Change of pace: 70 million Americans cooler than average this week

WEATHER NEWS: Change of pace: 70 million Americans cooler than average this week

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After you’ve dealt with relentless heat and tropical humidity for months on end, even the slightest hint of autumn is alluring. Large parts of the Lower 48 are forecast to see below-normal temperatures this week, with some areas 20 to 30 degrees cooler than the week before.

D.C.-area forecast: Showery and cool into Tuesday, then some warm sunshine

After enduring a sweltering first half of August, and the hottest nights on record during July, the Weather Channel calculates that 50 million Americans will see cooler-than-average high temperatures Monday and sees that number growing to 74 million by Wednesday.

For a large part of the workweek, cooler-than-average weather will stretch from the Mountain West to the Mid-Atlantic.

In some areas, the changes will be drastic.

Boston hit 98 degrees three days in a row to begin last week, completing its hottest 30-day stretch on record. Now the city is hovering in the upper 70s to lower 80s, with more comfortable humidity and clearing skies.

St. Louis also started last week in the upper 90s but is in the 70s to begin this week.

In the Mid-Atlantic, it’s an early taste of September and October, with highs only in the 60s to mid-70s and a cool, damp rain to kick off the workweek.

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While it’s forecast to be cooler than average in much of the eastern two-thirds of the country over the coming days, parts of the Northwest and California will bake, with temperatures 10 to 20 degrees above normal.

Although the current weather certainly doesn’t bear the stamp of Jack Frost, the source for this cooler weather is the Arctic.

Using NOAA’s HYSPLIT model, which simulates the movement and origins of air parcels all around the world, we can deduce that this air mass actually began over the Arctic back on Aug. 3. It was north of Greenland, then traced a loop before sauntering south over Hudson Bay and settling over the interior Northeast and Mid-Atlantic over the weekend. Now it’s spread across much of the eastern United States.

A cold front stretches from near Charlotte to Nashville before kinking north toward Springfield, Mo., and Wichita. It then bends back southward, and is draped along the New Mexico-Colorado border.

To the north, highs are sitting 10 to 15 degrees below average, with temperatures remaining hotter than normal to the south.

The coolest temperatures are pooling immediately along and to the north of the front. St. Louis, for example, is looking at a high of 74 degrees Tuesday, about 15 degrees below average. Columbia, Mo., might see a 72, 16 degrees below average, and Quincy, Ill., will wind up more than a dozen degrees below average.

The remainder of the week in those places will be cool too, with highs Wednesday around 80 in St. Louis. That may sound balmy, and it is, but it’s still nine degrees below what’s typical. That’s the coolest air mass most have felt since late May into June.

The cold had already settled into Columbus, Ohio, on Monday, where the high temperature only hit 70 degrees. That ties for a record daily minimum. Columbus’s average high this time of year is about 85 degrees.

New York City went from a high of 97 degrees last Tuesday to only 79 degrees Saturday, and will remain with highs in the 70s through Wednesday.

In the nation’s capital, temperatures have stood in the 80s, but were only predicted to peak in the lower 70s on Monday and mid-70s on Tuesday. That’s thanks to a zone of low pressure at high altitudes containing a pocket of cold air over the area.

Washington hasn’t had a high in the 70s since July 9. The air mass is much more comfortable than the steamy, sultry humidity characteristic of the past several weeks.

Even in Texas, where the cold front technically hasn’t made it, there are signs of cooler weather lurking nearby. San Antonio, which has hit 100 degrees 58 times this year — one day shy of an all-time annual record — only made it to 88 degrees Sunday. That’s the coolest high temperature observed there since May 25.

Signs point to the cooler temperatures sticking around and actually expanding over most of the Plains, the central United States and the Rockies through the end of the week. Highs could run 5 to 15 degrees cooler than average for most folks east of the Continental Divide.

Temperatures should gradually warm up in the eastern U.S., but odds are pointing to near-average or slightly below-average temperatures prevailing for much of the month.

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