RAPID CITY, S.D. (KOTA/KEVN) – Severe weather season is fast approaching and it is time to learn a little bit more about what a few common things we meteorologists talk about on severe weather days and leading up to the storms themselves. The first topic of this episode highlights the severe risk categories and explains what each one means.
There are five different categories and we will start with the lowest risk and work our way to the highest risk. The first category we will talk about is called a “marginal risk”. This means that isolated severe storms are possible, where wind gusts could reach 60 mph, hail could be up to the size of quarters and the tornado risk is very low. The second and next threat level up is “slight risk”. This is where scattered severe thunderstorms are possible with damaging winds of 60 mph or higher, hailstones 1” in diameter or larger and the possibility of an isolated tornado or two. Now, these two categories are most common here in western South Dakota on any given summer day with a severe thunderstorm threat.
Next up, “enhanced risk”, which is the third highest severe category. With this threat, numerous severe storms are possible with damaging winds of 60-80 mph or higher, Hailstones of 2” in diameter or larger, and a few tornadoes are to be expected. This category is issued for western South Dakota and northeast Wyoming roughly a dozen times a year.
A “moderate risk” is the fourth highest category out of five, and not very common in the Black Hills region. Widespread severe storms are expected with this category. Wind and hail damage are expected with thunderstorms and even a few strong tornadoes Moderate risks for the strong tornadoes are typically for Tornado Alley and Dixie Alley. The highest category of them all is the “high risk” threat. These are typically associated with the threat of extensive wind damage or a tornado outbreak. Significant wind and hail damage are possible with this threat, along with the chance for violent, long lived tornadoes. This threat is also more likely for Tornado Alley and Dixie Alley.
Onto the next topic of explaining the difference between a watch and a warning. A “watch” is commonly issued hours before any thunderstorms pop up. Sometimes it is issued once a couple of storms are strengthening. Watches indicate the risk of hazardous weather, such as damaging winds, hail and even tornadoes. When a watch is issued, it is best to have a plan in place and be ready in case a warning is issued for your location.
Warnings are issued when the event is just starting, or minutes prior to it beginning. Warnings mean the event is occurring, imminent, or likely. When a warning is issued, it means that a storm is producing damaging wind, hail or even a tornado. It is best to take action once a warning is issued, preferably following your severe weather plan you went over when the watch was issued.
A great way to remember the difference between a watch and warning is thinking about baking. A watch is similar to having all the ingredients to a recipe set out, but not actually baking just yet. A warning is similar to a cupcake, or any other baked good, being complete and coming out of the oven, the baked good is happening now.
Last, but not least, we talk about the generic pieces of a supercell thunderstorm, commonly found during the summer. A supercell has a classic “hook” to it the majority of the time. Supercells form when warm air rapidly rises and forms into a cloud. The wind at the surface and way up in the atmosphere help shape it into a thunderstorm that will exist for a while. In the main core of the storm, that is where the heavy rain and hail is likely. Where the storm begins to hook, that is part of a storm that a tornado is most likely to form, due to rotating winds in that location.
On the next KOTA Territory Weather School episode, we will dive into how tornadoes, lightning and hail form, and talk about the world’s largest hailstorm ever recorded, which fell here in South Dakota.