Severe thunderstorms developed along the Rocky Mountain Front during the late afternoon/early evening hours of the 20th. Wind gusts to 60 mph were reported.
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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 TFX wrote it up.
Severe thunderstorms developed along the Rocky Mountain Front during the late afternoon/early evening hours of the 20th. Wind gusts to 60 mph were reported.
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 May 20, 2:17 PM MST, 2 hours 49 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 317 PM MDT TUE MAY 20 2008 .DISCUSSION... TONIGHT THROUGH THURSDAY...COLD FRONT EXTENDED FROM NW MONTANA THROUGH SW IDAHO AT 20Z AND WILL CONTINUE MARCHING EAST. IT SHOULD BE NEAR A HAVRE-LEWISTOWN LINE NEAR MIDNIGHT. STILL EXPECTING SHOWERS AND THUNDERSTORMS TO ACCOMPANY THE FRONT. ALSO EXPECT A BAND OF SHOWERS AND POSSIBLY THUNDERSTORMS BEHIND THE FRONT DUE TO A WEATHER DISTURBANCE ALOFT. ON WEDNESDAY THERE WILL BE MOIST SOUTHERLY FLOW ALOFT. WEATHER DISTURBANCES ARE EXPECTED TO AFFECT MAINLY THE EASTERN FORECAST ZONES. INHERITED FORECAST WHICH HAD LIKELY OR HIGHER POPS IN THE EAST AND CHANCE POPS OVER THE WESTERN PLAINS AND VALLEYS STILL LOOKS GOOD. THEN AS AN UPPER LOW DEVELOPS OVER THE GREAT BASIN WEDNESDAY NIGHT AND THURSDAY THE FLOW ALOFT WILL TURN TO THE SOUTHEAST AND BRING PRECIPITATION TO WESTERN PORTIONS OF THE FORECAST AREA AS WELL. EXPECT WIDESPREAD RAIN BY THURSDAY. LIFT WILL BE GENERATED BY UPSLOPE FLOW PARTICULARLY OVER THE PLAINS AS WELL AS LIFT OVER A COLDER AIRMASS OVER WESTERN PORTIONS OF THE FORECAST AREA. AS HAS BEEN ADVERTISED EXPECT SNOW LEVELS TO LOWER TO NEAR 6000 FEET BY LATE TONIGHT IN THE WEST AND CONTINUE ABOUT THAT LEVEL THROUGH THURSDAY. BLANK THURSDAY NIGHT THROUGH SUNDAY NIGHT...A VERY WET AND UNSETTLED WEATHER PATTERN LOOKS TO BE SHAPING UP FOR THE HOLIDAY WEEKEND OVER MUCH OF NORTH CENTRAL AND SOUTHWEST MONTANA. BOTH THE GFS AND ECMWF ARE IN GOOD AGREEMENT THROUGH SATURDAY...THEN THEY DIVERGE A BIT SAT NIGHT THRU SUN...BUT THEY ARE SHOWING SIMILAR RESULTS. THUS EXPECT WET CONDITIONS FRIDAY AND SATURDAY AS AN AN UPPER LEVEL LOW OVER SOUTHERN IDAHO CONTINUES TO ROTATE SHOWERS UP INTO CENTRAL MONTANA. ON SATURDAY NIGHT THE GFS WEAKENS THE STORM SYSTEM A BIT...WHILE THE ECMWF CONTINUES TO MAINTAIN THE UPPER LOWS STRENGTH AND ALSO MOVE THE CENTER OF THE LOW TOWARDS CENTRAL MONTANA. GIVEN THAT CLIMATOLOGY THIS IS THE WETTEST TIME OF THE YEAR...THE ECMWF IS PREFERRED AND A WET/COOL WEEKEND IS POSSIBLE. RIGHT NOW PRECIP CHANCES ARE ONLY IN THE SLIGHT CHANCE/CHANCEY CATEGORY FOR SATURDAY NIGHT THROUGH SUNDAY NIGHT...BUT IF THE ECMWF CONTINUES TO LOOK LIKE IT WILL BE THE CORRECT MODEL...THEN POPS COULD BE RAISED SIGNIFICANTLY INTO THE HIGH CHANCE/LIKELY CATEGORY BY TOMORROW FOR THE REMAINDER OF THE WEEKEND. (BASICALLY THE CURRENT FORECAST IS GOING FOR SCATTERED SHOWERS THROUGH THE WEEKEND...BUT A WASHOUT IS POSSIBLE IF THE ECMWF MODEL IS CORRECT.) OTHERWISE...EXPECT GENERALLY CLOUDY CONDITIONS AND WELL BELOW NORMAL TEMPERATURES ACROSS THE REGION FROM FRIDAY THROUGH SUNDAY. BRUSDA MONDAY THROUGH TUESDAY...MODEL DIFFERENCES CONTINUE TO DETRACT FROM FORECAST CONFIDENCE DURING THIS PERIOD. THE GFS AND ECMWF DISAGREE IN POSITIONS AND STRENGTH OF SYSTEMS AFFECTING THE REGION DURING THIS PERIOD...HOWEVER BOTH SOLUTIONS WOULD INDICATE A COOL UNSETTLED PERIOD. MOSTLY CLOUDY SKIES ARE EXPECTED WITH ISOLATED TO SCATTERED SHOWERS. TEMPERATURES SHOULD BE A LITTLE BELOW SEASONAL AVERAGES. EK && .AVIATION... AN UPPER LEVEL TROUGH AND SURFACE COLD FRONT WILL APPROACH THE REGION FROM THE WEST AND CROSS THE REGION THIS EVENING. EXPECT INCREASING CLOUDS AS THE AIRMASS BECOMES UNSTABLE THIS AFTERNOON. SHOWERS AND THUNDERSTORMS PRECEDING THE COLD FRONT WILL REACH WESTERN TERMINALS BY 00Z AND EASTERN TERMINALS BY 04Z WITH THE FRONT CLEARING EASTERN AREAS AROUND 06Z TONIGHT. SHOWERS AND THUNDERSTORMS WILL BE NUMEROUS ALONG THE COLD FRONT WITH GUSTY SURFACE WINDS AND SMALL HAIL POSSIBLE. WINDS WILL BE FROM THE SOUTH TO SOUTHEAST THROUGH THIS AFTERNOON AHEAD OF THE FRONT...SHIFTING TO THE WEST BEHIND THE FRONT TONIGHT. SHOWERS WILL CONTINUE TONIGHT BEHIND THE COLD FRONT WITH WIDESPREAD MVFR AND LOCAL IFR CONDITIONS IN SHOWERS OVER MUCH OF CENTRAL AND SW MT. HOENISCH && .HYDROLOGY... FOR WEDNESDAY INTO THE WEEKEND RAINFALL TOTALS OF 1 TO 2 INCHES ARE A GOOD BET OVER MUCH OF THE FORECAST AREA. TOTALS OF 2 TO 3 INCHES ARE POSSIBLE WHILE LOCALLY HIGHER RAINFALL TOTAL ARE NOT OUT OF THE QUESTION. WITH STREAMS AND SOME RIVERS RUNNING HIGH DUE TO RECENT SNOWMELT AND NOW AN EXPECTTATION OF SIGNIFICANT RAINFALL..WILL ISSUE A FLOOD WATCH FROM WEDNESDAY NIGHT THROUGH SUNDAY FOR THE ENTIRE FORECAST AREA WITH THE EXCEPTION OF NORTH CENTRAL MONTANA. BLANK && .PRELIMINARY POINT TEMPS/POPS... GTF 45 52 40 48 / 80 50 60 100 CTB 43 53 39 45 / 70 30 80 100 HLN 49 52 45 51 / 80 50 40 80 BZN 44 49 40 50 / 80 80 40 80 WEY 38 42 33 45 / 80 60 60 70 DLN 42 48 36 48 / 70 70 50 70 HVR 49 56 44 53 / 80 70 70 100 LWT 44 50 39 46 / 60 80 80 100 && .TFX WATCHES/WARNINGS/ADVISORIES... FLOOD WATCH FROM WEDNESDAY EVENING THROUGH SUNDAY AFTERNOON FOR MTZ008>010-012>015-044>046-048>055. SMALL STREAM FLOOD ADVISORY THROUGH THIS AFTERNOON FOR MTZ009. SMALL STREAM FLOOD ADVISORY THROUGH WEDNESDAY AFTERNOON FOR MTZ008. && SHORT TERM...BLANK LONG TERM...HOENISCH AVIATION...HOENISCH WEATHER.GOV/GREATFALLS
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE GREAT FALLS MT 503 PM MDT TUE MAY 20 2008 MTZ008>015-044>055-211200- 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- 503 PM MDT TUE MAY 20 2008 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA. .DAY ONE...TONIGHT A SMALL STREAM FLOOD ADVISORY IS IN EFFECT FOR NORTHWESTERN BEAVERHEAD COUNTY THROUGH NOON MDT WEDNESDAY DUE TO RUNOFF FROM MELTING SNOW. RIVERS...STREAMS...AND CREEKS ALONG THE ROCKY MOUNTAIN FRONT SOUTH INTO SOUTHWEST MONTANA MAY ALSO RUN NEAR TO SLIGHTLY ABOVE FLOOD STAGE THROUGH TONIGHT DUE TO SNOW MELT...WHICH MAY CAUSE VERY LOCALIZED LOW LAND FLOODING. OTHERWISE...A COLD FRONT WILL MOVE ACROSS SOUTHWEST AND NORTH CENTRAL MONTANA THIS EVENING. THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE CONTINENTAL DIVIDE AND SOUTHWEST MONTANA AND MOVE NORTHEAST ACROSS THE AREA TONIGHT. SOME THUNDERSTORMS WILL BE STRONG WITH GUSTY WINDS...AND POSSIBLY SMALL HAIL. AN ISOLATED SEVERE THUNDERSTORM WITH DAMAGING WINDS WILL ALSO BE POSSIBLE. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY PERIODS OF RAIN ARE EXPECTED THROUGH THE WEEKEND AND LOCAL FLOODING IS POSSIBLE. THEREFORE...A FLOOD WATCH IS IN EFFECT FROM WEDNESDAY EVENING THROUGH SUNDAY AFTERNOON FOR MOST OF SOUTHWEST AND NORTH CENTRAL MONTANA...EXCEPT FOR HILL AND BLAINE COUNTIES. FLOOD PRONE AREAS WILL CONTINUE TO BE MONITORED THROUGH THIS PERIOD. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.
The Great Falls radar (KTFX), 75 km away, was scanning. The volume nearest the first event began at 00:07 UTC.
1 thunderstorm wind. Local standard time, as filed.
A severe thunderstorm produced a wind gust to 60 mph at Augusta.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2008Every state in 2008This day in weather historyWarnings in Montana, May 2008
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: 103639.