The greatest number of tornadoes worldwide occur in the United States. Tornadoes occur frequently in Missouri, Arkansas, Kansas, Oklahoma, Texas, Tennessee, and Mississippi. They are a bit less frequent in the northern plains states and Ohio Valley. Every state in the USA has had tornadoes at some time.
Tornadoes are not common in Maryland but they do occur there. It is inevitable that there will be more.
Tornadoes can occur any time of the year, but are most likely in the months of April through June. Spotters would most likely be able to see a tornado in an open area, with an unobstructed view. Most tornadoes occur between the hours of 4 and 9 PM, but can occur at any time of the day.
Since tornadoes are a form of weather they would be studied mostly by meteorologists. Some of these may be storm chasers, who conduct research in the field with tornadoes as they occur, though most storm chasers are not scientists.
Hail and tornadoes are most often associated with cold fronts, but can occur with dry lines or, lest often, warm fronts.
Severe thunderstorms most often occur ahead of cold fronts.
"Fire tornadoes," more properly called firewhirls, are most common in states prone to intense wildfires. Statistical data is not available, but California would likely be a good candidate.
It would be highly unusual for a tornado to strike an area where there is snow on the ground. Tornadoes generally occur during periods of warm weather. If such an event were to occur it would be little different from a tornado striking under ordinary circumstances. The tornado would likely lift some snow into the air, but that would be of little to no consequence compared with the damage tornadoes usually inflict.
Tornadoes occur the most in Tornado Alley, a region in the United states that includes Texas, Kansas, Oklahoma, Nebraska, Missouri, South Dakota and Iowa. While tornadoes can occur elsewhere, nowhere else in the world do they occur more frequently.
Tornadoes are likely to be rare near the equator due to the lack of organized weather systems. Those that would occur would probably be weak and cloud likely be found spinning clockwise or counterclockwise in equal numbers. Unlike large-scale systems such as hurricanes, tornadoes to not get their rotation from the Coriolis effect, but rather from local or regional wind shear.
Fire tornadoes, more properly called firewhirls, can occur in any area prone to major fires.This would include most of the Southwestern United States.
Hail and tornadoes would most likely be associated with a cold front or dry line.
That would be the United States. It gets more tornadoes than any other country, averaging about 1,200 per year. The United Kingdom is the country in which you are most likely to see a tornado, as it has more tornadoes per square mile than anywhere else in the world.