The Storm Prediction Center (SPC) is located in Norman, Oklahoma and is part of the National Weather Service (NWS) and the National Centers for Environmental Prediction (NCEP). Their mission is to, "provide timely and accurate forecasts and watches for severe thunderstorms and tornadoes over the contiguous United States. The SPC also monitors heavy rain, heavy snow, and fire weather events across the U.S. and issues specific products for those hazards." Their web site with a suite of information is available at:
The convective outlooks issued by the SPC are available at:
Included with the discussion is a convective outlook for DAY 1 (today) and DAY 2 (tomorrow) and DAY 3. In each outlook a risk of severe thunderstorms is given. The 5 categories are an unclassified risk (labeled as SEE TEXT), general thunderstorms (GEN TSTMS), a slight risk (SLGT), a moderate risk (MDT), and a high risk (HIGH). Each of these risks is for an area of 50,000 square miles (about the size of Oklahoma). The number of severe reports will increase as the area of risk increases. Below is the interpretation SPC uses to classify each of the risks:
SEE TEXT: Situation in which a SLGT risk was considered but not warranted at the current time. It is referenced within the convective discussion text.
GEN TSTMS: Although the environment is favorable for thunderstorms, severe thunderstorms will not be widespread.
SLGT RISK: Less than 5 tornadoes and less than 30 reports of hail greater than 3/4" in diameter and wind greater than 58 mph (50 knots) is expected in the slight risk region.
MDT RISK: 6-19 tornadoes are expected with more than 30 reports of hail greater than 3/4" in diameter and wind greater than 58 mph (50 knots) is expected in the moderate risk region.
HIGH RISK: 20 or more tornadoes are expected with a at least 2 tornadoes being strong or violent (having the potential to produce F3 or greater damage) or for a derecho producing situation with more than 50 wind reports.
This and additional information on this topic can be found at:
Severe weather outlooks are made to help set the stages for a severe weather event. They are used to help determine areas where "watches" may need to be issued as the severe weather treat evolves.