaving behind conditions favorable for lake effect snow
to develop. Let’s take a look at the elements required for lake effect snow to develop.
The elements needed for lake effect snow are: Instability, moisture, lift, and wind direction
oriented along a long fetch of the lake. The picture on this slide are from a previous
lake effect snow event in November of 2000 at Pyramid Lake, which really shows the contrast
between snow developing over the lake and effecting the east shore with no snow across
the west shore. With arctic air around 10 degrees Fahrenheit
moving across warmer lakes, around 50 degrees Fahrenheit, there was a large enough temperature
difference to create a very unstable atmosphere. As the cold, moist air sweeps over the warm
water, it is heated from below making it even more buoyant. The air quickly pulls moisture
off the lake, saturating the air mass and prompting condensation.
Clouds develop as the air becomes increasingly unstable and then latent heat is released
providing more fuel for lift. Upper level features, also known as short waves, can enhance
vertical motion and result in deeper convection. As showers intensify, lake effect snow accumulations
start downwind of the lake. Wind shear is also an important element when
it comes to lake effect snow bands forming. Wind shear is the change of wind speed or
direction with height. Light winds with little directional wind shear create better chances
for organized bands of snow to develop off of either Lake Tahoe or Pyramid Lake. The
next couple of slides will explain which wind directions occurred on November 9th and 10th
that resulted in lake effect conditions near Lake Tahoe and Pyramid Lake.
The distance that an air mass travels over a body of water is called its fetch. The event
on November 9th and 10th had a light north to northwest flow along Pyramid Lake’s ideal
fetch which allowed lake effect snow to impact Nixon and the Pah Rah Range.
For Lake Tahoe, a west wind along a shorter fetch of the lake resulted in lake effect
snow across parts of Carson City and Minden. Although that is one of the shorter fetches,
the very unstable atmosphere resulted in stronger snow showers.
What resulted from all of the conditions described in the previous slides was some significant
lake effect snow across areas highlighted on the image. Highlighted in area #2, lake
effect snow developed southeast of Pyramid Lake and produced heavy snow mainly across
unpopulated areas. From Friday afternoon through Saturday morning, Lake effect snow developed
east-southeast of Lake Tahoe and produced 5-9 inches of snow in Carson City and up to
4 inches in Minden, shown in area #3. On Thursday night, thunderstorms formed in north central
California and strengthened to produce 18-22 inches of snow in Janesville and 5-9 inches
in Susanville, which is highlighted in area #1. Those snow showers were not a result of
lake effect snow, but it shows just how unstable the atmosphere was Thursday night through
Saturday morning.
Thanks for listening to a summary of the lake effect snow event from November 9th-10th,
2012.