On April 17, a strong negatively tilted short wave trough with favorable wind shear aloft moved across Southwest Montana. Strong to severe thunderstorms developed along the surface front and tracked northeast across the area.
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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 MSO wrote it up.
On April 17, a strong negatively tilted short wave trough with favorable wind shear aloft moved across Southwest Montana. Strong to severe thunderstorms developed along the surface front and tracked northeast across the area. These thunderstorms were hail producers.
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 Apr 17, 3:06 PM MST, 3 hours 42 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
406 PM MDT TUE APR 17 2007
.UPDATE...JUST ISSUED A ZONE UPDATE TO ADD ISOLATED THUNDERSTORMS
INTO THE FORECAST NEAR LOST TRAIL PASS AND OVER LEMHI COUNTY.
LATEST SATELLITE DATA SHOWS GOOD CLEARING OVER ACROSS EAST CENTRAL
IDAHO. INFRARED SATELLITE IMAGERY SHOWS SOME COOLING CLOUD TOPS
(WHICH ARE INDICATIVE OF DEEPENING CONVECTION) AS WELL. LIGHTNING
PLOTS SHOW 3 STRIKES HAVING JUST NOW OCCURRED A ONLY COUPLE OF
MILES NORTH OF SALMON.
THE REST OF THE FORECAST APPEARS TO BE RIGHT ON TRACK. LATEST 18Z
MODEL RUNS APPEAR TO HAVE A GOOD HANDLE ON THE INSTABILITY AXIS
OVER THE AFFECTED AREA...SO EXPECT FOR THE ISOLATED ACTIVITY TO
END BY LATE EVENING JUST BEFORE THE MAIN (WINTER) EVENT BEGINS.
&&
.PREV DISCUSSION... /ISSUED 243 PM MDT TUE APR 17 2007/
DISCUSSION...A POTENT WEATHER SYSTEM WILL MOVE THROUGH THE
NORTHERN ROCKIES OVER THE NEXT 36 HOURS. AN UPPER LEVEL WAVE AHEAD
OF THE MAIN SYSTEM WILL KEEP SHOWERS OVER THE REGION THIS EVENING.
THEN THE MAIN TROUGH WILL SLOWLY MOVE INTO THE NORTHERN ROCKIES
OVERNIGHT. THIS SYSTEM IS A SLOW MOVER AND HAS A FORECASTED TRACK
THAT IS INDICATIVE OF A GOOD SNOW PRODUCER FOR SOUTHWEST MONTANA AND
AREAS ALONG THE DIVIDE. THE WATCH THAT WAS PREVIOUSLY ISSUED HAS
BEEN UPGRADED TO HEAVY SNOW WARNINGS TONIGHT THROUGH WEDNESDAY EVENING.
PLEASE SEE GTFWSWMSO FOR DETAILS.
THE DYNAMICS ASSOCIATED WITH THIS SYSTEM WILL MAKE FOR A TOUGH
FORECAST FOR THE CENTRAL AND SOUTHERN VALLEYS OF WESTERN MONTANA...ESPECIALLY
MISSOULA AND BITTERROOT VALLEYS. THEY ARE IN A GOOD WRAP AROUND
POSITION...HOWEVER NOT SURE THERE WILL BE ACCUMULATING SNOW ON THE
LOWEST VALLEY FLOORS. COULD SEE UP TO AN INCH ON THE GRASSY
SURFACES...BUT BELIEVE THE ROADS WILL REMAIN WET...EXCEPT UNDER
HEAVIER BANDS. THE FOOTHILLS OF THE MISSOULA AND BITTERROOT VALLEYS
COULD SEE UP TO 3 INCHES THROUGH WEDNESDAY.
THE BEST DYNAMICS WITH THE MAIN LOW WILL PUSH OFF TO THE SOUTHEAST
WEDNESDAY EVENING SO MOST HEADLINES ARE ANTICIPATED TO END THEN.
HOWEVER...LOW LEVEL UPSLOPE FLOW AND DIFFLUENT FLOW ALOFT OVER THE
PARK IS EXPECTED TO KEEP ACCUMULATING SNOW GOING AT LEAST UNTIL
MIDNIGHT.
TEMPERATURES THROUGH THE PERIOD WILL BE TRICKY AS AREAS UNDER MOST
PERSISTENT PRECIPITATION WILL HAVE A TOUGH TIME WARMING MORE THAN
A FEW DEGREES. THEREFORE...THERE WILL BE A GOOD NORTH TO SOUTH
SPLIT IN TEMPERATURES ACROSS WESTERN MONTANA...WITH WARMER
TEMPERATURES IN THE NORTH AND COLDER TEMPERATURES SOUTH.
BY THURSDAY A BROAD UPPER LEVEL TROUGH WILL ENCOMPASS MUCH OF THE
WESTERN UNITED STATES. THE LOW PRESSURE SYSTEM WHICH BROUGHT WINTER
WEATHER TO MUCH OF WESTERN MONTANA AND CENTRAL IDAHO WEDNESDAY WILL
BE SITUATED OVER EASTERN MONTANA. SCATTERED SHOWERS WILL REMAIN
POSSIBLE OVER WESTERN MONTANA THROUGHOUT THE DAY ON THURSDAY AS
COOL...NORTHERLY FLOW WRAPS MOISTURE AROUND THE EXITING WEATHER
SYSTEM. YET ANOTHER UPPER LEVEL LOW WITHIN BROAD TROUGHING WILL
MOVE ON SHORE OVER NORTHERN CALIFORNIA FRIDAY. FORECAST MODELS
CONTINUE TO TAKE THE BULK OF THIS SYSTEM SOUTH THROUGH THE GREAT
BASIN LEAVING THE NORTHERN ROCKIES UNDER WEAKER AND SOMEWHAT DRIER
TROUGHING. UNDER THIS PATTERN WIDELY SCATTERED CONVECTIVE SHOWERS
CANNOT BE RULED OUT DURING THE AFTERNOON.
THE FORECAST THROUGH THIS WEEKEND IS FOR NEAR TO SLIGHTLY BELOW
NORMAL TEMPERATURES AS WE REMAIN UNDER AN ACTIVE SPRING TIME WEATHER
PATTERN. FORECAST MODELS CONTINUE TO SUGGEST THE NEXT WEATHER SYSTEM
WILL IMPACT THE NORTHERN ROCKIES WITH RAIN AND HIGH MOUNTAIN SNOW
BEGINNING SATURDAY AND CONTINUE THROUGH MONDAY.
AVIATION...SHOWERS THIS EVENING WILL GIVE WAY TO MORE WIDESPREAD
STRATIFORM PRECIPITATION WITH LOWERING CEILINGS THROUGH WEDNESDAY.
MAINLY THE CENTRAL AND SOUTHERN TERMINALS AND ROUTES WILL BE
AFFECTED. PLEASE SEE APPROPRIATE TAFS AND TWEBS.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...HEAVY SNOW WARNING FROM 3 AM TO 6 PM MDT WEDNESDAY FOR
BUTTE/BLACKFOOT REGION-POTOMAC/SEELEY LAKE REGION.
HEAVY SNOW WARNING UNTIL 6 PM MDT WEDNESDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS.
HEAVY SNOW WARNING FROM 3 AM WEDNESDAY TO MIDNIGHT MDT WEDNESDAY
NIGHT FOR WEST GLACIER REGION.
ID...HEAVY SNOW WARNING UNTIL 5 PM PDT WEDNESDAY FOR SOUTHERN
CLEARWATER MOUNTAINS.
HEAVY SNOW WARNING FROM 9 PM THIS EVENING TO 6 AM MDT WEDNESDAY
ABOVE 6000 FEET FOR EASTERN LEMHI COUNTY-WESTERN LEMHI
COUNTY.
&&
UPDATE...HENRY
PREVIOUS DISCUSSION....MEAD/DICKERSON
AVIATION...MEADThe Missoula radar (KMSX), 97 km away, was scanning. The volume nearest the first event began at 01:45 UTC.
1 hail. Local standard time, as filed.
A weather spotter in Philipsburg reported .75 inch hail as a severe thunderstorm moved northeast across Granite County. Several other reports of pea to half inch sized hail were received from this storm.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2007Every state in 2007This day in weather historyWarnings in Montana, April 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: 22719.