Storm Prediction Center

The Storm Prediction Center began in 1952 as SELS (Severe Local Storms Unit), the U.S. Weather Bureau in Washington, D.C. In 1954, the unit moved its forecast operations to Kansas City, Missouri. SELS began issuing convective outlooks for predicted thunderstorm activity in 1955, and began issuing radar summaries in three-hour intervals in 1960; with the increased duties of compiling and disseminating radar summaries, this unit became the National Severe Storms Forecast Center (NSSFC) in 1966, remaining headquartered in Kansas City. In 1968, the National Severe Storms Forecast Center began issuing status reports on weather watches; the agency then made its first computerized data transmission in 1971. Since the agency's relocation to Norman, the 557th Weather Wing at Offutt Air Force Base would assume control of issuing the Storm Prediction Center's severe weather products in the event that the SPC is no longer able to issue them in the event of an outage (such as a computer system failure or building-wide power disruption) or emergency (such as an approaching strong tornadic circulation or tornado on the ground) affecting the Norman campus; on April 1, 2009, the SPC reassigned responsibilities for issuing the center's products in such situations to the 15th Operational Weather Squadron based out of Scott Air Force Base. On March 17, 2025, ABC News, reporting from the word of an anonymous NOAA spokesperson, stated the Storm Prediction Center was set to be closed by the Department of Government Efficiency (DOGE), a branch of the U.S. government created by President Donald Trump to eliminate government waste. DOGE had announced other NOAA office terminations during March 2025. ABC News also reported the SPC office was listed on DOGE's website, however, as of March 18, DOGE's website says its most recent update was on March 11. Brief history timeline • 1948: Following Weather Bureau (WB) researchers' work by on a 20 March tornado at Tinker AFB, two officers (Fawbush and Miller) successfully predict another one five days later on 25 March at same base, given responsibility for AF tornado predictions. • 1951: Severe Weather Warning Center (SWWC) established as an Air Weather Service unit, headed by Fawbush and Miller. • 1952: WB establishes its own Weather Bureau-Army-Navy (WBAN) Analysis Center in Washington in March as a trial unit, made permanent on 21 May as the Weather Bureau Severe Weather Unit (SWU). • 1953: SWU renamed Severe Local Storm (SELS) Warning Center on 17 June. • 1954: SELS relocates from the WBAN Center in Washington to the WB's District Forecast Office (DFO) in downtown Kansas City in September. • 1955: National Severe Storms Project (NSSP) formed SELS' as research component. • 1958: SELS assumes authority for all public severe weather forecasts. • 1962: Some from NSSP move to Norman's Weather Radar Laboratory to work with a new Weather Surveillance Radar-1957 (WSR-57). • 1964: Remainder of NSSP moves to Norman and is reorganized as National Severe Storms Laboratory (NSSL). • 1965: Environmental Science Services Administration (ESSA) formed, and entire WB office (SELS and DFO) in Kansas City renamed National Severe Storms Forecast Center (NSSFC). • 1976: Techniques Development Unit (TDU) established in April to provide software development and evaluate forecast methods. • 1995: NSSFC renamed Storm Prediction Center (SPC) in October. • 1997: SPC moves from Kansas City to Norman. • 2006: SPC moves a few miles south to the National Weather Center (NWC) on the University of Oklahoma Research Campus. • 2023: On February 15, 2023, Meteorologist Elizabeth Leitman becomes the first woman at the SPC to issue a convective weather watch. ==Overview==

The Storm Prediction Center is responsible for forecasting the risk of severe weather caused by severe thunderstorms, specifically those producing tornadoes, hail of in diameter or larger, and/or winds of [50 knots] or greater. The agency also forecasts hazardous winter and fire weather conditions. It does so primarily by issuing convective outlooks, severe thunderstorm watches, tornado watches and mesoscale discussions. Many SPC forecasters and support staff are heavily involved in scientific research into severe and hazardous weather. This involves conducting applied research and writing technical papers, developing training materials, giving seminars and other presentations locally and nationwide, attending scientific conferences, and participating in weather experiments. ==Convective outlooks==

The Storm Prediction Center issues convective outlooks (AC), consisting of categorical and probabilistic forecasts describing the general threat of severe convective storms over the contiguous United States for the next six to 192 hours (Day 1 through Day 8). These outlooks are labeled and issued by day, and are issued up to five times per day. In April 2011, the SPC introduced a new graphical format for its categorical and probability outlooks, which included the shading of risk areas (with the colors corresponding to each category, as mentioned above, being changed as well) and population, county/parish/borough and interstate overlays. The new shaded maps also incorporated a revised color palette for the shaded probability categories in each outlook. In 2013, the SPC incorporated a small table under the Convective Outlook's risk category map that indicates the total coverage area by square miles, the total estimated population affected and major cities included within a severe weather risk area. Public severe weather outlooks (PWO) are issued when a significant or widespread outbreak is expected, especially for tornadoes. From November to March, it can also be issued for any threat of significant tornadoes in the nighttime hours, noting the lower awareness and greater danger of tornadoes at that time of year. The Storm Prediction Center broadened this system beginning on October 22, 2014 by adding two new risk categories to the three used originally. The new categories that were added are a "marginal risk" (replacing the "SEE TEXT" contours, see below) and an "enhanced risk". The latter is used to delineate areas where severe weather will occur that would fall under the previous probability criteria of an upper-end slight risk, but do not warrant the issuance of a moderate risk. In order from least to greatest threat, these categories are ranked as: marginal, slight, enhanced, moderate, and high. Conditional Intensity Groups (CIG) In January 2026, the Storm Prediction Center outlined three additional "conditional" risk levels that were implemented in March of the same year. These three levels, titled CIG1, CIG2, and CIG3, are utilized to communicate increasing intensity of significant severe weather hazards on a conditional basis. Issuance and usage Convective outlooks are issued by the Storm Prediction Center in Zulu time (also known as Universal Coordinated Time or UTC). Day 3 outlooks refer to the day after tomorrow, issued twice daily since August 13, 2024 at 0730Z in Daylight Saving Time or 0830Z in Standard Time and 1930Z and include the same products (categorical outline, text description, and probability graph) as the Day 2 outlook. As of June 2012, the SPC forecasts general thunderstorm risk areas. Higher probability forecasts are less and less likely as the forecast period increases due to lessening forecast ability farther in advance. Day 3 moderate risks are quite rare; these have been issued only twenty-two times since the product became operational (most recently for April 28, 2025). Day 3 high risks are never issued and the operational standards do not allow for such. This is most likely because it would require both a very high degree of certainty (60%) for an event which was still at least 48 hours away and a reasonable level of confidence that said severe thunderstorm outbreak would include significant severe weather (EF2+ tornadoes, hurricane-force winds, and/or egg-sized hail). Day 4–8 outlooks are the longest-term official SPC Forecast Product, and often change significantly from day to day. This extended forecast for severe weather was an experimental product until March 22, 2007, when the Storm Prediction Center incorporated it as an official product. Areas are delineated in this forecast that have least a 15% or 30% chance of severe weather in the Day 4–8 period (equivalent to a slight risk and an enhanced risk, respectively); as forecaster confidence is not fully resolute on how severe weather will evolve more than three days out, the Day 4–8 outlook only outlines the areas in which severe thunderstorms are forecast to occur during the period at the 15% and 30% likelihood, and does not utilize other categorical risk areas or outline where general (non-severe) thunderstorm activity will occur. Local forecast offices of the National Weather Service, radio and television stations, and emergency planners often use the forecasts to gauge the potential severe weather threats to their areas. Even after the marginal and enhanced risk categories were added in October 2014, some television stations have continued to use the original three-category system to outline forecasted severe weather risks (though stations that do this may utilize in-house severe weather outlooks that vary to some degree from the SPC convective outlooks), while certain others that have switched to the current system have chosen not to outline marginal risk areas. Generally, the convective outlook boundaries or lines – general thunderstorms (light green), marginal (dark green), slight (yellow), enhanced (orange), moderate (red) and high (purple) – will be continued as an arrow or line not filled with color if the risk area enters another country (Canada or Mexico) or across waters beyond the United States coastline. This indicates that the risk for severe weather is also valid in that general area of the other side of the border or oceanic boundary. ==Mesoscale discussions==

SPC mesoscale discussions (MDs) once covered convection (mesoscale convective discussions [MCDs]) and precipitation (mesoscale precipitation discussions [MPDs]); MPDs are now issued by the Weather Prediction Center (WPC). MCDs generally precede the issuance of a tornado or severe thunderstorm watch, by one to three hours when possible. Meso-gamma mesoscale discussions are rarely issued by the SPC. , the Storm Prediction Center has issued 44 meso-gamma mesoscale discussions. ==Weather watches==

Watches (WWs) issued by the SPC are generally less than in area and are normally preceded by a mesoscale discussion. Watches are intended to be issued preceding the arrival of severe weather by one to six hours. They indicate that conditions are favorable for thunderstorms capable of producing various modes of severe weather, including large hail, damaging straight-line winds and/or tornadoes. In the case of severe thunderstorm watches organized severe thunderstorms are expected but conditions are not thought to be especially favorable for tornadoes (although they can occur in such areas where one is in effect, and some severe thunderstorm watch statements issued by the SPC may note a threat of isolated tornadic activity if conditions are of modest favorability for storm rotation capable of inducing them), whereas for tornado watches conditions are thought to be favorable for severe thunderstorms to produce tornadoes. In situations where a forecaster expects a significant threat of extremely severe and life-threatening weather, a watch with special enhanced wording, "Particularly Dangerous Situation" (PDS), is subjectively issued. It is occasionally issued with tornado watches, normally for the potential of major tornado outbreaks, especially those with a significant threat of multiple tornadoes capable of producing F4/EF4 and F5/EF5 damage and/or staying on the ground for long-duration – sometimes uninterrupted – paths. A PDS severe thunderstorm watch is very rare and is typically reserved for derecho events impacting densely populated areas. Watches are not "warnings", where there is an immediate severe weather threat to life and property. Although severe thunderstorm and tornado warnings are ideally the next step after watches, watches cover a threat of organized severe thunderstorms over a larger area and may not always precede a warning; watch "busts" do sometimes occur should thunderstorm activity not occur at all or that which does develop never reaches the originally forecast level of severity. Warnings are issued by local National Weather Service offices, not the Storm Prediction Center, which is a national guidance center. The process of issuing a convective watch begins with a conference call from SPC to local NWS offices. If after collaboration a watch is deemed necessary, the Storm Prediction Center will issue a watch approximation product which is followed by the local NWS office issuing a specific county-based watch product. The latter product is responsible for triggering public alert messages via television, radio stations and NOAA Weather Radio. The watch approximation product outlines specific regions covered by the watch (including the approximate outlined area in statute miles) and its time of expiration (based on the local time zone(s) of the areas under the watch), associated potential threats, a meteorological synopsis of atmospheric conditions favorable for severe thunderstorm development, forecasted aviation conditions, and a pre-determined message informing the public of the meaning behind the watch and to be vigilant of any warnings or weather statements that may be issued by their local National Weather Service office. Watch outline products provide a visual map depiction of the issued watch; the SPC typically delineates watches within this product in the form of "boxes", which technically are represented as either squares, rectangles (horizontal or vertical) or parallelograms depending on the area it covers. Jurisdictions outlined by the county-based watch product as being included in the watch area may differ from the actual watch box; as such, certain counties, parishes or boroughs not covered by the fringes of the watch box may actually be included in the watch and vice versa. Watches can be expanded, contracted (by removing jurisdictions where SPC and NWS forecasters no longer consider there to be a viable threat of severe weather, in which case, the watch box may take on a trapezoidal representation in map-based watch products) or canceled before their set time of expiration by local NWS offices. Example ==Fire weather products==

fire conditions over portions of New Mexico and Texas The Storm Prediction Center also is responsible for issuing fire weather outlooks (FWD) for the continental United States. These outlooks are a guidance product for local, state and federal government agencies, including local National Weather Service offices, in forecasting the potential for wildfires. The outlooks issued are for Day 1, Day 2, and Days 3–8. The Day 1 product is issued at 4:00 a.m. Central Time and is updated at 1700Z, and is valid from 1200Z to 1200Z the following day. The Day 2 outlook is issued at 1000Z and is updated at 2000Z for the forecast period of 1200Z to 1200Z the following day. The Day 3–8 outlook is issued at 2200Z, and is valid from 1200Z two days after the current calendar date to 1200Z seven days after the current calendar date. ==See also==