|NWS Information for Spotters|
Warning Coordination Meteorologist
National Weather Service La Crosse
This information and page layout was originally developed by NWS Norman.
Last Updated: 6/9/06
While everyone should keep a close eye on weather conditions whenever storms threaten, storm spotters have a definite need to know what's going on before, during, and after a severe weather event. The National Weather Service (NWS) provides an entire suite of forecast products to keep you informed about severe weather from days to minutes before the storms.
Is today a severe weather day?
During the peak of the severe weather season (May - August), this is a question that spotters should ask daily. The NWS provides information and forecasts to help answer this question:
Issued by the Storm Prediction Center, these convective outlooks cover the current day, tomorrow and the next day (day three). They are issued for the 48 contiguous states of the U.S. and offer guidance to NWS offices and others on where severe weather may occur.
HAZARDOUS WEATHER OUTLOOK
Based in part on the Storm Prediction Center (SPC) convective outlooks, these outlooks provide a heads-up description of any hazardous weather thats expected in the next week. The main focus is on today and tomorrow, with more general information provided further into the future.
The HWO is written specifically for storm spotters, emergency managers and others who need specific severe weather forecast information for planning purposes. However, the HWO is available to everyone via the Internet and Weather Radio.
The HWO provides details on what is expected (including what types of storms and hazards), when it is likely to happen and the meteorological reasoning behind it. It is written by NWS forecasters who are the experts in your local area and is updated as often as needed.
AREA FORECAST DISCUSSION
This technical discussion comes from your local NWS office and provides the reasoning and explanation behind what the forecasters are thinking. This can be used to supplement the information contained in the Hazardous Weather Outlook.
SHORT TERM FORECAST
The local NWS office issues short term forecasts to describe whats expected in the next few hours over small groups of counties. These forecasts may include information on where storms are anticipated, or details on what existing severe storms are expected to do in the next few hours.
TORNADO/SEVERE THUNDERSTORM WATCH
Tornado and severe thunderstorm watches are issued by the National Weather Services Storm Prediction Center. Watches typically cover a large geographic area and are in effect for several hours. Watches may prompt the beginning of formal spotter activities in a community.
A watch means conditions are favorable for severe thunderstorms and perhaps tornadoes to develop in and close to the watch area. Remember that people in and close to a watch area should be alert to severe storm development. Also remember that watches are not issued for every single severe storm.
A tornado warning is an urgent message from your local National Weather Service office. The warning means a tornado is imminent or occurring and indicates that immediate action is needed to avoid injury.
A tornado warning is usually based on a combination of radar information and storm spotter observations. Tornado warnings are issued for parts of counties and are in effect for about half an hour.
A tornado warning may prompt local officials to sound outdoor warning sirens.
SEVERE THUNDERSTORM WARNING
A severe thunderstorm warning is an urgent message that means a severe thunderstorm (containing hail at least dime size and/or winds in excess of 58 mph) is imminent or occurring.
DO NOT IGNORE severe thunderstorm warnings! These warnings give specific details as to what is expected and may cover a wide range of storms from dime size hail and 50 mph winds to destructive deadly storms producing softball size hail and 100 mph winds. And, severe thunderstorm warnings often precede tornado warnings, giving you even more advance notice that a dangerous storm is nearby.
SEVERE WEATHER STATEMENT
The NWS issues severe weather statements to update warnings. Statements provide critical new information on a warning, including spotter reports, updated radar analysis, the latest storm motion and expected hazards.
LOCAL STORM REPORT
These reports include the latest severe weather reports received by the National Weather Service, and include the time, location and a description of what happened. Spotter reports are the primary source for local storm report information.