Temperature Outlook Through Late Summer: Southwest Heat May Spread East as Northwest Stays Cool

Chris Dolce
Published: June 16,2017
Persistent above-average heat through late summer is most likely to occur over the Southwest, potentially spreading east with time, according to the latest outlook from The Weather Company, an IBM Business. Meanwhile, the Northwest is primed to be a location that could experience below-average temperatures overall into September.
It now appears a significant El Niño will not develop this year, so it's not a factor in the forecast through late summer. The state of the atmosphere is still tilting a bit towards the La Niña event that occurred this past winter.

Overall temperature outlook, July through September. Month-by-month details are below.

"Even though tropical Pacific sea-surface temperatures are slightly warmer than normal, the atmospheric base state is still leaning a bit toward a La Niña base state and this will likely not change," said Dr. Todd Crawford, chief meteorologist with The Weather Company.
(MAPS: Average Monthly Temperatures)
Another factor to consider is the historically low Arctic sea ice values, which may lead to negative North Atlantic Oscillation (NAO) conditions this summer. That typically favors the greatest above-average temperatures to occur across the southern tier, with any below-average temperatures farther north, notes Crawford.

"Our August-September maps have a La Niña look, with less heat across the north-central and northeastern states due to concerns about negative NAO conditions developing again," said Crawford.
But Crawford cautions if the negative NAO pattern does not redevelop, the north-central and northeastern regions could see hotter temperatures than currently forecast. For now, the forecast for "big sustained heat" has been limited to the Southwest through the next few months.

July

The West will have the greatest temperature dichotomy in July, and that will be a consistent theme into September.
Below-average temperatures are forecast to be entrenched in the Northwest while the Southwest bakes in hotter-than-average conditions for July.
In the East, most areas are forecast to see temperatures near or just above or below seasonal averages.
The Midwest and Northeast have the highest odds for somewhat above-average temperatures.
Although the Southeast is expected to see temperatures slightly below average, typical summer heat and humidity can still be expected.

July temperature outlook.

August

Just like July, the Northwest is once again favored to see cooler-than-average temperatures in August.
Most areas east of the Rockies could see temperatures near or slightly above average. As mentioned before, northern areas east of the Rockies could be hotter than currently forecast, depending on the state of the NAO.

August temperature outlook.

September

The transition from summer to fall in September may be marked by above-average warmth spreading across the nation's southern tier, as well as northward toward the Great Lakes and mid-Atlantic.
Cooler-than-average readings are forecast to be locked in once again in the Northwest.

September temperature outlook.

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