Wednesday, September 21, 2016

Rockies Snow and Plains Storms Will Ring In The Fall Season

Tom Moore
Published: September 21,2016

As fall begins Thursday, a brewing storm system in the Rockies will celebrate its arrival in appropriate fashion.
Rain will change to snow by Thursday evening across higher elevations of Idaho, Nevada and Utah. Snow will spread eastward to Montana, Wyoming and Colorado on Friday night and Saturday.
Meanwhile, rain and thunderstorms will develop across the Intermountain West on Thursday, and this activity will spread to the Plains on Friday and Saturday.
(MORE: A Handy Guide to When Your first Freeze Typically Arrives)

Storm Timing and Impacts


Rainfall Forecast Through Saturday
Thursday
An area of low pressure and an associated cold front will move eastward from the Pacific Northwest into the Intermountain West. This system will produce a large area of rain and thunderstorms from northern Arizona northward to Idaho and Montana.
Rainfall totals of 3 inches or more are possible for lower elevations of northern Utah and western Wyoming up through Montana.
A few thunderstorms could approach severe limits with strong wind gusts, especially across parts of eastern Utah and central Wyoming.
As cold air moves in behind the front, rain will change to snow on Thursday night in the higher elevations of eastern Nevada, Idaho, southwestern Montana, western Wyoming and along the Wasatch Range of Utah. Snow levels will be generally around 7,000 feet.
Friday
Rain and thunderstorms will develop ahead of the cold front from northern New Mexico through central Colorado to eastern sections of Wyoming and Montana. The heaviest rainfall totals will likely be across eastern Montana, where 1 to 2 inches are expected.
By Friday afternoon, thunderstorm activity will increase across the Dakotas and western Nebraska as a southerly wind flow increases and a cold front approaches. Meanwhile, rain and higher-elevation snow will wrap around the low-pressure system back to western Montana, Idaho and Utah. Accumulating snow will generally be above 7,500 feet.
Scattered thunderstorms will continue across the central and northern Plains Friday night, while showers and higher elevation snow showers will linger across Montana, Wyoming and northern Colorado.
Weekend
Thunderstorms with locally heavy rain will be present across North Dakota on Saturday. Rainfall totals up to 3 inches (with locally heavier amounts) are possible in the western part of the state. Meanwhile, scattered thunderstorms will develop down through the Plains as a cold front advances eastward.
A few thunderstorms could approach severe limits, with strong wind gusts from western South Dakota to western Kansas.
Rain and mountain snow showers will be winding down from Montana to northern Colorado with little accumulation.
All told, the higher elevations of southwest Montana, northwest Wyoming and northern Utah could see 8 to 12 inches of snow, mainly above 8,000 feet, from this storm.
Lighter amounts will fall between 7,000 and 8,000 feet. Parts of Idaho, Nevada and northern Colorado could see from 3 to 5 inches of snow at elevations above 8,000 feet, and lower amounts between 7,000 and 8,000 feet.

Snowfall Forecast Through Saturday
(FORECAST: Great Falls, Montana | Yellowstone National Park | Salt Lake City, Utah | Williston, North Dakota)

Setup For Early Fall Storm


Late Week Jet Stream Forecast
A combination of factors will come together to produce this widespread storm system. In the upper atmosphere, a deep trough of low pressure (dip in the jet stream) will move into the West.
This will allow a low-pressure system to rapidly develop at the surface Thursday.
(MORE: How Temperatures Daylight 'Fall' From Late September to Late December)
The trough will also pull tropical moisture northward into the Intermountain West and the western Plains (a remnant of Tropical Storm Paine). This will help to enhance overall precipitation from this storm.
At the surface, cold air will move rapidly into the region, setting the stage for lower elevation rain and thunderstorms along with higher elevation snow.
It will be too warm to snow across the Plains as we move into the weekend, but there will be plenty of rain and thunderstorms.
MORE: Rocky Mountain Snowfall

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