First freeze and potential winter ice

This is the time of year when local gardeners will have to start monitoring the weather more closely as our region will eventually be heading toward freezing temperatures. The first area to feel the frigid conditions this season has been across the northern and central Great Plains. From North Dakota to Nebraska, morning lows dipped to near or below the freezing mark after highs were well into the 80s in the northern regions early in the month.

In our part of the country, low temperatures are expected to stay above the 32-degree mark for at least the next several weeks. The best chance for temperatures to drop to the freezing mark in Coeur d’Alene is likely around the full moon cycle Oct. 28. However, some of the higher elevations, and perhaps a few outlying areas, may see readings close to the freezing mark in a matter of weeks.

As I’ve mentioned in previous articles, sea-surface temperatures have been warming up along the equatorial regions. We’re currently in a moderately warmer El Niño pattern. In fact, ocean temperatures continue to be well above average in the northern Pacific Ocean, much of the Atlantic Ocean, the Gulf of Mexico, the Indian Ocean, and many regions of the Arctic Ocean. With much of the globe having above-normal sea-surface temperatures, air temperatures have also been much warmer in both hemispheres. The warming of ocean waters may, at least in part, contribute to our first fall freeze arriving a bit later than normal.

Since 1895, the average date for the first freeze in Coeur d’Alene is Oct. 16. Since 2000, the average date for Coeur d’Alene’s first freeze is Oct. 14. The coldest reading ever recorded for October occurred Oct. 31, 1935, with a low of 2 degrees. More recently, the chilliest temperature was 13 degrees Halloween 2006. It was 20 degrees Oct. 10, 2009. Two days later, in the same year Oct. 12, the mercury dipped to a frigid 15 degrees. That was one of the worst early October cold waves to hit the region in history.

On the flip side, one of the latest freezes to occur in the Coeur d’Alene region happened in 2014. The mercury didn’t drop below 32 degrees until Nov. 10 with a low of 27 degrees. In 2021, we had our first 32-degree temperature of the fall season occur Oct. 7, but in 2022, we didn’t have temperatures at or below the freezing mark until Nov. 3, when the mercury dipped to 30 degrees.

The earliest freeze in Coeur d’Alene since 1895 happened Aug. 25, 1910, with a low of 32 degrees. In Kellogg, it was a cold morning in 1969 when the morning low dipped to 31 degrees Aug. 9. On Sept. 10, 1895, Spokane had the earliest 32-degree temperature after the summer season.

For the upcoming late fall and winter season, the biggest concern with this El Niño, which could be very strong in the coming months, is also the increased probability of ice in the lower elevations. Many can remember the big ice storm Nov. 19, 1996, across the Inland Empire.

During that time, the Inland Empire experienced a pattern of very cold air settling into the lower elevations. Temperatures at the surface were near or below freezing, so on that November day. However, readings were much warmer from above the surface to nearly 6,500 feet. Since the air temperature above the surface was above freezing, the raindrops did not change to snow. They become “supercooled” when they hit the ground as rain, and once they come in contact with buildings, power lines or other objects that are below freezing, the raindrops freeze almost instantly. These are the conditions for freezing rain and ice storms.

In November 1996, about an inch-and-a-half of rain fell on the frozen surface. There was also freezing fog, snow, and mist. It was a mess as trees and branches were coming down due to the heavy weight of the ice. Ice-covered power lines and transformers were exploding as over 100,000 people lost power. Other structures like homes, buildings and vehicles were caked with layers of ice up to an in thick. Total damage was about $22 million in Spokane and Kootenai County. Most recently, in early January 2019, close to a half-inch of ice was reported in Coeur d’Alene.

In terms of precipitation, we are expecting some rain this week from a series of Pacific storms. We’ll likely have occasional showers for the rest of the month. The best chance for rain across the region is at the end of the month around the full moon Oct. 28. In August and September, we did receive our heaviest rainfall at the end of each month. It’s possible this pattern could repeat itself once again.

• • •

Contact Randy Mann at randy@longrangeweather.com.