Summer arrives in just a few days

The first day of summer arrives Wednesday at 7:58 a.m. On that day, the sun angle is the highest in the sky and the Northern Hemisphere will experience the highest number of daylight hours. The exact number of hours and minutes will have some slight variances across most towns and cities due to differences in elevation, terrain and proximity within the time zone. For this year, Coeur d’Alene’s longest day is June 21 as we’ll have 15 hours, 59 minutes and 47 seconds of day length. After Wednesday, our daylight hours will slowly start to decrease.

On June 21, the sun’s rays will be directly overhead at 23.5 degrees North latitude in the Northern Hemisphere, called the Tropic of Cancer. It’s also named the June Solstice as the Southern Hemisphere is experiencing its first day of winter, the complete opposite.

Our weather in June has been warm, despite some cool and wet days, across much of the Inland Northwest as other parts of the world have been sweltering with record heat. Parts of Siberia, China, Mexico and Europe have experienced some of the hottest weather in history in history. I’ll have more details on that next week.

Through the first half of the month, our average high in Coeur d’Alene has been approximately 80 degrees, which is above average. The normal high temperature for this month is about 75 degrees. Our warmest day thus far for 2023 was June 7 with a high of 91 degrees.

The feels like summer temperatures are also known as a “heat index.” This was developed by R.I. Steadman of the National Weather Service back in 1979. The heat index is calculated by combining air temperature and relative humidity levels. For example, a 90-degree temperature combined with a 90% relative humidity level would push the heat index up to a very dangerous 122 degrees Fahrenheit. In the southwestern U.S., a 120-degree temperature often feels more like dry heat as humidity levels are very low.

The region of the country with the highest levels of heat and humidity is east of the Rockies, especially in the southern portions of the country. Depending on the age and health of individuals, prolonged exposure to heat index temperatures over 100 degrees can lead to sunstroke, heat exhaustion, muscle cramps and even heart attacks. Since the 1930s, it’s estimated that close to 30,000 Americans have died during big heatwaves.

Here in North Idaho, most of our very hot days typically have lower humidity values. Thanks to the Rocky Mountains, the humid air from the Gulf of Mexico is blocked from entering the Far West. Although we may receive some triple‑digit readings, the relative humidity levels are generally less than 20%, hence only a slight rise in the overall heat index.

The hottest day ever recorded in our region was Aug. 4, 1961. On that particular afternoon, Coeur d’Alene hit 109 degrees, our all-time record high. It was 108 degrees in Spokane. The Wenatchee Airport hit 109 degrees while Ephrata, Wash., and Lewiston each observed a very hot 115 degrees.

The most torrid summer season in our region, especially during the 20th century, occurred in August of 1967. Cliff’s records indicate there were an all-time record 16 days that year with temperatures at or above 100 degrees with 45 days with readings at or above 90 degrees.

However, it was about two years ago when our region experienced the hottest late June heatwave in recorded history. The Spokane International Airport had its hottest day ever recorded June 29, 2021, with a blistering high of 109 degrees. That beat the old record of 108 degrees set back Aug. 4, 1961, the same day Coeur d’Alene hit its all-time record high of 109 degrees. In northwestern Coeur d'Alene, it was 107 degrees on that blistering afternoon.

The Coeur d’Alene Airport in Hayden also topped out at 109 degrees June 29, which tied its all-time record for the highest temperature. It was even hotter at North Idaho College as the thermometer hit 110 degrees on that date. Kellogg, Worley and Rathdrum each reported 108 degrees on that torrid Tuesday. Hayden and Athol hit 107 while Post Falls went to 106 degrees.

June’s average high temperature in 2021 was 81.1 degrees, which was over 8 degrees above normal. There were also 10 days with highs at or above 90 degrees. Only .49 inches of rain fell, compared to the normal of 1.93 inches.

The end of June for 2023 will certainly be much different than from the one several years ago. We’ll have more warm days, but we don’t believe that a big heatwave will hit the region until at least next month. For the rest of June, we’ll have periods of more showers and thunderstorms as this summer’s weather is not expected to be as dry as last year.

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Contact Randy Mann at randy@longrangeweather.com.