November pattern change brings September-like warmth to East and mountain snow, cold to West
As the calendar turns to November, a significant change in the weather pattern over the U.S. is leading to a pronounced split between winter cold and snow in the West and warmth more reminiscent of early fall in the East.
The polar jet stream will take a sharp southward nosedive in the West while simultaneously bulging northward into eastern Canada.
Let's break down the two distinct weather regimes that will be in place as November kicks off.
Midwest, South, East: September in November
Despite a sharp cold front delivering a chillier reality check to parts of the Midwest and Great Lakes in recent days, November's chilly, raw brand name couldn't be further from the truth in the week ahead.
With high pressure eventually setting up shop near the Eastern Seaboard, and generally lower pressure in the western U.S., a belt of warm air will flow northward from the southern Plains into the Upper Midwest, Great Lakes, Ohio Valley, and eventually into the Northeast in November's first week.
Jacksonville, Florida already set an all-time record high temperature for November on Sunday, reaching 89 degrees. That broke the previous record of 88 degrees that was set in 1961 and 1986.
For some, this warm spell will feel more like a typical late September air mass than an early November one and could flirt with some daily records.
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The warm-up has already begun in the central to northern Plains, where Imperial, Nebraska tied their daily record high temperature on Sunday. The warmth will spread east through the week.
Here are some forecast "high"-lights by region:
Midwest: 60s return to the northern Plains, Upper Midwest, southern Great Lakes through early in the week ahead. 70s expected from the central Plains to the southern Great Lakes, Ohio Valley for multiple days.
South: 70s in most areas with the exception of the Gulf Coast, Florida, central and south Texas where 80s will dominate.
Northeast: 60s in most areas except a few 50s in northern New England and some 70s primarily in the mid-Atlantic states.
Unfortunately, we do have to rain a little on this warm parade. The November kickoff warm spell won't always be accompanied by ample sunshine.
One weather system will spread rain through the Southeast and Mid-Atlantic states early in the week ahead.
Then, as a more vigorous weather system lifts into the Plains from the Desert Southwest, rain should become more widespread in the Plains, Midwest and East late in the week into next weekend.
West: Early-Season Ski Fever
The first nine months of 2015 were the hottest January-through-September period on record in California, Nevada, Oregon and Washington. Of the other Western states in the Lower 48, only New Mexico hasn't chalked up at least a top three warmest first nine months of the year. It was their sixth warmest January-September period.
That was largely due to a dominant jet stream pattern featuring a pronounced northward detour of the jet stream into western Canada, keeping the West warm, relatively dry and lacking mountain snowpack last winter.
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As November begins, this pattern will be flipped.
The jet stream will plunge into the West, ushering in colder air. Like spokes in a wheel, upper-level disturbances rotating through that jet stream dip will lift moist air and wring out valley rain and mountain snow much of the week ahead.
If you're already itching to hit the slopes to carve your first powder of the season, the forecast of significant snow in the Rockies and Wasatch in the week ahead ought to get your pulse racing, or drive you crazy if your favorite resort won't open yet.
Mountain snowpack is also of critical importance for water supply in the West, particularly in California. Some snow is also expected in the Sierra, Siskiyous, Cascades, and possibly the Tehachapis and San Gabriels of Southern California in the week ahead.
Winter storm warnings have been posted by the National Weather Service for the Cascades and Olympics in Washington, for the potential for heavy snow Sunday into Monday. Fortunately for travelers, Snoqualmie Pass on Interstate 90 will be too warm for accumulating snow during the heaviest precipitation. Higher Cascade mountain passes, however, will see several inches of accumulation.
The snow may not simply be for the high country, either.
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Rain may change to accumulating wet snow along Utah's Wasatch Front Monday night into Tuesday, then in the northern High Plains of eastern Montana and western North Dakota Tuesday into Wednesday. This would be the first accumulations of the season in locations such as Salt Lake City and Williston, North Dakota.
Then, later in the week, a second system may bring significant snow at least to Front Range foothills of Colorado and far southeast Wyoming, if not some wet snow to the Front Range Urban Corridor itself, including Denver, Boulder, Fort Collins and Cheyenne.
Some rain is expected, as well, in central to northern California, but given the orientation of the jet stream, it is not expected to be heavy.
Then, there's the cooldown.
While high temperatures will be below average across much of the West, low temperatures will mostly be near normal for this time of year. That's an indication that cloud cover will play a role in the cool weather pattern.
There are some indications the general warm East, cold West pattern may linger into November's second week.
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