The Cache La Poudre and South Platte River rose above flood stage producing a prolonged period of minor to moderate lowland flooding. Numerous county roads along the rivers remain closed due to floodwaters.
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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 BOU wrote it up.
The Cache La Poudre and South Platte River rose above flood stage producing a prolonged period of minor to moderate lowland flooding. Numerous county roads along the rivers remain closed due to floodwaters.
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 Denver/Boulder, CO wrote its last area forecast discussion before the first event at May 20, 1:58 AM MST, 1 hour 2 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DENVER/BOULDER CO 258 AM MDT WED MAY 20 2015 .SHORT TERM...(TODAY THROUGH TONIGHT ) ISSUED AT 258 AM MDT WED MAY 20 2015 A MOIST EASTERLY FLOW AROUND A SURFACE HIGH OVER THE NORTHERN PLAINS WILL CONTINUE TO BRING LOW CLOUDS...DRIZZLE AND PATCHY FOG THROUGH MID MORNING. FOG AND DRIZZLE WILL END AND CLOUDS WILL LIFT DUE TO SURFACE HEATING. THE EASTERLY FLOW WILL LINGER THROUGH THE DAY AND MAKE IT DIFFICULT FOR THE CLOUDS TO BURN OFF. WILL KEEP MOSTLY CLOUDY SKIES IN THE FORECAST THROUGH THE DAY. THIS WILL KEEP TEMPERATURES COOL WITH HIGHS STRUGGLING TO REACH 50 DEGREES. AIRMASS OVER THE MOUNTAINS BECOMES SLIGHTLY UNSTABLE. CAPES STAY BELOW 500 J/KG. WEAK UP SLOPE FLOW ALONG WITH BEING UNDER THE FAVORABLE PART OF THE JET COULD TRIGGER A FEW SHOWERS OR THUNDERSTORMS ALONG WITH THE INSTABILITY OVER THE MOUNTAINS. APPEARS THE LOWER ELEVATIONS WILL BE TOO STABLE FOR STORMS SO WILL KEEP THE MENTION OF THUNDERSTORMS CONFINED TO THE HIGHER TERRAIN AND PALMER DIVIDE FOR THIS AFTERNOON AND EVENING. RAINFALL WILL BE ON THE LIGHT SIDE WITH MOST LOCATIONS RECEIVING LESS THAN A TENTH INCH. MOST MODELS INDICATING THE BEST CHANCE FOR PRECIPITATION BEING THIS EVENING OVER THE SOUTHERN FOOTHILLS...PALMER DIVIDE AND PARK COUNTY. .LONG TERM...(THURSDAY THROUGH TUESDAY) ISSUED AT 258 AM MDT WED MAY 20 2015 AN ANOMALOUSLY DEEP LONGWAVE TROUGH OVER THE WEST COAST IS PROGGED TO SLOWLY MOVE INLAND ACROSS THE GREAT BASIN AND DESERT SOUTHWEST DURING THE NEXT FEW DAYS. AND AS THE UPPER TROUGH MIGRATES EAST...UNUSUALLY STRONG PACIFIC AND SUBTROPICAL JETS FOR THIS TIME OF YEAR CONVERGING NEAR THE BOTTOM OF THIS TROUGH WILL CONTINUE TO TRANSPORT MOIST SUBTROPICAL AIR UP OVER THE SWRN U.S.. THE 00Z MODEL RUN SHOWS A MID-LEVEL SHORTWAVE TROUGH/VORT LOBE RACING UP THE FRONT SIDE OF THE MAIN TROUGH OVER ARIZONA LATE WEDNESDAY NIGHT AND REACHING NORTHEAST COLORADO BY THURSDAY NIGHT. NAM...GFS...ECMWF...CANADIAN MODELS ALL INDICATE AN INFLUX OF LOW-LEVEL MOISTURE EAST OF THE MTNS WITH 10-20KT SELY FLOW DURING THE DAY THURSDAY IN ADVANCE OF THE UPPER AIR DISTURBANCE. THE ECMWF SHOWS A SFC LOW AND AN ASSOCIATED VORTICITY CONVERGENCE BOUNDARY FORMING JUST EAST-SOUTHEAST OF THE DENVER METRO AREA LATE THURSDAY AFTERNOON AS THE TAIL END OF AN 80KT JET PASSES OVERHEAD. NAM SHOWS SFC BASED CAPES IN THE 200-500 J/KG RANGE IN THE VICINITY OF THIS FEATURE. HOWEVER WITH INCREASING CLOUD COVER THROUGH THE DAY...T-STORM CHANCES ON THE PLAINS SHOULD BE LOW. MORE LIKE SCATTERED RAIN SHOWERS BY MID TO LATE AFTERNOON. WHEREAS IN THE HIGH COUNTRY...STEEPER LAPSE RATES...INCREASING MOISTURE AND LIFT GENERATED BY THE APPROACHING SHORTWAVE SHOULD RESULT IN SCATTERED SHOWERS AND T-STORMS AS EARLY AS MID-AFTERNOON. MODELS SHOW THE AMBIENT AIRMASS CONTINUING TO MOISTEN THURSDAY NIGHT ESPLY EAST OF THE CONTINENTAL DIVIDE. HOWEVER...MODELS DO NOT INDICATE AS MUCH UPSLOPE FLOW OR THETA-E AS WERE PRESENT DURING THE HEAVY PRECIP EVENT OBSERVED THIS PAST MONDAY NIGHT AND TUESDAY. 12-HOUR FCST QPF AMOUNTS VARY QUITE A BIT FROM MODEL TO MODEL...ANYWHERE FROM A COUPLE TENTHS OF AN INCH TO 0.90 INCH ON THE PLAINS...AND IN THE HIGH COUNTRY FROM A FEW TENTHS OF AN INCH TO AROUND 1.40 INCHES OVERNIGHT. WETBULB ZERO REMAINS RELATIVELY HIGH WITH THIS SYSTEM...ROUGHLY UP AROUND 9500-10,000 FT ASL. SO ANY NEW SNOW ACCUMULATION SHOULD REMAIN CONFINED TO THE HIGHER MTN SLOPES AND PASSES WHERE ANYWHERE FROM 2-5 INCHES OF WET SNOW COULD PILE UP BY FRIDAY MORNING. ON FRIDAY...THIS WEATHER DISTURBANCE LIFTS OUT ALLOWING FOR MORE SUNSHINE AND A 2-3 DEG C WARM-UP WITH A SOUTH-SOUTHWESTERLY FLOW IN PLACE. WHILE THE OVERALL AIRMASS APPEARS DRIER ON FRIDAY...DAYTIME HEATING AND WET SOIL CONDITIONS SHOULD HAVE LITTLE PROBLEM SUPPORTING ISOLATED TO SCATTERED SHOWERS/T-STORMS BY MID TO LATE AFTERNOON OVER THE MTNS AND ADJACENT PLAINS. ADDITIONAL RAIN AMOUNTS THIS GO ROUND SHOULD BE ON THE LIGHT SIDE. FRIDAY NIGHT-SATURDAY...THE MAIN UPPER TROUGH CONTINUES ITS INLAND MARCH...BUT MODELS DIFFER REGARDING THE SPEED AND DIRECTION OF THE TROUGH AND 500 MB LOW. THE GFS WEAKENS THE TROUGH AND QUICKLY LIFTS ITS NORTHEASTWARD ACROSS THE NRN ROCKIES ON SATURDAY WHICH PLACES NORTHEAST COLORADO UNDER A RELATIVELY DRY SOUTHWEST FLOW ALOFT AND A DRIER DOWNSLOPE FLOW OFF THE FRONT RANGE. THE ECMWF SHOWS THE TROUGH WITH ITS CLOSED LOW TAKING A MORE EASTERLY PATH ACROSS UTAH ON SATURDAY AND THEN OPENING IT UP AS IT PASSES OVER COLORADO ON SUNDAY. THE CANADIAN MODEL DRIVES THE UPPER TROUGH AND 500 MB LOW SOUTHEASTWARD OVER THE LOWER DESERTS WHERE THE UPPER LOW WOBBLES AROUND THROUGH SUNDAY BEFORE TRACKING EAST AND STAYING WELL SOUTH OF COLORADO ON MONDAY. THAT SAID...AIRMASS OVER NERN COLORADO APPEARS TO REMAIN RELATIVELY MOIST AND UNSTABLE SATURDAY THROUGH MONDAY...ENOUGH TO WARRANT MENTIONING A CHANCE OF SHOWERS AND A SLIGHT CHANCE OF T- STORMS EACH DAY. TUESDAY LOOKS DRIER AND SLIGHTLY WARMER...ALTHOUGH THE GFS SHOWS ANOTHER WEATHER DISTURBANCE SWINGING ACROSS WYOMING AND NORTHERN COLORADO BRINGING ANOTHER ROUND OF LATE DAY SHOWERS AND T-STORMS FOR PORTIONS OF THE FORECAST AREA. && .AVIATION...(FOR THE TAFS THROUGH 12Z THURSDAY MORNING) ISSUED AT 258 AM MDT WED MAY 20 2015 LOW CLOUDS AND FOG WILL SLOWLY RISE AFTER 13Z. THERE WILL BE AREAS WHERE VISIBILITY WILL BE LESS THAN A QUARTER MILE WITH CEILINGS OF 100 TO 200 FEET. EXPECT CEILINGS TO RISE TO 2000 TO 4000 FEET AFTER 18Z. A WEAK SYSTEM WILL BRING SCATTERED SHOWERS LATE THIS AFTERNOON AND TONIGHT. CEILINGS WILL LOWER TONIGHT INTO THE 500 TO 2000 FOOT RANGE. WINDS WILL BE EAST TO NORTHEAST TODAY AND TURN SOUTHEASTERLY TONIGHT. && .HYDROLOGY... ISSUED AT 258 AM MDT WED MAY 20 2015 ADDITIONAL RAINFALL TODAY AND TONIGHT WILL BE LIGHT AND IS NOT EXPECTED TO CAUSE ANY ADDITIONAL FLOODING ISSUES. THE CACHE LA POUDRE AT GREELEY AND THE SOUTH PLATTE RIVER FROM KERSEY TO WELDONA ARE EXPECTED TO JUST REACH FLOOD STAGE. A FLOOD WARNING REMAINS IN EFFECT FOR THIS. RIVER LEVELS ARE EXPECTED TO BE LESS THAN THE WHAT OCCURRED LAST WEEK. && .BOU WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...MEIER LONG TERM...BAKER AVIATION...MEIER HYDROLOGY...MEIER
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DENVER/BOULDER CO 1035 AM MDT TUE MAY 19 2015 COZ030>051-201645- JACKSON COUNTY BELOW 9000 FEET- WEST JACKSON AND WEST GRAND COUNTIES ABOVE 9000 FEET- GRAND AND SUMMIT COUNTIES BELOW 9000 FEET- SOUTH AND EAST JACKSON/LARIMER/NORTH AND NORTHEAST GRAND/ NORTHWEST BOULDER COUNTIES ABOVE 9000 FEET- SOUTH AND SOUTHEAST GRAND/WEST CENTRAL AND SOUTHWEST BOULDER/ GILPIN/CLEAR CREEK/SUMMIT/NORTH AND WEST PARK COUNTIES ABOVE 9000 FEET-LARIMER AND BOULDER COUNTIES BETWEEN 6000 AND 9000 FEET- JEFFERSON AND WEST DOUGLAS COUNTIES ABOVE 6000 FEET/GILPIN/CLEAR CREEK/NORTHEAST PARK COUNTIES BELOW 9000 FEET- CENTRAL AND SOUTHEAST PARK COUNTY- LARIMER COUNTY BELOW 6000 FEET/NORTHWEST WELD COUNTY- BOULDER AND JEFFERSON COUNTIES BELOW 6000 FEET/WEST BROOMFIELD COUNTY- NORTH DOUGLAS COUNTY BELOW 6000 FEET/DENVER/WEST ADAMS AND ARAPAHOE COUNTIES/EAST BROOMFIELD COUNTY- ELBERT/CENTRAL AND EAST DOUGLAS COUNTIES ABOVE 6000 FEET- NORTHEAST WELD COUNTY-CENTRAL AND SOUTH WELD COUNTY-MORGAN COUNTY- CENTRAL AND EAST ADAMS AND ARAPAHOE COUNTIES- NORTH AND NORTHEAST ELBERT COUNTY BELOW 6000 FEET/NORTH LINCOLN COUNTY- SOUTHEAST ELBERT COUNTY BELOW 6000 FEET/SOUTH LINCOLN COUNTY- LOGAN COUNTY-WASHINGTON COUNTY-SEDGWICK COUNTY-PHILLIPS COUNTY- 1035 AM MDT TUE MAY 19 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST AND NORTH CENTRAL COLORADO. .DAY ONE...TODAY AND TONIGHT RAIN AND HEAVY MOUNTAIN SNOW WILL CONTINUE INTO EARLY THIS AFTERNOON. TOTAL RAINFALL FROM THE FOOTHILLS EASTWARD ACROSS THE PLAINS IS EXPECTED TO RANGE BETWEEN 1 AND 1.5 INCHES...POSSIBLY UP TO 2 INCHES IN THE NORTHERN FOOTHILLS AND IN SOUTHERN WASHINGTON AND LINCOLN COUNTIES. SMALL CREEKS AND STREAMS WILL LIKELY SEE MINOR FLOODING CONCERNS...SPREADING TO MAINSTREAM RIVERS INCLUDING THE CACHE LA POUDRE AND SOUTH PLATTE ALONG THE FRONT RANGE TONIGHT AND CONTINUE FARTHER EAST ON THE PLAINS THROUGH THE REST OF THE WEEK. PEOPLE ALONG STREAMS AND IN LOW LYING AREAS SHOULD REMAIN ALERT FOR RISING WATER LEVELS. SNOW IS EXPECTED ABOVE 9000 FEET AND POSSIBLY MIXED WITH RAIN DOWN TO 8000 FEET. TOTAL SNOWFALL OF 10 TO 20 INCHES CAN BE EXPECTED BY THIS EVENING ABOVE 10 THOUSAND FEET. A FEW THUNDERSTORMS ARE EXPECTED THIS AFTERNOON OVER THE HIGHER TERRAIN WHICH MAY PRODUCE HAZARDOUS DRIVING CONDITIONS INCLUDING LOW VISIBILITY AND SLUSHY OR SNOWPACKED ROADS UNDER THE HEAVER SHOWERS/STORMS. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY WEDNESDAY AND THURSDAY MORNING WILL BE DRIER...BUT THERE WILL STILL BE A CHANCE OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS ESPECIALLY IN THE MOUNTAINS AND FOOTHILLS. ANOTHER SYSTEM WILL AFFECT THE AREA THURSDAY NIGHT THROUGH FRIDAY. THIS SYSTEM MAY BRING MORE WIDESPREAD AND SIGNIFICANT PRECIPITATION TO THE AREA. TEMPERATURES LOOK SLIGHTLY WARMER AS WELL...WHICH MAY BRING HIGHER SNOW LEVELS. WILL BE WATCHING CLOSELY TO TODAY'S SNOWPACK AND HOW MUCH MELTING HAPPENS THROUGH THURSDAY MORNING BEFORE THE POTENTIAL OF GETTING RAIN THURSDAY NIGHT THROUGH FRIDAY. FOR THE WEEKEND IT WILL REMAIN UNSETTLED WITH A CHANCE OF SHOWERS AND THUNDERSTORMS BOTH DAYS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY OR TONIGHT. KRIEDERMAN
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
A prolonged period of minor to moderate lowland flooding occurred along the South Platte River.
Widespread minor to moderate lowland flooding was observed along the Cache La Poudre River.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2015Every state in 2015This day in weather historyWarnings in Colorado, 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: 582804, 582799.