Favorable upper level dynamics ahead of a shortwave trough combined with diurnal heating to create thunderstorms capable of producing small, non damaging hail and strong gusty outflow winds.
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The episode as NWS TFX wrote it up.
Favorable upper level dynamics ahead of a shortwave trough combined with diurnal heating to create thunderstorms capable of producing small, non damaging hail and strong gusty outflow winds.
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 Aug 14, 10:50 AM MST, 56 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 1150 AM MDT FRI AUG 14 2015 UPDATED AVIATION DISCUSSION .UPDATE... A LEAD SHORTWAVE IS MOVING THROUGH MONTANA AT THIS TIME AHEAD OF THE MAIN UPPER LEVEL TROUGH...WHICH IS STILL BACK OVER WESTERN OREGON. WITH THE LEAD DISTURBANCE...SKIES ARE MOSTLY CLOUDY AND SCATTERED SHOWERS AND THUNDERSTORMS HAVE DEVELOPED FROM SOUTHWEST THROUGH SOUTH- CENTRAL MONTANA. THESE SHOWERS AND STORMS WILL TRACK NE THROUGH THE MORNING. THE MAIN THREAT INITIALLY WILL BE FREQUENT LIGHTNING AND WIND GUSTS OF 30-35 MPH. ACROSS SW MONTANA...CLOUDS ARE ALREADY BEGINNING TO BREAK UP IN THE WAKE OF THE INITIAL SHOWER ACTIVITY. THIS WILL ALLOW THE ATMOSPHERE TO DESTABILIZE FURTHER THROUGH THE AFTERNOON. AT THE SAME TIME...THE UPPER LEVEL TROUGH TO THE WEST WILL BEGIN APPROACHING THIS AFTERNOON WITH INCREASING WIND SHEAR FOR STORM ORGANIZATION. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO REDEVELOP BY EARLY TO MID AFTERNOON ACROSS SW MONTANA THEN MOVE NE ACROSS THE REMAINDER OF THE AREA THROUGH THIS EVENING. SHORT TERM GUIDANCE STILL POINTS TO THE POSSIBILITY OF A FEW STORMS BECOMING STRONG TO SEVERE THIS AFTERNOON. THE MAIN THREAT WILL BE FREQUENT LIGHTNING AND WIND GUSTS OF 40-60 MPH. WITH HIGHER FREEZING LEVEL HEIGHTS...THE THREAT OF HAIL APPEARS LOWER AT THIS TIME. AT THIS POINT...THE BEST COMBINATION OF SHEAR AND INSTABILITY LOOKS TO BE FROM SOUTHWEST THROUGH SOUTH-CENTRAL MONTANA. FOR THE UPDATE...UPPED POPS THIS MORNING ESPECIALLY ALONG AND SOUTH OF GREAT FALLS PER LATEST RADAR TRENDS. THE REST OF THE FORECAST LOOKS GOOD. MARTIN && .AVIATION... UPDATED 1750Z. THERE ARE EXPECTED TO BE 3 MAIN PERIODS OF SHOWER AND THUNDERSTORM ACTIVITY THROUGH THE PERIOD. THE FIRST WILL MOVE NORTHEAST THROUGH NORTH CENTRAL MONTANA THIS AFTERNOON. THE NEXT IS EXPECTED TO DEVELOP OVER SOUTHWEST MONTANA THIS AFTERNOON THEN SPREAD INTO THE EASTERN PLAINS (KHVR AND KLWT) NEAR AND AFTER 00Z. THE THIRD WILL AFFECT MAINLY THE NORTHERN PORTION OF THE FORECAST AREA (KCTB AND KHVR) NEAR AND AFTER MIDNIGHT. BEHIND THE THIRD AREA EXPECT DECREASING CLOUDS. EXPECT LOCAL WIND GUSTS TO 40 KTS AND MVFR CONDITIONS WITH THE THUNDERSTORMS LATE THIS AFTERNOON AND EARLY THIS EVENING. IN ADDITION A PACIFIC COLD FRONT WILL BE MOVING THROUGH THE FORECAST AREA OVERNIGHT. HAVE LOW CONFIDENCE WITH FORECAST WINDS AND ESPECIALLY WITH WIND DIRECTIONS BOTH BEFORE AND AFTER THE COLD FRONT AS GUIDANCE SHOWS WIDELY VARYING SOLUTIONS. ACTUALLY HAVE THE MOST CONFIDENCE WITH FORECAST WINDS AT THE END OF THE PERIOD AS EXPECT GUSTY WESTERLY WINDS OVER THE PLAINS. BLANK && .PREV DISCUSSION... /ISSUED 545 AM MDT FRI AUG 14 2015/ TODAY THROUGH SUNDAY...A CHANGE TO A MORE ACTIVE WEATHER PATTERN WILL BEGIN TODAY...AS SEVERAL UPPER LEVEL DISTURBANCES AND A PACIFIC COOL FRONT MOVE THROUGH THE REGION OVER THE NEXT 24 TO 36 HOURS. WITH TEMPERATURES IN THE MID 70S THIS MORNING...ELEVATED CONVECTION IS POSSIBLE THIS MORNING...THUS MOST AREAS HAVE A CHANCE FOR ISOLATED STORMS THRU THE MORNING. THE STORMS BECOME AT BIT MORE SCATTERED EARLY THIS AFTERNOON AS THE UPPER LEVEL DISTURBANCE MOVES THROUGH. PRECIP AMOUNTS WILL BE HIT/MISS...WITH SOME HEAVIER SHOWERS PRODUCING UP TO 0.20 INCHES...WHILE OTHER AREAS RECEIVE LESS THAN 0.05 INCHES. STRONG/DAMAGING WIND GUSTS WILL BE THE MAIN THREAT WITH THE STORMS TODAY...WITH A SLIGHT RISK FOR SEVERE STORMS OVER THE WESTERN PORTION OF THE CWA. EXPECT TEMPERATURES TO WARM INTO THE 90S THIS AFTERNOON WITH A FEW BREAKS IN THE CLOUD COVER. WINDS WILL START TO INCREASE THIS AFTERNOON/EVENING...WITH THE MAIN PACIFIC COOL FRONT MOVING THROUGH THE REGION FROM WEST TO EAST FROM AROUND MIDNIGHT THRU 4 AM SATURDAY. STRONG WINDS ARE POSSIBLE OVER THE ROCKY MOUNTAIN FRONT...THUS THE HIGH WIND WATCH CONTINUES. TEMPERATURES WILL BE A BIT COOLER ON SATURDAY...ESPECIALLY OVER THE NORTH...WHILE IT WILL REMAIN WARM IN SOUTHWEST MT. THE STORMS ON SATURDAY BECOME MORE ISOLATED AND CONFINED MAINLY TO THE MOUNTAINS. FOR SUNDAY...COOLER AIR CONTINUES TO SLIDE INTO THE REGION...WITH ANY STORMS ONCE AGAIN MAINLY CONFINED MOSTLY TO THE MOUNTAINS. BRUSDA SUNDAY NIGHT THROUGH FRIDAY. FORECAST CONFIDENCE IS MARGINAL TO LOW FOR THIS PERIOD AS FORECAST MODELS CAN'T SEEM TO SETTLE ON A CONSISTENT SOLUTION, ESPECIALLY ON THE TIMING OF THE PACIFIC SHORTWAVE TROF THAT WILL MOVE THROUGH THE REGION EARLY NEXT WEEK. AS NOTED IN DAY SHIFT'S DISCUSSION YESTERDAY, GFS MODEL WENT BACK TO A SLOWER PROGRESSION ON THE TROF. LATEST GFS RUN (14 AUG/00Z) CONTINUES THE SLOW EVOLUTION, KEEPING ONSET OF PRECIPITATION OUT OF OUR REGION UNTIL LATE MON NIGHT WHILE FASTER ECMWF SOLUTION INDICATES PRECIP BEGINNING BY MIDDAY MON AND ENDING BY TUES MORNING. CURRENT FORECAST IS A ROUGH COMPROMISE BETWEEN THESE DISPARATE PREDICTIONS, WITH PRECIP STARTING IN NORTHWEST PORTION OF CWA ON MON AFTN AND SPREADING EAST AND SOUTH ON TUES BEFORE ENDING WED MORNING. AS THE SHORTWAVE EXITS, WEAK RIDGING RETURNS WITH NORTHWEST FLOW ALOFT. WED TO FRI PERIOD STILL LOOKING MOSTLY DRY AS MOST PASSING MOISTURE REMAINS IN SOUTHERN CANADA. HOWEVER, DID KEEP A SLIGHT CHANCE OF SHOWERS ON WED AFTN/EVE IN PREFERRED UPSLOPE AREAS OF THE ROCKY MTN FRONT AND CENTRAL/SOUTHWEST MTNS. HIGH TEMPERATURES WILL BE CLOSE TO OR A FEW DEGREES BELOW SEASONAL VALUES EACH DAY, EXCEPT ON TUES WHEN COOLER AIRMASS AND WIDESPREAD CLOUDS/PRECIP WILL KEEP HIGHS ONLY IN THE LOW-MID 70S. WARANAUSKAS && .PRELIMINARY POINT TEMPS/POPS... GTF 95 60 77 49 / 40 20 10 0 CTB 90 56 71 44 / 40 20 10 10 HLN 93 54 80 48 / 40 20 0 0 BZN 91 53 82 48 / 40 30 10 0 WEY 83 47 77 37 / 30 30 10 0 DLN 87 52 80 45 / 50 20 10 0 HVR 97 62 77 50 / 30 20 10 10 LWT 96 60 78 47 / 30 20 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... RED FLAG WARNING UNTIL 9 PM MDT SATURDAY FOR MTZ112>118. HIGH WIND WATCH FROM 6 PM MDT THIS EVENING THROUGH SATURDAY MORNING FOR MTZ009-048. && WEATHER.GOV/GREATFALLS
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE GREAT FALLS MT 849 AM MDT FRI AUG 14 2015 MTZ015-052-053-055-141530- JEFFERSON MT-BROADWATER MT-MADISON MT-GALLATIN MT- 849 AM MDT FRI AUG 14 2015 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN JEFFERSON... NORTHEASTERN MADISON...SOUTHERN BROADWATER AND NORTHWESTERN GALLATIN COUNTIES UNTIL 930 AM MDT... AT 849 AM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 11 MILES NORTHWEST OF ENNIS...OR 11 MILES NORTH OF VIRGINIA CITY... MOVING NORTHEAST AT 40 MPH. WIND GUSTS UP TO 50 MPH WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... PONY...HARRISON AND WILLOW CREEK. LAT...LON 4536 11197 4547 11217 4593 11175 4576 11144 TIME...MOT...LOC 1449Z 229DEG 33KT 4547 11190
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1119 AM MDT FRI AUG 14 2015
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1117 AM HAIL 1 N GREAT FALLS 47.52N 111.29W
08/14/2015 E0.25 INCH CASCADE MT TRAINED SPOTTER
&&
MARTINPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1152 AM MDT FRI AUG 14 2015
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1122 AM HAIL 1 N GREAT FALLS 47.52N 111.29W
08/14/2015 M0.25 INCH CASCADE MT PUBLIC
SMALL HAIL ALONG WITH BRIEF POWER OUTAGE
&&
MARTINThe Great Falls radar (KTFX), 118 km away, was scanning. The volume nearest the first event began at 18:45 UTC.
6 thunderstorm wind. Local standard time, as filed.
Thunderstorm outflow measured at a Department of Defense Site.
A 66 mph wind gust measured 6 miles north of Great Falls.
A 67 mph wind gust at the Crooked Coulee Mesonet site.
A 66 mph wind gust from the mesonet site north of Rudyard.
A 63 mph wind gust at the DOT sensor near Inverness.
A 59 mph wind gust at the Monida Pass DOT sensor on Interstate 15.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2015Every state in 2015This day in weather historyWarnings in Montana, August 2015
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: 595739, 595740, 595749, 595750, 595748, 595747.