An unseasonably strong and cold low pressure system brought rain, snow, and cold temperatures to northern Arizona.
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 FGZ wrote it up.
An unseasonably strong and cold low pressure system brought rain, snow, and cold temperatures to northern Arizona.
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 Flagstaff, AZ wrote its last area forecast discussion before the first event at May 18, 9:47 AM MST, 13 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE FLAGSTAFF AZ 947 AM MST WED MAY 18 2011 .SYNOPSIS...NORTHERN ARIZONA WILL EXPERIENCE GUSTY WINDS AGAIN TODAY AS A COLD STORM SYSTEM MOVES SLOWLY ACROSS THE GREAT BASIN. THIS SYSTEM WILL ALSO BRING SCATTERED RAIN AND HIGH ELEVATION SNOW FROM NOW INTO THURSDAY...ALONG WITH MUCH COLDER TEMPERATURES. FAIR WEATHER SHOULD RETURN FOR LATE FRIDAY INTO THE WEEKEND. && .DISCUSSION...SCATTERED SHOWERS ARE UNDERWAY THIS MORNING ACROSS NORTHERN ARIZONA...ESPECIALLY ACROSS MOGOLLON RIM COUNTRY AND NORTH-CENTRAL AZ NEAR THE UTAH BORDER. THESE SHOWERS WILL CONTINUE TO EXPAND THROUGH THE DAY...WITH WINDY CONDITIONS ALSO LIKELY FOR EAST-CENTRAL AZ. THIS UNSEASONABLY COLD SYSTEM WILL ALSO DROP SNOW LEVELS TO DOWN AROUND 6500 FEET OVER THE COMING 24HRS. ANY LIGHT SNOWFALL ACCUMULATIONS ARE LIKELY TO REMAIN ABOVE ABOUT 7000 FEET AND UNTIL AFTER SUNSET TONIGHT. && .PREV DISCUSSION /345 AM MST/...A DEEP AND UNSEASONABLY COLD LOW PRESSURE SYSTEM WAS CENTERED OVER CENTRAL CALIFORNIA AND NEVADA THIS MORNING. A STRONG DISTURBANCE ROTATING AROUND THE SOUTHERN PART OF THE SYSTEM WILL AFFECT OUR REGION LATER THIS MORNING INTO THIS EVENING. A MOISTURE PLUME HAS ALREADY MOVED INTO CENTRAL AND WESTERN AZ WITH LIGHT PRECIPITATION BEGINNING TO BREAK OUT. AS THE STRONGER DISTURBANCE MOVES IN...EXPECT PRECIPITATION TO RAPIDLY INCREASE ACROSS MUCH OF THE AREA. SNOW LEVELS WILL RANGE FROM 6500 TO 7500 FEET WITH SOME LIGHT ACCUMULATIONS POSSIBLE...THOUGH EVEN A BRIEF BREAK IN THE PRECIPITATION WILL ALLOW FOR RAPID MELTING DUE TO THE HIGHER SUN ANGLE THIS TIME OF YEAR. AREAS ABOVE 8000 FEET COULD SEE A FEW INCHES OF SNOW THROUGH TONIGHT. IT WILL ALSO BE UNSTABLE ENOUGH FROM LATE MORNING INTO EARLY EVENING FOR A FEW THUNDERSTORMS. TEMPERATURES TODAY WILL BE UP TO 20 DEGREES BELOW NORMAL. THE OTHER STORY TODAY WILL BE STRONG AND GUSTY WINDS FROM THE MOGOLLON RIM AND WHITE MTNS EASTWARD...AND A WIND ADVISORY REMAINS IN EFFECT THROUGH 8 PM MST. COLD AIR ALOFT WILL LINGER ACROSS THE REGION ON THURSDAY KEEPING HIGH TEMPERATURES MUCH BELOW NORMAL. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP DURING THE AFTERNOON ESPECIALLY OVER THE HIGHER TERRAIN. THE SYSTEM WILL SHIFT OFF TO THE NORTHEAST BY FRIDAY WITH ONLY A SLIGHT CHANCE OF SHOWERS NEAR THE 4-CORNERS. TEMPERATURES WILL BE AROUND 10 DEGREES WARMER FRIDAY AFTERNOON. BRIEF RIDGING DEVELOPS OVER ARIZONA SATURDAY BEFORE THE NEXT TROUGH APPROACHES BY LATE SUNDAY INTO EARLY NEXT WEEK. THE LATEST MODEL TRENDS HAVE BEEN TO DELAY PRECIP CHANCES UNTIL SUNDAY NIGHT OR MONDAY...AND ALSO FOR A WEAKER AND DRIER TROUGH MOVING MOSTLY NORTH OF ARIZONA. WILL CONTINUE THE CURRENT FORECAST OF COOLER AND BREEZY WEATHER EARLY IN THE WEEK...WITH RAIN CHANCES ONLY AROUND 20 PERCENT FOR NOW. && .AVIATION...FOR THE 18Z PACKAGE...A COLD FRONT WILL CROSS NORTHERN AZ TODAY. SCATTERED RAIN/SNOW SHOWERS AND ISOLATED THUNDERSTORMS WEST OF A KCEZ-KPAN LINE AT 18Z WILL SPREAD EASTWARD THIS AFTERNOON WITH AREAS MVFR AND LOCAL IFR. TIL 03Z EXPECT SOUTHWEST WINDS 15-30KT GUSTING 40KT. AFT 00Z THU EXPECT STEADY PRECIPITATION ACROSS THE AREA...WITH WIDESPREAD MVFR AND AREAS IFR. SNOW LEVELS DROPPING TO BETWEEN 6000-7000 FEET. && .FIRE WEATHER...AN UNSEASONABLY STRONG UPPER-LEVEL LOW OVER THE WEST WILL BRING A CONTINUATION OF STRONG AND GUSTY WINDS THROUGH THURSDAY. SIGNIFICANT INCREASES IN MOISTURE AND MUCH COOLER TEMPERATURES WILL SPREAD EASTWARD ACROSS THE REGION AND CRITICAL FIRE WEATHER CONDITIONS ARE NOT EXPECTED. AREAS OF RAIN AND HIGH ELEVATION SNOW WILL SPREAD ACROSS NORTHERN ARIZONA TODAY AND LINGER THROUGH THURSDAY. FRIDAY THROUGH SUNDAY...WARMER TEMPERATURES...A FEW SHOWERS.. AND LIGHTER WINDS CAN BE EXPECTED FRIDAY. DRIER WEATHER WILL ARRIVE SATURDAY AS THE TROUGH PUSHES EAST AND HIGH PRESSURE DEVELOPS ACROSS THE REGION. BY SUNDAY...ANOTHER STRONG UPPER-LEVEL LOW WILL APPROACH THE AREA WITH INCREASING WINDS. && .FGZ WATCHES/WARNINGS/ADVISORIES... WIND ADVISORY UNTIL 8 PM MST THIS EVENING FOR AZZ009-011>017-039- 040. && PUBLIC.....................KD/JJ AVIATION/FIRE WX...........DL FOR NORTHERN ARIZONA WEATHER INFORMATION VISIT WEATHER.GOV/FLAGSTAFF.
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE FLAGSTAFF AZ 408 AM MST WED MAY 18 2011 AZZ004>018-037>040-190700- KAIBAB PLATEAU-MARBLE AND GLEN CANYONS-GRAND CANYON COUNTRY- COCONINO PLATEAU-YAVAPAI COUNTY MOUNTAINS- NORTHEAST PLATEAUS AND MESAS HWY 264 NORTHWARD-CHINLE VALLEY- CHUSKA MOUNTAINS AND DEFIANCE PLATEAU- LITTLE COLORADO RIVER VALLEY IN COCONINO COUNTY- LITTLE COLORADO RIVER VALLEY IN NAVAJO COUNTY- LITTLE COLORADO RIVER VALLEY IN APACHE COUNTY- WESTERN MOGOLLON RIM-EASTERN MOGOLLON RIM-WHITE MOUNTAINS- NORTHERN GILA COUNTY-YAVAPAI COUNTY VALLEYS AND BASINS- OAK CREEK AND SYCAMORE CANYONS-BLACK MESA AREA- NORTHEAST PLATEAUS AND MESAS SOUTH OF HWY 264- 408 AM MST WED MAY 18 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL ARIZONA...NORTH CENTRAL ARIZONA...NORTHEAST ARIZONA AND WEST CENTRAL ARIZONA. .DAY ONE...TODAY AND TONIGHT AN UNSEASONABLY STRONG AND COLD STORM SYSTEM WILL APPROACH THE AREA TODAY. EXPECT STRONG SOUTHWEST WINDS TO DEVELOP THIS MORNING AND CONTINUE THROUGH EARLY EVENING. A WIND ADVISORY IS IN EFFECT FROM 8 AM UNTIL 8 PM MST TODAY FROM THE MOGOLLON RIM AND WHITE MOUNTAINS NORTHWARD WHERE WIND GUSTS NEAR 45 MPH ARE EXPECTED. IN ADDITION...THIS WEATHER SYSTEM WILL BRING MUCH COLDER TEMPERATURES WITH WIDESPREAD RAIN AND HIGH ELEVATION SNOW SHOWERS TODAY AND TONIGHT. A FEW THUNDERSTORMS ARE ALSO POSSIBLE. LIGHT SNOW ACCUMULATION CAN BE EXPECTED ABOVE 7000 FEET ELEVATION...WITH SEVERAL INCHES LIKELY ABOVE 8000 FEET. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED THURSDAY...THEN FAIR WEATHER WILL RETURN FOR FRIDAY INTO THE WEEKEND. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.
The national radar mosaic for the moment the first event began.
1 dust storm, 1 winter storm. Local standard time, as filed.
Blowing dust along Interstate 40 between Flagstaff and Winslow reduced the visibility to the point where the Department of Public Safety began escorting vehicles along a 5 mile stretch of the freeway.
Snow, blowing snow, and icy roads caused several accidents along Interstate 40 and Interstate 17 around Flagstaff. There was a vehicle roll over on Lake Mary Road. A SUV lost control on the snow and collided with a school bus that was carrying children. Seven inches of snow fell about 5 miles south of Williams at an elevation of 7200 feet. Two to three inches of snow fell in and around Flagstaff.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2011Every state in 2011This day in weather historyWarnings in Arizona, 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: 312006, 312004.