Here's what advisories, warnings mean
With the official start to winter less than a month away, the biggest question I’m getting is, “How much snow are we going to get this winter?” We’re off to a slow start, as expected, as snowfall totals for November 2015 are only going to end up at 2.9 inches. This is below the normal of 8.7 inches. Total precipitation for November will finish at 2.03 inches, compared to the average of 3.07 inches.
As many are aware, we still have a very strong El Nino, the warmer than normal sea-surface temperature event in the south-central Pacific Ocean. The strength of this El Nino rivals the record-breaking event in 1996-97. However, the recent period of chilly temperatures is the result of colder air moving southward from Canada. We don’t often see too many patterns like this one during El Nino years.
As we head into December, there are indications that upper-level wind flow patterns across the Inland Northwest will be changing once again. Milder air is expected to move into our region from a more southwesterly direction with rain and snow increasing across the Inland Northwest later this week. Many of the long-range computer models are leaning toward more storms systems invading our area with rain and heavy, wet snow during the second week of December, which is more typical of El Nino.
We still think the chances of a White Christmas are less than 50/50. But, we start a “full moon” cycle on Christmas Day and during that time, the chances for colder weather are a little higher. It’s going to be close as the warmer El Nino may hold back the colder air from Canada.
Rainfall has been increasing in California where much of the state is still suffering from severe to extreme drought conditions. Many forecasters are still predicting flooding rains for the Golden State early next year as the El Nino is likely to have a big influence on worldwide weather patterns.
Despite predictions of a drier and milder than normal winter expected in North Idaho, there will still be a number of weather advisories and warnings issued by the National Weather Service in Spokane. The criteria for issuing some of the advisories or warnings can depend on the time of year and/or the elevation.
During the upcoming Christmas and New Year’s holiday, 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.
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.
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 this El Nino year, 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.
Cliff and I hope everyone had a safe and happy Thanksgiving. Next week, I’ll have an update on the big El Nino event.
Contact Randy Mann at randy@longrangeweather.com