Cold air to plunge into US next week -- but how quickly will it reach the East?

Alex Sosnowski

Much colder air will surge into the north-central United States during the last week of October, but how fast will that cold air reach the Eastern states and what storms may spin up during the transition?

The coldest air of the season so far is poised to plunge from northern Canada to areas from the Rockies, Plains and Midwest in multiple waves through early November.

It is conceivable that some locations over the North Central states have temperature departures of 15-25 degrees Fahrenheit below average for daytime highs on multiple days next week. Normal high temperatures range from near 50 over northern North Dakota to the middle 60s in northern Kansas.

However, how quickly cold air reaches the Appalachians and then spills across the Eastern Seaboard is likely to be dependent on where an anticipated dip in the jet stream sets up next week.

The jet stream buckle will also help to pump warm air northward over Alaska for a time later this weekend to early next week.

The range of possibilities can be explained by two scenarios, according to AccuWeather Senior Meteorologist Jack Boston.

"If the jet stream dip is centered over the northern Plains, then cold air may may be delayed and diminished by the the time it reaches the Eastern Seaboard during early November," Boston said.

"If the jet stream dip ends up over the central or eastern Great Lakes region, then cold air will quickly blast eastward toward the Atlantic coast before the end of October," Boston added.

While the answer may lie somewhere in between both extremes, AccuWeather meteorologists are leaning toward the first scenario with somewhat of a delay in the arrival of cold air in the East.

That prognostication comes with complications in the form of one or more storms along the leading edge of the cold air next week.

The latest indications are that one storm will quickly drop southeastward over the northern Rockies this weekend, but will gather moisture over the southern and central Rockies and Plains early next week.

A swath of accumulating snow is likely to extend from the southern Rockies to the Upper Midwest from Monday into Tuesday.

However, the position and extent of that snow is subject to change until that parent storm finishes its southward drop across the Rockies this weekend.

There is the potential for some areas along this swath of snow to receive a heavy accumulation, perhaps on the order of 6-12 inches. The greatest risk for this to occur is likely to be across the central and southern Rockies.

As if that were not enough, a second storm may take shape farther to the east over the southern Plains at midweek, and then it may track northward across the Great Lakes by the end of the week.

Heavy snow may end up close to Kansas City, Missouri, Chicago and Milwaukee, Wisconsin, with the storm during the second half of next week.

Both storms will bring rain on their southeastern flank. The second storm may be much stronger than the first in terms of wind and could help to push the cold air farther along.

The details on the magnitude and speed of the cold air along with the speed, track and intensity of storms during the transition will unfold in the coming days. Faster or slower movement of the storms will have a profound impact on the arrival and departure of rain and snow and the spread of the cold air.

Most likely, the magnitude of the cold air that reaches the Northeast and the cool air that reaches the Southeast will be diminished substantially in either scenario.

This is because during the autumn, cold air is modified by the open, warm waters of the Great Lakes. Also, as the air descends over the Appalachians to the Atlantic coastal plain, it tends to warm at the rate of 5.5 degrees per thousand feet. The relatively mild waters of the Atlantic greatly warm the air right along the coast as well.

Factoring in that normal temperatures are trending downward at a swift pace this time of the year, actual temperatures may only be a few degrees below average by the time the air reaches the Atlantic coast and perhaps 5-10 degrees below average for a few days over the Appalachians.

Normal highs by early November range from the middle 40s in northern New England to the middle 60s in southeastern Virginia and the upper 60s in northern Georgia.

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