Better know your advisories, North Idaho
The snowfall season for the 2019-20 season is off to a very early start. Rare snows in late September and October resulted in 6.6 inches of snow at Cliff’s station in Coeur d’Alene.
At the Spokane International Airport, 6.9 inches has been measured so far this season. In other parts of North Idaho, snowfall totals surrounding Coeur d’Alene have been near 8 inches in the lower elevations to over a foot in the mountains.
Therefore, with the holiday season fast-approaching, it’s a good idea to keep an eye on the weather and any watches and warnings issued by the National Weather Service, especially since Cliff and I believe that moisture totals are expected to be above normal in December and the early portion of 2020.
For much of the Inland Northwest, the higher elevations can see extreme weather changes in a short time. The mountains in this part of the country 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, 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 visibility.
Oh, the cold
In terms of our local weather, once this Pacific storm moves on to the east, high pressure is expected to bring drier than normal weather to North Idaho for about the next 7 to 10 days. So far, November is turning out to have moisture totals well below average as high pressure has been dominating the western U.S. and the cold and frigid air has been to our east.
In fact, the early to mid-November cold snap in the central U.S. has been labeled “historic” by many forecasters. Record lows have been set from the Dakotas southward to Texas and eastward across the Tennessee and Ohio Valleys and into Maine. Officials estimate that hundreds of cold records have been broken.
Readings in the Deep South last week were down into the teens. A low of 13 degrees was reported down into central Alabama.
It was the fourth-coldest November temperature ever recorded at the weather station at Mount Washington, N. H., with an extremely cold minus 17 degrees.
Last Wednesday, lows were down into the low 20s in New York City and in the mid-teens in eastern Canada. High temperatures were only in the upper teens near the Great Lakes last week, breaking more cold records for the date. Historically, when we see frigid air and snow to our east, this pattern eventually “backs up” over the West and we get the snow and cold.
As we get toward the end of month and into early December, it does look like the big ridge of high pressure that has brought much of the western U.S. the drier than average conditions should start to weaken and allow some Pacific storms to move into the region. It still looks like snowfall totals will also be increasing in December, which should give us a very good chance for a White Christmas. Stay tuned.
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Contact Randy Mann at randy@longrangeweather.com