Sunday, April 21, 2024
45.0°F

Heed these winter weather advisories

| December 7, 2020 1:00 AM

Despite the recent lack of snow across Coeur d’Alene and the Inland Northwest, we’re still above average for snowfall this season. As of today, Dec. 7, Cliff has measured 16.1 inches of snow at his station in northwestern Coeur d’Alene. The normal to date is 12.3 inches.

At Spokane International Airport, where it usually snows less than Coeur d’Alene, a total of 17 inches has fallen since October. That’s about double its normal at this time of year.

Conditions are looking much better for snow around the middle of this month. We’re already seeing major changes starting to take place that will open the storm door and bring more snow into the region. Even the long-range computer models are showing this big change.

However, there may be a few occasions when we see some rain mixing in at times as warmer air may work its way northward into the region.

The New Year’s holiday weekend is also another time when the chances for snowfall are higher in our region because it’s in the middle of the full moon lunar cycle. During the winter season, we can get some hefty snowfall totals from storms and very cold temperatures during that time, so be careful if you’re going to be out on the roadways.

The new moon lunar cycle that begins on Jan. 12 could also be very snowy for North Idaho residents.

With increasing rain and snow activity expected across the Inland Northwest and other parts of the western portions of the country, it’s a good idea to know what’s in store weather-wise, especially if one is planning to hit the roadways to go to the mountains or visit friends and relatives over the Christmas and New Year’s holiday. The mountain passes, including the ones over the Cascades, can change very quickly and roads can become extremely slick in a short period of time.

For much of the Inland Northwest, the mountains generally refer to any elevation above 3,000 feet. A winter weather advisory, snow advisory, winter storm warning, and a heavy snow warning are usually the most common statements issued by the National Weather Service, sometimes days in advance.

A winter weather advisory is issued when a precipitation mix of snow, sleet, freezing rain and strong wind events are expected. The advisory is upgraded to a winter storm warning if snowfall in the valleys is expected to exceed 4 inches in a 12‑hour period in addition to the sleet, freezing rain or wind.

In the mountains, the expected snowfall must exceed 8 inches in that time frame to prompt a warning. If the precipitation is expected to be all snow, a snow advisory is issued when 2‑4 inches is likely in a 12‑hour period. When more than 4 inches of snow is forecast for the valleys (8 inches in the mountains) in a 12‑hour period, we’ll see a heavy snow warning. For early or late season storms in the mountains, like in April or October, lesser snow amounts can also prompt warnings.

Another type of advisory one might see, mostly during an El Nino year, when sea-surface temperatures are warmer than normal, is the freezing rain or sleet advisory. These are issued any time the surface becomes hazardous due to those types of precipitation.

When more than a half inch of sleet is expected, a heavy sleet warning is issued. Since we’re in the cooler La Nina sea-surface temperature event, the chances of a freezing rain or sleet advisory are much lower.

An ice storm warning is issued when the area is threatened by more than a quarter inch of ice. A blizzard warning is rare in the Inland Empire, but is issued when visibility due to blowing snow is reduced to a quarter mile or less and winds are 35 mph or stronger.

Also, we can have blizzard-type conditions even after it has stopped snowing, especially if there are strong winds that reduce visibilities.

Many of the region’s local roadways can be very slick, especially with packed snow. Some of the toughest conditions occur after we’ve had snow, then rain or drizzle will fall on top of the snow changing the surface to glare ice. There were several occasions when my car, equipped with 4-wheel drive and snow tires, would slide past a stop sign, even going very slowly, due to icy roads.

Keep an eye to the sky and Cliff and I hope everyone has a safe holiday season.

• • •

Contact Randy Mann at randy@longrangeweather.com.