Heavy rain and small hail producing thunderstorms developed the afternoon of May 30th, 2015. The strongest cell was a supercell in Western Montana which held together for over 2 hours and produced nickel-sized hail and torrential downpours over I-90 west of Superior, MT.
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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.
Heavy rain and small hail producing thunderstorms developed the afternoon of May 30th, 2015. The strongest cell was a supercell in Western Montana which held together for over 2 hours and produced nickel-sized hail and torrential downpours over I-90 west of Superior, MT.
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 30, 1:33 PM MST, 29 minutes earlier.
Area Forecast Discussion National Weather Service Missoula MT 233 PM MDT SAT MAY 30 2015 .DISCUSSION...Numerous showers and thunderstorms have developed across north central Idaho and in Northwest Montana down to the I-90 corridor including Missoula and the Northern Bitterroot valley. Storms are expected to increase in coverage and persist through mid to late evening. Impacts include, small hail, lightning, gusty winds and locally heavy rain. A weak ridge builds Sunday along with it warmer temperatures and scattered afternoon showers or a thunderstorm. Monday will be a pretty active day with thunderstorms likely. Convection will begin fairly early in central Idaho then move north to encompass all of western Montana along with the vigorous short wave. There is plenty of dynamic support and moisture available for the potential of some pretty intense thunderstorms, especially in west central and northwest Montana. Very heavy rains, hail and gusty winds are likely with storms Monday afternoon and well into the evening. There is pretty good dynamics to support thunderstorms through Tuesday morning, especially in Northwest Montana. Another significant impact from this system could be the potential for significant rain in far Northwest Montana Monday night through Tuesday. Models are indicating a mid level low pressure system closing off and wrapping precipitation around which could bring some health amounts of rain. There is some uncertainty to the location of this circulation but wherever it ends up (Canada or northwest Montana) significant rain is expected. The rest of next week will bring scattered showers and isolated storms each day. && .AVIATION...Scattered thunderstorms will impact kgpi and kmso through 31/0400z. Some storms will be strong with gusty winds to 40 mph at times, lightning, intense rain and small hail. KBTM and KSMN may see a shower or thunderstorm but they will be less intense and more scattered in nature. Expect lingering showers at all terminals after 31/0400z through Sunday morning. && .MSO WATCHES/WARNINGS/ADVISORIES... MT...None. ID...None. &&
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MISSOULA MT
202 PM MDT SAT MAY 30 2015
MTZ001-004-302045-
KOOTENAI/CABINET REGION MT-LOWER CLARK FORK REGION MT-
202 PM MDT SAT MAY 30 2015
...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL SANDERS AND
NORTHWESTERN MINERAL COUNTIES UNTIL 245 PM MDT...
AT 202 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR
HAUGAN...OR 10 MILES SOUTHWEST OF THOMPSON FALLS...MOVING EAST AT 20
MPH.
PEA SIZE HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.
LOCATIONS IMPACTED INCLUDE...
ST. REGIS...HAUGAN...DE BORGIA...TAFT...SALTESE...EAST PORTAL AND
EDDY.
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.
LAT...LON 4756 11560 4756 11500 4729 11505 4735 11557
4736 11558 4737 11558 4738 11562 4738 11564
TIME...MOT...LOC 2002Z 276DEG 16KT 4746 11547SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MISSOULA MT 213 PM MDT SAT MAY 30 2015 MTZ001-003-004-302100- FLATHEAD/MISSION VALLEYS MT-KOOTENAI/CABINET REGION MT- LOWER CLARK FORK REGION MT- 213 PM MDT SAT MAY 30 2015 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN SANDERS AND NORTH CENTRAL MINERAL COUNTIES UNTIL 300 PM MDT... AT 213 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR PLAINS...OR 18 MILES NORTH OF SUPERIOR...MOVING EAST AT 25 MPH. PEA SIZE HAIL AND WINDS IN EXCESS OF 30 MPH WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... PLAINS...PARADISE...HOT SPRINGS...CAMAS...WEEKSVILLE AND CAMAS PRAIRIE. 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. LAT...LON 4737 11514 4748 11522 4763 11465 4740 11454 TIME...MOT...LOC 2013Z 255DEG 22KT 4745 11499
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MISSOULA MT 225 PM MDT SAT MAY 30 2015 MTZ001>003-302100- FLATHEAD/MISSION VALLEYS MT-WEST GLACIER REGION MT- KOOTENAI/CABINET REGION MT- 225 PM MDT SAT MAY 30 2015 ...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL FLATHEAD COUNTY UNTIL 300 PM MDT... AT 225 PM MDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 13 MILES WEST OF WHITEFISH...OR 23 MILES NORTHWEST OF EVERGREEN...MOVING NORTHEAST AT 15 MPH. PEA SIZE HAIL AND WINDS IN EXCESS OF 30 MPH WILL BE POSSIBLE WITH THIS STORM. LOCATIONS IMPACTED INCLUDE... OLNEY AND LUPFER. 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. LAT...LON 4837 11465 4842 11478 4866 11458 4851 11429 TIME...MOT...LOC 2025Z 207DEG 14KT 4847 11462
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MISSOULA MT 233 PM MDT SAT MAY 30 2015 MTZ001>003-302115- FLATHEAD/MISSION VALLEYS MT-WEST GLACIER REGION MT- KOOTENAI/CABINET REGION MT- 233 PM MDT SAT MAY 30 2015 ...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL FLATHEAD COUNTY UNTIL 315 PM MDT... AT 232 PM MDT...DOPPLER RADAR WAS TRACKING A LINE OF STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 9 MILES WEST OF WHITEFISH TO 18 MILES WEST OF KALISPELL...AND MOVING NORTHEAST AT 30 MPH. HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH THESE STORMS. LOCATIONS IMPACTED INCLUDE... KALISPELL...EVERGREEN AND WHITEFISH. PRECAUTIONARY/PREPAREDNESS ACTIONS... FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THESE STORMS. LIGHTNING CAN STRIKE 15 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE SHELTER INSIDE A BUILDING OR VEHICLE. THESE STORMS 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. && LAT...LON 4856 11425 4815 11429 4813 11477 4837 11466 TIME...MOT...LOC 2032Z 222DEG 27KT 4838 11453 4816 11470
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
253 PM MDT SAT MAY 30 2015
...TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
...DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0230 PM HAIL 1 NNW DE BORGIA 47.39N 115.35W
05/30/2015 E0.88 INCH MINERAL MT TRAINED SPOTTER
MOST OF THE HAIL WERE DIME SIZE, BUT A FEW
WERE PENNY TO NICKEL SIZE. THIS SPOTTER WAS
NOT UNDER THE STORM CORE ACCORDING TO RADAR.
STRONG GUSTY WINDS EST. TO 50 MPH.
&&
DTNThe Missoula radar (KMSX), 90 km away, was scanning. The volume nearest the first event began at 21:02 UTC.
3 hail, 1 heavy rain. Local standard time, as filed.
The Montana Mesonet weather station near St. Regis reported 0.80 inches of rain in one hour, from 2:02pm to 3:02pm local time.
An NWS Employee experienced torrential rainfall and 0.50 inch hail while driving on I-90. The hail lasted 5 min, and rain rates were so high cars on the 75 mph interstate slowed to around 25 mph for a few minutes due to reduced visibility. A nearby RAWS weather station reported 0.55 inches of rain from the storm shortly before it crossed I-90.
A trained spotter reported penny-sized hail in Superior, with 0.50 inches of rain falling in 30 min. Winds estimated at 40 to 50 mph accompanied this report.
A trained spotter reported mostly 0.50 inch to 0.75 inch hail, with a few nickel-sized hailstones (0.88 in). Winds were estimated to be gusting at 50 mph with the storm's passage.
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, May 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: 578675, 578645, 578682, 578661.