Winter advisories and warnings

It’s been an interesting month, weatherwise, across North Idaho and the rest of the Inland Empire. It was a snowy start as 8.8 inches fell in early November, compared to a normal of 8.7 inches. The total is now at 8.9 inches. Then, milder air from the south pushed the mercury up to 50 degrees last Wednesday. The rest of the month now looks like more rain than snow as the warmer southwesterly air flow moves into the region.

According to Cliff’s records, there are many occasions when we start off with decent snowfalls in late October or early November. Coeur d’Alene and other areas, usually below 3,000 feet, don’t receive much of the white stuff until around at least early to mid December. After that, the pattern changes to the colder side with a lot more snow, even the lower elevations.

It still looks wet over the early portion of the Thanksgiving holiday weekend, but much of the moisture will be falling as rain. But, there could be some snowflakes in the region at the end of the month.

With the milder air flowing in from the south, the air masses that are expected to move into our region over the next several weeks should have more moisture. We’re well above average for this year, despite having one of the driest summer seasons ever recorded. Cliff has measured nearly 33 inches of rain and melted snow for 2017. The normal is 26.77 inches and he and I both agree that our final total at the end of the year could be close to 40 inches. That’s not a record, but it’s close. In 2012, a whopping 43.27 inches of moisture fell in Coeur d’Alene, the highest in recorded history.

Right now, the National Oceanic and Atmospheric Administration (NOAA) says that we’re currently experiencing weak “La Nina” conditions. La Nina is the abnormal cooling of sea-surface temperatures in the south-central Pacific Ocean. During La Nina years, our part of country often experiences snowier than normal winters. Cliff and I still expect about 85 to 90 inches of snow for the 2017-18 season.

If the cooler-than-normal sea-surface temperature event holds on to life into next year, as many forecasters are predicting, then the chances of a white Christmas are pretty good. I’ll have more details on that forecast in the coming weeks.

During the upcoming holiday season, it’s a good idea to know what’s in store weatherwise, especially if one is planning to hit the roadways to go to the mountains or visit friends and relatives. The mountain passes, especially over the Cascades, can change very quickly and the 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 is 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, especially 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.

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.

Keep an eye to the sky, and Cliff and I hope everyone has a safe and happy Thanksgiving.

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Contact Randy Mann at [email protected]