Widespread Weather Pattern Change Bound For Much of the U.S.

Chris Dolce
Published: August 25,2015

A large-scale weather pattern change is set to take shape across North America that will bring big changes to multiple regions of the United States starting this weekend.
For those currently enjoying relief from summer's humidity east of the Rockies, get ready to heat up as the calendar flips from August to September. Meanwhile, the Northwest will finally see some much needed relief for the ongoing widespread wildfire activity.
(MORE: Latest Wildfire News)

Pattern Change Overview

Jet Stream Pattern

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.
Right now, the jet stream is dipping south to the east of the Rockies. This has brought a cooler, refreshing air mass to parts of the Midwest, East and even the Deep South. By this weekend, the main ribbon of strong winds associated with the jet stream will build north into Canada, though there will be some lagging upper-level energy in the East south of the main jet stream. The end result is building warmth across the nation's midsection and points east.
At the same time, the jet stream will buckle southward along the West Coast in response to its northward shift in the East. This will bring much cooler air and the potential for some welcome rainfall to the Pacific Northwest.
The pattern change may also play a role in helping to steer the latest Atlantic named storm, Erika. However this will depend on Erika's future path and intensity. For more on that story, click here.
(NEW: Interactive Storm Tracker For Erika)
Below we discuss the impacts of this pattern change for the West and the East.

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.
The combination of hot and dry conditions has led to widespread wildfire activity in the region. Some cities in interior parts of Oregon and Washington haven't seen any measurable rain since May, including Pasco, Washington, which had seen a record 88 days without rain as of Aug. 24.
(MORE: Wildfire Smoke From Space)
This pattern change will not only bring cooler temperatures to the region, but also some much needed rainfall starting this weekend as an area of low pressure nears the coast. The cooler temperatures and increased moisture/rain chances should help lower the wildfire danger, though gusty winds will be a negative factor as the storm system moves inland this weekend.
(FORECAST: Seattle | Portland | Boise)
Overall, expect temperatures in the Northwest and northern Rockies to go from several degrees above average Wednesday and Thursday to below average by this weekend and into next week.

Warming Up East of the Rockies

Forecast Highs

As mentioned before, a southward dip in the jet stream has ushered in a delightful air mass for late-August standards to parts of the Midwest, East, and even the South. Not only are temperatures cooler, but the humidity is gone as well across those regions.
In fact, we've even seen a few daily record lows in the Mid-South and Plains the last couple of days. On 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 on Tuesday morning.
Perhaps this air mass has even been a bit too cool for those wanting to enjoy the tail end of summer in the Great Lakes. For example, the National Weather Service office near Marquette, Michigan, set a record cold high temperature for Aug. 24 of 54 degrees. That's more like the average high in mid-October.
(MORE: Forecast Weather Maps)
This pattern change is good news for those that want another dose of summer's warmth as we make the transition into September. Here are a few examples of the temperature increases we'll see in the coming days. In general, most of these cities will go from near- or below-average temperatures midweek to above average by early next week.

• Chicago: Highs in the low 70s through Wednesday will jump into the middle or upper 80s by Sunday or Monday.
• Marquette, Michigan: Highs in the 50s or low 60s to start this week will be followed by low to middle 80s early next week.
• Detroit and Cincinnati: Highs in the 70s midweek will increase into the middle 80s by early next week.
• Philadelphia and Washington, D.C.: Middle 80s through this week may rise into the low 90s by Sunday or Monday.

According to the latest 8-14 day temperature outlook from NOAA's Climate Prediction Center, it appears that this pattern change has an above-average probability of sticking around for the long haul. The forecast shows that for the period of Sept. 1-7, parts of the Mississippi Valley, Ohio Valley, Great Lakes, South and East have a 50 percent or greater probability of seeing above-average temperature during the first week of September.

NOAA 6-10 Temperature Probability Forecast

Photos: Western Wildfires in Early August 2015