A moist southwest flow aloft ahead of a Pacific low pressure system produced significant snowfall in the western San Juan Mountains.
Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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 GJT wrote it up.
A moist southwest flow aloft ahead of a Pacific low pressure system produced significant snowfall in the western San Juan Mountains.
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 Grand Junction, CO wrote its last area forecast discussion before the first event at May 9, 2:50 AM MST, 5 hours 10 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND JUNCTION CO 350 AM MDT MON MAY 9 2011 .SHORT TERM...TONIGHT THROUGH TUESDAY... SURFACE COLD FRONT WILL CONTINUE TO PUSH EAST ACROSS THE FORECAST AREA THIS MORNING...USHERING IN COOLER CONDITIONS ALONG WITH INCREASED CLOUD COVER AND SLIGHTLY HIGHER SFC DEW POINTS. SOME LIGHT SHOWERS DEVELOPING ALONG THE LEADING EDGE OF THE FRONT...ALTHOUGH MOISTURE REMAINS LIMITED INITIALLY...SO MORE WIND THAN RAIN EXPECTED THIS MORNING. MORE IMPRESSIVE LINE OF CONVECTION EXPECTED FOR THIS AFTERNOON AND EARLY EVENING AS SHRTWV ENERGY ROUNDING THE BASE OF THE DIGGING UPPER LEVEL LOW KICKS OUT NEAR PEAK HEATING WITH 110KT JET STREAKING MOVING THROUGH. DECENT SPEED SHEAR WILL BE PRESENT...AND WITH VALLEY INTERACTION WITH LOW LEVEL WIND FIELDS...RESULTING IN AREAS OF DIRECTIONAL SHEAR...COULD SEE A FEW ORGANIZED STORMS PRODUCING STRONG OUTFLOW WINDS AND MARGINAL HAIL. SNOW WILL ALSO BE POSSIBLE ABOVE 10K THIS AFTERNOON...ALTHOUGH NO SIGNIFICANT ACCUMULATIONS EXPECTED TODAY. THIS EJECTING WAVE EXITS BY MIDNIGHT WITH A DECREASE IN SHOWERS OVERNIGHT. THIS WILL BE SHORT-LIVED AS COLD POOL ALOFT AND WARMING TEMPS ON TUESDAY HELP TO TRIGGER ANOTHER ROUND OF CONVECTION TUESDAY AFTERNOON AND EVENING. THE MAIN LOW LOOKS TO KICK OUT TUESDAY NIGHT...WITH SNOW LEVELS DROPPING. THIS WILL BE THE TIMEFRAME FOR THE BEST CHANCE OF ACCUMULATING SNOW ACROSS THE CENTRAL AND SOUTHWEST MOUNTAINS. ATTM...LOOKS LIKE A FEW AREAS ABOVE 8500 FEET COULD SEE UPWARDS OF 5 INCHES LATE TUESDAY THROUGH EARLY WEDNESDAY. WILL CONTINUE TO MONITOR...BUT NOT ANTICIPATING ANY HIGHLIGHTS RIGHT NOW. AFTER A WEEKEND OF ABOVE NORMAL TEMPERATURES...READINGS WILL BE COOLING DOWN SIGNIFICANTLY TODAY AND TUESDAY...HEADING TO THE COOL SIDE OF NORMAL. MOS NUMBERS LOOK GOOD...SO WONT STRAY FAR. .LONG TERM...WEDNESDAY THROUGH SUNDAY... UPPER CLOSED LOW DEPICTED TO BE NEAR THE 4 CORNERS REGION EARLY WED MORNING BY BOTH THE NAM AND GFS. THIS PROVIDES PLENTY OF DYNAMICAL FORCING OVER CO MTNS TO WORK ON AVAILABLE MSTR. SYSTEM WEAKENS TO OPEN TROF BY AFTERNOON AS IT LIFTS EAST OF OUR CWA. OVERALL RAISED POPS ESPECIALLY DURING THE MORNING PERIOD. MODEL QPF OUTPUT SUGGESTS POSSIBILITY OF ACCUMULATING SNOW DURING THIS PERIOD AND SNOW ADVISORY MAY BE NECESSARY FOR THE HIGHER ELEVATIONS. WEDNESDAY NIGHT THE FLOW VEERS TO THE NW AS A RIDGE OF HIGH PRESSURE BUILDS OVER THE GRT BASIN. ENOUGH MSTR AND INSTABILITY WILL REMAIN FOR MTN SHOWERS MOSTLY ACROSS THE NRN ZONES. FREEZING LEVEL LOWERS SOME BUT STILL REMAINS AROUND OR ABOVE 8500 FEET. HIGH PRESSURE WILL SHIFT EWRD OVER WRN UT THU AND AMPLIFY BRINGING A WARMING AND DRYING PERIOD. THE RIDGE AXIS THEN SHIFTS EASTWARD TO THE CO/UT BORDER FRIDAY WITH TEMPS WARMING ABOVE SEASONAL NORMALS. ALSO SOME HINT OF MSTR BRINGS A THREAT OF ISOLD MTN TSTMS. CONDITIONS WILL REVERT BACK TO DRY AND WARM FOR THE LAST PART OF THE WEEK. AFTERNOON HIGHS WILL RISE TO BETWEEN 10 AND 15 DEGREES ABOVE NORMAL WHICH WILL RESULT IN INCREASED SNOWMELT. MODELS HINTED THAT THIS ADDED MOISTURE MAY BE SUFFICIENT TO GENERATE ISOLATED AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS FOR THE NORTHERN DIVIDE MOUNTAINS THURSDAY...FRIDAY AND SATURDAY. SUNDAY LOOKS BREEZY AND CONTINUED WARM AS FLOW BACKS TO THE SOUTHWEST IN RESPONSE TO ANOTHER TROUGH ALONG THE WEST COAST. THOUGH THE UPPER LEVEL RIDGE SHIFTS EAST...DRIER AIR ADVECTING OVER THE AREA FROM THE DESERT SOUTHWEST WILL PREVENT AFTERNOON THUNDERSTORM DEVELOPMENT. && .AVIATION... A COLD FRONT MOVING THROUGH THE REGION WILL USHER IN COOLER WEATHER TODAY WITH SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING. STRONG OUTFLOW WINDS WILL OCCUR NEAR THE SHOWERS...WITH CIGS BRIEFLY DROPPING INTO MVFR THRESHOLDS POSSIBLE. UNSETTLED CONDITIONS WILL REMAIN IN PLACE THROUGH WEDNESDAY AS A DEEP UPPER LEVEL LOW PRESSURE SYSTEM BECOMES NEARLY STATIONARY OVER THE GREAT BASIN. SOME SNOW WILL ALSO FALL OVER THE HIGHER TERRAIN...MAINLY ABOVE 9K. && .FIRE WEATHER... COOLER CONDITIONS MOVING INTO THE REGION ALONG WITH INCREASED LOW LEVEL MOISTURE WILL RESULT IN IMPROVED FIRE WEATHER CONDITIONS OVER THE NEXT SEVERAL DAYS. HOWEVER...GUSTY WINDS WILL CONTINUE WITH SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS EXPECTED THIS AFTERNOON AND AGAIN TUESDAY AFTERNOON. && .HYDROLOGY... SNOWMELT HAS ACCELERATED OVER THE PAST FEW DAYS UNDER A RIDGE OF HIGH PRESSURE. THE INCREASED SNOWMELT HAS BROUGHT A RAPID RISE OF MANY SMALLER STREAMS...CREEKS AND A MORE GRADUAL RISE IN RIVERS THROUGHOUT WESTERN COLORADO AND EASTERN UTAH. COOLER WEATHER ARRIVING TODAY AND CONTINUING THROUGH WEDNESDAY WILL SLOW THE SNOWMELT AND HELP STABILIZE RIVER FLOWS BY MIDWEEK. HOWEVER...LEVELS COULD BEGIN TO RISE AGAIN BY THIS COMING WEEKEND AS WARMER WEATHER RETURNS THURSDAY AND FRIDAY. THE GREEN RIVER IN NORTHEAST UTAH WILL CONTINUE TO RUN HIGH THROUGH MIDWEEK DUE TO A COMBINATION OF SNOWMELT AND INCREASED RELEASES FROM THE FLAMING GORGE RESERVOIR. THE RIVER IS EXPECTED TO RUN AROUND BANKFULL FOR SEVERAL DAYS. THE RELEASE OF WATER FROM THE RESERVOIR WILL CONTINUE UNTIL NATURAL PEAK FLOWS BEGIN. A FLOOD ADVISORY CONTINUES FOR THE GREEN RIVER NEAR JENSEN...WHERE IT IS EXPECTED TO EXCEED BANKFULL THIS MORNING. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...NONE UT...NONE && SHORT TERM.....JDC LONG TERM......MC/NL AVIATION.......JDC FIRE WEATHER...JDC HYDROLOGY......TGJT
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GRAND JUNCTION CO 545 AM MDT MON MAY 9 2011 COZ001>014-017>023-UTZ022>025-027>029-101145- ANIMAS RIVER BASIN-ARCHES/GRAND FLAT-CANYONLANDS/NATURAL BRIDGES- CENTRAL COLORADO RIVER BASIN- CENTRAL GUNNISON AND UNCOMPAHGRE RIVER BASIN- CENTRAL YAMPA RIVER BASIN-DEBEQUE TO SILT CORRIDOR- EASTERN UINTA BASIN-EASTERN UINTA MOUNTAINS- ELKHEAD AND PARK MOUNTAINS-FLAT TOPS- FOUR CORNERS/UPPER DOLORES RIVER- GORE AND ELK MOUNTAINS/CENTRAL MOUNTAINS-GRAND AND BATTLEMENT MESAS- GRAND VALLEY-LA SAL AND ABAJO MOUNTAINS-LOWER YAMPA RIVER BASIN- NORTHWEST SAN JUAN MOUNTAINS-PARADOX VALLEY/LOWER DOLORES RIVER- ROAN AND TAVAPUTS PLATEAUS-SAN JUAN RIVER BASIN-SOUTHEAST UTAH- SOUTHWEST SAN JUAN MOUNTAINS-TAVAPUTS PLATEAU- UNCOMPAHGRE PLATEAU AND DALLAS DIVIDE-UPPER GUNNISON RIVER VALLEY- UPPER YAMPA RIVER BASIN-WEST ELK AND SAWATCH MOUNTAINS- 545 AM MDT MON MAY 9 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN UTAH AND WESTERN COLORADO. .DAY ONE...TODAY AND TONIGHT... SCATTERED SHOWERS AND THUNDERSTORMS CAN BE EXPECTED THIS AFTERNOON AND TONIGHT. THE STRONGEST STORMS WILL PRODUCE GUSTY OUTFLOW WINDS TO NEAR 50 MPH AND SMALL HAIL. BRIEF HEAVY RAIN AND SNOW WILL ALSO FALL FROM THE STORMS...WITH SNOW LEVELS AROUND 10000 FEET TODAY... LOWERING TO AROUND 8500 FEET TONIGHT. NO SIGNIFICANT SNOWFALL ACCUMULATIONS ARE EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY... UNSETTLED WEATHER WILL CONTINUE THROUGH WEDNESDAY WITH AREAS OF VALLEY RAIN AND MOUNTAIN SNOW. A FEW THUNDERSTORMS WILL ALSO BE POSSIBLE TUESDAY AFTERNOON AND EVENING. DRY AND WARMER CONDITIONS THEN MOVE BACK IN TO CLOSE OUT THE WORK WEEK. THE RETURN TO WARMER WEATHER WILL AGAIN ACCELERATE THE MELTING OF SNOW ACROSS THE MOUNTAINS. RIVERS AND SMALL STREAMS WILL BE RUNNING HIGH AND FAST AS THE WEEKEND APPROACHES. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED TODAY OR TONIGHT.
The national radar mosaic for the moment the first event began.
2 winter weather. Local standard time, as filed.
Snowfall of 5 to 9 inches was measured across the area. Winds gusted 25 to 50 mph and produced areas of blowing and drifting snow.
Snowfall of 5 to 10 inches was measured across the area. Winds gusted 25 to 50 mph and produced areas of blowing and drifting snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2011Every state in 2011This day in weather historyWarnings in Colorado, May 2011
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: 314319, 314321.