Hail and Damaging Wind in Montana, May 20, 2006

Name: Hail and Damaging Wind in Montana, May 20, 2006
Start: 2006-05-20T14:40
End: 2006-05-20T15:30
Location: Montana

May 20, 2006 · NWS TFX · 2 events in 2 counties and zones

75 inch diameter hail at Gearldine 15NE and produced a wind gust to 58 mph at Roy 1E. Thunderstorms also produced wind gusts to 54 mph at Grant 8SW, a gust to 53 mph at Dillon and a gust to 50 mph at Winifred..

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 2

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.

What happened

The episode as NWS TFX wrote it up.

A severe thunderstorm dropped .75 inch diameter hail at Gearldine 15NE and produced a wind gust to 58 mph at Roy 1E. Thunderstorms also produced wind gusts to 54 mph at Grant 8SW, a gust to 53 mph at Dillon and a gust to 50 mph at Winifred.. Thunderstorms also dropped 1 inch of rain at Warrick 6W.Lightning from a thunderstorm struck an unoccupied home in Great Falls resulting in approximate damages of $25000.

What forecasters said that day

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, 1:45 PM MST, 55 minutes earlier.

Area forecast discussion, May 20, 1:45 PM MST, 55 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
245 PM MDT SAT MAY 20 2006

.DISCUSSION...

TONIGHT THROUGH MONDAY...UPPER RIDGE AXIS HAS SHIFTED TO EASTERN
MONTANA ALLOWING FOR A MOIST SOUTHWEST FLOW ALOFT OVER THE COUNTY
WARNING AREA. SHORT WAVE ENERGY MOVES ACROSS THE AREA THIS
AFTERNOON AND EARLY EVENING AND HAS INITIATED SCATTERED
THUNDERSTORMS. A PORTION OF THE COUNTY WARNING AREA REMAINS UNDER
A SEVERE THUNDERSTORM WATCH AND THE POTENTIAL FOR SEVERE
THUNDERSTORMS EXISTS...ESPECIALLY OVER THE EAST. THE AIRMASS
STABILIZES TONIGHT BUT ADDITIONAL SHORT WAVE ENERGY WILL MOVE OVER
THE AREA SUNDAY AFTERNOON FOR A CONTINUED THREAT OF THUNDERSTORM
ACTIVITY SUNDAY AFTERNOON AND AGAIN MONDAY. TEMPERATURES WILL
REMAIN WELL ABOVE SEASONAL AVERAGES. EMANUEL

MONDAY NIGHT THROUGH SATURDAY...AN UPPER LEVEL RIDGE OVER THE REGION
EARLY IN THE PERIOD WILL GET SHUNTED EAST AND DEAMPLIFY AS HEIGHTS
LOWER ACROSS THE PACIFIC NORTHWEST. MODELS ARE STILL ADVERTISING A
STRONG SHORT WAVE TROUGH TO SWING THROUGH THE REGION MONDAY NIGHT.
CHANCE POPS WERE MAINTAINED ACROSS THE ENTIRE FORECAST AREA WITH
SCATTERED SHOWERS AND THUNDERSTORMS EXPECTED. A GENERAL SOUTHWEST
FLOW WILL THEN SETUP OVER THE REGION BY MIDWEEK WITH AN UPPER LEVEL
LOW SLOWLY APPROACHING THE PACIFIC NORTHWEST COAST. LOW CHANCE TO
CHANCE POPS WERE CONTINUED INTO SATURDAY AS WEAK DISTURBANCES EJECT
FROM THE PARENT LOW. WITH THE MAIN LOW EXPECTED TO REMAIN WEST OF
THE AREA UNTIL NEXT WEEKEND...DECIDED TO RAISE TEMPERATURES FOR THE
WEDNESDAY THROUGH FRIDAY PERIOD. SCHAUMANN

&&

.AVIATION...
UPDATED 1805Z.
A SHORTWAVE TROUGH IN THE SOUTHWEST FLOW ALOFT OVER SOUTHWEST AND
NORTH CENTRAL MONTANA WILL CONTINUE GENERATING SCATTERED
THUNDERSTORMS OVER SOUTHWEST MONTANA AND SPREADING THEM NORTHEAST
OVER NORTH CENTRAL MONTANA. THE STORMS WILL CONTAIN GUSTY WINDS AND
BRIEF HEAVY RAIN...WITH SOME OF THE STRONGER ONES PRODUCING HAIL AND
WIND GUSTS IN EXCESS OF 55 MPH. THE GREATEST THREAT FOR THESE
STRONGER STORMS WILL BE IN THE MORE UNSTABLE AIR NORTH AND EAST OF A
KGPI-KHLN-KLVM LINE. STORMS WILL DECREASE AND SKIES WILL CLEAR FROM
THE SOUTHWEST LATER THIS AFTERNOON THROUGH THE EVENING. VFR
CONDITIONS WILL BE THE NORM INTO THE EVENING...WITH MVFR TO LOCAL
IFR CONDITIONS POSSIBLE WITH THUNDERSTORMS. A SURFACE BOUNDARY WILL
MOVE EAST ACROSS THE AREA DURING THE PERIOD...SHIFTING BREEZY
SOUTHEASTERLY WINDS AHEAD OF IT MORE WESTERLY BEHIND IT.  COULSTON

&&

.HYDROLOGY...
NO SIGNIFICANT HYDROLOGICAL PROBLEMS ARE EXPECTED. HOWEVER SOME AREA
STREAMS/RIVERS ARE RUNNING HIGH DUE TO SNOWMELT OR RELEASES FROM
UPSTREAM RESERVOIRS. TWO DIFFERENT RIVER STATEMENTS HAVE BEEN ISSUED
TO HIGHLIGHT THESE CONDITIONS.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  83  52  86 /  30  20  20  20
CTB  48  81  49  84 /  20  20  20  20
HLN  53  82  52  85 /  10  20  10  20
BZN  47  80  46  83 /  20  20  20  20
WEY  37  73  37  75 /  20  20  20  40
DLN  48  80  46  82 /  10  10  10  30
HVR  52  83  54  90 /  40  10  20  20
LWT  48  80  51  85 /  40  20  30  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
SEVERE THUNDERSTORM WATCH UNTIL 8 PM FOR A PORTION OF NORTH
CENTRAL MONTANA.

&&

SHORT TERM...EMANUEL
LONG TERM...SCHAUMANN
AVIATION...COULSTON

WEATHER.GOV/GREATFALLS

Hazardous weather outlook, May 20, 12:32 PM MST, 2 hours 8 minutes before

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
132 PM MDT SAT MAY 20 2006

MTZ012>015-046-048>055-211200-
CASCADE-CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-
EASTERN PONDERA-SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-
JUDITH BASIN-FERGUS-JEFFERSON-BROADWATER-MEAGHER-GALLATIN-
132 PM MDT SAT MAY 20 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A RISK OF SEVERE THUNDERSTORMS WITH LARGE HAIL AND
DAMAGING WINDS THIS AFTERNOON AND EARLY THIS EVENING.
THUNDERSTORMS WILL CONTINUE TO DEVELOP OVER THE MOUNTAINS OF
SOUTHWEST MONTANA THEN INTENSIFY AS THEY MOVE INTO CENTRAL
MONTANA. THEREFORE...A SEVERE THUNDERSTORM WATCH HAS BEEN ISSUED FOR
MOST OF SOUTHWEST AND CENTRAL MONTANA...AND IS IN EFFECT UNTIL 8 PM
MDT.

THE THUNDERSTORMS SHOULD MOVE EAST OF THE AREA BY DARK.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

MTZ009>011-044-045-047-211200-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-TOOLE-LIBERTY-
BLAINE-
132 PM MDT SAT MAY 20 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL SPREAD NORTHEAST INTO NORTH
CENTRAL MONTANA THIS AFTERNOON AND EARLY THIS EVENING. A FEW
STORMS MAY EVEN BECOME SEVERE WITH STRONG GUSTY WINDS AND HAIL
GREATER THAN ONE HALF INCH IN DIAMETER.

THESE STORMS WILL MOVE EAST OF THE AREA AROUND DARK.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

MTZ008-211200-
BEAVERHEAD-
132 PM MDT SAT MAY 20 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE TO DEVELOP OVER
BEAVERHEAD COUNTY THIS AFTERNOON AND SPREAD NORTHEAST. A FEW
STORMS MAY EVEN BECOME SEVERE WITH STRONG GUSTY WINDS AND HAIL
GREATER THAN ONE HALF INCH IN DIAMETER.

THESE STORMS WILL DIMINISH BY DARK.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

In the hours before

Local storm report, May 20, 1:23 PM MST, 1 hour 17 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
223 PM MDT SAT MAY 20 2006

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1245 AM     TSTM WND GST     DILLON                  45.22N 112.63W
05/20/2006  M53.00 MPH       BEAVERHEAD         MT   MESONET

            DILLON RAWS LOCATION

1015 AM     TSTM WND GST     8 SW GRANT              44.93N 113.18W
05/20/2006  M54.00 MPH       BEAVERHEAD         MT   MESONET

            BRENNER RAWS LOCATION

0130 PM     HAIL             25 N BOZEMAN            46.04N 111.04W
05/20/2006  E0.25 INCH       GALLATIN           MT   TRAINED SPOTTER

            HEAVY RAIN AND BRIEF HAIL.

0135 PM     HAIL             5 W BOZEMAN             45.68N 111.15W
05/20/2006  E0.25 INCH       GALLATIN           MT   TRAINED SPOTTER

            HEAVY RAIN AND BRIEF HAIL.

0145 PM     HAIL             20 S RINGLING           45.98N 110.81W
05/20/2006  E0.50 INCH       GALLATIN           MT   TRAINED SPOTTER

            OCCURRED NEAR WILSALL WITH GUSTY WINDS.

&&

SAUCIER

The radar

The Great Falls radar (KTFX), 109 km away, was scanning. The volume nearest the first event began at 21:41 UTC.

Open the radar archive at this moment

Event by event

1 hail, 1 thunderstorm wind. Local standard time, as filed.

Hail, Chouteau

When: May 20, 2:40 PM MST
Where: Chouteau County, 15 mi NE of Geraldine
Measured: 0.75 in hail
Reported by: TRAINED SPOTTER
Coordinates: 47.783, -110.017

Thunderstorm Wind, Fergus

When: May 20, 3:30 PM MST
Where: Fergus County, 1 mi E of Roy
Measured: 50 kt (58 mph) measured gust
Reported by: AWOS,ASOS,MESONET,ETC
Coordinates: 47.333, -108.917

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Montana in 2006 Every state in 2006 This day in weather history Warnings in Montana, May 2006

Sources

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: 5506912, 5506913.