September Temperature Outlook: A Taste of Fall in Central US While West and East Remain Hot

The Temperature Outlook for September
  • Cooler than average temperatures are anticipated in parts of the Plains, Midwest in September.
  • The heat will persist into September in much of the West and East.

A hot start to fall is expected in much of the western and eastern U.S., but parts of the nation’s midsection may see a cool September.

Temperatures will be the greatest above average in September from western Washington southeastward into southwestern Utah and western New Mexico, as well as in Maine, according to the latest outlook from The Weather Company, an IBM Business. The continuation of the hot and dry conditions in the West is not good news for the wildfires in the region.

A warmer than average September is also expected from New England to eastern South Carolina and as far west as eastern Ohio. Areas from Texas to most locations west of the Rockies will also experience above average temperatures. Much of the South, as well as parts of the Midwest and Rockies can expect temperatures to be near or slightly warmer than average.

Meanwhile, cooler than average conditions will be felt in the first month of meteorological fall from northwestern Wisconsin westward into parts of the Dakotas and far northeastern Montana. Temperatures will trend near or slightly below average from eastern Montana into central Missouri and as far east as parts of Michigan.

September temperature outlook from The Weather Company, an IBM Business

What Factors Are Driving the Forecast?

A shift in the upper-level pattern developed in August, which focused the heat in the West and parts of the East. This allowed cooler temperatures at times in parts of the Plains and Midwest.

There are indications that this general weather pattern will be present during much of September.

“The pattern change in August, towards very warm temperatures in the West and cooler temperatures in the Midwest/Southeast, will likely continue in September,” said Todd Crawford, chief meteorologist at The Weather Company.

The jet stream pattern expected in early September, with a southward dip over parts of the Plains and Midwest, highlights the potential for cooler weather in portions of the central United States. In addition, the jetstream will bulge northward over the West and East which will allow summer heat to persist. This general theme is anticipated to persist into at least mid-September, according to NOAA’s Climate Prediction Center.

Early September forecast pattern

Another important factor in the temperature outlook is soil moisture.

It has been a wet summer in parts of the north-central U.S. and in parts of the South and mid-Atlantic and soil moisture remains higher than average as a result. Higher soil moisture can lead to cooler conditions as more solar radiation is used in the process of evaporation instead of increasing the air temperature.

Soil Moisture Anomaly

(NOAA’s Climate Prediction Center)

Although the recent weather pattern, soil moisture and climate forecast models support the idea for cooler temperatures in parts of the central U.S. and hot conditions in the West and East, September forecasts can be difficult due to tropical activity.

“The September pattern can be quite volatile during an active tropical season, so confidence is lower than it would be other months,” said Crawford.

Average September Temperatures

Signs of fall emerge in September and average temperatures dip.

Average highs top out in the 60s and 70s for much of the northern tier in September and 80s replace 90s for highs in much of the South.

Warmer than average temperatures in the West suggest a hot start to fall, especially in the Southwest where highs average in the 90s and 100s. Above average temperatures may make September feel more like summer for much of the East, where average highs range from the 60s to the 80s.

Average Highs in September

Morning low temperatures also take a tumble in September. Lows in the 30s return in parts of the Rockies, with 40s for many locations in the West and northern tier. The Desert Southwest experiences average lows in the 60s and 70s instead of the 70s and 80s.

Cooler than average conditions in the Plains and Midwest indicate some chilly mornings will return.

(MORE: Average Monthly Temperatures)

Average Lows in September

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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