Particularly Dangerous Situation

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A Particularly Dangerous Situation (PDS) is a type of 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. 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 (much less often) a long-lived, extreme derecho event, but possibly another weather hazard such as an exceptional flash flood or fire.[1][2]

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.[3] 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[edit]

The short history of the origin of the option of issuing a tornado watch with the enhanced Particularly Dangerous Situation (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. 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. 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.[4]

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. 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.

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[edit]

PDS Flash Flood Watch[edit]

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.[5]

Particularly Dangerous Situation (PDS) Flash Flood Watch
URGENT - IMMEDIATE BROADCAST REQUESTED
 FLOOD WATCH
 NATIONAL WEATHER SERVICE MEMPHIS TN
 239 PM CDT SUN APR 24 2011
 
 ...VERY HEAVY RAINFALL THROUGH THE MIDDLE OF THIS WEEK WILL LIKELY
 LEAD TO SIGNIFICANT...WIDESPREAD FLASH FLOODING...
 
 ...THIS IS A PARTICULARLY DANGEROUS SITUATION...
 
 A BOUNDARY WILL CONTINUE TO REMAIN STATIONARY ACROSS SOUTHERN
 MISSOURI INTO KENTUCKY THROUGH MONDAY. REPEATED ROUNDS OF
 THUNDERSTORMS WILL TRACK ALONG THE FRONT BRINGING HEAVY RAINFALL.
 THEN A LOW PRESSURE SYSTEM WILL TRACK ALONG IT INTO MISSOURI AND
 PUSH THE FRONT FURTHER SOUTH TO ALONG THE I-40 CORRIDOR MONDAY
 NIGHT THROUGH TUESDAY NIGHT. THIS WILL SHIFT THE HEAVY RAIN AXIS
 FURTHER SOUTH TO ALONG AND JUST NORTH OF THE I-40 CORRIDOR.
 
 A SECOND LOW PRESSURE SYSTEM WILL TRACK ALONG THE NEWLY STALLED
 BOUNDARY AND SET OFF ADDITIONAL TRAINING THUNDERSTORMS LATE
 TUESDAY NIGHT AND WEDNESDAY. THE FINAL COLD FRONT WILL PASS
 THROUGH LATE WEDNESDAY AFTERNOON...ENDING THE PERSISTENT HEAVY
 RAINFALL.
 
 ARZ026>028-035-036-048-049-058-MSZ001>014-TNZ003-004-019>021-
 048>055-088>092-250400-
 /O.NEW.KMEG.FF.A.0007.110426T0000Z-110428T0000Z/
 /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
 CRAIGHEAD-POINSETT-MISSISSIPPI-CROSS- 
 CRITTENDEN-ST. FRANCIS-
 LEE AR-PHILLIPS-DESOTO-MARSHALL-BENTON MS-TIPPAH-ALCORN-
 TISHOMINGO-TUNICA-TATE-PRENTISS- 
 COAHOMA-QUITMAN-PANOLA-LAFAYETTE- 
 
 UNION-WEAKLEY-HENRY-DYER-GIBSON-CARROLL-LAUDERDALE-TIPTON-HAYWOOD-
 CROCKETT-MADISON-CHESTER-HENDERSON- 
 DECATUR-SHELBY-FAYETTE-
 HARDEMAN-MCNAIRY-HARDIN-
 INCLUDING THE CITIES OF...JONESBORO...HARRISBURG...BLYTHEVILLE...
 WYNNE...WEST MEMPHIS...FORREST CITY...HELENA... 
 SOUTHAVEN...
 OLIVE BRANCH...CORINTH...IUKA...TUNICA...[[Booneville, 
 Mississippi|BOONEVILLE]]...
 CLARKSDALE...BATESVILLE...OXFORD...NEW ALBANY... 
 MARTIN...
 DRESDEN...PARIS...DYERSBURG...HUMBOLDT...MILAN...HUNTINGDON...
 COVINGTON...JACKSON...LEXINGTON...BARTLETT...GERMANTOWN...
 COLLIERVILLE...MEMPHIS...MILLINGTON...SOMERVILLE... 
 BOLIVAR...
 SAVANNAH
 239 PM CDT SUN APR 24 2011
 
 ...FLASH FLOOD WATCH IN EFFECT FROM MONDAY EVENING THROUGH
 WEDNESDAY EVENING...
 
 THE NATIONAL WEATHER SERVICE IN MEMPHIS HAS ISSUED A
 
 * FLASH FLOOD WATCH FOR PORTIONS OF EAST ARKANSAS...NORTH MISSISSIPPI
 AND WEST TENNESSEE...INCLUDING THE FOLLOWING AREAS...IN EAST
 ARKANSAS...CRAIGHEAD...CRITTENDEN...CROSS...
 LEE...MISSISSIPPI...PHILLIPS...POINSETT AND ST. FRANCIS. IN
 NORTH MISSISSIPPI...ALCORN...BENTON...COAHOMA...DESOTO...
 LAFAYETTE...MARSHALL...PANOLA...PRENTISS...QUITMAN...TATE...
 TIPPAH...TISHOMINGO...TUNICA AND UNION. IN WEST TENNESSEE...
 CARROLL...CHESTER...CROCKETT...DECATUR...DYER...FAYETTE...
 GIBSON...HARDEMAN...HARDIN...HAYWOOD...HENDERSON...HENRY...
 LAUDERDALE...MADISON...MCNAIRY...SHELBY...TIPTON AND WEAKLEY.
 
 * FROM MONDAY EVENING THROUGH WEDNESDAY EVENING.
 * THIS IS A PARTICULARLY DANGEROUS SITUATION
 * TOTAL RAINFALL AMOUNTS OF 5 TO 8 INCHES ARE EXPECTED ALONG AND
 NORTH OF I-40 WITH 2 TO 5 INCHES EXPECTED SOUTH OF I-40. LOCALLY
 HIGHER AMOUNTS ARE LIKELY.
 
 * RAINFALL AMOUNTS SUCH AS THESE MAY LEAD TO WIDESPREAD...
 SIGNIFICANT...AND LIFE THREATENING FLASH FLOODING. THIS EVENT
 MAY BE AS SEVERE AS THE MAY 1–2, 2010 FLOODING IN PLACES. FLASH
 FLOODING OF CITIES...RURAL AREAS...RIVERS...AND SMALL STREAMS
 ARE POSSIBLE.
 
 PRECAUTIONARY/PREPAREDNESS ACTIONS...
 
 A FLASH FLOOD WATCH MEANS THAT CONDITIONS MAY DEVELOP THAT LEAD
 TO FLASH FLOODING. FLASH FLOODING IS A VERY DANGEROUS SITUATION.
 
 YOU SHOULD MONITOR LATER FORECASTS AND BE PREPARED TO TAKE ACTION
 SHOULD FLASH FLOOD WARNINGS BE ISSUED.
 
 &&
 
 $$
 
 ARZ008-009-017-018-MOZ113-115-TNZ001-002-250400-
 /O.EXT.KMEG.FF.A.0006.000000T0000Z-110428T0000Z/
 /00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
 RANDOLPH-CLAY-LAWRENCE-GREENE-DUNKLIN-PEMISCOT-LAKE-OBION-
 INCLUDING THE CITIES OF...WALNUT RIDGE...PARAGOULD...KENNETT...
 CARUTHERSVILLE...UNION CITY
 239 PM CDT SUN APR 24 2011
 
 ...FLASH FLOOD WATCH NOW IN EFFECT THROUGH WEDNESDAY EVENING...
 
 THE FLASH FLOOD WATCH IS NOW IN EFFECT FOR
 
 * PORTIONS OF EAST ARKANSAS...SOUTHEAST MISSOURI AND WEST
 TENNESSEE...INCLUDING THE FOLLOWING AREAS...IN EAST ARKANSAS...
 CLAY...GREENE...LAWRENCE AND RANDOLPH. IN SOUTHEAST MISSOURI...
 DUNKLIN AND PEMISCOT. IN WEST TENNESSEE...LAKE AND OBION.
 
 * THROUGH WEDNESDAY EVENING.
 * THIS IS A PARTICULARLY DANGEROUS SITUATION
 * ADDITIONAL RAINFALL AMOUNTS OF 6 TO 9 INCHES ARE EXPECTED.
 LOCALLY HIGHER AMOUNTS ARE LIKELY. THIS...IN COMBINATION OF
 THE 2 TO 4 INCHES THAT HAVE ALREADY FALLEN MAY LEAD TO TOTAL
 RAINFALL AMOUNTS IN EXCESS OF 12 INCHES IN MANY LOCATIONS.
 
 * RAINFALL AMOUNTS SUCH AS THESE WILL LIKELY LEAD TO WIDESPREAD...
 SIGNIFICANT...AND LIFE THREATENING FLASH FLOODING. THIS EVENT
 MAY BE AS SEVERE AS THE MAY 1-2 2010 FLOODING IN MANY PLACES.
 FLASH FLOODING OF CITIES...RURAL AREAS...RIVERS...AND SMALL
 STREAMS ARE POSSIBLE.
 
 PRECAUTIONARY/PREPAREDNESS ACTIONS...
 
 A FLASH FLOOD WATCH MEANS THAT CONDITIONS MAY DEVELOP THAT LEAD
 TO FLASH FLOODING. FLASH FLOODING IS A VERY DANGEROUS SITUATION.
 
 YOU SHOULD MONITOR LATER FORECASTS AND BE PREPARED TO TAKE ACTION
 SHOULD FLASH FLOOD WARNINGS BE ISSUED.
 
 &&
 
 $$
 
 BORGHOFF

PDS Flash Flood Warning[edit]

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.[6]

Particularly Dangerous Situation (PDS) Flash Flood Warning
 NCC111-301630-
 /O.EXT.KGSP.FF.W.0034.000000T0000Z-180530T1630Z/
 00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO
 
 BULLETIN - EAS ACTIVATION REQUESTED
 Flash Flood Warning
 National Weather Service Greenville-Spartanburg SC
 626 AM EDT WED MAY 30 2018
 
 ...FLASH FLOOD EMERGENCY CONTINUES FOR AREAS DOWNSTREAM OF LAKE TAHOMA
 DUE TO POTENTIAL IMMINENT FAILURE OF TAHOMA DAM...MANDATORY
 EVACUATIONS UNDERWAY...
 
 The National Weather Service in Greenville-Spartanburg has extended
 the 
 
 * Flash Flood Warning for...
 Central McDowell County in western North Carolina...
 
 * Until 1230 PM EDT Wednesday.
 * At 611 AM EDT, Emergency Management is reporting that the risk of
 imminent failure remains at Lake Tahoma Dam and mandatory
 evacuations remain in effect.  This emergency evacuation was
 issued at the recommendation of dam engineers who remain on scene
 to monitor the dam.  Lake Tahoma Dam is currently in a Level 1 or
 Imminent Failure Condition.  This condition will continue until
 the engineers have the opportunity to thoroughly inspect the dam
 during daylight hours.  THIS IS AN EXTREMELY DANGEROUS
 SITUATION! MANDATORY EVACUATIONS are underway for ALL residents
 and businesses downstream of Lake Tahoma along Buck Creek and
 along the Catawba River from Buck Creek and Lake Tahoma Rd (NC 80)
 to the mouth of Lake James.  To save your life, please heed all
 county evacuation notices and take action to leave the vicinity
 immediately!
 
 Repeating, this is a FLASH FLOOD EMERGENCY for McDowell County for
 areas downstream of Lake Tahoma and Lake Tahoma Dam to the mouth
 of Lake James along the Catawba River. This is a PARTICULARLY
 DANGEROUS SITUATION. SEEK HIGHER GROUND NOW!
 
 * Repeating, mandatory evacuations remain underway from Lake Tahoma
 Dam at Lake Shore Dr down Lake Tahoma Rd (NC 80) to the confluence
 of the Catawba River near US 70, Resistoflex Rd, and Riverside
 Park. Residences and businesses along US 70 from Lake Tahoma Rd to
 US 221 Business near Garden Creek, as well as areas along Hankins
 Rd. to the mouth of Lake James are included in the mandatory
 evacuation.  LEAVE NOW!
 
 * Evacuees are being asked to seek shelter at the Glenwood Baptist
 Church, the Old Fort Baptist Church, or the YMCA in Marion near
 McDowell Hospital.
 
 * Some locations that are experiencing flooding include...
 Pleasant Gardens, northwest Marion, and Lake James.
 
 * The excessive rainfall over the warned area has caused numerous
 mud slides and additional mud slides are possible near steep
 terrain. The mud slide can consist of rock, mud, vegetation and
 other loose materials and are very powerful.
 
 PRECAUTIONARY/PREPAREDNESS ACTIONS...
 
 Move to higher ground NOW. This is an extremely dangerous and
 life-threatening situation. Do NOT attempt to travel unless you are
 fleeing an area subject to flooding or under an evacuation order.
 
 Most flood deaths occur in vehicles. Do not attempt to cross
 water-covered roadways, bridges, or low-level crossings. Only a few
 inches of rapidly flowing water can carry away your vehicle. It is
 not worth the risk. Please TURN AROUND, DON`T DROWN.
 
 The floodwave along Buck Creek above and below Lake Tahoma will
 increase the risk of landslides, especially in areas where slides
 have occurred in the past. Be especially alert if you are near a
 stream, especially at the base of a mountain or in a cove. Watch
 for loose-moving soil and rocks or a sudden increase in streamflow.
 Leave the area quickly if this is observed. When driving along
 roads where the terrain is steep or rocky, watch and listen for
 falling rocks, mud, trees and other debris.
 
 &&
 
 LAT...LON 3574 8207 3572 8205 3574 8202 3574 8198
 3570 8196 3570 8200 3567 8206 3573 8211
 
 $$
 
 JMP

PDS Red Flag Warning[edit]

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.[7]

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.

Particularly Dangerous Situation (PDS) Red Flag Warning
 URGENT - FIRE WEATHER MESSAGE
 National Weather Service Reno NV
 140 PM PST Tue Dec 19 2017
 
 CAZ273-201500-
 /O.CON.KREV.FW.W.0017.171220T0300Z-171221T0300Z/
 Mono and Eastern Alpine Counties-
 140 PM PST Tue Dec 19 2017
 
 ...RED FLAG WARNING REMAINS IN EFFECT FROM 7 PM THIS EVENING TO
 7 PM PST WEDNESDAY FOR GUSTY WINDS AND LOW HUMIDITY FOR MONO
 COUNTY SOUTH OF MONO LAKE...
 
 ...THIS IS A PARTICULARLY DANGEROUS SITUATION...
 
 AFFECTED AREA...Fire Zone 273 Mono and Eastern Alpine Counties.
 
 Winds...Southwest 25 to 40 mph with gusts up to 70 mph late
 tonight into Wednesday morning. The winds will shift to the
 north by early Wednesday afternoon with speeds of 20 to 30 mph
 and gusts to 55 mph.
 
 Location and timing of strongest wind gusts...The strongest
 wind gusts will be along the 395 corridor tonight into
 Wednesday morning. Wednesday afternoon the strongest gusts
 will be in the Owens and Chalfant Valleys.
 
 Humidity...As low as 10 to 20% tonight and again late
 Wednesday afternoon. Brief recovery near or above 50% is
 possible late Wednesday morning.
 
 Duration...10 to 15 hours, locally up to 20 hours.
 
 Impacts...The combination of gusty winds and low humidity can
 cause fire to rapidly grow in size and intensity.
 
 PRECAUTIONARY/PREPAREDNESS ACTIONS...
 
 This is a particularly dangerous situation with low humidity and
 very high winds. New fires will grow rapidly out of control, in
 some cases people may not be able to evacuate safely in time
 should a fire approach. Avoid outdoor activities that can cause a
 spark near dry vegetation, such as yard work, target shooting, or
 campfires. Follow local fire restrictions. Check weather.gov/reno
 for updates and livingwithfire.info for preparedness tips.
 

PDS Severe Thunderstorm Watch[edit]

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 (accounting 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).[3]

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.[8]

Particularly Dangerous Situation (PDS) Severe Thunderstorm Watch 525
  SEL5
  
  URGENT - IMMEDIATE BROADCAST REQUESTED
  Severe Thunderstorm Watch Number 525
  NWS Storm Prediction Center Norman OK
  550 PM CDT Fri Jul 19 2019
  
  The NWS Storm Prediction Center has issued a
  
  * Severe Thunderstorm Watch for portions of 
    Much of north central and northeastern Wisconsin
    Lake Michigan
  
  * Effective this Friday afternoon and Saturday morning from 550
    PM until 100 AM CDT.
  
  ...THIS IS A PARTICULARLY DANGEROUS SITUATION...
  
  * Primary threats include...
    Widespread damaging winds and scattered significant gusts to 105
      mph expected
    Scattered large hail and isolated very large hail events to 2.5
      inches in diameter possible
    A few tornadoes likely
  
  SUMMARY...An intense supercell cluster in northwestern Wisconsin is
  expected to evolve into a damaging bow echo that will accelerate
  east-southeastward across northern/northeastern Wisconsin this
  evening.  The storm environment will favor swaths of high-end,
  destructive outflow winds potentially exceeding 100 mph.  Tornadoes
  will also be possible with embedded circulations, as well as large
  hail in the next few hours with lingering supercell structures.
  
  The severe thunderstorm watch area is approximately along and 55
  statute miles north and south of a line from 70 miles west northwest
  of Wausau WI to 30 miles northeast of Manitowoc WI. For a complete
  depiction of the watch see the associated watch outline update
  (WOUS64 KWNS WOU5).
  
  PRECAUTIONARY/PREPAREDNESS ACTIONS...
  
  REMEMBER...A Severe Thunderstorm Watch means conditions are
  favorable for severe thunderstorms in and close to the watch area.
  Persons in these areas should be on the lookout for threatening
  weather conditions and listen for later statements and possible
  warnings. Severe thunderstorms can and occasionally do produce
  tornadoes.
  
  &&
  
  OTHER WATCH INFORMATION...CONTINUE...WW 523...WW 524...
  
  AVIATION...A few severe thunderstorms with hail surface and aloft to
  2.5 inches. Extreme turbulence and surface wind gusts to 90 knots. A
  few cumulonimbi with maximum tops to 650. Mean storm motion vector
  29050.
  
  ...Thompson

PDS Special Marine Warning[edit]

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.[9]

Particularly Dangerous Situation (PDS) Special Marine Warning
National Weather Service Baltimore MD/Washington DC
 1138 AM EDT THU APR 19 2018
 
 ANZ537-191700- 
 /O.CON.KLWX.MA.W.0020.000000T0000Z-180419T1700Z/
 1138 AM EDT THU APR 19 2018
 
 ...A SPECIAL MARINE WARNING REMAINS IN EFFECT UNTIL 100 PM EDT...
 
 For the following areas...
 Tidal Potomac from Cobb Island MD to Smith Point VA...
 
 At 1137 AM EDT, a gust front was located near Quantico Marine Base,
 moving southeast at 25 knots. Numerous wind gusts of 35 to 45 knots
 have been observed with this line.
 
 HAZARD...Wind gusts 34 knots or greater.
 
 SOURCE...Radar indicated.
 
 IMPACT...Boaters in small craft could be thrown overboard by
 suddenly higher winds and waves capsizing their vessel.
 
 Locations impacted include...
 Yeocomico River...
 Breton Bay...
 Point Lookout...
 Coltons Point...
 Saint Clements Bay...
 Coles Point...
 Mouth Of The Potomac River...
 Saint George Island...
 White Point Beach...
 Tall Timbers...
 and Piney Point.
 
 PRECAUTIONARY/PREPAREDNESS ACTIONS...
 
 This is a particularly dangerous situation. Sudden onset of gale
 force winds can cause even experienced mariners to capsize.
 Capsizing in cold water is especially dangerous and can quickly
 result in hypothermia. If you haven't already done so, move to safe
 harbor now!
 
 &&
 
 LAT...LON 3797 7641 3801 7647 3802 7651 3807 7654
 3811 7660 3815 7661 3817 7676 3817 7685
 3826 7686 3825 7684 3823 7660 3821 7657
 3814 7652 3806 7633 3801 7629 3791 7627
 TIME...MOT...LOC 1537Z 310DEG 27KT 3871 7777 3813 7848
 
 
 HAIL...0.00in
 WIND...>34kts
 
 $$
 
 DHOF

PDS Special Weather Statement[edit]

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.[citation needed] The same office issued a PDS Special Weather Statement for hurricane-force winds forecast to hit the Buffalo area on February 24, 2019.

Particularly Dangerous Situation (PDS) Special Weather Statement
 SPECIAL WEATHER STATEMENT
 NATIONAL WEATHER SERVICE BUFFALO NY
 255 PM EST WED DEC 11 2013
 
 NYZ006>008-112200-
 OSWEGO-JEFFERSON-LEWIS-
 INCLUDING THE CITIES OF...OSWEGO...WATERTOWN...LOWVILLE
 255 PM EST WED DEC 11 2013
 
 ...EXTREMELY HEAVY LAKE EFFECT SNOW TO CONTINUE THROUGH THE
 EVENING COMMUTE...
 
 A BAND OF VERY INTENSE LAKE EFFECT SNOW EXTENDING FROM BETWEEN
 SANDY CREEK AND ADAMS ALONG I-81...EASTWARD TO LOWVILLE AND
 CROGHAN WILL CONTINUE THROUGH THE AFTERNOON. OTHER AREAS IMPACTED
 BY THIS SNOW BAND INCLUDE BUT ARE NOT LIMITED TO
 MONTAGUE...MARTINSBURG...HIGHMARKET...TURIN...SANDY
 CREEK...LACONA...PULASKI...LOWVILLE AND LYONS FALLS. THIS BAND
 WILL DRIFT SLIGHTLY NORTH OVER THE NEXT COUPLE OF HOURS. SNOWFALL
 RATES OF 3 TO 5 INCHES PER HOUR CAN BE EXPECTED WITHIN THE MOST
 INTENSE LAKE BANDS. IN ADDITION...WEST WINDS BETWEEN 15 TO 30 MPH
 WILL RESULT IN CONSIDERABLE BLOWING AND DRIFTING SNOW...REDUCING
 VISIBILITIES TO NEAR ZERO AT TIMES MAKING FOR WHITE OUT
 CONDITIONS.
 
 ...THIS IS A PARTICULARLY DANGEROUS SITUATION...
 
 THIS WILL PRODUCE TREACHEROUS TRAVEL CONDITIONS ACROSS THE TUG
  HILL...INTERSTATE 81 FROM PULASKI TO ADAMS...AND ALONG STATE
  ROUTE 12 FROM TURIN TO LOWVILLE. TRAVEL ACROSS THESE AREAS WILL
 BE NEARLY IMPOSSIBLE THIS AFTERNOON...AND IS HIGHLY DISCOURAGED.
 
 $$
 
 JAM

PDS Tornado Watch[edit]

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 (usually amounting to damage consistent with EF4 or EF5 tornadoes at maximum), 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.[10]

Particularly Dangerous Situation (PDS) Tornado Watch 197
  SEL7
  
  URGENT - IMMEDIATE BROADCAST REQUESTED
  Tornado Watch Number 197
  NWS Storm Prediction Center Norman OK
  1235 PM CDT Mon May 20 2019
  
  The NWS Storm Prediction Center has issued a
  
  * Tornado Watch for portions of 
    West Texas including much of the Panhandle
  
  * Effective this Monday afternoon and evening from 1235 PM until
    800 PM CDT.
  
  ...THIS IS A PARTICULARLY DANGEROUS SITUATION...
  
  * Primary threats include...
    Numerous tornadoes expected with a few intense tornadoes likely
    Widespread large hail and scattered very large hail events to 4
      inches in diameter expected
    Widespread damaging wind gusts to 70 mph likely
  
  SUMMARY...Intense tornadic supercell thunderstorms are expected to
  develop across west Texas as the eastern half of the Texas
  Panhandle.  In addition to the risk of strong tornadoes, very large
  hail and damaging winds are likely in the strongest cells.
  
  The tornado watch area is approximately along and 55 statute miles
  east and west of a line from 50 miles east northeast of Amarillo TX
  to 35 miles east of Big Spring TX. For a complete depiction of the
  watch see the associated watch outline update (WOUS64 KWNS WOU7).
  
  PRECAUTIONARY/PREPAREDNESS ACTIONS...
  
  REMEMBER...A Tornado Watch means conditions are favorable for
  tornadoes and severe thunderstorms in and close to the watch
  area. Persons in these areas should be on the lookout for
  threatening weather conditions and listen for later statements
  and possible warnings.
  
  &&
  
  OTHER WATCH INFORMATION...CONTINUE...WW 196...
  
  AVIATION...Tornadoes and a few severe thunderstorms with hail
  surface and aloft to 4 inches. Extreme turbulence and surface wind
  gusts to 60 knots. A few cumulonimbi with maximum tops to 600. Mean
  storm motion vector 24035.
  
  ...Hart

[11]

The most recent PDS Tornado Watches were Tornado Watch 211 and 212 issued on May 22, 2019.

PDS Tornado Warning[edit]

PDS tornado warnings are currently issued on an experimental basis by the 38 National Weather Service Weather Forecast Offices within the Central Region.[12] 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 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 (an experiment – which also includes tags within warning products illustrating radar indications or physical observations of tornadoes, and damage potential – participated by the 33 Weather Forecast Offices within the Central Region, as well as eight additional offices within the Western, Eastern and Southern regions that began utilizing the system in the spring of 2014[13]); 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.[14][15]

Below is an example of a PDS Tornado Warning from the Rochelle/Fairdale, IL Tornado on April 9, 2015

Particularly Dangerous Situation (PDS) Tornado Warning

153
WFU553 KLOT 092358
TORLOT
ILC007-037-141-201-100045
/O.NEW.KLOT.TO.W.0008.150409T2358Z-150410T0045Z/

BULLETIN - EAS ACTIVIATION REUQESTED
TORNADO WARNING
NATIONAL WAETHER SERVICE CHICAGO/ROMEOVILLE IL
658 PM CDT THU APR 9 2015

THE NATIONAL WEATHER SERVICE IN CHICAGO HAS ISSUED A

* TORNADO WARNING FOR...
  NORTHWESTERN DE KALB COUNTY IN NORTH CENTRAL ILLINOIS...
  SOUTHWESTERN BOONE COUNTY IN NORTH CENTRAL ILLINOIS...
  SOUTHEASTERN OGLE COUNTY IN NORTH CENTRAL ILLINOIS...
  SOUTHEASTERN WINNEBAGO COUNTY IN NORTH CENTRAL ILLINOIS...

* UNTIL 745 PM CDT

* AT 657 PM CDT...A CONFIRMED LARGE AND EXTREMELY DANGEROUS TORNADO
  WAS LOCATED NEAR HILLCREST...OR JUST NORTHWEST OF ROCHELLE AND
  MOVING NORTHEAST AT MPH.
 
  THIS IS A PARTICULARLY DANGEROUS SITUATION.

  HAZARD...DAMAGING TORNADO.

  SOURCE...Radar confirmed tornado.

  IMPACT...YOU ARE IN A LIFE THREATENING SITUATION. FLYING DEBRIS
           MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE
           HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO
           HOMES...BUSINESSES AND VEHICLES IS LIKELY AND COMPLETE
           DESTRUCTION IS POSSIBLE.

* THE TORNADO WILL BE NEAR...
  KIRKLAND AROUND 715 PM CDT.
  KINGSTON AROUND 720 PM CDT.
  GENOA AROUND 725 PM CDT. 

THIS TORNADO WILL CROSS INTERSTATE 39 BETWEEN MILE MARKERS 101 AND
115.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A LARGE AND EXTREMELY DANGEROUS TORNADO IS ON THE GROUND. TAKE
IMMEDIATE TORNADO PRECAUTIONS. THIS IS AN EMERGENCY SITUATION.

&&

LAT...LON 4190 8914 4198 8920 4225 8894 4207 8870
TIME...MOT...LOC 2357Z 229DEG 38KT 4199 8909

TORNADO...OBSERVED
TORNADO DAMAGE THREAT...CONSIDERABLE
HAIL...2.75IN

$$

IZZI [16] 

PDS Wind Chill Warning[edit]

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.[17]

Particularly Dangerous Situation (PDS) Wind Chill Warning
629 WWUS43 KMPX 050957 WSWMPX URGENT - WINTER WEATHER MESSAGE NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 357 AM CST SUN JAN 5 2014 ...HISTORIC AND LIFE-THREATENING COLD AIR HAS ARRIVED... ...THIS IS A PARTICULARLY DANGEROUS SITUATION... THE COLDEST AIRMASS SINCE 1996 CONTINUES TO MOVE SOUTHEAST OUT OF CANADA AND INTO MINNESOTA AND WISCONSIN. WIND CHILL VALUES WILL RANGE BETWEEN 30 AND 45 BELOW TODAY AND CONTINUE TO FALL THROUGH MONDAY MORNING. AIR TEMPERATURES TONIGHT WILL DROP INTO THE 20S AND 30S BELOW ZERO. GUSTY WEST OR NORTHWEST WINDS COMBINED WITH THESE EXTREMELY COLD TEMPERATURES WILL PRODUCE WIND CHILLS OF 50 TO 65 BELOW ZERO LATE TONIGHT AND EARLY MONDAY. WIND CHILLS COLDER THAN 50 BELOW CAN CAUSE EXPOSED FLESH TO FREEZE IN ONLY 5 MINUTES. A WIND CHILL WARNING IS IN EFFECT FOR CENTRAL AND SOUTHERN MINNESOTA AND WEST CENTRAL WISCONSIN THROUGH NOON TUESDAY. THE GUSTY WINDS WILL ALSO BRING AREAS OF BLOWING SNOW TO MUCH OF THE AREA TODAY AND TONIGHT. WHERE GUSTS REACH 35 TO 45 MPH OVER WESTERN AND SOUTHERN MINNESOTA...VISIBILITIES MAY OCCASIONALLY BE REDUCED TO LESS THAN A HALF MILE IN NEAR BLIZZARD CONDITIONS. THIS WILL BRING AN ADDITIONAL LEVEL OF DANGER TO ANYONE STRANDED. MNZ041-047-048-054>057-064-065-067-073>075-082>085-091>093-052115- /O.CON.KMPX.WC.W.0001.000000T0000Z-140107T1800Z/ DOUGLAS-STEVENS-POPE-LAC QUI PARLE-SWIFT-CHIPPEWA-KANDIYOHI- YELLOW MEDICINE-RENVILLE-SIBLEY-REDWOOD-BROWN-NICOLLET-WATONWAN- BLUE EARTH-WASECA-STEELE-MARTIN-FARIBAULT-FREEBORN- INCLUDING THE CITIES OF...ALEXANDRIA...MORRIS...GLENWOOD... MADISON...BENSON...MONTEVIDEO...WILLMAR...GRANITE FALLS... OLIVIA...GAYLORD...REDWOOD FALLS...NEW ULM...ST. PETER... ST. JAMES...MANKATO...WASECA...OWATONNA...FAIRMONT...BLUE EARTH... ALBERT LEA 357 AM CST SUN JAN 5 2014 ...WIND CHILL WARNING REMAINS IN EFFECT UNTIL NOON CST TUESDAY... A WIND CHILL WARNING REMAINS IN EFFECT UNTIL NOON CST TUESDAY. * THIS IS A PARTICULARLY DANGEROUS SITUATION! * WIND CHILL VALUES: 35 TO 65 BELOW...WITH THE COLDEST READINGS TONIGHT AND MONDAY MORNING. * IMPACTS: EXPOSED FLESH WILL FREEZE IN 10 MINUTES WITH WIND CHILLS OF 35 BELOW...AND IN 5 MINUTES WITH WIND CHILLS OF 50 BELOW OR COLDER. * OTHER IMPACTS...WINDS GUSTING BETWEEN 35 AND 45 MPH THIS AFTERNOON AND TONIGHT WILL LEAD TO BLOWING SNOW WITH VISIBILITIES OCCASIONALLY DROPPING TO 1/2 MILE OR LESS IN NEAR BLIZZARD CONDITIONS. SHOULD YOUR VEHICLE BECOME STRANDED...YOUR LIFE WILL BE AT RISK. CONSIDER POSTPONING ALL TRAVEL. PRECAUTIONARY/PREPAREDNESS ACTIONS... A WIND CHILL WARNING MEANS THE COMBINATION OF VERY COLD AIR AND STRONG WINDS WILL CREATE DANGEROUSLY LOW WIND CHILL VALUES. THIS WILL RESULT IN FROST BITE AND LEAD TO HYPOTHERMIA OR DEATH IF PRECAUTIONS ARE NOT TAKEN. && $$ MNZ042>045-049>053-058>063-066-068>070-076>078-WIZ014>016-023>028- 052115 /O.CON.KMPX.WC.W.0001.000000T0000Z-140107T1800Z/ TODD-MORRISON-MILLE LACS-KANABEC-STEARNS-BENTON-SHERBURNE-ISANTI- CHISAGO-MEEKER-WRIGHT-HENNEPIN-ANOKA-RAMSEY-WASHINGTON-MCLEOD- CARVER-SCOTT-DAKOTA-LE SUEUR-RICE-GOODHUE-POLK-BARRON RUSK- ST. CROIX-PIERCE-DUNN-PEPIN-CHIPPEWA-EAU CLAIRE- INCLUDING THE CITIES OF...LONG PRAIRIE...LITTLE FALLS... PRINCETON...MORA...ST. CLOUD...FOLEY...ELK RIVER...CAMBRIDGE... CENTER CITY...LITCHFIELD...MONTICELLO...MINNEAPOLIS...BLAINE... ST. PAUL...STILLWATER...HUTCHINSON...CHASKA...SHAKOPEE... BURNSVILLE...LE SUEUR...FARIBAULT...RED WING...AMERY... BALSAM LAKE...RICE LAKE...BARRON...LADYSMITH...HUDSON... NEW RICHMOND...RIVER FALLS...PRESCOTT...MENOMONIE...BOYCEVILLE... DURAND...PEPIN...CHIPPEWA FALLS...BLOOMER...EAU CLAIRE...ALTOONA 357 AM CST SUN JAN 5 2014 ...WIND CHILL WARNING REMAINS IN EFFECT UNTIL NOON CST TUESDAY... A WIND CHILL WARNING REMAINS IN EFFECT UNTIL NOON CST TUESDAY. * THIS IS A PARTICULARLY DANGEROUS SITUATION! * WIND CHILL VALUES: 35 TO 65 BELOW...WITH THE COLDEST READINGS TONIGHT AND MONDAY MORNING. * IMPACTS: EXPOSED FLESH WILL FREEZE IN 10 MINUTES WITH WIND CHILLS OF 35 BELOW...AND IN 5 MINUTES WITH WIND CHILLS OF 50 BELOW OR COLDER. * OTHER IMPACTS...AREAS OF BLOWING SNOW ARE POSSIBLE AS WINDS GUST AS HIGH AS 35 MPH THIS AFTERNOON AND TONIGHT. PRECAUTIONARY/PREPAREDNESS ACTIONS... A WIND CHILL WARNING MEANS THE COMBINATION OF VERY COLD AIR AND STRONG WINDS WILL CREATE DANGEROUSLY LOW WIND CHILL VALUES. THIS WILL RESULT IN FROST BITE AND LEAD TO HYPOTHERMIA OR DEATH IF PRECAUTIONS ARE NOT TAKEN. && $$ BORGHOFF

Other watches and warnings[edit]

While the use of PDS wording for other types of watches and warnings has not been used, PDS wording could theoretically be applied to any kind of watch or warning to alert the public to weather events where there exists an increased risk of loss of life or widespread damage to property. Such situations could include PDS watches or warnings for blizzards, ice storms, high winds, or extreme heat. For example, on October 29, 2012 in advance of Hurricane Sandy, which was expected to become post-tropical prior to making landfall, a high wind warning was issued for New Jersey stating "THIS IS AN EXTREMELY DANGEROUS SITUATION!"[18] Similarly, on May 26, 2015 during the flood disaster in Texas, Oklahoma, Arkansas, and Louisiana, a flood warning was issued similar to a PDS flood warning stating "...THIS IS A DANGEROUS AND LIFE-THREATENING SITUATION..."[19] A severe thunderstorm warning bulletin issued by the National Weather Service at Tampa Bay/Ruskin regarding a strong, tornadic storm system moving through the area contained the following: "THIS STORM MAY CAUSE SERIOUS INJURY AND SIGNIFICANT PROPERTY DAMAGE."[20]

References[edit]

  1. ^ NOAA (2004-04-18). "Storm Prediction Center Frequently Asked Questions (FAQ)". Retrieved 2008-05-23.
  2. ^ "National Weather Service Issues Area Red Flag Warning". Retrieved 2018-08-04.
  3. ^ a b Dean, Andrew R. (2006-11-07). "PDS watches: how dangerous are these "particularly dangerous situations?" (2006 - 23SLS_23sls)". American Meteorological Society. Retrieved 2008-05-23.
  4. ^ Lewis, John (2007-11-03). "A Forecaster's Story: Robert H. Johns". Electronic Journal of Severe Storms Meteorology. 2 (7).
  5. ^ "IEM Valid Time Extent Code (VTEC) App". Mesonet.agron.iastate.edu. Retrieved 2014-01-22.
  6. ^ "Flash Flood Warning". National Weather Service. 2018-05-30. Retrieved 2018-05-30.
  7. ^ National Weather Service (2017-12-19). "Iowa Environmental Mesonet NWS Product Archive". Retrieved 2018-04-18.
  8. ^ NOAA (2019-07-19). "Storm Prediction Center: Particularly Dangerous Situation (PDS) Severe Thunderstorm Watch 525".
  9. ^ akrherz@iastate.edu, daryl herzmann. "IEM :: Valid Time Event Code (VTEC) App". mesonet.agron.iastate.edu. Retrieved 2018-04-19.
  10. ^ "Storm Prediction Center PDS Tornado Watch 197". Storm Prediction Center. Storm Prediction Center. Retrieved 28 June 2019.
  11. ^ Brugge, R. (December 1994). "The Alabama tornado outbreak of 27 March 1994 - an example of tornado formation". Weather. 49 (12): 407–411. doi:10.1002/j.1477-8696.1994.tb05961.x. ISSN 0043-1656.
  12. ^ "Impact Based Warning Experimental Product". Crh.noaa.gov. Retrieved 2014-01-22.
  13. ^ National Weather Service (2014). "Impact Based Warnings". National Oceanic and Atmospheric Administration. Retrieved March 12, 2014.
  14. ^ "NWS Expirements" (PDF). NWS. Archived from the original (PDF) on 13 April 2012. Retrieved 15 April 2012.
  15. ^ "'CATASTROPHIC': Experimental Tornado Warnings to be Explicit". AccuWeather. 2012-04-05. Retrieved 2014-03-12.
  16. ^ Iowa State University Iowa Environmental Mesonet https://mesonet.agron.iastate.edu/vtec/#2015-O-NEW-KLOT-TO-W-0008/USCOMP-N0Q-201504100040. Retrieved 28 June 2019. Missing or empty |title= (help)
  17. ^ National Weather Service (2014-01-05). "Iowa Environmental Mesonet NWS Product Archive". Retrieved 2014-01-06.
  18. ^ "High Wind Warning - Hurricane Sandy". National Weather Service - Philadelphia/Mount Holly. Retrieved 29 October 2017.
  19. ^ Payne, Ed; Shoichet, Catherine. "Running updates: Storms slam Houston, kill 31 in Texas, Oklahoma, Mexico". CNN. Retrieved 30 October 2017.
  20. ^ "Tampa Bay/Ruskin - Severe Thunderstorm Warning". National Weather Service. Retrieved 30 October 2017.

 This article incorporates public domain material from websites or documents of the National Oceanic and Atmospheric Administration.

External links[edit]

* NOAA-NWS Storm Prediction Center