Alert archive / Montana / Tornado Watches in 2002

Tornado Watch 318

May 21, 20028 counties in Montana

The Storm Prediction Center issued this tornado watch at May 21, 2002, 3:45 PM MDT for 8 counties in Montana. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: May 21, 2002, 3:45 PM MDT (21:45 UTC)
Expired: May 21, 2002, 9:00 PM MDT
In force: 5 hr
Issued by: the Storm Prediction Center

Counties Chouteau County, MT, Fergus County, MT, Golden Valley County, MT, Hill County, MT, Judith Basin County, MT, Liberty County, MT, Musselshell County, MT, Wheatland County, MT

The radar

The Great Falls radar (KTFX), 134 km from the middle of the area, began a volume at 21:44 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

Warnings issued inside it

5 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
May 21, 4:26 PM MDT	Severe Thunderstorm Warning	TFX	Judith Basin	34 min
May 21, 5:54 PM MDT	Severe Thunderstorm Warning	BYZ	Musselshell	66 min
May 21, 6:23 PM MDT	Severe Thunderstorm Warning	TFX	Fergus	37 min
May 21, 6:35 PM MDT	Severe Thunderstorm Warning	TFX	Hill	40 min
May 21, 7:15 PM MDT	Severe Thunderstorm Warning	TFX	Hill	45 min

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 9.8 hours before the alert went out and 82 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1038 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 7 m²/s²
0-3 km storm-relative helicity: 189 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.2

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

000 
WWUS20 KWNS 212135
SEL8  
SPC WW 212130
MTZ000-220300-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 318
STORM PREDICTION CENTER NORMAN OK
330 PM MDT TUE MAY 21 2002

THE STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

   CENTRAL MONTANA                            

EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 345 PM UNTIL 900
PM MDT.

TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS
TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE TORNADO WATCH AREA IS ALONG AND 50 STATUTE MILES EAST AND WEST
OF A LINE FROM 45 MILES NORTHWEST OF HAVRE MONTANA TO 35 MILES EAST
SOUTHEAST OF HARLOWTON MONTANA.

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. 
PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING
WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE
WARNINGS.

OTHER WATCH INFORMATION...  CONTINUE...WW 317...

DISCUSSION...THUNDERSTORMS ARE INTENSIFYING RAPIDLY JUST N OF
DEEPENING SURFACE LOW TO W OF BIL.  STRONG UPWARD MOTION WITH
APPROACH OF VIGOROUS UPPER TROUGH AND AVAILABILITY OF MODERATE
INSTABILITY MOVING WWD TO N OF SURFACE LOW WILL RESULT IN FAVORABLE
ENVIRONMENT FOR SUPERCELLS.  ISOLATED TORNADOES AS WELL AS LARGE
HAIL WILL ACCOMPANY SUPERCELLS AS THEY DEVELOP/MOVE MOSTLY NWD
VICINTY N/S FRONTAL BOUNDARY.


AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES.  EXTREME TURBULENCE AND SURFACE WIND
GUSTS TO 60 KNOTS.  A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. 
MEAN STORM MOTION VECTOR 18030.


...HALES

461,1101 490,1113 490,1092 461,1080

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 21, 3:00 PM MDT	Severe Thunderstorm Watch	SPC	Big Horn, Musselshell, Rosebud, Treasure, Yellowstone	5 hr

Nearby

Tornado Watches in Montana, 2002 Every tornado watch in 2002

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.