In order for a thunderstorm to be classified as severe on the basis of hail, the hailstones must be of a diameter of at least 3/4". There are many different reference objects that people have used over the years to try and estimate hail size instead of getting pounded by hailstones trying to measure the largest ones. Some of them have various misconceptions. For instance, the diameter of a dime is actually 7/10" while many people still consider it to be 3/4". It is very close, but a penny is a better estimator of 3/4". Since it is so close, a lot of times you will see dime sized hail entered in official reports as 3/4". There is a lot of discrepancy at the top end of the scale. Softballs were generally used to estimate 4.5" diameter hail. This is the official regulation size, but softballs come in several different sizes, and depending on what people are used to, they could be estimating incorrectly.

Generally 1.25" diameter hailstones, or half-dollar size hail, is approximately the point when property damage begins to occur in addition to agricultural damage. Of course this will vary based on the hardness of the hailstone, the amount of wind driving the hailstone, etc. Spotters should be careful when reporting hail sizes. If it's possible, you should measure the hail to get the most accurate reading. If this isn't possible you should use a reference object, but try to use objects that you are familiar with and reasonable assumptions. Many people aren't necessarily familiar with a half dollar or how big it is. So, many people will either use a golfball or quarter as a reference. In fact, there was a statistic, I forget which time period but it was at least 5 years, where golfball size hail was reported 7 times more frequently than half dollar size hail. Is this because 1.75" diameter hail occurred much more frequently than 1.25" diameter hail. Probably not. Therefore, use good judgement when estimating. The following are hail diameters and associated descriptions.

Wind gusts are extremely hard to estimate, possibly the most difficult task a spotter will have. It is extremely subjective and largely based on past experiences. When you report a wind gust it is important to give a range as there is no way you can be precise to +/- 0.5 mph. Generally it's a good idea to report in ranges of 10. If I think the wind gust was 50 mph, it would be a good idea to report it as 45 to 55 mph gusts. A lot of the error comes when there is a warning in effect so the spotter is biased to expect stronger winds than they are really experiencing or when the spotter isn't necessarily paying attention to their surroundings. Both are important to be cautious for. If there is a warning in effect, but all that happens in your backyard is the trees are swaying back and forth, the gusts are probably not even 50 mph. Look for what isn't happening to rule things out. No large branches are coming off? Well then, in this case, something less than 50 mph would probably be right. The warning may include your community in a certain county, but the wind gusts may be isolated and sporadic, so someone a mile away could have some damage and you could have nothing.

Of course, nothing is a substitute for a measured wind gust. However, many people don't have access to such equipment. Some live in too sheltered of a location to get an accurate measurement. My recommendation is to use an estimated wind gust speed as a last resort, instead first look for damage. Damage is objective. Either a tree is blown over or it isn't. Below are general wind speed ranges and expected results.

A tornado is obviously a tornado! If there is a condensation funnel in contact with the ground and you can see clear rotation then you have a tornado. Of course, not all tornadoes have a completely formed condensation funnel. If this occurs you need to differentiate between a funnel cloud and a tornado. Look at the horizon. If you can see debris or dust getting kicked up, then the tornado probably has spun up. Otherwise you are witnessing a funnel cloud. This is one of the origins of false tornado reports.

Also, report rotating thunderstorms that have a rotating wall cloud. This is one of the early signs of a possible tornado. It could be helpful to the National Weather Service in providing valuable lead time for warnings.

DO NOT REPORT SCUD CLOUDS AS FUNNEL CLOUDS! This has to be one of the top sources of false funnel cloud reports. Scud clouds are low-hanging clouds that hang down typically from the edges of storms, especially on the front edge of a line of storms. Many people will call in and report a funnel cloud but these menacing looking clouds are harmless. Make sure you observe them to see if they are rotating first. This is an image of harmless scud clouds. They weren't rotating and they were totally isolated from any features that would give off the appearance of a possible tornado. A funnel cloud typically has the more traditional "funnel look" and it will be rotating.

Despite how terrible it may seem, torrential downpours, frequent cloud-to-ground lightning or really dark clouds do not necessarily mean a storm is severe. Of course these things (with the possible exception of really dark clouds) have an impact on the public, but they do not fit the definition of a severe thunderstorm. Lightning is one of the deadliest weather phenomina. Therefore, even if a storm is not necessarily severe, but is producing a lot of lightning, you should still move indoors to safety. Downpours on the other hand are more of a hazard to motorists. They reduce visibility and traction.