Heat Wave Kicks Off September in Midwest, Northeast as Northwest Finally Cools Off

Chris Dolce
Published: September 1,2015 



 
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

Jet Stream Pattern Midweek

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.
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

Forecast Highs

Forecast Highs Compared To Average

This pattern change is good news for those that may have found summer's warmth lacking.
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 upper 80s or low 90s are expected this week. Last week's highs were in the 60s and 70s.
• 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: Tuesday marked the third day in a row with highs in the 90s in New York City. Three or more days in a row with 90s is typically considered a heat wave in parts of the Northeast region. Upper 80s to low 90s are expected through Thursday.

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

Forecast Highs and Weather

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.

Photos: Western Wildfires in Early August 2015