Runoff from melting snow in the Bighorn Mountains and heavy rain over the upper Powder River Basin caused significant flooding along the Powder River in northeastern Wyoming.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS UNR wrote it up.
Runoff from melting snow in the Bighorn Mountains and heavy rain over the upper Powder River Basin caused significant flooding along the Powder River in northeastern Wyoming.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Rapid City, SD wrote its last area forecast discussion before the first event at May 27, 1:25 PM MST, 20 minutes earlier.
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 225 PM MDT WED MAY 27 2015 .SHORT TERM...THIS EVENING THROUGH THURSDAY NIGHT ISSUED AT 225 PM MDT WED MAY 27 2015 CLOSED UPPER LOW OVER THE PAC NW WILL CONTINUE TO SLOWLY PUSH EAST IN THE PERIOD. A EASTERN PERIPHERY WEAK IMPULSE/JET STREAK IS IN THE PROCESS OF LIFTING NE OUT OF WY...SUPPORTING SCT-NUMEROUS SHRA AND TS ACROSS THE FA. JET STREAK WILL LIFT NE THIS EVENING...WITH FORCING AND ASSOCIATED CONVECTION LIFTING NE. HIRES ANALYSIS FIELDS INDICATE AOA 1000-1500 J/KG OF CAPE MAINLY IN A NORTH/SOUTH AXIS ON THE SD PLAINS. AS CONVECTION LIFTS NE INTO THIS AREA OF HIGHER INSTABILITY...A FEW STRONGER STORMS CAN BE EXPECTED. BEST CHANCES/COVERAGE OF SHRA/TS WILL BE ACROSS NW SD WHERE THE BEST LL CONVERGENCE AND LSA WILL OVERLAP. LL SFC TROUGH WILL SHIFT SE INTO THE FA THIS EVENING...EVENTUALLY STALLING OVER SCENTRAL SD. MAIN UPPER LOW OVER THE PAC NW IS EXPECTED TO DRIFT EAST OVERNIGHT...EVENTUALLY SUPPORTING AN INCREASE IN LSA AND ASSOCIATED DEEP CYCLONIC FLOW...POTENTIALLY SUPPORTING LINGERING SHRA INTO THE FAR WESTERN FA BY LATE IN THE NIGHT. DRIED MOST PLACES OUT AFTER MIDNIGHT...WITH A SLIGHT UPTICK TO CHANCE POPS OVER THE FAR WEST TOWARD DAWN. DEEP CYCLONIC FLOW WILL SPREAD OVER THE AREA AND SUPPORT INCREASING LSA OVER MOST OF THE REGION THURSDAY. MORE THAN SUFFICIENT LL MOISTURE IN PLACE/DIURNAL HEATING/AND ENHANCED CONVERGENCE ALONG A STALLED SFC TROUGH WILL SUPPORT WIDESPREAD CONNECTIVE SHOWERS OVER THE FA...ESP IN THE BH WHERE CIN WILL BE NEGLIGIBLE. A FEW STRONGER STORMS WILL BE POSSIBLE OVER SCENTRAL SD AHEAD OF THE SFC TROUGH WHERE ONGOING MOISTURE TRANSPORT IN THE WARMER SECTOR WILL SUPPORT ML CAPES OF AROUND 1500 J/KG BY AFTERNOON. HOWEVER...SHEAR REMAINS QUITE LIMITED WITH 20-25 KNOTS PROGGED WHERE THE HIGHEST CAPE WILL BE. THE MAIN CONCERN IS LOCALLY HEAVY RAINFALL OVER THE BH. STEEP LL LAPSE RATES/HIGH PW/S OVER AN INCH/ENHANCED CONVERGENCE PER EDDY EFFECTS/AND SLOW STORM MOTION VECTORS WILL BE IN PLACE OVER THE BH FOR MUCH OF THUR AFTERNOON. WOULD NOT BE SURPRISE TO SEE A WIDESPREAD HALF INCH OF RAIN ACROSS MUCH OF THE BLACK HILLS WHICH COULD AGGRAVATE ONGOING FLOODING CONCERNS. A SECONDARY TROUGH WILL SHIFT SOUTH THUR NIGHT AND SUPPORT AN ENHANCED AREA OF CONVERGENCE WITH SHRA CHANCES CONTINUING OVERNIGHT. KEPT POPS FAIRLY HIGH THROUGH THUR NIGHT...WITH A SOUTHWARD SHIFT AS THE MAIN TROUGH AXIS SHIFTS SOUTH ALONG WITH LSA. .LONG TERM...FRIDAY THROUGH WEDNESDAY ISSUED AT 225 PM MDT WED MAY 27 2015 UPPER LEVEL TROF WILL SHIFT EAST OF THE NORTHERN PLAINS ON FRIDAY AS SURFACE HIGH PRESSURE DROPS SOUTH OUT OF CANADA. LINGERING SHOWERS ARE EXPECTED ON FRIDAY...SHIFTING SOUTH THROUGHOUT THE DAY AS DRIER AIR MOVES IN. COOL HIGH PRESSURE WILL KEEP TEMPERATURES SLIGHTLY BELOW AVERAGE ON SATURDAY...WITH A FEW SHOWERS AND THUNDERSTORMS POSSIBLE IN THE AFTERNOON AS A WEAK WAVE PASSES THROUGH. THERMAL RIDGE WILL BUILD INTO THE REGION SUNDAY AND MONDAY...ALLOWING FOR A WARMUP...WITH SMALL CHANCES OF SHOWERS AND THUNDERSTORMS. GREATER PRECIPITATION CHANCES RETURN FOR THE MIDDLE OF NEXT WEEK AS UPPER FLOW BECOMES SOUTHWESTERLY. && .AVIATION...FOR THE 18Z TAFS THROUGH 18Z THURSDAY ISSUED AT 225 PM MDT WED MAY 27 2015 SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE THIS AFTERNOON AND GRADUALLY DIMINISH THIS EVENING. VFR CONDITIONS EXPECTED OUTSIDE OF PRECIPITATION...WITH MVFR CIGS/VSBYS AND GUSTY WINDS NEAR ANY STORMS. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...NONE. WY...NONE. && SHORT TERM...JC LONG TERM...POJORLIE AVIATION...POJORLIE
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE RAPID CITY SD 236 PM MDT WED MAY 27 2015 SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058- 071-281300- HARDING-PERKINS-BUTTE-NORTHERN MEADE CO PLAINS-ZIEBACH- NORTHERN BLACK HILLS-NORTHERN FOOT HILLS-RAPID CITY- SOUTHERN FOOT HILLS-CENTRAL BLACK HILLS-SOUTHERN BLACK HILLS- CUSTER CO PLAINS-PENNINGTON CO PLAINS-HAAKON-FALL RIVER-SHANNON- JACKSON-BENNETT-MELLETTE-TODD-TRIPP-STURGIS/PIEDMONT FOOT HILLS- SOUTHERN MEADE CO PLAINS-HERMOSA FOOT HILLS-NORTHERN CAMPBELL- SOUTHERN CAMPBELL-WESTERN CROOK-WYOMING BLACK HILLS-WESTON- NORTHEASTERN CROOK- 236 PM MDT WED MAY 27 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN SOUTH DAKOTA AND NORTHEASTERN WYOMING. .DAY ONE...THIS AFTERNOON AND TONIGHT SHOWERS AND THUNDERSTORMS WILL SHIFT NORTHEAST ACROSS THE AREA THROUGH THIS EVENING...WITH LOCALLY HEAVY RAIN POSSIBLE OVER NORTHWEST SOUTH DAKOTA. WIDESPREAD SEVERE WEATHER IS NOT EXPECTED. HOWEVER...A FEW STRONGER STORMS COULD PRODUCE HAIL. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY THUNDERSTORMS ARE EXPECTED AGAIN ON THURSDAY. THE BEST CHANCE FOR A FEW SEVERE STORMS IS OVER SOUTH CENTRAL SOUTH DAKOTA. LOCALLY HEAVY RAIN IS ALSO POSSIBLE OVER THE BLACK HILLS WHICH COULD AGGRAVATE FLOODING CONCERNS. HIGH STREAM FLOW WITH SOME MINOR FLOODING WILL CONTINUE ON SOME CREEKS AND STREAMS IN THE BLACK HILLS AND ADJACENT PLAINS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY. && STAY TUNED TO NOAA WEATHER RADIO FOR FURTHER DETAILS OR UPDATES... OR CHECK OUR WEB SITE AT WEATHER.GOV/RAPIDCITY JC
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RAPID CITY SD 1248 PM MDT WED MAY 27 2015 SDZ012-025-072-073-271930- NORTHERN FOOT HILLS SD-BUTTE SD-SOUTHERN MEADE CO PLAINS SD- STURGIS/PIEDMONT FOOT HILLS SD- 1248 PM MDT WED MAY 27 2015 ...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN LAWRENCE...WESTERN MEADE AND SOUTH CENTRAL BUTTE COUNTIES UNTIL 130 PM MDT... AT 1248 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR BEAR BUTTE STATE PARK...OR 7 MILES NORTH OF STURGIS...MOVING NORTH AT 15 MPH. NICKEL SIZE HAIL WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... NISLAND...SAINT ONGE AND BEAR BUTTE STATE PARK. LAT...LON 4448 10344 4443 10356 4461 10382 4471 10346 TIME...MOT...LOC 1848Z 157DEG 13KT 4451 10354 CALDERON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RAPID CITY SD 132 PM MDT WED MAY 27 2015 SDZ072-073-272015- SOUTHERN MEADE CO PLAINS SD-STURGIS/PIEDMONT FOOT HILLS SD- 132 PM MDT WED MAY 27 2015 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN MEADE COUNTY UNTIL 215 PM MDT... AT 131 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM OVER PIEDMONT...OR 11 MILES NORTHWEST OF RAPID CITY...MOVING NORTHEAST AT 10 MPH. NICKEL SIZE HAIL WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... SUMMERSET AND PIEDMONT. THIS INCLUDES INTERSTATE 90 IN SOUTH DAKOTA BETWEEN MILE MARKERS 42 AND 49. PRECAUTIONARY/PREPAREDNESS ACTIONS... TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD TO PONDING OF WATER ON ROADWAYS. && LAT...LON 4418 10338 4427 10345 4438 10329 4422 10313 TIME...MOT...LOC 1931Z 231DEG 9KT 4422 10336 CALDERON
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RAPID CITY SD
136 PM MDT WED MAY 27 2015
SDZ029-074-272015-
HERMOSA FOOT HILLS SD-SOUTHERN BLACK HILLS SD-
136 PM MDT WED MAY 27 2015
...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL CUSTER COUNTY UNTIL
215 PM MDT...
AT 135 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM OVER
EASTERN CUSTER STATE PARK...OR 10 MILES EAST OF CUSTER...MOVING
NORTHEAST AT 5 MPH.
NICKEL SIZE HAIL WILL BE POSSIBLE WITH THIS STORM.
LOCATIONS IMPACTED INCLUDE...
HERMOSA...CUSTER PARK GAME LODGE...BLUE BELL...CUSTER STATE PARK AND
CENTER LAKE.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...WHICH MAY
LEAD TO CREEKS RUNNING HIGH.
&&
LAT...LON 4373 10352 4386 10336 4386 10318 4378 10310
4377 10310 4364 10341
TIME...MOT...LOC 1935Z 230DEG 5KT 4373 10340
CALDERONSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RAPID CITY SD 149 PM MDT WED MAY 27 2015 SDZ031-272030- PENNINGTON CO PLAINS SD- 149 PM MDT WED MAY 27 2015 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN PENNINGTON COUNTY UNTIL 230 PM MDT... AT 148 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR PINNACLES RANGER STATION...OR 29 MILES WEST OF PHILIP...MOVING NORTH AT 25 MPH. NICKEL SIZE HAIL WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... WALL...QUINN...PINNACLES RANGER STATION AND NORTHERN BADLANDS NATIONAL PARK. THIS INCLUDES INTERSTATE 90 IN SOUTH DAKOTA BETWEEN MILE MARKERS 102 AND 120. PRECAUTIONARY/PREPAREDNESS ACTIONS... TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD TO MINOR FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED ROADWAYS. && LAT...LON 4378 10213 4381 10236 4418 10238 4417 10201 TIME...MOT...LOC 1948Z 187DEG 21KT 4393 10224 CALDERON
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Major flooding of agricultural land occurred along the Powder River. The flows were the highest since 1978.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2015Every state in 2015This day in weather historyWarnings in Wyoming, May 2015
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 576908.