Particularly Dangerous Situation
A Particularly Dangerous Situation is a type of enhanced wording first used by the Storm Prediction Center, a national guidance center of the United States National Weather Service, for tornado watches and eventually expanded to use for other severe weather watches and warnings by local NWS forecast offices. It is issued at the discretion of the forecaster composing the watch or warning and implies that there is an enhanced risk of very severe and life-threatening weather, usually a major tornado outbreak or a long-lived, extreme derecho event, but possibly another weather hazard such as an exceptional flash flood or fire.
PDS watches are quite uncommon; less than 3% of watches issued by the SPC from 1996 to 2005 were PDS watches, or an average of 24 each year. When a PDS watch is issued, there are often more PDS watches issued for the same weather system, even on the same day during major outbreaks, so the number of days per year that a PDS watch is issued is significantly lower.
Background
The short history of the origin of the option of issuing a tornado watch with the enhanced Particularly Dangerous Situation wording occurred during the winter of 1981-82 when the Severe Local Storms unit transitioned to a more flexible method of issuing weather products. Ed Ferguson, Deputy Director of the National Severe Storms Forecast Center, suggested to Lead Forecaster Jack Hales that the guidance center could provide an opportunity to give more resolution to the tornado watch product. Hales suggested the PDS option to identify areas where, a few times each year, conditions are most likely to aid in the development of large and intense tornadoes. The first PDS tornado watch was issued by Robert H. Johns for the April 2, 1982 tornado outbreak across the southern and central Great Plains.While historically applied only to severe thunderstorm, tornado and flash flood watches, PDS wording could theoretically be applied to other types of weather watches when an enhanced threat for such conditions exists. These watches have generally been issued during a high risk or an upper-end moderate risk either of severe storms from the SPC's convective outlooks or of flash flooding from the Weather Prediction Center 's Excessive Rainfall Outlooks.
On April 24, 2011, the National Weather Service Weather Forecast Office in Memphis, Tennessee issued the first PDS flash flood watch to highlight the threat for widespread, significant and potentially life-threatening flash flooding due to repeated rounds of severe thunderstorms.
On December 19, 2017 and August 3, 2018, the National Weather Service Weather Forecast Office in Reno, Nevada issued PDS Red Flag Warnings to highlight the threat for potentially life-threatening fire danger due to strong gusty winds and low humidity.
Issuance
PDS Flash Flood Watch
PDS flash flood watches are issued when there is a higher-than-normal risk of widespread, life-threatening flash flooding. These watches are issued by local NWS Weather Forecast Offices, not the Storm Prediction Center.Below is the first PDS Flash Flood Watch, which was issued by the National Weather Service Forecast Office in Memphis, Tennessee on April 24, 2011, as mentioned above.
PDS Flash Flood Warning
PDS flash flood warnings are issued when there is a higher than normal risk of widespread, life-threatening flash flooding. Like PDS Flash Flood Watches, they are issued by the local NWS Weather Forecast Offices, rather than the Storm Prediction Center. Recently, they have been issued as PDS Flash Flood Emergencies, most notably by the National Weather Service offices in Houston, TX and Corpus Christi, TX.This warning was issued in the morning of May 30, 2018 by the National Weather Service Forecast Office in Greenville-Spartanburg, South Carolina, while Subtropical Storm Alberto was affecting the area. It also contains the Flash Flood Emergency phrase, which further underscores the risk of life-threatening flash flooding.
PDS Red Flag Warning
PDS red flag warnings are issued by the National Weather Service to inform the public that there is an unusually high threat of wildland fire combustion, and rapid spread of wildfires, due to very dry fuels, very low humidity levels, and strong winds.The PDS Red Flag Warning below was issued by the National Weather Service in Reno, Nevada on December 19, 2017.
On August 3, 2018, the National Weather Service in Reno, Nevada issued another PDS red flag warning to communicate the threat of life-threatening fire danger due to strong gusty winds and low humidity.
PDS Severe Thunderstorm Watch
PDS severe thunderstorm watches are issued when there is a higher than normal risk of severe thunderstorm winds capable of major structural damage, usually due to a strong and persistent derecho. These watches are very rare, as the risk for tornadoes must remain low enough to not warrant a tornado watch.This PDS Severe Thunderstorm Watch shown below was issued by the Storm Prediction Center in Norman, Oklahoma on July 19, 2019 for an extreme wind threat in northern Wisconsin.
PDS Special Marine Warning
PDS Special marine warnings are issued by the National Weather Service to inform mariners of weather conditions that present a considerable threat to life and property.On April 19, 2018, the Baltimore/Washington, D.C. forecast office upgraded a Special Marine Warning to PDS status as a gust front approached Chesapeake Bay.
PDS Special Weather Statement
PDS special weather statements are usually for issued by the NWS for hazards that do not have a specific code of their own, and pose an exceptionally high risk of damage and loss of life.The PDS Special Weather Statement below was issued by the National Weather Service in Buffalo, New York on December 11, 2013, regarding extreme amounts of lake effect snow to impact the defined area. The same office issued a PDS Special Weather Statement for hurricane-force winds forecast to hit the Buffalo area on February 24, 2019.
PDS Tornado Watch
PDS tornado watches are issued when there is a higher than normal risk of multiple strong to violent tornadoes – especially those that are predicted to be long-track in nature, with path lengths of more than 20 miles – in the watch area, in addition to including significant wind and hail damage. This enhanced wording in a Tornado Watch is meant to alert the public of the potential for very life-threatening severe weather. While there are no set criteria for a PDS watch to be issued, they are usually issued when the potential exists for a major tornado outbreak. These types of tornado watches represent about 90% of PDS watches issued by the Storm Prediction Center. PDS Tornado Watches are often issued on high risk days for severe weather.The PDS Tornado Watch shown below was issued on May 20, 2019.
The most recent PDS Tornado Watches were Tornado Watch 106 and 110 on April 12, 2020 covering parts of Alabama, Mississippi, Arkansas, Louisiana and the Florida Panhandle.
PDS Tornado Warning
PDS tornado warnings are currently issued on an experimental basis by the 38 National Weather Service Weather Forecast Offices within the Central Region. The criteria for a PDS warning are when a tornado on the ground has been spotted or confirmed, or a significant tornado is expected based on radar signatures. While the intention of this experimental warning may be to replace the loosely defined tornado emergency, PDS tornado warnings are structured as the second highest level of tornado warning within the Impact Based Warning system ; a tornado emergency, the highest warning level, is used within the United States for destructive tornadoes approaching more densely populated areas. These are the first warnings issued with PDS wording, and like PDS flash flood watches, are issued by local forecast offices.Below is an example of a PDS Tornado Warning from the Rochelle/Fairdale, IL Tornado on April 9, 2015 In Taylorville a EF-3 Was confirmed by every confirmer And NWS In Lincoln issued a PDS Tornado Warning in December 1st 2018
PDS Wind Chill Warning
PDS wind chill warnings are issued when there is an enhanced risk of frost bite, hypothermia, and eventually death due to extremely low wind chills. These warnings are issued by the National Weather Service Weather Forecast Offices rather than the Storm Prediction Center.The PDS Wind Chill Warning shown below was issued by the National Weather Service in the Twin Cities on January 5, 2014.