Convective activity developed early in the afternoon with thunderstorms rapidly developing over West and Southwest Montana in response to an upper trough moving across Northwest Montana into southern Alberta. Though jet streak energy supported the system, convective parameters were not overly impressive.
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.
Convective activity developed early in the afternoon with thunderstorms rapidly developing over West and Southwest Montana in response to an upper trough moving across Northwest Montana into southern Alberta. Though jet streak energy supported the system, convective parameters were not overly impressive. Additionally, precipitable water values were very high across the CWA translating to heavy rain with some isolated to scattered severe storms.
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 17, 4:03 PM MST, 2 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 503 PM MDT Wed Jul 17 2013 .DISCUSSION... Tonight through Friday...Convective activity getting started this afternoon with thunderstorms rapidly developing over west and southwest Montana in response to an upper trof moving across northwest Montana and into southern Alberta along with jet streak energy. Convective parameters are not overly impressive but strong to severe storms are possible. Additionally, precipitable water values are very high across the area and may translate to heavy rain with some storms. Convective activity should end after midnight with an upper ridge rebuilding over the area Thursday. With a stronger westerly flow aloft on Thursday, along with favorable mixing, surface winds will become breezy during the afternoon. As the ridge axis retrogrades a little to the west on Friday, northwest flow aloft will develop over the area but conditions will remain dry. Temperatures will warm to above seasonal averages through the period. Emanuel Friday night through Wednesday...Models appear to be in decent agreement for the early portion of the medium range period. The weekend starts off with a broad upper level ridge centered over Nevada and the associated ridge axis extending into British Columbia. Models indicate that the core of the high pressure system will move to the California coast while shortwave energy moving over the top of the ridge brings a dry west to northwest flow aloft to Montana by Sunday night. Models differ on the strength of this shortwave but both agree that the airmass will remain dry during this period. Model solutions diverge beyond the weekend with the GFS rebuilding the ridge over the Northern Rocky Mountains while the ECMWF keeps high pressure over the Eastern Pacific and nearly zonal flow aloft over Montana. Despite these differences in upper air patterns both models remain dry and warm through the middle of next week. Have made only minor temperatures to the going forecast for what appears to be shaping up as a relatively quiet mid summer. mpj && .AVIATION... UPDATED 2302Z. Scattered showers and thunderstorms will move east and diminish during the evening...most storms should be east of KLWT by 08z. Some storms could have large hail and gusty winds. Dry conditions will continue through Thursday. MVFR conditions are possible near showers and thunderstorms this evening...elsewhere VFR conditions will prevail through the next 24 hours. && .FIRE WEATHER... Widespread rain and thunderstorms are possible this afternoon and evening as ample monsoonal moisture, instability and wind shear combined with an upper-level disturbance move over the forecast area. Some storms may be strong to severe with strong erratic winds, hail and locally heavy rainfall, however confidence remains low with regards to heavy rainfall location and coverage. Over recent burn areas, heavy rain could cause rapid runoff and/or debris flows. With better chances of widespread thunderstorms, the threat for lightning- induced fire starts will increase with holdover ignitions possibly triggering some fires later in the week. && .PRELIMINARY POINT TEMPS/POPS... GTF 58 89 54 89 / 40 10 0 0 CTB 56 83 52 84 / 20 10 0 0 HLN 59 90 56 90 / 50 10 0 0 BZN 55 88 51 89 / 40 20 10 0 WEY 45 82 42 83 / 40 20 10 10 DLN 56 87 51 88 / 40 10 0 10 HVR 60 85 55 88 / 20 10 10 10 LWT 57 84 53 84 / 50 10 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... SEVERE THUNDERSTORM WATCH until 10 PM MDT this evening Beaverhead...Broadwater...Cascade...Central and Southern Lewis and Clark...Chouteau...Eastern Glacier...Eastern Pondera... Eastern Teton...Gallatin...Hill...Jefferson...Judith Basin... Liberty...Madison...Meagher...Northern Rocky Mountain Front... Southern Rocky Mountain Front...Toole. && weather.gov/greatfalls
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE GREAT FALLS MT 416 AM MDT WED JUL 17 2013 MTZ008>015-044>055-181030- 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- 416 AM MDT WED JUL 17 2013 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TODAY AND TONIGHT STRONG TO SEVERE THUNDERSTORMS WITH STRONG TO DAMAGING WINDS...HAIL AND LOCALLY HEAVY RAIN ARE EXPECTED THIS AFTERNOON AND EVENING. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY THE PROBABILITY IS LOW FOR WIDESPREAD HAZARDOUS WEATHER. .SPOTTER INFORMATION STATEMENT... ANY REPORTS OF STRONG WINDS...HAIL AND/OR STORM DAMAGE WOULD BE GREATLY APPRECIATED AND CAN BE RELAYED TO THE NWS GREAT FALLS OR LOCAL LAW ENFORCEMENT.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
445 PM MDT WED JUL 17 2013
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0444 PM HAIL 2 N HELENA 46.63N 112.02W
07/17/2013 E0.50 INCH LEWIS AND CLARK MT TRAINED SPOTTER
HALF INCH HAIL ON THE NORTH SIDE OF HELENA.
&&
BRUSDASPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
445 PM MDT WED JUL 17 2013
MTZ008-172330-
BEAVERHEAD MT-
445 PM MDT WED JUL 17 2013
...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN BEAVERHEAD COUNTY
UNTIL 530 PM MDT...
AT 442 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 5 MILES SOUTH OF LIMA...OR 35 MILES WEST OF
IDMON...MOVING EAST AT 30 MPH.
HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.
* LOCATIONS IMPACTED INCLUDE...
MONIDA...
THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO AND
TV STATIONS...AS WELL AS LOCAL CABLE TV OUTLETS...FOR ADDITIONAL
INFORMATION AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.
A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1000 PM MDT
WEDNESDAY EVENING FOR WESTERN MONTANA.
LAT...LON 4447 11246 4446 11250 4448 11260 4448 11268
4449 11270 4479 11261 4474 11184 4455 11187
4452 11212 4456 11229 4453 11234 4446 11236
4444 11243
TIME...MOT...LOC 2245Z 279DEG 28KT 4456 11253
NLPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
446 PM MDT WED JUL 17 2013
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0438 PM HAIL 3 W HELENA 46.60N 112.08W
07/17/2013 E0.75 INCH LEWIS AND CLARK MT TRAINED SPOTTER
PENNY SIZE HAIL ON THE WEST SIDE OF HELENA.
&&
BRUSDAPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
448 PM MDT WED JUL 17 2013
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0446 PM HAIL ENNIS 45.35N 111.73W
07/17/2013 E0.25 INCH MADISON MT TRAINED SPOTTER
PEA SIZE HAIL
&&
BRUSDASPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE GREAT FALLS MT 451 PM MDT WED JUL 17 2013 MTZ015-172330- MADISON MT- 451 PM MDT WED JUL 17 2013 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL MADISON COUNTY UNTIL 530 PM MDT... AT 448 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 8 MILES SOUTHWEST OF SHERIDAN...MOVING NORTHEAST AT 25 MPH. HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING. * LOCATIONS IMPACTED INCLUDE... LAURIN AND ALDER... SHERIDAN AND LAURIN... A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1000 PM MDT WEDNESDAY EVENING FOR WESTERN MONTANA. LAT...LON 4573 11192 4541 11170 4526 11231 4541 11245 TIME...MOT...LOC 2251Z 239DEG 23KT 4538 11227 NL
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GREAT FALLS MT
452 PM MDT WED JUL 17 2013
MTZ008-015-172330-
BEAVERHEAD MT-MADISON MT-
452 PM MDT WED JUL 17 2013
...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN MADISON AND NORTHERN
BEAVERHEAD COUNTIES UNTIL 530 PM MDT...
AT 454 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM 13 MILES WEST OF TWIN BRIDGES...OR 21 MILES
NORTHWEST OF SHERIDAN...MOVING NORTHEAST AT 20 MPH.
HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 50 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.
* LOCATIONS IMPACTED INCLUDE...
RURAL NORTHWESTERN MADISON COUNTY...
RURAL NORTHERN BEAVERHEAD COUNTY...
A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1000 PM MDT
WEDNESDAY EVENING FOR WESTERN MONTANA.
LAT...LON 4566 11270 4564 11269 4569 11257 4577 11250
4575 11247 4575 11217 4569 11207 4547 11255
4556 11277
TIME...MOT...LOC 2252Z 211DEG 18KT 4559 11259
NLThe Missoula radar (KMSX), 210 km away, was scanning. The volume nearest the first event began at 23:07 UTC.
4 hail, 2 flash flood, 1 lightning, 1 thunderstorm wind. Local standard time, as filed.
Flash flooding reported in Bannack State Park created a small debris flow and 5 injuries were reported by Beaverhead County DES Manager. Heavy rain of .77 inches was reported in about 30 minutes in the park.
Thunderstorms over Glacier Park injured 3 people hiking on the St Mary Falls trail. Time of event is estimated.
Hail measuring 1.00 inches (quarter sized) was reported 19 mi S of Alder, MT.
Flash flooding reported around the Corral Fire burn scar. Water and debris covered the intersection of Green Meadow Drive and Norris Road. No injuries or damage were reported.
Hail measuring 1.25 inches (half dollar sized) was reported 2 mi SE of Helena, MT.
Hail measuring 1.00 inches (quarter sized) was reported 5 mi W of Cut Bank, MT.
High winds estimated at 52KT (60MPH) were reported 9 mi NE of Big Sky, MT. A 2.5 foot diameter tree was blown down, blocking highway 191.
Hail measuring 1.00 inches (quarter sized) was reported 5 mi WNW of Sand Coulee, MT.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2013Every state in 2013This day in weather historyWarnings in Montana, July 2013
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: 470403, 470404, 470407, 470411, 470409, 470412, 470414, 470415.