Lightning ignited the Arnica wildfire on Sunday, September 13 in old growth, Lodgepole timber west of Bridge Bay in Yellowstone National Park. The fire was not detected until September 23 when it was discovered to be four acres in size.
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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 RIW wrote it up.
Lightning ignited the Arnica wildfire on Sunday, September 13 in old growth, Lodgepole timber west of Bridge Bay in Yellowstone National Park. The fire was not detected until September 23 when it was discovered to be four acres in size. Warm, dry, and windy conditions allowed the fire to grow to about 1,600 acres over the following two days. A ridge of high pressure and unseasonably warm temperatures on September 26 allowed the fire to expand to an estimated 8,300 acres in size. Additional growth on September 27 of 1,000 acres enabled the fire to burn within 3.5 miles of Lake Village. Burnt trees were brought to the ground on the Grand Loop Road between Fishing Bridge and West Thumb during the afternoon as fire swept across the road. At its peak, the fire burned actively along a 1.5 mile stretch of the road.
Over 200 people and five helicopters actively fought the fire and protected nearby structures. Brush was cleared from around structures and hose lays and sprinkler systems were set-up at Bridge Bay and Lake Village. A change in the weather pattern brought rain, snow, and colder temperatures to the fire on September 30. Personnel were quickly demobilized and sprinklers were removed from structures. All told, the fire charred approximately 10,700 acres of land.
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 Riverton, WY wrote its last area forecast discussion before the first event at Sep 13, 1:46 AM MST, 12 hours 14 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 246 AM MDT SUN SEP 13 2009 .SHORT TERM...TODAY THROUGH TUESDAY NIGHT MOVEMENT OF UPPER LOW CONTINUES TO LINGER SHOWER ACTIVITY ACROSS THE EASTERN PORTION OF THE CWA...ESPECIALLY AROUND THE SOUTHERN BIG HORN BASIN AND BIGHORN MOUNTAINS. ELSEWHERE...CLEARING SKIES NOTED FOR THE MAJORITY OF THE AREA WEST OF THE CONTINENTAL DIVIDE. EXPECT SHOWER ACTIVITY TO PERSIST OVER THE EASTERN AREAS THROUGH THE DAY AS THE UPPER LOW WOBBLES A BIT AND MOVES NORTH INTO MONTANA. SOME MID LEVEL MOISTURE AND INSTABILITY WILL CAUSE ISOLATED THUNDERSTORMS TO DEVELOP...PRIMARILY OVER THE MOUNTAINS AND SOUTHERN WYOMING. BEHIND THE EXIT OF THIS SYSTEM...AN INCREASED SOUTHWEST FLOW WILL DEVELOP...WITH INCREASED WIND ANTICIPATED OVER THE FAVORED LOCATIONS. A WAVE OF LOW PRESSURE WILL MOVE OFF THE CALIFORNIA COAST TONIGHT AND INTO MONDAY MORNING. THIS WAVE IS EXPECTED TO MOVE QUICKLY TOWARDS WYOMING WITH ITS INFLUENCES REACHING THE AREA BY MONDAY AFTERNOON...THOUGH THE AXIS WILL REMAIN OVER NEVADA. WITH THE COMBINATION OF THIS SYSTEM...AND THE SOUTHWEST FLOW TAPPING ADDITIONAL MOISTURE...EXPECTED ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS MONDAY AFTERNOON AND EVENING. THE GFS MODEL CLOSES OFF THIS WAVE MONDAY AFTERNOON...AND THE AREA OF LOW PRESSURE WILL THEN CONTINUE TO ADVANCE INTO THE INTERMOUNTAIN WEST INTO TUESDAY MORNING. THE GFS IS MUCH MORE AGGRESSIVE WITH THIS SYSTEM DEMONSTRATING THE POTENTIAL FOR WIDESPREAD SHOWER ACTIVITY OVER THE WESTERN THIRD OF THE STATE. INCREASED POPS SLIGHTLY...MAINLY OVER SOUTHWESTERN WYOMING WITH SOME CONSISTENCY SEEN IN THE LAST TWO GFS SOLUTIONS. THE NAM CONTINUES THE FEATURE AS A WAVE...AND DOES NOT WRAP INTO A LOW PRESSURE SYSTEM UNTIL TUESDAY AFTERNOON WHEN BOTH MODELS HAVE THE SYSTEM OVER NORTHWESTERN UTAH. MODELS INDICATE SOME INSTABILITY...BUT WITHOUT MORE SUPPORT...LEFT MENTION OF ONLY ISOLATED THUNDERSTORMS FOR TUESDAY AFTERNOON AND EVENING. THE AREA OF LOW PRESSURE STALLS OVER UTAH TUESDAY AFTERNOON AND EVENING AND APPEARS TO WOBBLE A BIT SOUTHWESTWARD DURING THE EVENING HOURS...KEEPING ISOLATED SHOWER ACTIVITY ACROSS SOUTHWESTERN WYOMING THROUGH TUESDAY NIGHT. .LONG TERM...WEDNESDAY THROUGH SUNDAY THE CHANCES FOR SHOWERS AND THUNDERSTORMS REMAIN OVER THE SOUTH AND WEST THROUGH SUNDAY WITH MAINLY DRY CONDITIONS AND ABOVE NORMAL TEMPERATURES EXPECTED OVER WEST AND CENTRAL WYOMING THURSDAY THROUGH SUNDAY. MEDIUM-RANGE MODELS IN GOOD AGREEMENT THROUGH FRIDAY WITH INCREASING SPREAD AND LOWER CONFIDENCE IN FORECAST THROUGH THE WEEKEND. GFS AND ECMWF CONTINUE TO DRIFT UTAH UPPER LOW FURTHER SOUTHEAST WEDNESDAY INTO FOUR CORNERS AREA WITH UPPER HIGH CENTERED OVER MONTANA. GFS KEEPS ADEQUATE MOISTURE...PWATS NEAR 0.75 OF AN INCH...AND SLIGHT INSTABILITY OVER SOUTH AND WEST TO JUSTIFY KEEPING 20-30 POPS OVER AREA. LATEST ECMWF COMING IN LINE WITH PREVIOUS AND CURRENT GFS SOLUTIONS IN DRYING AREA OUT THURSDAY AND FRIDAY UNDER PREVAILING EASTERLY FLOW WITH UPPER HIGH CENTERED OVER THE NORTHERN HIGH PLAINS. H7 TEMPERATURES AVERAGING 10C-12C THURSDAY AND FRIDAY WITH VALLEY AND BASIN HIGHS MOSTLY IN THE 75-85F RANGE...OR APPROXIMATELY 10F ABOVE NORMAL. ECMWF AND GFS SHOW INCREASING SPREAD ON DEVELOPMENT OF STRONGER WESTERLIES NEAR THE U.S./CANADIAN BORDER OVER THE WEEKEND WITH THE ECMWF BRINGING IN A STRONGER SHARPER TROUGH INTO THE NORTHWEST U.S. SATURDAY AND ACROSS MONTANA SUNDAY. GFS/GEFS MEAN MUCH FLATTER WITH THIS FLOW AS THESE SOLUTIONS PROGRESS UPPER HIGH PRESSURE INTO THE INTERMOUNTAIN WEST WHILE ECMWF HOLDS IT BACK OVER THE EASTERN PACIFIC. PREVIOUS INDIVIDUAL RUNS...ESPECIALLY ECMWF...HAVE BEEN QUICK TO BREAK DOWN WESTERN RIDGE IN THE LATTER PERIODS WITH STRONGER WESTERLIES ONLY TO BACK OFF IN SUBSEQUENT RUNS. WILL WAIT FOR SOME CONSISTENCY BEFORE MAKING ANY CHANGES...OR DRY WEATHER AND ABOVE NORMAL TEMPERATURES CONTINUE THROUGH WEEKEND UNDER INFLUENCE OF CLIMATOLOGICALLY FAVORED UPPER HIGH OVER THE WEST PER GFS/GEFS MEAN. && .AVIATION... NORTHERLY FLOW WILL BRING SOME LOW CLOUDS AND SCATTERED LIGHT RAIN SHOWERS TO THE EAST THROUGH THE MORNING WITH ISOLATED MVFR CEILINGS...THEN THE LOWER CLOUDS WILL DISSIPATE FROM SOUTHWEST TO NORTHEAST THROUGH THE DAY. AREAS OF HIGH AND MID CLOUDS WILL CONTINUE ACROSS THE AREA WITH VFR CONDITIONS. && .FIRE WEATHER... THE LOW PRESSURE SYSTEM WILL MOVE NORTH OF WYOMING BY THIS AFTERNOON. MOVEMENT OF THIS SYSTEM WILL CAUSE AN INCREASED SOUTHWEST FLOW OVER THE AREA...ESPECIALLY OVER ZONES 280...289 AND THE EASTERN HALF OF ZONE 279. WIND IS EXPECTED TO WEAKEN DURING THE OVERNIGHT HOURS. SHOWERS AND THUNDERSTORMS WILL BE OVER THE MOUNTAINS AND SOUTHERN WYOMING THIS AFTERNOON. TEMPERATURES OVER THE AREA ARE EXPECTED TO REBOUND WITH THE NORTHERLY MOVEMENT OF THE LOW PRESSURE SYSTEM...ALLOWING AREAS EAST OF THE DIVIDE TO REACH INTO THE MID TO UPPER 70S...AND HUMIDITY DECREASING INTO THE LOW TO MID TEENS. SOUTHWEST FLOW OVER THE AREA WILL KEEP AFTERNOON SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE AREA. ANOTHER APPROACHING SYSTEM WILL INCREASE SHOWER ACTIVITY OVER WESTERN WYOMING BY MONDAY AFTERNOON AND EVENING...AND CONTINUE INTO TUESDAY. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...BRANHAM LONG TERM...AEM AVIATION...C.BAKER FIRE WEATHER...BRANHAM
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RIVERTON WY 500 AM MDT SUN SEP 13 2009 WYZ001>020-022>030-141100- ABSAROKA MOUNTAINS-BIGHORN MOUNTAINS SOUTHEAST- BIGHORN MOUNTAINS WEST-CASPER MOUNTAIN-CODY FOOTHILLS- EAST SWEETWATER COUNTY-FLAMING GORGE- GREEN MOUNTAINS AND RATTLESNAKE RANGE-JACKSON HOLE-LANDER FOOTHILLS- NATRONA COUNTY LOWER ELEVATIONS-NORTH BIG HORN BASIN- NORTHEAST JOHNSON COUNTY-OWL CREEK AND BRIDGER MOUNTAINS- ROCK SPRINGS AND GREEN RIVER-SALT RIVER AND WYOMING RANGES- SOUTH LINCOLN COUNTY-SOUTHEAST BIG HORN BASIN- SOUTHEAST JOHNSON COUNTY-SOUTHWEST BIG HORN BASIN-STAR VALLEY- TETON AND GROS VENTRE MOUNTAINS-UPPER GREEN RIVER BASIN- UPPER GREEN RIVER BASIN FOOTHILLS-UPPER WIND RIVER BASIN- WIND RIVER BASIN-WIND RIVER MOUNTAINS EAST-WIND RIVER MOUNTAINS WEST- YELLOWSTONE NATIONAL PARK- 500 AM MDT SUN SEP 13 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN AND CENTRAL WYOMING. .DAY ONE...TODAY AND TONIGHT ISOLATED AFTERNOON SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE OVER THE MOUNTAINS...SOUTHERN WYOMING AND NORTHERN JOHNSON COUNTY TODAY. LIGHTNING AND GUSTY WIND TO 40 MPH WILL BE POSSIBLE WITH STORM ACTIVITY. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE MONDAY AND TUESDAY AFTERNOONS AND EVENINGS MAINLY WEST OF THE DIVIDE. GUSTY WIND AND LIGHTNING WILL BE THE PRIMARY HAZARDS. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT WIND GUSTS IN EXCESS OF 40 MPH THIS AFTERNOON. THANK YOU. TEAM RIVERTON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE RIVERTON WY 225 PM MDT SUN SEP 13 2009 WYZ029-030-132100- EAST SWEETWATER COUNTY-FLAMING GORGE- 225 PM MDT SUN SEP 13 2009 AN AREA OF SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL BE TRACKING EAST NORTHEAST FROM JUST EAST OF FLAMING GORGE RESERVOIR THROUGH EASTERN SWEETWATER COUNTY. THESE STORMS WILL BE AFFECTING HIGHWAY 191 IN SOUTHERN SWEETWATER COUNTY THROUGH 3 PM. EXPECT ISOLATED CLOUD TO GROUND LIGHTNING STRIKES...BRIEF MODERATE TO HEAVY RAINFALL AS WELL AS SOUTHWEST WINDS OF 30 TO 40 MPH WINDS WITH SOME OF THESE STORMS. LIPSON
The national radar mosaic for the moment the first event began.
1 wildfire. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2009Every state in 2009This day in weather historyWarnings in Wyoming, September 2009
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: 191852.