*Updated 9/26* Significant Snowfall Possible Tonight Thru Friday


The National Weather Service

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Summary | Forecast | Monitoring & Reporting Snowfall | Safety


Pick the tomatoes, put away the hose, and clear a spot in the garage - it's going to snow - and just about everywhere!

After a bit of a lull this morning, snowfall will continue across the west this afternoon with a few heavy bursts possible this evening. Much colder temperatures will filter east of the Divide tonight along with plenty of moisture and wind directions favorable for snow accumulation in the lower elevations east of the Divide.
Periods of light to moderate snow are expected to continue through Friday morning, slowly clearing in the afternoon.

Stay up to date with our current products, and what they mean as they will be updated throughout the night!

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This seems early, right? 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.

An area of low pressure will continue to dig further south today, with precipitation becoming more widespread across the area. We will be in a bit of a lull early today as this occurs. The storm will transition into a surface low forming in Northern Colorado as a cold front sweeps east across the area, reaching Casper before the early evening hours. Low level Upslope Flow will eventually establish itself as the surface low forms in Northeastern Colorado later today. This upslope flow will wrap in a good supply of low level moisture and push it up against the mountains, squeezing every last bit of moisture out of the air. The newly established colder air will allow this precipitation to quickly change over to snow. Upper level support from the jet stream will further enhance this favorable setup to encourage bursts of heavy snow at times - peaking after midnight tonight and lasting through the early morning hours on Friday.

Below is an animation demonstrating the current model snow projections of this system, this should show you where and when the heavier snow will fall (in 6 hourly periods beginning at Midnight Wednesday Night/Thursday Morning and ending early Saturday morning. Also included is a graphic showing current possible snowfall amounts from Today through Friday. For more information on the weather for tonight and tomorrow, and for the weekend...Click Here!


Snow Forecast and Pattern - Click to enlarge Snowfall Forecast - Click to enlarge
Click Loop To Enlarge
Loop of expected snowfall (does not include moisture falling as rain) in 6 hourly time steps with wind arrows overlaid (the longer the tail, the stronger the wind speed). The loop begins at 06Z Thursday (Midnight Thursday) and ends at 12Z Saturday (6AM Saturday).

Image Key:

Light Purple = Less than 1 inch of snow accumulation

Gray = 1 to 2 inches

Yellow = 2 to 3 inches

Blue = 3 to 6 inches

Red = 6 inches or More (or about an inch per hour!)

Click Image To Enlarge

Graphic of current storm total snowfall forecast (inches). The snow will be wet and heavy with a high water content so there will be a lot of compaction and melting as the snow accumulates. 

Falling temperatures are expected through the day with snowfall working east of the Continental Divide. The most snowfall is expected to fall across the Wind River and Absaroka Mountains, with the Lander foothills likely receiving the most snowfall in the lower elevations.

The snow expected to fall east of the divide could cause significant damage as most trees still have their leaves and could pose a hazard as the weight of the snow breaks branches. These breaking branches could cause property damage or power outages east of the Divide late tonight into Friday morning. In addition, since heavy snow is possible tonight, this may complicate the morning commute on Friday in Lander, Riverton, Dubois, Casper, Thermopolis, Wind River Canyon, South Pass, and Rock Springs.

Know Before You Go! More Mountain Passes Could Close

Togwotee Pass was closed for quite a while on Wednesday due to a crash. Expect visibility and road conditions to deteriorate rapidly over mountain passes again tonight and Friday Morning. Be sure to check your route and plan for difficult travel if you are in an area with a Winter Storm Warning or Winter Weather Advisory.

 If you must go, be sure to have these items in your car (click here).

Know Before You Go!        http://map.wyoroad.info/hi.html

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