An active weather pattern was over the northern Rockies with a disturbance |moving across southern Idaho. A well organized mid level circulation produced some significant snow.
Every event with a place to put it; 3 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 MSO wrote it up.
An active weather pattern was over the northern Rockies with a disturbance |moving across southern Idaho. A well organized mid level circulation produced some significant snow.
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 Missoula, MT wrote its last area forecast discussion before the first event at Mar 21, 7:24 PM MST, 6 hours 36 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
824 PM MDT MON MAR 21 2011
.UPDATE...
WINTER WEATHER ADVISORIES EXPANDED TO COVER WHITEBIRD GRADE AND
CAMAS PRAIRIE IN IDAHO.
&&
.DISCUSSION...
A BROAD STORM SYSTEM CONTINUES TO APPROACH THE NORTHERN ROCKIES
FROM THE SOUTHWEST THIS EVENING. SNOW HAS DEVELOPED ACROSS THE
CAMAS PRAIRIE IN IDAHO AND OVER WHITEBIRD GRADE DURING THE PAST
SEVERAL HOURS. THIS SNOWFALL IS EXPECTED TO CONTINUE THROUGH TUESDAY
MORNING...IMPACTING TRAVEL ALONG HIGHWAY 95 AND OTHER AREA
ROADWAYS. A WINTER WEATHER ADVISORY FOR SNOW HAS BEEN ISSUED TO
ADDRESS THE SNOW ACCUMULATION AND HAZARDOUS TRAVEL CONDITIONS THAT
WILL BE PRESENT DURING THIS TIME.
&&
.AVIATION...CONDITIONS WILL FURTHER DETERIORATE THIS EVENING AS
PRECIPITATION INTENSIFIES OVER THE NORTHERN ROCKIES. KGPI AND
KMSO WILL BEGIN TO SEE LOWERED VISIBILITIES AND CEILINGS AROUND
22/0400Z DUE TO A RAIN/SNOW MIX...BECOMING ALL SNOW BY TUESDAY
MORNING. KSMN AND KBTM WILL EXPERIENCE LOWERED VISIBILITIES AND
CEILINGS AROUND 22/0200Z. KSMN AND KBTM WILL START OUT AS A RAIN
BUT QUICKLY TRANSITION TO ALL SNOW AROUND 22/0600Z AS
PRECIPITATION INTENSIFIES. HEAVY SNOW AND LIFR CONDITIONS ARE
ANTICIPATED AT KBTM NEAR 22/0900Z THROUGH TUESDAY MORNING.
MOUNTAIN SHOWERS WILL LINGER THROUGH TUESDAY...OBSCURING
MOUNTAIN TOPS AND POSSIBLY PASSES.
&&
.PREV DISCUSSION... /ISSUED 223 PM MDT MON MAR 21 2011/
..AN EARLY SPRING STORM SYSTEM TO IMPACT THE NORTHERN ROCKIES
BEGINNING TONIGHT...
DISCUSSION...A RATHER ENERGETIC LOW PRESSURE SYSTEM HAS BEGUN
DELIVERING LIGHT BUT PERSISTENT SNOWFALL TO THE HIGHER TERRAIN OF
WESTERN MONTANA AND CENTRAL IDAHO. WE ARE STILL IN THE FAIRLY
WARMER REGION ASSOCIATED WITH THIS STORM SYSTEM...SO SNOW THAT HAS
BEEN FALLING HAS NOT BEEN MUCH OF AN IMPACT TO ROADWAYS OR TO
MOUNTAIN PASS TRAVEL. THIS WILL CHANGE AS THE EVENING CONTINUES
AND PRECIPITATION INTENSIFIES OVERNIGHT. SNOW LEVELS WILL
GRADUALLY LOWER AND HELP SNOWFALL TO QUICKLY ACCUMULATE ON
SURFACES. MODERATE SNOW ACCUMULATIONS ARE ANTICIPATED OVER
LOOKOUT...LOLO...LOST TRAIL...AND MARIAS PASSES THROUGH TUESDAY
MORNING.
MUCH HEAVIER SNOWFALL AMOUNTS ARE EXPECTED TO OCCUR IN THE
BUTTE/BLACKFOOT REGION. GIVEN THE TRAJECTORY THIS STORM IS
EXPECTED TO TAKE OVERNIGHT...THIS IS A FAVORABLE SETUP FOR THE
AREA TO RECEIVE HEAVY SNOWFALL AMOUNTS...PARTICULARLY IN THE
GEORGETOWN LAKE/ANACONDA/BUTTE AREAS. AS A RESULT...THIS ZONE HAS
BEEN UPGRADED TO A WINTER STORM WARNING BEGINNING THIS EVENING
THROUGH NOON TUESDAY.
VALLEY LOCATIONS AREAWIDE CAN EXPECT PRECIPITATION TO BEGIN AS RAIN
TONIGHT AND CHANGE OVER TO A RAIN/SNOW MIX BY TUESDAY MORNING. A
BURST OF SNOWFALL COULD OCCUR OVERNIGHT TONIGHT ACROSS THE
MISSOULA/BITTERROOT VALLEYS...CAUSING ROADWAYS TO BE SLICK FOR THE
TUESDAY MORNING COMMUTE...BUT ROADWAYS ARE EXPECTED TO REBOUND AND
BECOME MAINLY WET/SLOPPY BY MID MORNING.
THE SYSTEM WILL THEN SHIFT FURTHER EAST BY LATE IN THE DAY
TUESDAY WITH A BRIEF RIDGE OF HIGH PRESSURE TAKING ITS PLACE. THIS
WILL KEEP SHOWERY CONDITIONS IN THE HIGHER TERRAIN BUT HELP TO END
PRECIPITATION FOR MOST VALLEY AREAS BY EARLY WEDNESDAY.
WEDNESDAY THROUGH MONDAY...THIS PERIOD WILL REMAIN ACTIVE WITH A
SERIES OF DISTURBANCES MOVING THROUGH THE AREA. A COLD LONGWAVE
TROUGH WILL BE PARKED NEAR THE WEST COAST WITH WEAKENING WAVES
MOVING OUT OF THE TROUGH AND ACROSS THE FORECAST AREA. THERE MAY
BE A BREAK SATURDAY BUT CONFIDENCE IS LOW IN EXACT TIMING OF DRIER
PERIODS. TEMPERATURES SHOULD REMAIN MODERATE AND ONLY A LITTLE
BELOW NORMAL WITH THE WESTERLY FLOW PERSISTING.
AVIATION...CONDITIONS WILL FURTHER DETERIORATE THIS EVENING AS
PRECIPITATION INTENSIFIES OVER THE NORTHERN ROCKIES. KGPI AND
KMSO WILL BEGIN TO SEE LOWERED VISIBILITIES AND CEILINGS AROUND
22/0400Z DUE TO A RAIN/SNOW MIX...BECOMING ALL SNOW BY TUESDAY
MORNING. KSMN AND KBTM WILL EXPERIENCE LOWERED VISIBILITIES AND
CEILINGS AROUND 22/0200Z. KSMN AND KBTM WILL START OUT AS A RAIN
BUT QUICKLY TRANSITION TO ALL SNOW AROUND 22/0600Z AS
PRECIPITATION INTENSIFIES. HEAVY SNOW AND LIFR CONDITIONS ARE
ANTICIPATED AT KBTM NEAR 22/0900Z THROUGH TUESDAY MORNING.
MOUNTAIN SHOWERS WILL LINGER THROUGH TUESDAY...OBSCURING
MOUNTAIN TOPS AND POSSIBLY PASSES.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY UNTIL NOON MDT TUESDAY ABOVE 4000 FEET
FOR THE BITTERROOT/SAPPHIRE MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 6 PM MDT TUESDAY POTOMAC/SEELEY
LAKE REGION...WEST GLACIER REGION.
WINTER STORM WARNING UNTIL NOON MDT TUESDAY BUTTE/BLACKFOOT
REGION.
WINTER WEATHER ADVISORY UNTIL 9 AM MDT TUESDAY ABOVE 4000 FEET
FOR THE LOWER CLARK FORK REGION.
ID...WINTER WEATHER ADVISORY UNTIL 11 AM PDT TUESDAY ABOVE 3000 FEET
FOR THE LOWER HELLS CANYON/SALMON RIVER REGION...
OROFINO/GRANGEVILLE REGION.
WINTER WEATHER ADVISORY UNTIL NOON MDT TUESDAY ABOVE 4500 FEET
FOR THE EASTERN LEMHI COUNTY.
WINTER WEATHER ADVISORY UNTIL 11 AM PDT TUESDAY ABOVE 3000 FEET
FOR THE NORTHERN CLEARWATER MOUNTAINS...SOUTHERN CLEARWATER
MOUNTAINS.
&&
UPDATE...ZUMPFE
SHORT TERM...ALLEGRETTO
LONG TERM....GIBSON
AVIATION...DE ROSAThe national radar mosaic for the moment the first event began.
3 heavy snow. Local standard time, as filed.
Bart Bonney, the DES coordinator reported 7 inch snowfall at Georgetown Lake and 10 inches north of highway 1.
Snowfall amounts reported were, 11 inches at Warm Springs, elevation 7798 feet, 8 inches at Peterson Meadows, elevation 7200 feet and North Fork Elk Creek, elevation 6250.
Anaconda spotter at 5800 feet reported 5 inches of snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2011Every state in 2011This day in weather historyWarnings in Montana, March 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: 284781, 284783, 284782.