Wisconsin’s Winter Weather Awareness Week continues, and today’s topic from the Stormtracker 18 Weather team distinguishes the different types of watches, warnings, and advisories that the NWS can issue for winter systems and what they mean. It really comes down to a couple subcategories: time scale, impacts, and how much area the threat covers.
There are two different categories for the time scale: the earliest alert we could receive is a Winter Storm Watch. This means that impacts to travel are increasing in likelihood starting at least 24 hours from time issued, and can be issued up to two days in advance of the start of a storm. This means that it’s time to adjust your travel plans if you plan on driving during the potential storm.
In the immediate time scale, there are two options for widespread alerts. They are a Winter Weather Advisory and the more impactful Warnings (of which there are three types), though at the same level as Winter Storm Warning is a Blizzard Warning and Ice Storm Warning.
The Winter Weather Advisory means that travel will be hazardous, but can be done if precautions are taken such as slowing down and leaving plenty of extra following distance. However, it’s important to note that advisory level systems tend to lead to similar number of crashes as warning systems, and sometimes more, and that’s because more people still think they can drive at the speed limit and follow too closely, and people tend to heed warnings better so there are less cars on the road.
Warnings mean that travel will be dangerous and you should stay home, if possible.
There are three different types of widespread area warnings. Winter Storm Warnings are issued for heavy snow rates and snow totals, Ice storm Warnings are issued for major freezing rain events that thankfully aren’t too common this far north. Blizzard Warnings, contrary to popular belief, have nothing to do with snow totals. Instead, the threat is the combination of snow, wind, and visibility.
In fact, snow does not even have to be falling for a Blizzard Warning to be issued, rather it can be from either falling snow or blowing snow off of the ground. The criteria for a Blizzard Warning are: sustained winds of at least 35 mph, visibility from falling or blowing snow at or less than 1/4 mile, and both those parameters must be met for at least three consecutive hours.
There is one new warning that came into existence last year and has not been used in Western Wisconsin yet, and that’s called a Snow Squall Warning. Those are issued for the immediate time scale, but are usually only in effect for an hour or two and cover a smaller area that isn’t constrained to county borders like the previously mentioned alerts as they also are issued with polygons for parts of counties.
In that sense of the space they cover, they are more like tornado or severe thunderstorm warnings. If one were to be issued for you, it means that very heavy snow is falling and travel will be dangerous to impossible for a short period of time and you should find a safe place to wait it out.
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