Montana, 2002

Flash Flooding and Hail in Montana, August 21, 2002

August 21, 2002 · NWS BYZ · 3 events in 2 counties and zones

2 flash flood, 1 hail, as filed by the National Weather Service.

Where it happened

Every event with a place to put it; 2 filed by county or forecast zone are drawn at its center, in a lighter ring. 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
3

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 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 Billings, MT wrote its last area forecast discussion before the first event at Aug 21, 8:10 AM MST, 55 minutes earlier.

Area forecast discussion, Aug 21, 8:10 AM MST, 55 minutes before
SOUTH CENTRAL AND SOUTHEAST MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
ISSUED BY GLASGOW MT NWS
910 AM MDT WED AUG 21 2002

.SHORT TERM...VALID FOR TDY AND THU...

CONVECTIVE ACTIVITY HAS DEVELOPED ALONG A NORTHWEST TO SOUTHEAST
ORIENTED AXIS FROM NORTHERN ROSEBUD COUNTY INTO CUSTER COUNTY.
CONVECTION APPEARS TO BE ASSOCIATED WITH A WEAK SHORT WAVE MOVING
NORTHEAST OUT OF WYOMING. MESO-ETA DOING A GOOD JOB OF PICKING UP
AREA OF OMEGA AND RELATIVELY STEEP LAPSE RATES OVER CUSTER COUNTY.
SOME SHOWERS ALSO OCCURING ALONG THE EAST SLOPE OF THE BIG HORN
MOUNTAINS. MESO-ETA INDICATING A BRIEF REPRIEVE FROM CONVECTIVE
ACTIVITY OVER THE NEXT FEW HOURS. CONVECTION SHOULD INTENSIFY THIS
AFTERNOON AS 850-500MB LAPSE RATES INCREASE ABOVE 7 C/KM. ALTHOUGH
THUNDERSTORMS SHOULD DEVELOP ACROSS ENTIRE CWA...EXPECT STRONGEST
STORMS OVER THE EASTERN HALF OF THE CWA WHERE CAPES VALUES WILL
EXCEED 1000 J/KG BY 21Z. GOING FORECAST IN GOOD SHAPE. NO UPDATES.
POHL

.LONG TERM...VALID FOR FRI...SAT...SUN...MON...TUE...

CONSISTENCY IN THE AVN SUPPORTS THE CHANGES MADE EARLIER IN THE DAY
KEEPING A RISK OF CONVECTION IN THE FORECAST THROUGH SUNDAY. PATTERN
BECOMES A BIT NEGATIVELY TILTED BY FRIDAY EVENING AND THIS CONTINUES
INTO SATURDAY. SURFACE PRESSURE PATTERNS DONT LOOK REAL SUPPORTIVE
FOR DEWPOINT ADVECTION INTO THE AREA BUT RETURN FLOW BEHIND THE EACH
DAYS CONVECTION COULD HELP KEEP THE LOW LEVEL AIRMASS MOIST. BORSUM

    TDY THU     FRI     SAT     SUN     MON     TUE
-------------------------------------------------------
BIL 083 056/085 054/084 052/086 054/086 053/083 051/082
    4/T 43/T    32/T    33/T    33/T    30/E    00/B
LVM 080 051/081 050/082 048/083 048/084 047/081 045/080
    4/T 43/T    33/T    33/T    33/T    30/E    00/B
HDN 085 055/087 052/087 050/088 052/088 050/085 048/084
    4/T 43/T    32/T    33/T    33/T    30/E    00/B
MLS 085 058/086 056/085 055/087 057/087 056/083 054/082
    4/T 42/T    22/T    33/T    33/T    30/E    00/B
4BQ 086 056/085 055/084 054/086 056/086 055/082 053/081
    4/T 42/T    22/T    33/T    33/T    30/E    00/B
BHK 083 055/083 053/083 052/084 053/084 053/080 051/079
    4/T 42/T    22/T    33/T    33/T    30/E    00/B
SHR 084 053/084 051/084 051/085 050/084 049/080 047/079
    4/T 43/T    33/T    33/T    33/T    30/E    00/B

.BYZ...
MT...NONE.
WY...NONE.

The radar

The Glasgow radar (KGGW), 204 km away, was scanning. The volume nearest the first event began at 16:06 UTC.

Open the radar archive at this moment

Event by event

2 flash flood, 1 hail. Local standard time, as filed.

Hail, Custer

When
August 21, 9:05 AM MST
Where
Custer County, 3 mi N of Miles City
Measured
0.75 in hail
Reported by
TRAINED SPOTTER
Coordinates
46.450, -105.833

Flash Flood, Musselshell

When
August 21, 4:19 PM MST
Where
Musselshell County, 15 mi S of Roundup
Reported by
LAW ENFORCEMENT
Coordinates
46.497, -108.398 (the zone’s center; the record gives no point)

Flash flood occurred near Mile Marker 30 on U.S. Highway 87

Flash Flood, Musselshell

When
August 21, 4:23 PM MST
Where
Musselshell County, 15 mi S of Roundup
Reported by
LAW ENFORCEMENT
Coordinates
46.497, -108.398 (the zone’s center; the record gives no point)

Flash flood near Mile Marker 30 caused a motorist to take an alternate route home.Water over U.S. Highway 87.

What these are

Hail
Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Flash Flood
Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

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

The same day elsewhere

More

Every storm in Montana in 2002Every state in 2002This day in weather historyWarnings in Montana, August 2002

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: 5314983, 5314981, 5314982.