A particularly dangerous situation (PDS) is a type of enhanced wording first used by the National Weather Service's Storm Prediction Center in Norman, Oklahoma on certain severe weather watches. It is issued at the discretion of the forecaster composing the watch and implies that there is an enhanced risk of very severe and life-threatening weather, usually a major tornado outbreak or (much less often) a long-lived, extreme derecho event, but possibly another weather hazard. On April 24, 2011, the National Weather Service office in Memphis 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.
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.
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 (i.e. Severe Local Storm "polygonal" events), PDS wording could theoretically be applied to other types of weather watches (i.e., Winter Storm, High Wind, Hurricane, or Fire Weather watches) when an enhanced threat for such conditions exists. 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 WPC's Excessive Rainfall Outlooks.
PDS tornado watches are issued when there is a higher than normal risk of multiple strong, violent tornadoes in the watch area (usually amounting to damage consistent with EF4 or EF5 tornadoes), also including significant wind and hail damage, when in addition to tornadoes. 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. They represent about 90% of PDS watches issued.
PDS severe thunderstorm watches are issued when there is a higher than normal risk of severe thunderstorm winds capable of major structural damage (in addition to large hail and perhaps a few isolated tornadoes), usually due to a strong and persistent derecho. These watches are very rare (an average of only two each year), as the risk for tornadoes must remain low enough to not warrant a tornado watch (a normal tornado watch would be issued if the tornado risk is significant alongside the extreme wind threat).
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 the NWS Local Forecast Offices, not the Storm Prediction Center.
PDS tornado warnings are currently issued on an experimental basis by five Forecast Offices in Kansas and Missouri. The criteria for a PDS warning is when a tornado on the ground has been spotted or confirmed, or a significant tornado is expected (due to radar signatures). The intention of this experimental warning may be to replace the loosely-defined tornado emergency. These are the first warnings issued with PDS wording, and like PDS flash flood watches, are issued by local forecast offices.
Read more about Particularly Dangerous Situation: Sample PDS Tornado Watch, Sample PDS Severe Thunderstorm Watch, Sample PDS Flash Flood Watch, Sample PDS Tornado Warning
Famous quotes containing the words dangerous and/or situation:
“Charity is a cop-out so traditionally female in its apparent self-effacement that there seems resonant comfort in it. We’re no longer supposed to serve the imaginations of men who have dominated us. We are to give up ourselves instead to those whose suffering is greater than our own. Looking down is just as distorting as looking up and as dangerous in perpetuating hierarchies.”
—Jane Rule (b. 1931)
“All of Western tradition, from the late bloom of the British Empire right through the early doom of Vietnam, dictates that you do something spectacular and irreversible whenever you find yourself in or whenever you impose yourself upon a wholly unfamiliar situation belonging to somebody else. Frequently it’s your soul or your honor or your manhood, or democracy itself, at stake.”
—June Jordan (b. 1939)