First arctic blast of season to shift weather patterns across US
By Linda Lam for Weather.com
The record warmth that much of the U.S. experienced this fall will just be a distant memory this week. A change is coming, courtesy of the first arctic blast of the season, arriving first in the western states early in the week, then spreading east throughout much of the Lower 48 into next weekend.
The pool of arctic air that is set to invade the Lower 48 is currently located in Alaska and northwest Canada. A pattern change will dislodge that arctic air and allow it to spill southward in the days ahead.
Specifically, a southward dip in the jet stream, or upper-level trough, will dig southward from the Gulf of Alaska and western Canada into the western U.S., and will then slide eastward as the week progresses. High pressure at the surface will then dive southward, allowing arctic air to spread into parts of the Lower 48.
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This will be the first arctic air mass of the season for the U.S., just in time for the first full week of December.
How Cold Will It Get, and When?
The coldest temperatures of the season, so far, are expected to arrive in the week ahead. Big temperature drops are anticipated, with highs and lows falling 20 to 30 degrees.
These very cold conditions will first be felt in the northern Rockies on Monday and will spread through much of the West and into portions of the northern and central Plains by Tuesday.
The first sub-zero temperatures of the season for some locations are expected Tuesday through Thursday mornings from the Rockies to the northern Plains.
High and low temperatures will be as much as 35 degrees colder than average. This translates to high temperatures below freezing for much of the West and into the northern and central Plains and Midwest. In fact, highs will struggle to reach double digits midweek in parts of the northern Rockies and northern Plains.
Even with these very cold temperatures, widespread record lows are not expected.
It will be windy as well, which will make it feel even colder than what the thermometer reads, resulting in brutal wind chills.
In addition, snow will accompany the cold temperatures in some locations.
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Arctic air will continue to plunge through the Plains and into the Midwest midweek. Above-average temperatures will be replaced with below-average readings. Highs will drop from the 40s to the 20s for much of the Midwest.
Late in the week, the colder conditions will reach the East Coast.
At this time, it appears that temperatures will not be as cold for the East as for the West and Plains. However, it will feel more like winter.
High temperatures will drop from the mid-40s to the low to mid-30s for much of the Northeast, and many areas of the South will see highs in the 50s and 60s replaced with highs only in the 30s and 40s.
The chilly conditions will reach all the way to Florida. Temperatures in central Florida will only reach the upper 50s by late week, compared to 80s early in the week. Lows in the 40s may push into the central Florida peninsula, including Orlando, by Saturday morning.
Check back to weather.com for forecast updates as we get closer to this expected cold blast.