Summary: September Snow in Central Wyoming - Updated 2 PM Friday

 

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An upper level low pressure system over northern Utah brought moisture north across Wyoming Thursday night and early Friday.  Colder temperatures filtered into the central Wyoming basins during the afternoon setting the stage for the development of a cold rain.  Light to moderate rain gradually changed to snow across the central basins between about 8 PM Thursday and 1AM early Friday.  A heavy, wet snow ensued for the remainder of the night.  Snowfall totals in Fremont, northern Johnson, and southern Hot Springs counties generally ranged from 4" to 8", with 8" to near 1 foot in the Wind River and Bighorn mountains.  Snowfall of 2" to 5" fell across a large portion of Natrona and southern Johnson counties.  Elsewhere, snowfall was mainly less than 2", with much of the eastern Big Horn Basin seeing little more than a trace.  Click here for a complete listing of snowfall and rainfall reports from Thursday night and Friday. 

Snow and Rain Maps - 6AM Thursday thru 6AM Friday
Rain Totals - Click to enlarge Snow Totals - Click to enlarge
 Observed Rainfall Map - Click to Enlarge   Observed Snowfall Map - Click to Enlarge

The question has been raised, "This is early for snow."  Well, yes and no.  Let's use the town of Riverton as an example.  The average date of first measurable snowfall in Riverton is October 22nd; however, there have been several major September snow storms in Riverton's history.  The earliest snow was on September 6th, 1929 when 3" of snow fell.

The three largest September snow storms in history were:

Date Amount (inches)
9/14/1982 10"
9/22-9/24 2000 5.7"
9/16-9/18 1965 5"

 Click here for more information on the rarity of low elevation September snow.


The Riverton COOP station reported 1.50" of water and 5.7" of snow for the 24-hour period ending Friday, September 27, 2013, at 7 AM.  That snowfall totals ties the storm that struck September 22-24, 2000, for the second largest September snow storm.  September 2013 is now tied with September 2000 as the second snowiest September behind only the 13" mark recorded in September 1982.  Also, the monthly precipitation total at the Riverton COOP station now stands at 3.04", which is the 5th wettest September total since records began in 1907.  What's the wettest September since 1907 in Riverton?  Well, it happened in 1923 when 5.72" of moisture fell.

A comprehensive photo gallery of the tree damage around Fremont County is available on our Facebook page.

The low pressure will gradually track northeast and out of Wyoming late Friday and early Saturday.  As a result, the rain and snow that has impacted much of western Wyoming for the latter half of the week will decrease.  This will leave behind a clearing sky Friday night.  The lack of cloud cover and a wet or snow-covered ground will allow for good radiational cooling Friday night into Saturday morning.  Sub-freezing temperatures will be widespread.  Also, the lower atmopshere will be wet, so as the clouds clear and temperatures fall fog is expected to develop.  The fog will be most prevalent in those areas with melting snow late Friday afternoon.  The fog could be dense depending upon the amount of clearing that occurs.

The fog will erode Saturday morning as the sun rises and the temperature climbs.  High temperatures will rebound into the 50s in most areas Saturday afternoon under a mostly sunny sky.  Continued sunshine on Sunday will boost temperatures to more seasonal readings in the 60s across the lower elevations.

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