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Boise weekend forecast: 17-day streak of highs in 90s will continue

A small fire in the Boise Foothills contributed to hazy conditions over the city Friday.
A small fire in the Boise Foothills contributed to hazy conditions over the city Friday.

Boise is in the middle of a heat streak, with Friday counting as the 17th day consecutive day of 90-degree heat, according to National Weather Service climate data. The hottest days this month were July 5 and July 9, when the high was 102.

The forecast high temperatures for the weekend are the low 90s for Saturday and Sunday. Then things will warm up into the high 90s early in next week, possibly to 100 by Wednesday, forecasters say.

July of 2017 was the second hottest on record for Boise. The daily mean temperature for July 2017 was 81.6 degrees, trailing July 2007’s record of 83.1 degrees. Data collection began in 1877. This July’s monthly average temperature, after 19 days, is 78.6 — not as hot as last year, but still 3.8 degrees above normal.

The good news is that the air quality in Boise — which was hazy even before a 15-acre fire in the Foothills added a layer of smoke — isn’t expected to get worse over the weekend. In fact, by late Friday afternoon it appeared much better than earlier in the day.

The Idaho Department of Environmental Quality has issued four yellow air quality alerts this week, and similar alerts have been issued for the weekend. Ozone formation, which is typical during hot weather and clear skies, was the main reason for the yellow air quality alerts this week, Regional Airshed Coordinator Michael Toole said Friday.

A yellow air quality alert means “moderate” pollution conditions could impact people in sensitive groups, including children, the elderly and those with heart or lung conditions.

Treasure Valley residents are asked to limit mowing until after the alert is over to reduce ozone-forming chemicals added to the air. Limiting vehicle trips and eliminating idling is urged.

Here are the all-time Boise heat streak records:

90 degrees and above streaks

1. 50 days. Set in 1875, the streak ended Aug. 22.

2. 44 days. Set in 1994, the streak ended Aug. 20.

3. 40 days. Set in 1961, the streak ended Aug. 15.

100 degrees and above streaks

1. 9 days. (three-way tie)

Set in 2015, the streak ended July 4.

Katy Moeller: 208-377-6413