On May 21 and 22, a very strong, moist and slow moving closed low pressure system moved across North Central Idaho bringing very heavy snowfall to both the mountains and high elevated valleys.
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 MSO wrote it up.
On May 21 and 22, a very strong, moist and slow moving closed low pressure system moved across North Central Idaho bringing very heavy snowfall to both the mountains and high elevated valleys.
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 May 21, 2:34 AM PST, 26 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
434 AM MDT MON MAY 21 2007
.DISCUSSION...A VERY ACTIVE AND SLOW MOVING WEATHER DISTURBANCE
WILL CONTINUE TO MOVE THROUGH THE NORTHERN ROCKIES TODAY AND
TONIGHT. MODELS ARE IN AGREEMENT OF A CLOSED UPPER LOW PRESSURE
SYSTEM TRACKING ACROSS CENTRAL IDAHO TODAY AND THROUGH SOUTHWEST
MONTANA THIS EVENING AND TONIGHT. THE DIFFICULTY WITH THIS COMPLEX
SYSTEM WILL BE TO PINPOINT THE AREAS OF MOST SIGNIFICANT
PRECIPITATION. IT CURRENTLY LOOKS LIKE THE FOCUS OF THE MOST
SIGNIFICANT PRECIPITATION WILL BE CENTRAL IDAHO AS MODELS ARE
SHOWING A COUPLE SHOTS OF SIGNIFICANT PRECIPITATION OVER THE NEXT
24 HOURS. WRAP AROUND MOISTURE WILL HAVE TO BE MONITORED CLOSELY
ALONG THE CONTINENTAL DIVIDE WHERE SOME MODELS ARE SHOWING
ENHANCED PRECIPITATION THIS EVENING IN THE GLACIER NATIONAL PARK
VICINITY.
SOME INSTABILITY AHEAD OF THE LOW PRESSURE SYSTEM THIS MORNING HAS
PRODUCED SOME ISOLATED THUNDERSTORMS IN CENTRAL IDAHO AND
SOUTHWEST MONTANA. SUFFICIENT DYNAMICS WILL CONTINUE TO SUPPORT A
POSSIBLE THUNDERSTORM OR TWO THIS REGION EARLY THIS MORNING.
COLDER AIR AND INCREASING MOISTURE WILL ENTER CENTRAL IDAHO AND
NORTHWEST MONTANA AS THE DAY PROGRESSES. SNOW LEVELS WILL LOWER TO
4500-5000 FEET BY THE END OF THE DAY ACROSS THE ENTIRE REGION. THE
UPPER CLOSED LOW MOVES SOUTH AND EAST OF THE REGION THIS EVENING.
THE BEST CHANCES FOR ACCUMULATING SNOWS IN SOUTHWEST MONTANA AND
ALONG THE CONTINENTAL DIVIDE WILL BE THIS EVENING AND OVERNIGHT AS
WRAP AROUND MOISTURE FROM THIS LOW INCREASES.
TUESDAY THROUGH SUNDAY...MAIN CHANGE TO THE EXTENDED FORECAST WAS
TO BUMP UP PRECIPITATION CHANCES TUESDAY WITH LATEST NUMERICAL
MODEL DATA SUGGESTING AN UNSTABLE AIRMASS THROUGHOUT THE DAY ON
TUESDAY AND WITH PLENTY OF RESIDUAL MOISTURE TO WORK WITH...EXPECT
SCATTERED TO NUMEROUS SHOWERS TO DEVELOP..ESPECIALLY IN THE
AFTERNOON. -24 DEGREE C AIR AT 500 MB FORECAST TO BE OVER THE
NORTHERN ROCKIES BY MIDDAY TUESDAY AND WITH A FEW BREAKS IN THE
CLOUDS AND SURFACE WARMING...ANTICIPATE SHOWERS TO RAPIDLY DEVELOP
DESPITE MAIN UPPER LOW AND AREA OF ATMOSPHERIC LIFT OFF TO THE
SOUTHEAST OF THE AREA. WEAK HIGH PRESSURE BEGINS TO BUILD OVER THE
REGION ON WEDNESDAY WITH ONLY A SLIGHT CHANCE OF LIGHT RAIN
SHOWERS OVER EXTREME NORTHWEST MONTANA DURING THE AFTERNOON.
GLOBAL MODELS NOW IN VERY GOOD AGREEMENT MAINTAINING A LARGE/LONG-
WAVE TROUGH OVER THE WESTERN AND CENTRAL U.S. WITH REINFORCING
SHORT-WAVE TROUGHS DIVING SOUTHEAST INTO THE TROUGH INTO THE
NORTHWEST U.S. THE ASSOCIATED COOL AIRMASS AND RESULTANT SURFACE
HIGH WILL BEGIN TO PUSH SOUTHWARD ALONG THE CANADIAN ROCKIES
WEDNESDAY NIGHT. THE COOL AIRMASS WILL THEN PUSH OVER THE
CONTINENTAL DIVIDE DURING THE DAY THURSDAY AND COMBINE WITH LIFT
FROM THE POLAR JET STREAM NOSING IN FROM THE NORTH TO PRODUCE
SHOWERS OVER THE AREA THURSDAY INTO FRIDAY MORNING. INCREASED
PRECIPITATION CHANCES AND COOLED MAX TEMPERATURES THURSDAY AND
THURSDAY NIGHT AS A RESULT. UPPER LEVEL HIGH PRESSURE ALONG WITH
TEMPERATURES RETURNING TO ABOVE SEASONAL AVERAGES ARE EXPECTED
FRIDAY AFTERNOON INTO SATURDAY AHEAD OF THE NEXT PACIFIC TROUGH.
&&
.AVIATION...PERSISTENT LOW LEVEL MOISTURE FROM EVENING RAIN AND
MORE TO COME LATER TONIGHT WILL CONTINUE WIDESPREAD LOWER CEILINGS
AND OBSCURATIONS THROUGH MONDAY. PLEASE SEE APPROPRIATE TAFS AND
TWEBS.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...SNOW ADVISORY FROM NOON TODAY TO 6 AM MDT TUESDAY ABOVE 5000
FEET FOR BITTERROOT/SAPPHIRE MOUNTAINS-BUTTE/BLACKFOOT
REGION.
SNOW ADVISORY UNTIL 6 PM MDT THIS AFTERNOON ABOVE 4500 FEET FOR
LOWER CLARK FORK REGION.
SNOW ADVISORY FROM 6 PM THIS EVENING TO 6 AM MDT TUESDAY FOR
POTOMAC/SEELEY LAKE REGION-WEST GLACIER REGION.
ID...HEAVY SNOW WARNING UNTIL 5 PM PDT THIS AFTERNOON ABOVE 4500 FEET
FOR NORTHERN CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER
MOUNTAINS.
&&
SHORT TERM...RPN
LONG TERM....RPN
AVIATION...RPNThe national radar mosaic for the moment the first event began.
2 heavy snow. Local standard time, as filed.
Heavy snowfall was recorded at most Snotel sites across the southern Clearwater Mountains. Mountain Meadows received 10.0 inches, Savage Pass 9.0 inches, and Red River Hot Springs 9.5 inches of wet snow.
Heavy snowfall was recorded at most Snotel sites across the northern Clearwater Mountains. Cool Creek received 6.0 inches, Crater Meadows 10.0 inches and Hemlock Butte 9.0 inches of wet snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2007Every state in 2007This day in weather historyWarnings in Idaho, May 2007
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: 22903, 22902.