Storm Prediction Center

The Storm Prediction Center (SPC) is a US government agency that is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service (NWS), which in turn is part of the National Oceanic and Atmospheric Administration (NOAA) of the United States Department of Commerce (DoC).

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 (issued separately for Day 1, Day 2, Day 3, and Days 4–8), 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 (A Day 3 High risk cannot be issued), while Days 4–8 use a probabilistic scale determining the probability for a severe weather event in percentage categories (15%/yellow and 30%/orange).

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 (such as via weather spotters, radar, river gages, etc), 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 (indicating conditions that are favorable for wildfires) 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 (such as fire levels and fire alerts).

History

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.

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

{| class="wikitable"

|+ Categorical outlook and Conditional Intensity Group conversion

|colspan="5"|Tornado probability to categorical outlook/CIG conversion (Days 1–2)

! scope="col" | Outlook probability

! scope="col" | <CIG1

! scope="col" | CIG1

! scope="col" | CIG2

! scope="col" | CIG3

| scope="row" style="background:green;”|2% || scope="row" style="background:lime;”|MRGL || scope="row" style="background:lime;”|MRGL || scope="row" style="background:yellow;"|SLGT ||

| scope="row" style="background:brown;"|5% || scope="row" style="background:yellow;"|SLGT || scope="row" style="background:yellow;"|SLGT || scope="row" style="background:orange;"|ENH ||

| scope="row" style="background:yellow;"|10% || scope="row" style="background:yellow;"|SLGT || scope="row" style="background:orange;"|ENH || scope="row" style="background:orange;"|ENH || scope="row" style="background:orange;"|ENH

| scope="row" style="background:red;"|15% || scope="row" style="background:orange;"|ENH || scope="row" style="background:orange;"|ENH || scope="row" style="background:red;"|MDT || scope="row" style="background:red;"|MDT

| scope="row" style="background:magenta;"|30% || scope="row" style="background:orange;"|ENH || scope="row" style="background:red;"|MDT || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:magenta;"|HIGH

| scope="row" style="background:#912CEE; color:white"|45% || scope="row" style="background:orange;"|ENH || scope="row" style="background:red;"|MDT || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:magenta;"|HIGH

| scope="row" style="background:#104E8B; color:white;"|60% || scope="row" style="background:orange;"|ENH || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:magenta;"|HIGH

|colspan="5"|Wind probability to categorical outlook/CIG conversion (Days 1–2)

thumb|"Hazard Intensites in SPC MDs and Outlooks", a presentation on the future of convective outlooks by the SPC

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. 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.

! Outlook probability !! CRITICAL !! DRY TSTM

| < 10% || ||No Area

| 10% || || style="background:orange;"|ELEVATED

| < 40% || No Area ||

| 40% || style="background:orange;"|ELEVATED || style="background:red;"|CRITICAL

| 70% || style="background:red;"|CRITICAL ||

</div>

thumb|right|Day 1 Fire Outlook map issued by the Storm Prediction Center on April 10, 2019, depicting [[List of Storm Prediction Center extremely critical days|extremely critical 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.

References

External links

SPC products descriptions