Storm Prediction Center


The Storm Prediction Center is a US government agency that is part of the National Centers for Environmental Prediction, operating under the control of the National Weather Service, which in turn is part of the National Oceanic and Atmospheric Administration of the United States Department of Commerce.
Headquartered at the National Weather Center in Norman, Oklahoma, the Storm Prediction Center is tasked with forecasting the risk of severe thunderstorms and tornadoes in the contiguous United States. It issues convective outlooks, [|mesoscale discussions], and [|watches] as a part of this process. Convective outlooks are issued for the following eight days, and detail the risk of severe thunderstorms and tornadoes during the given forecast period, although tornado, hail and wind details are only available for Days 1 and 2. Day 3 uses a probabilistic scale from a Marginal to Moderate risk, while Days 4–8 use a probabilistic scale determining the probability for a severe weather event in percentage categories.
Mesoscale discussions are issued to provide information on certain individual regions where severe weather is becoming a threat and states whether a watch is likely and details thereof, particularly concerning conditions conducive for the development of severe thunderstorms in the short term, as well as situations of isolated severe weather when watches are not necessary. Watches are issued when atmospheric conditions favor the development of severe weather. Once a storm/tornado is imminent or occurring, a warning will be issued, and it usually precedes the onset of severe weather by one hour, although this sometimes varies depending on certain atmospheric conditions that may inhibit or accelerate convective development.
The agency is also responsible for forecasting fire weather in the contiguous U.S., issuing fire weather outlooks for Days 1, 2, and 3–8, which detail areas with various levels of risk for fire conditions.

History

The Storm Prediction Center began in 1952 as SELS, 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 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. On April 2, 1982, the agency issued the first "Particularly Dangerous Situation" watch, which indicates the imminent threat of a major severe weather event over the watch's timespan. In 1986, the NSSFC introduced two new forecast products: the Day 2 Convective Outlook and the Mesoscale Discussion.
In October 1995, the National Severe Storms Forecast Center relocated its operations to Norman, Oklahoma, and was rechristened the Storm Prediction Center. At that time, the guidance center was housed at Max Westheimer Airport, co-located in the same building as the National Severe Storms Laboratory and the local National Weather Service Weather Forecast Office. In 1998, the center began issuing the National Fire Weather Outlook to provide forecasts for areas potentially susceptible to the development and spread of wildfires based on certain meteorological factors. The Day 3 Convective Outlook was first issued on an experimental basis in 2000, and was made an official product in 2001.
In 2006, the Storm Prediction Center, National Severe Storms Laboratory and National Weather Service Norman Forecast Office moved their respective operations into the newly constructed National Weather Center, near Westheimer Airport. 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 or emergency 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, 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 researchers' work by on a 20 March tornado at Tinker AFB, two officers successfully predict another one five days later on 25 March at same base, given responsibility for AF tornado predictions.
  • 1951: Severe Weather Warning Center established as an Air Weather Service unit, headed by Fawbush and Miller.
  • 1952: WB establishes its own Weather Bureau-Army-Navy Analysis Center in Washington in March as a trial unit, made permanent on 21 May as the Weather Bureau Severe Weather Unit.
  • 1953: SWU renamed Severe Local Storm Warning Center on 17 June.
  • 1954: SELS relocates from the WBAN Center in Washington to the WB's District Forecast Office in downtown Kansas City in September.
  • 1955: National Severe Storms Project 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.
  • 1964: Remainder of NSSP moves to Norman and is reorganized as National Severe Storms Laboratory.
  • 1965: Environmental Science Services Administration formed, and entire WB office in Kansas City renamed National Severe Storms Forecast Center.
  • 1976: Techniques Development Unit established in April to provide software development and evaluate forecast methods.
  • 1995: NSSFC renamed Storm Prediction Center in October.
  • 1997: SPC moves from Kansas City to Norman.
  • 2006: SPC moves a few miles south to the National Weather Center 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 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.
There is a three-stage process in which the area, time period, and details of a severe weather forecast are refined from a broad-scale forecast of potential hazards to a more specific and detailed forecast of what hazards are expected, and where and in what time frame they are expected to occur. If warranted, forecasts will also increase in severity through this three-stage process.
The Storm Prediction Center employs a total of 43 personnel, including five lead forecasters, ten mesoscale/outlook forecasters, and seven assistant mesoscale forecasters. 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, 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. These outlooks are labeled and issued by day, and are issued up to five times per day.
The categorical levels of risks are TSTM, "MRGL" ; "SLGT" ; "ENH" ; "MDT" ; and "HIGH". Significant severe areas refer to a threat of increased storm intensity that is of "significant severe" levels.
In April 2011, the SPC introduced a new graphical format for its categorical and probability outlooks, which included the shading of risk areas 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 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.

Categories

A marginal risk day indicates storms of only limited organization, longevity, coverage and/or intensity, typically isolated severe or near-severe storms with limited wind damage, large hail and possibly a low tornado risk. Wind gusts of at least and hailstones of around in diameter are common storm threats within a marginal risk; depending on the sufficient wind shear, a tornado – usually of weak intensity and short duration – may be possible. This category replaced the "SEE TEXT" category on October 22, 2014.
A slight risk day typically will indicate that the threat exists for scattered severe weather, including scattered wind damage, scattered severe hail and/or isolated tornadoes. During the peak severe weather season, most days will have a slight risk somewhere in the United States. Isolated significant severe events are possible in some circumstances, but are generally not widespread.
An enhanced risk day indicates that there is a greater threat for severe weather than that which would be indicated by a slight risk, but conditions are not adequate for the development of widespread significant severe weather to necessitate a moderate category, with more numerous areas of wind damage, along with severe hail and several tornadoes. Severe storms are expected to be more concentrated and of varying intensities. These days are quite frequent in the peak severe weather season and occur occasionally at other times of year. This risk category replaced the upper end of "slight" on October 22, 2014, although a few situations that previously warranted a moderate risk were reclassified as enhanced.
A moderate risk day indicates that more widespread and/or more dangerous severe weather is possible, with significant severe weather often more likely. Numerous tornadoes, more widespread or severe wind damage and/or very large/destructive hail could occur. Major events, such as large tornado outbreaks or widespread straight-line wind events, are sometimes also possible on moderate risk days, but with greater uncertainty. Moderate risk days are not terribly uncommon, and typically occur several times a month during the peak of the severe weather season, and occasionally at other times of the year. Slight and enhanced risk areas typically surround areas under a moderate risk, where the threat is lower.
A high risk day indicates a considerable likelihood of significant to extreme severe weather, generally a major tornado outbreak or an extreme derecho event. On these days, the potential exists for extremely severe and life-threatening weather. This includes a large number of tornadoes - many of which will likely be strong to violent and on the ground for a half-hour or longer, or widespread and very destructive straight-line winds, likely in excess of. Hail cannot verify or produce a high risk on its own, although such a day usually involves a threat for widespread very large and damaging hail as well. Many of the most prolific severe weather days were high risk days. Such days are rare; a high risk is typically issued only a few times each year. High risk areas are usually surrounded by a larger moderate risk area, where uncertainty is greater or the threat is somewhat lower.
The Storm Prediction Center began asking for public comment on proposed categorical additions to the Day 1-3 Convective Outlooks on April 21, 2014, for a two-month period. 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" 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.