Recently, the Storm Prediction Center (SPC) in Norman, Okla., where they assess the risk for severe thunderstorms and tornadoes across the entire USA, added a new category of risk. It is called “enhanced risk”, and, sits squarely in the middle of the 5 risk categories, which we’ll get to in this column.
It is the forecasters at the Storm Prediction Center who issue Severe Thunderstorm or Tornado Watches. A watch means that conditions are favorable, whereas a warning means it’s happening or is about to. A “Watch” comes from the SPC, whereas a warning comes from your local NWS office; in our case, Caribou.
OK, back to the categories. When the SPC deems there to be a minimal but not zero risk for severe thunderstorms, they will, in their convective outlook, use the word “Marginal”. Going up the risk ladder, the next category is “Slight”, followed by “Enhanced”, “Moderate”, and “High”. In the technical discussions that they issue (found beneath the map showing the outlook colors), under “High Risk” you might find things like “intense, long-track tornadoes are possible”. If you are not familiar with what an intense (EF4 or EF5 tornado can do, just look at image of the Joplin tornado of May 2011. Be prepared to be stunned.
When the SPC paints a region in the “Moderate” category, it means there is a pretty significant risk of severe weather somewhere within that region. “High Risk” is not used very often, but when it is, people in that area really need to be on alert.
Now, in the previous paragraph, I used the term “severe weather”. In this application, we use it synonymously with “severe thunderstorm”. And just to refresh your memory, the minimum threshold for a severe thunderstorm is 50 knot (58 mph) winds and/or hail that is 1 inch in diameter. These are the thresholds because it has been found that significant damage can occur once wind reaches that speed, or hail reaches that size.
Those SPC technical discussions really are excellent, so if you have a budding meteorologist in the house, and he or she needs help deciphering some of those words, shoot me an email and I’ll help them out.
Here is the URL for the convective outlooks from the SPC:
http://www.spc.noaa.gov/products/outlook/.
Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.comtshapiro@wagmtv.com.
