An unstable airmass produced severe thunderstorms over North Central Montana during the late afternoon hours. An eight inch diameter tree was reported to have been snapped off and strong winds blewthe roof off a vacant mobile home.
Every event with a place to put it. 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 TFX wrote it up.
An unstable airmass produced severe thunderstorms over North Central Montana during the late afternoon hours. An eight inch diameter tree was reported to have been snapped off and strong winds blewthe roof off a vacant mobile home.
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 Great Falls, MT wrote its last area forecast discussion before the first event at Jul 30, 2:13 PM MST, 1 hour 27 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 313 PM MDT SAT JUL 30 2011 .DISCUSSION... TONIGHT THROUGH MONDAY...AN INCREASINGLY MOIST AND UNSTABLE SOUTHWESTERLY FLOW ALOFT WILL BRING ISOLATED TO SCATTERED THUNDERSTORMS TO THE SOUTHERN AND EASTERN PORTIONS OF THE TFX CWA TONIGHT THROUGH SUNDAY NIGHT. DRY LOW LEVELS OF THE ATMOSPHERE WILL KEEP THE THREAT OF GUSTY WINDS WITH THESE STORMS...AND MAKING HEAVY RAINFALL FROM THEM UNLIKELY. THIS WEATHER PATTERN WILL ALSO KEEP TEMPERATURES UP TO 10 DEGREES ABOVE NORMAL THROUGH THIS PERIOD. THESE CONDITIONS WILL MOST LIKELY ENHANCE FIRE DANGER ACROSS THE AREA...WHICH IS DISCUSSED IN FURTHER DETAIL IN THE FIRE WEATHER SECTION BELOW. AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL MOVE ACROSS SOUTHWEST CANADA ON MONDAY...SHIFTING THE FLOW ALOFT MORE WESTERLY AND COOLING TEMPERATURES OFF BY ONLY ABOUT 5 DEGREES BEHIND A WEAK CANADIAN COLD FRONT. HOWEVER...A DECENT FEED OF MOISTURE IN THE STILL UNSTABLE FLOW ALOFT WILL PERSIST ACROSS THE SOUTHERN HALF OF THE TFX CWA (MAINLY SOUTH OF A GREAT FALLS TO LEWISTOWN LINE) WHICH WILL KEEP A GOOD CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS THAT AREA. COULSTON MONDAY NIGHT THROUGH SATURDAY...ALTHOUGH MODELS CONTINUE TO BE SOMEWHAT CONSISTENT WITH THE UPPER LEVEL FLOW PATTERN THEY ARE HAVING A DIFFICULT TIME AGREEING WITH THE MONSOONAL MOISTURE MAKING ITS WAY INTO THE NORTHERN ROCKIES. CURRENT THINKING IS THAT THE MODELS ARE GENERALLY UNDERPLAYING THE NORTHERN EXTENT OF THE MOISTURE...THUS POPS WERE INCREASED FOR SOUTHWEST MONTANA FOR MOST OF THE EXTENDED GRIDS. WITH AN UNSTABLE FLOW ALOFT AND MONSOONAL MOISTURE MAKING ITS WAY UP FROM THE SOUTH EXPECT ISOLATED TO SCATTERED THUNDERSTORMS IN SOUTHWEST MONTANA THROUGH THE PERIOD. EXPECT TEMPERATURES TO BE ABOUT 5 DEGREES ABOVE NORMAL. MERCER && .AVIATION... UPDATED 1720Z. RIDGE OF HIGH PRESSURE WILL REMAIN OVER THE REGION PRODUCING MOSTLY CLEAR SKIES. EXPECT VFR CONDITIONS THROUGHOUT THE AREA. MONSOONAL MOISTURE WILL CONTINUE TO PUSH NORTHWARD FOR ISOLATED THUNDERSTORMS IN THE WESTERN AND SOUTHWESTERN PORTIONS THIS AFTERNOON AND EVENING...HOWEVER AS THE MOISTURE MOVES OVER THE MOUNTAINS IT WILL RUN INTO DRY AIR AND SHOULD DISSIPATE. EXPECT LIGHT WINDS EXCEPT NEAR KCTB AND IN OR AROUND THUNDERSTORMS. VFR CONDITIONS WILL PREVAIL. WILLIAMSON DC && .FIRE WEATHER... AN UNSTABLE SOUTHWESTERLY FLOW ALOFT WILL MOVE ISOLATED TO SCATTERED THUNDERSTORMS NORTHEAST THROUGH THE AREA OVERNIGHT TONIGHT. BECAUSE OF VERY DRY LOW LEVELS...GUSTY WINDS ARE POSSIBLE FROM THESE STORMS. HOWEVER...WILL HOLD OFF ON ANY FIRE WEATHER HIGHLIGHTS DUE TO THE RELATIVE LACK OF COVERAGE. THE FLOW ALOFT WILL TAP INTO A BETTER FEED OF PACIFIC/MONSOONAL MOISTURE ON SUNDAY...WHICH WILL INCREASE THE COVERAGE OF THUNDERSTORMS IN THE AFTERNOON/EVENING. HOWEVER...BECAUSE OF THE INCREASED MOISTURE...THERE WILL LIKELY BE A MIX OF WET AND DRY THUNDERSTORMS...BUT GUSTY WINDS WILL LIKELY ACCOMPANY THEM DUE TO THE PERSISTENT DRY LOW LEVELS. AGAIN...AM NOT ANTICIPATING FIRE WEATHER HIGHLIGHTS AT THIS TIME...BUT THE SITUATION WILL CONTINUE TO BE MONITORED. COULSTON && .PRELIMINARY POINT TEMPS/POPS... GTF 60 94 61 87 / 20 20 20 10 CTB 55 92 54 83 / 10 10 10 10 HLN 57 94 58 86 / 20 20 30 20 BZN 52 92 55 83 / 20 30 40 30 WEY 42 78 46 69 / 20 40 40 50 DLN 53 88 55 79 / 20 30 40 40 HVR 58 97 60 85 / 20 10 20 10 LWT 58 93 59 81 / 20 20 30 20 && .TFX WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM...COULSTON LONG TERM...MERCER AVIATION...WILLIAMSON DC WEATHER.GOV/GREATFALLS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GREAT FALLS MT 406 AM MDT SAT JUL 30 2011 MTZ008>015-044>055-311015- BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL- CASCADE-CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON- TOOLE-LIBERTY-EASTERN PONDERA-BLAINE- SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-JUDITH BASIN-FERGUS- JEFFERSON-BROADWATER-MEAGHER-GALLATIN- 406 AM MDT SAT JUL 30 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TODAY AND TONIGHT THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
350 PM MDT SAT JUL 30 2011
MTZ014-302230-
CENTRAL AND SOUTHERN LEWIS AND CLARK MT-
350 PM MDT SAT JUL 30 2011
...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL LEWIS AND CLARK COUNTY
UNTIL 430 PM MDT...
AT 347 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 20 MILES NORTHWEST OF HELENA...MOVING NORTHEAST
AT 45 MPH.
WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH
OCCASIONAL LIGHTNING STRIKES.
* LOCATIONS IMPACTED INCLUDE...
MARYSVILLE...
CANYON CREEK...
WOLF CREEK...
IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.
LAT...LON 4712 11225 4687 11180 4663 11231 4665 11233
4665 11240 4666 11242 4669 11243 4669 11252
4671 11254 4679 11254
TIME...MOT...LOC 2149Z 224DEG 39KT 4673 11238
NLThe Great Falls radar (KTFX), 56 km away, was scanning. The volume nearest the first event began at 22:41 UTC.
3 thunderstorm wind. Local standard time, as filed.
A thunderstorm produced a wind gust to 58 mph at Hardy 9SW (the Gary Cooper Bridge DOT site).
Thunderstorm winds, estimated at 60 mph, snapped a tree with a diameter of 8 inches located near the Missouri River south of Great Falls.
Thunderstorm winds, estimated at 60 mph, blew the roof off a vacant mobile home located on the south side of Great Falls.
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, July 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: 326245, 326243, 326242.