Knowledge of the different kinds of weather threats possible is important in determining what type of safety measures may be needed. In Northcentral Wisconsin, these threats include:
A thunderstorm is considered severe if it produces any or all of the
following conditions: hail 1" diameter or larger, wind gusts of 58
m.p.h. or higher, or a tornado. Severe thunderstorms can also produce very heavy rain that can lead to flooding, as well as life-threatening lightning.
It is very important to remember that non-severe storms can produce enough rain to lead to the potential of flooding, as well as life-threatening lightning.
In the United States, the National Weather Service (NWS) has the
responsibility of issuing advisories related to threatening weather
conditions. Advisories called "watches" are issued in advance of a
potential threat, and "warnings"are issued when the threatening conditions are actually occurring or are imminent.
Here are some important definitions:
Severe Thunderstorm Watch: issued when atmospheric conditions are favorable for the development of severe storms which could produce large hail, damaging winds, and possibly a tornado.
Tornado Watch: issued when conditions are favorable for the
development of severe thunderstorms, with a reasonably high likelihood of tornadoes.
Flood Watch: issued when conditions appear to be favorable for heavy rain which could lead to rises is area rivers and streams resulting in eventual flooding.
Flash Flood Watch: issued when conditions are favorable for significant rainfall in a short enough period of time to lead to rapid rises in area streams and rivers with flooding soon to follow.
The corresponding warnings are issued when the particular threat is actually occurring or is imminent.
The National Weather Service issues warnings for these events based on two main sources of information, doppler radar analysis of the storm or specific reports from trained spotters deployed across the area. In either case, the warnings should be taken seriously. Improvements in radar technology and in the number and quality of trained spotters has allowed the NWS to now issue "storm specific warnings", in which the particular portion of a county most likely to be affected by the severe conditions will be listed in the warning.
There are times when severe weather can occur without a watch being issued in advance, one of many important reasons to have reliable sources of information available.