September Forecast Calls For Warm East, Cool West

Linda Lam
Published: August 28,2015
If you're sick of summer's persistent weather where you live, you may see big changes in September.
The latest September outlook from The Weather Channel indicates that warm temperatures will be found from the Great Lakes into the Ohio and Tennessee Valleys and into portions of the South. In general, locations east of the Rockies will see temperatures that are above average for this time of year. The opposite is true from western-most Montana into western Wyoming, central Colorado and New Mexico westward to the West Coast where cooler than average conditions are expected.
(MORE: Fall 2015 Forecast)

However, the temperature forecast in September could be impacted by tropical activity in both the Atlantic and Pacific.
"We fully expect an unusually warm September across much of the eastern U.S. It isn't completely clear whether the focus of the heat will be Great-Lakes-based or Southeast-based, so we have sort of hedged our bet and greatly enhanced the anomalies in the entire region. As always, September is fraught with forecast risks associated with tropical impacts, both from the tropical Pacific and tropical Atlantic," said Dr. Todd Crawford, chief meteorologist of WSI, a division of The Weather Company.
Astrong El Niño event is expected and will be an important contributor in the forecast heading into September. However, the strong blocking  seen this summer will also factor into the temperature forecast.
"The La Nina sub-seasonal signal is fighting an uphill battle in maintaining itself in the midst of a strong El Nino seasonal signal, so colder risks are very much in play later in the month especially," Crawford said.
The jet stream moving northward toward Canada will allow warmth to build across much of the central and eastern U.S. as the month begins. Temperatures will be above average for most areas east of the Rockies, especially in the northern tier.
(MORE: Widespread Pattern Change)
In the West the jet stream will dip southward bringing cooler conditions and below-average temperatures to the West the first week of September.
The latest outlook heading toward mid-September from the Climate Prediction Center also focuses the best chance for above-average temperatures east of the Mississippi River, while cooler than average temperatures are likely in the West.
MORE: Autumn Sunsets (PHOTOS)