September slightly warmer than Bend average, despite chilly end of month

Despite the end of September bringing snow and chilly weather to Bend, the month as a whole had slightly higher temperatures than average, mostly due to daily low temperatures being much warmer.

The average temperature in Bend for September was 57.8 degrees, or 1.3 degrees above normal, according to the National Weather Service office in Pendleton. But low temperatures averaged 44.7 degrees, which is 5.2 degrees warmer than the September average in Bend, according to the weather service’s monthly climate summary.

Meanwhile, September’s average high temperature was 2.7 degrees below average, at 70.8 degrees.

One possible reason for the warmer evenings and cooler days last month could be cloudier skies, according to Marilyn Lohmann from the Pendleton weather service office.

While clouds trap heat in during the night, they also block the sun from the region during the day, she said.

“We didn’t get the full effects of the sunshine we would normally see, and the warmth from it,” Lohmann said.

Another theory for warmer evenings in Bend could be the “heat island effect,” in which urban areas retain heat, according to Lohmann.

This is the second straight month that Bend saw hotter-than-normal temperatures. In August, the average temperature was 4.1 degrees higher than average, according to the weather service.

Fitting for a transitional month, September saw extremes on both sides of the thermometer in Bend. For the first few days of the month, temperatures were much higher than average, with highs above 85 degrees. But for a few days in the middle of the month and in the last two days, high temperatures dropped by more than 15 to 20 degrees compared to the average. Sept. 30 was Bend’s chilliest day of the month, with a high of 46 and a low of 31.

The end of September also lightly blanketed Bend with snow, something that Lohmann said was strange for early fall.

“A lot of these places hadn’t seen snow (in September) in 20 years,” she said. “It’s quite unusual for a late September snowfall.”

The reason for the snow was a cold air system from Canada, which brought arctic air to Central Oregon, Lohmann said.

September was wetter than average for Bend — the city collected 1.17 inches of precipitation during the month, 0.76 inches more than normal. This continues a damp year for the region, as Bend has received 4.54 more inches of precipitation than in a typical year, the climate report stated.

Pendleton’s meteorologists are predicting a cooler and wetter October than average for Bend. Lohmann said she expects rainy weather patterns to cycle through the region every three to four days.

“We expect precipitation from time to time, and it will also help keep those temperatures a little cooler than normal,” she said.

— Reporter: 541-617-7854, jhogan@bendbulletin.com