Heat wave kicks off September in Midwest, Northeast as Northwest finally cools off

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September Heat Wave in Northeast, Midwest

With the calendar now flipped to September, it only stands to reason parts of the Northeast and Midwest will sweat out heat and humidity this week.

Meanwhile, the weather pattern change is having the opposite impact in the Northwest, with refreshingly cooler temperatures and even some rainfall expected this week.

(MORE: Strong Storm System Batters the Northwest)

Pattern Change Overview

The key to this pattern change is the rearrangement of the jet stream across North America. The jet stream is a ribbon of fast winds aloft in the upper atmosphere that helps dictate the weather conditions we see near the surface of the earth.

Last week, the jet stream was dipping south across the eastern half of the United States. This brought a relatively, refreshing air mass to parts of the Midwest, East and even the Deep South.

Now, the main ribbon of strong winds associated with the jet stream has lifted north into central and eastern Canada. This is leading to widespread above-average warmth that will grip the nation's midsection and the Northeast this week.

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Heat wave kicks off September in Midwest, Northeast as Northwest finally cools off
NEW YORK, NY - AUGUST 17: People relax on a hot afternoon at the Astoria Pool in the borough of Queens on August 17, 2015 in New York City. The main pool, the biggest in New York City and administered by the New York City Department of Parks and Recreation, sees over 3,000 people on a typical summer weekday. New York city is in the middle of a heat wave, with temperatures in the high nineties and with a heat factor making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 20: A woman uses a sun umbrella along the boardwalk at Brighton Beach in Brooklyn on August 20, 2015 in New York City. The National Oceanic and Atmospheric Administration (NOAA) announced on Thursday that July was the planet's warmest month on record. July's average temperature was 61.86 degrees Fahrenheit, beating the previous global mark set in 1998 and 2010 by about one-seventh of a degree. NOAA began keeping records in1880. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 21: A man stands in the water on a sultry morning at Coney Island in Brooklyn on July 21, 2015 in New York City. Despite an overcast sky, thousands of New Yorkers headed to area beaches to cool off from the heat and humidity. The hot weather is expected to break tomorrow with temperatures expected only in the 80's. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 17: A child waits to get into the Astoria Pool in the borough of Queens on August 17, 2015 in New York City. The main pool, the biggest in New York City and administered by the New York City Department of Parks and Recreation, sees over 3,000 people on a typical summer weekday. New York city is in the middle of a heat wave, with temperatures in the high nineties and with a heat factor making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 17: People enjoy a hot afternoon at the Astoria Pool in the borough of Queens on August 17, 2015 in New York City. The main pool, the biggest in New York City and administered by the New York City Department of Parks and Recreation, sees over 3,000 people on a typical summer weekday. New York city is in the middle of a heat wave, with temperatures in the high nineties and with a heat factor making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 21: Life guards do their daily exercises on a sultry morning at Coney Island in Brooklyn on July 21, 2015 in New York City. Despite an overcast sky, thousands of New Yorkers headed to area beaches to cool off from the heat and humidity. The hot weather is expected to break tomorrow with temperatures expected only in the 80's. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 28: A woman sits in a line for ice cream along the East River in Brooklyn on a sweltering hot afternoon on July 28, 2015 in New York City. With temperatures in the 90's and the heat index feeling over 100 degrees, New Yorkers of all ages have been flocking to pools, beaches and air conditioned rooms to try and stay cool. More hot and humid days are forecast for the remainder of the week. (Photo by Spencer Platt/Getty Images)
People enjoy a warm day at the Astoria Park Pool in New York on August 16, 2015. At 330 feet in length, the Astoria Park Pool is the largest in New York City and one of the largest swimming facilities in the United States. AFP PHOTO / KENA BETANCUR (Photo credit should read KENA BETANCUR/AFP/Getty Images)
NEW YORK, NY - JULY 21: A man looks out at the Verrazano Bridge from a pedestrian promanade on a sultry morning in Brooklyn on July 21, 2015 in New York City. Despite an overcast sky, thousands of New Yorkers headed to area Parks and beaches to cool off from the heat and humidity. The hot weather is expected to break tomorrow with temperatures expected only in the 80's. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 20: A woman cools off in the shade at Brighton Beach in Brooklyn on August 20, 2015 in New York City. The National Oceanic and Atmospheric Administration (NOAA) announced on Thursday that July was the planet's warmest month on record. July's average temperature was 61.86 degrees Fahrenheit, beating the previous global mark set in 1998 and 2010 by about one-seventh of a degree. NOAA began keeping records in1880. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 20: A man who goes by Ricky Obama tries to keep cool in the heat at Brighton Beach in Brooklyn on August 20, 2015 in New York City. The National Oceanic and Atmospheric Administration (NOAA) announced on Thursday that July was the planet's warmest month on record. July's average temperature was 61.86 degrees Fahrenheit, beating the previous global mark set in 1998 and 2010 by about one-seventh of a degree. NOAA began keeping records in1880. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 20: Empty water containers are viewed in the trash at Brighton Beach in Brooklyn on August 20, 2015 in New York City. The National Oceanic and Atmospheric Administration (NOAA) announced on Thursday that July was the planet's warmest month on record. July's average temperature was 61.86 degrees Fahrenheit, beating the previous global mark set in 1998 and 2010 by about one-seventh of a degree. NOAA began keeping records in1880. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - AUGUST 20: A man uses a sun umbrella along the boardwalk at Brighton Beach in Brooklyn on August 20, 2015 in New York City. The National Oceanic and Atmospheric Administration (NOAA) announced on Thursday that July was the planet's warmest month on record. July's average temperature was 61.86 degrees Fahrenheit, beating the previous global mark set in 1998 and 2010 by about one-seventh of a degree. NOAA began keeping records in1880. (Photo by Spencer Platt/Getty Images)
Beathau Wazaninka, right, sits next to her daughter Ariella as she fans herself at the Marcy Avenue subway stop during a hot weather advisory, Monday July 20, 2015 in New York. Amid today's scorching weather, the state environmental department has issued an air quality health advisory for the New York City area until 10 p.m. (AP Photo/Bryan R. Smith)
NEW YORK, NY - JULY 20: Bottles of water sit for sale at a street vendor on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: People line-up for ice cream in Manhattan on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: A woman holds an umbrella on a Manhattan street on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: A woman carries a tired child along a Manhattan street on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: People sit on the steps of the James A. Farley Post Office Building on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: People wear shorts and other light clothing as they walk on a Manhattan street on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: People line-up for ice cream in Manhattan on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: People rest in the shade along a Manhattan street on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: A woman holds a sun umbrella in Manhattan on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
NEW YORK, NY - JULY 20: A woman holds an umbrella on a Manhattan street on one of the hottest days of the summer on July 20, 2015 in New York City. More than 20,000 homes and businesses in and around New York City have lost power as the electric network has been stressed due to the intense heat. New York and much of the East Coast has experienced temperatures in 90's for the past few days with the humidity making it feel over 100 degrees. (Photo by Spencer Platt/Getty Images)
Children play in the Salmon Street Springs fountain in Portland, Ore., Wednesday, July 1, 2015. A heat advisory is in effect for Portland from noon Wednesday to 8 p.m. Thursday, according to the national weather service. (AP Photo/Don Ryan)
Children play in the Salmon Street Springs fountain in Portland, Ore., Wednesday, July 1, 2015. A heat advisory is in effect for Portland from noon Wednesday to 8 p.m. Thursday, according to the national weather service. (AP Photo/Don Ryan)
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At the same time, the jet stream has buckled southward along the West Coast in response to its northward shift in the East. This will allow cooler air and the potential for some additional rainfall to persist this week.

Below we discuss the impacts of this pattern change for the East and the West.

Warming Up East of the Rockies

This pattern change is good news for those that may have found summer's warmth lacking.

A heat wave may have begun on Sunday in some locations as New York City climbed to 90 degrees and Philadelphia soared to 91 degrees, which was the first high at or above 90 degrees in 10 days. On Monday, New York reached 91 degrees and 90 degrees was the high in Philly. Washington, D.C. missed the 90-degree mark again on Monday, but Boston saw the mercury climb to 90 degrees on Monday afternoon.

Highs reached the mid-80s from Chicago to Marquette as well as into the Ohio Valley on Monday and most areas will see even warmer conditions on Tuesday.

Here are a few examples of the temperature increases we'll see this week compared to last week. In general, most of these cities were below average last week, but can expect above-average temperatures throughout this week.

Chicago: Highs were only in the 70s much of last week at O'Hare. This week, look for highs to top out in the upper 80s or low 90s, which is about 5-10 degrees above average.

Marquette, Michigan: After seeing highs in the 50s early last week, look for highs up to 20 degrees above average with temperatures in the 80s to near 90 this week.

Detroit and Cincinnati: Highs in the 60s and 70s last week will increase into the upper 80s or low 90s this week.

Philadelphia and Washington, D.C.: Highs in the low to middle 90s expected through much of this week. Last week temperatures topped out mainly in the 80s.

New York City: Upper 80s to low 90s are expected much of this week.

As mentioned before, a southward dip in the jet stream ushered in a delightful air mass for late-August standards to parts of the Midwest, East, and even the South last week. Not only were temperatures cooler, but the humidity was gone as well across those regions.

In fact, we even saw a few daily record lows in the Mid-South and Plains last week. Last Tuesday morning, daily record lows for Aug. 25 were set in Paducah, Kentucky (52 degrees), and Tulsa, Oklahoma (56 degrees). Wichita, Kansas (54 degrees), and Fayetteville, Arkansas (49 degrees), both tied daily record lows last Tuesday morning.

Last Wednesday morning, new daily record lows were set in Mobile, Alabama (63 degrees), and Macon, Georgia (57 degrees). Pensacola, Florida (66 degrees), Tuscaloosa, Alabama (59 degrees) and Hattiesburg, Mississippi (59 degrees) tied its daily record low for Aug. 26.

The cool conditions persisted into last Thursday with daily record lows broken in Jackson, Mississippi (56 degrees), Baton Rouge (60 degrees), Apalachicola, Florida (64 degrees), Vicksburg, Mississippi (53 degrees) and Jackson, Kentucky (56 degrees).

The National Weather Service office near Marquette, Michigan, set a record cold high temperature for Aug. 24 of 54 degrees. It was even cooler last Tuesday with the high only reaching 53 degrees. That's more like the average high in mid-October.

(MORE: Forecast Weather Maps)

Northwest Cooler and Wetter = Some Wildfire Help

The Northwest has endured one of its hottest summers on record. Both Seattle and Portland have seen a record number of days in the 90s, and Seattle recorded its hottest month on record in July. Salem, Oregon smashed its previous record hot summer -- June through August -- for the second year in a row.

The combination of hot and dry conditions has led to widespread wildfire activity in the region.

(MORE: Wildfire Smoke From Space)

This pattern change is not only bringing cooler temperatures to the region, but also some much needed rainfall into this week. The cooler temperatures and increased moisture/rain chances should help lower the wildfire danger.

Seattle measured 1.28 inches of rain on Saturday, which set a daily rainfall record. This was followed by an additional 0.4 inches on Sunday which has brought the total for August to 3.28 inches, becoming the fourth wettest August on record. Meanwhile, just over half an inch of rain was recorded in Portland, Oregon, this weekend.

In addition to the rain, the strong area of low pressure also brought damaging wind gusts, including a wind gust of 87 mph that was recorded on Destruction Island in Washington.

(FORECAST: Seattle | Portland | Boise)

After staying unseasonably warm for much of August, the start of September starts on a cooler note with more refreshing temperatures. While much of Washington and Oregon baked in the 80s and 90s last week, most of those locations will see highs in the 70s through Tuesday, with some spots not getting out of the 60s.

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