Winter and Meteorologists: What are they talking about
Story By: Jamie Smith
Source: KOAA
Last week, Halloween gave the Colorado Springs and Pueblo areas a treat with the unseasonably warm weather. But like all good things, this too will pass. In fact, this week we have already seen Winter Storm Warnings and Advisories in the Colorado Rocky Mountains; and even some snow showers for the northern El Paso County area.
As we come to grips with the typical weather realities of Colorado, there may be some questions as to what winter watches, warnings, and advisories might mean.
First, let’s examine what conditions are needed to create a winter storm. While there are many factors in creating a snow storm, there are three main ingredients that are needed: cold air, moisture and lift. The majority of the time cold air is supplied from the northwest at temperatures near or below freezing. Next we need moisture. While Colorado seems to be far from any major sources of water, the Rocky Mountains are very efficient in squeezing out what little moisture we do have. Last but not least, there needs to be a mechanism that lifts the moist air to form clouds and precipitation. Typically lift occurs when cold and warm air collides and the warm air rises, this usually occurs near cold fronts. In Colorado, we also have the Rocky Mountains to help provide a source for lift.
Once all three ingredients are in place, we have the makings of winter weather and potentially confusing terminology used by meteorologists. Understanding those terms will help you to know what to expect when the next winter storm hits.
A good starting point is to know the difference between a “Watch’ and a “Warning”. A “Watch” is a long range prediction and is issued when conditions are favorable for a winter storm. Watches are issued at least 12 to 36 hours before hazardous winter weather is expected to begin. A “Warning” is issued when hazardous and severe weather is imminent or has a high probability of occurring. Warnings are issued usually with in 12 hrs of the event happening.
During the winter in Colorado, the term winter storm is usually attached to those watches and warnings. A winter storm is defined as a threat of winter weather such as heavy snow, sleet, or ice accumulation from freezing rain. In the Colorado region, heavy snow is defined by 7 or more inches of accumulation in 24 hours or less.
Another popular term for Southern Colorado is a Winter Weather Advisory. This is issued when there is snowfall accumulation expected between 4 and 7 inches in a 24 hour period. An advisory can be issued for a combination of snow, sleet, and/or freezing rain. If the amount of snow will be minimal, less than 4 inches in a 24 hour period, a snow advisory may be issued. In general, an advisory is issued for weather conditions expected to cause significant inconvenience to the general public.
In cases of extreme weather, additional terms may be used to further define hazardous conditions. A blizzard warning is issued when winter storms have sustained winds or frequent gusts of 35 mph or greater and visibility reduced to 1/4 mile or less by falling or blowing snow. Typically a blizzard warning will be issued when these conditions will last for 3 hours or longer.
As winter begins knocking on our door, our KOAA 5/30 weather forecasters will be using these terminologies more frequently. Now knowing exactly what they mean will help you prepare and minimize the inconvenience the winter weather may bring.
