THUNDERSTORMS WILL TRACK ALONG THE FRONT BRINGING HEAVY RAINFALL. THIS IS A PARTICULARLY DANGEROUS SITUATION.Ī BOUNDARY WILL CONTINUE TO REMAIN STATIONARY ACROSS SOUTHERN LEAD TO SIGNIFICANT.WIDESPREAD FLASH FLOODING. VERY HEAVY RAINFALL THROUGH THE MIDDLE OF THIS WEEK WILL LIKELY These watches are issued by local NWS Weather Forecast Offices, not the Storm Prediction Center.īelow 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 watches are issued when there is a higher-than-normal risk of widespread, life-threatening flash flooding. 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. 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.
These watches have generally (but not always) 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 (WPC)'s excessive rainfall outlooks. While historically applied only to severe thunderstorm, tornado and flash flood watches (i.e., severe local storm "polygonal" events), PDS wording could theoretically be applied to other types of weather watches (such as winter storm, high wind, hurricane, or fire weather watches) when an enhanced threat for such conditions exists. Johns for the Aptornado outbreak across the southern and central Great Plains.
The first PDS tornado watch was issued by Robert H. 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. Ed Ferguson, Deputy Director of the National Severe Storms Forecast Center (NSSFC), suggested to Lead Forecaster Jack Hales that the guidance center could provide an opportunity to give more resolution to the tornado watch product.
The short history of the origin of the option of issuing a tornado watch with the enhanced PDS wording occurred during the winter of 1981–82 when the Severe Local Storms (SELS) unit transitioned to a more flexible method of issuing weather products. 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. 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. 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 wildfire. A particularly dangerous situation ( PDS) tag is enhanced wording first used by the Storm Prediction Center (SPC), 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.
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