At a Glance

A significant snowfall is possible is increasingly possible in the Colorado and Wyoming Rockies. Snow will fall in the Rockies early next week, but that's not too uncommon this time of year.Snow in September has been recorded in many locations in the U.S.A few cities experience snowfall in September fairly regularly.

The first significant snowfall of the season is possible for parts of the Rockies during the first part of the week ahead, following temperatures near the century mark.

A deep southward plunge of the jet stream will bring in a sharp drop in temperatures to the Rockies and Plains over the next few days.

A disturbance in that diving jet stream will also help to wring out moisture into the colder air, allowing snowfall or a chilly rain to develop in some areas by Tuesday.

The snowflakes could begin to fly by early Monday in the highest terrain of western Montana, then become more widespread Monday night in Wyoming and northern Colorado.

Monday Night - Tuesday Morning Forecast

(The green shadings depict where rain is expected. Areas that are shaded blue are expected to see snow. Purple-shaded locations may see either rain or snow. Temperatures shown will occur Tuesday morning. )

By Tuesday, snow, a rain/snow mix or rain will expand southward into the rest of Colorado and western parts of Nebraska and Kansas. This precipitation will arrive with rapidly dropping temperatures and gusty conditions.

You can see in the map below the areas from Montana to Colorado and northern New Mexico that could see at least some light accumulating snowfall, roughly from Monday through Tuesday. Snowflakes could even fall and even potentially accumulate in the Denver area, where the earliest snowfall on record was on Sept. 3, 1961, when 4.2 inches fell.

If snow falls in Denver, it will fall .

Snowfall is increasingly likely on the Interstate 25 urban corridor, including Cheyenne, Denver and Colorado Springs.

Elevations above 5,000 feet will likely see a significant snowfall for September, but exactly how much will fall ranges from 6 to 12 inches in the highest elevations.

However, we should note that changes are likely to this forecast since several factors are uncertain. This includes what elevation the snow will fall at and how much moisture there will be to produce snowfall. It is also uncertain how fast the cold air and snow will be able to overtake the very warm ground following highs in the 90s.

"It is worth repeating that a widespread, significant snowfall event is likely across much of the Front Range and foothills. There is considerably less certainty in snowfall amounts across the Denver metro, though confidence is increasing that the metro will see their first accumulating snowfall of the season. Subtle changes to the factors mentioned above could result in sufficient snow accumulation for broken tree limbs and power outages, " according to the National Weather Service in Denver on Saturday afternoon.

Given that this is the first significant snow and freeze for much of Colorado, many trees still have their foliage in the state and in neighboring states. Power outages are possible where the heavy, wet snow falls on trees with leaves still out.

Check back to weather.com for updates.

Snowfall Outlook

(This is a broad outlook showing where snowfall is possible. Changes to this forecast are likely.)

This amount of snow is on the high side for early September, but these areas have seen snowfall multiple times in September. Below is a closer look at what parts of the country can see snow during the month.

Where Snow Can Fall in September

While the first three weeks of September are still officially summer, there are several locations in the U.S. where September snow occurs just often enough to not be considered a freak event.

Most of these locations are in the mountains, but not all of them.

We scoured National Weather Service 30-year average snowfall data to find first-order observing stations which average at least 0.1 inch of snow in September, including parts of New England, the Great Lakes, Plains and West. You can see these locations plotted in the map below.

Other locations have picked up September snow, but just not frequently enough to register a 30-year average of greater than a trace. (We've listed some of those cities in our "other September notables" section below the regional charts.) Data from Mount Washington, New Hampshire, was provided by the .

Locations averaging at least 0.1 inch of snow in September, based on 1981-2010 averages from NOAA/NCDC.

West

It is no surprise that many locations of the Rockies have often experienced snow in September. Some locations in western Montana and central Colorado see the first measurable snow on average in September.

Just last year, Great Falls, Montana, picked up over 19 inches of snow as September came to a close.

The Washington Cascades usually see the first snow of the season in September, but even areas that typically wait until later in the fall have picked up measurable snow in September.

An asterisk means some months are missing in the data.

Midwest

The average first measurable snow of the seasonfor areas from western Nebraska into North Dakota, northern Minnesota and the Upper Peninsula of Michigan usually takes place in October. Much of the Midwest, however, waits until November on average for the first flakes to accumulate. However, snow does occur in September from time to time.

Northeast

The mountains of New England, the Adirondacks, and the higher elevations of northwestern Pennsylvania and the central Appalachians receive the first measurable snow of the season in October on average, but some locations in these areas have seen snow in September. The remainder of the region usually waits until November or December for the first accumulating snowfall.

Other September Snow-tables

Minneapolis/St. Paul: Measurable snow as early as Sep. 24, 1985 (0.4 inches). Also picked up 1.7 inches on Sep. 26, 1942.Omaha, Nebraska:Picked up 0.3 inches of snow on Sep. 29, 1985.Amarillo, Texas:Once snowed 0.3 inches on Sep. 29, 1984.Kenton, Oklahoma:This panhandle town measured 3 inches of snow on Sep. 18, 1971, five days before summer officially ended.Salt Lake City:Four inches of snow fell on Sep. 30, 1971.Flagstaff, Arizona:Two inches of snow fell on Sep. 19, 1965.Reno, Nevada:Picked up 1.5 inches of snow on Sep. 29, 1982.

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