Alert archive / Montana / Severe Thunderstorm Warnings in 2002

Severe Thunderstorm Warning 1, NWS Great Falls, MT

May 20, 2002Teton County, Montana

NWS Great Falls, MT issued this severe thunderstorm warning at May 20, 2002, 7:17 PM MDT for Teton County, Montana. It was in force for 28 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: May 20, 2002, 7:17 PM MDT (01:17 UTC)
Expired: May 20, 2002, 7:45 PM MDT
In force: 28 min
Issued by: NWS Great Falls, MT
Area: Counties, with a storm outline in the text

County Teton County, MT

The radar

The Great Falls radar (KTFX), 95 km from the middle of the area, began a volume at 01:18 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.

Did it verify

Not verified. The Iowa Environmental Mesonet's Cow found no qualifying storm report inside this severe thunderstorm warning while it was in force. That is not proof nothing happened: reports are thin where few people live.

Cow counts a report within 15 km of the polygon while the warning was in force: a tornado for a tornado warning; hail of 1 inch or more, a gust of 58 mph or more or wind damage for a severe thunderstorm warning; a flash flood report for a flash flood warning.

The watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
May 20, 4:15 PM MDT	Severe Thunderstorm Watch	SPC	5 hr

The nearest sounding before it

Great_falls, MT (KTFX), launched 00:00Z, 1.3 hours before the alert went out and 145 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: 166 J/kg
Mixed-layer CIN: -15 J/kg
Mixed-layer LCL: 3453 m above ground
0-6 km bulk shear: 40 kt
0-1 km storm-relative helicity: 10 m²/s²
0-3 km storm-relative helicity: 62 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

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

000 
WUUS55 KTFX 210117
SVRGTF
MTC099-210145-

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE GREAT FALLS MT
715 PM MDT MON MAY 20 2002

THE NATIONAL WEATHER SERVICE IN GREAT FALLS HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
  NORTH CENTRAL TETON COUNTY IN NORTH CENTRAL MONTANA

* UNTIL 745 PM MDT

* AT 715 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
  SEVERE THUNDERSTORM 8 MILES SOUTH OF BYNUM...OR ABOUT 9 MILES
  NORTHWEST OF CHOTEAU...MOVING NORTH AT 25 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
  BYNUM AT 725 PM MDT
  PENDROY AT 735 PM MDT

LARGE HAIL AND WINDS TO 60MPH ARE POSSIBLE WITH THIS SEVERE 
THUNDERSTORM. IF YOU ARE IN THE PATH OF THE STORM...MOVE TO A 
SUBSTANTIAL SHELTER.

REPORT SEVERE WEATHER TO THE NEAREST LAW ENFORCEMENT AGENCY. THEY
WILL RELAY YOUR REPORT TO THE NATIONAL WEATHER SERVICE FORECAST
OFFICE IN GREAT FALLS.

LAT...LON 4813 11225 4786 11223 4783 11248 4812 11255

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, 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 this severe thunderstorm warning went out at May 20, 3:00 PM MDT, 4 hours 17 minutes earlier.

Area forecast discussion, May 20, 3:00 PM MDT, 4 hours 17 minutes before

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
300 PM MDT MON MAY 20 2002

.SHORT TERM...AREA OF INSTABILITY STRETCHES ACROSS THE CWA BUT A
FAIRLY STRONG CAP HAS BEEN INHIBITING CONVECTION. WILL CONTINUE SOME
POPS AS THE CAP SHOULD DISAPPEAR LATER THIS AFTERNOON...BUT WILL NOT
INCLUDE SEVERE WORDING. THE LARGE TROF TO THE WEST IS MOVING SLOWLY
EAST AND TWO SURFACE FRONTS WILL AFFECT THE AREA DURING THE FORECAST
PERIOD. ONE WILL BE CROSSING THE ROCKIES TONIGHT. DESPITE THE AIRMASS
CHANGE DURING THE NIGHT...FRONT CROSSES ROCKIES AROUND 6Z TUE...THE
UPPER LEVEL TROF LINGERS AND KEEPS THE AREA UNSETTLED. ANOTHER
SURFACE FRONT WILL BE MOVING SOUTH ACROSS CANADIAN BORDER 24 HRS
LATER...INTO GTF AROUND 9AM WED. MAIN AREA OF COLD TEMPS CROSSES NE
MONTANA...ALTHOUGH NORTHERN CWA SHOULD SEE TEMPS BELOW FREEZING...AND
LOW TEMPS COULD ALSO SNEAK INTO CENTRAL CWA. COLD AIR MOVING OUT OF
CANADA WILL HELP CHANCE OF PRECIP...AND WILL ALSO MAKE SOME MENTION
OF SNOW...AT LEAST ABOVE 4000 FEET AND ALONG THE BORDER. ZELZER

.EXTENDED...MRF BRINGS AN UPPER LEVEL TROF THROUGH AREA ON
FRIDAY AND THEN ZONAL FLOW THROUGH SUNDAY WITH UPPER RIDGE
BUILDING IN ON MONDAY. MRF IS A LITTLE FASTER THAN ECMWF BUT TRENDS
ARE THE SAME. WILL STAY WITH LOW POPS AND A LITTLE COOLER TEMPS.
CAMP

.CCF NUMBERS

GTF WR 050/066 042/048 030 13257
    WBBBB 048/040 061/040 069/043 070/043 070 74311111111
CTB WR 046/060 040/045 028 13357
    WBBBB 044/035 058/040 064/040 065/040 065 74311111111
HLN WR 050/070 045/055 034 13358
    WBBBB 055/042 066/043 070/045 071/045 071 54311111111
BZN WR 045/065 038/055 030 13276
    WBBBB 050/036 060/038 065/038 065/038 065 54311111111
WEY WR 036/060 030/045 024 13376
    WBBBB 045/028 055/030 060/033 060/033 060 54311111111
DLN WR 044/059 038/055 030 13276
    WBBBB 048/036 060/038 065/038 065/038 065 54311111111
HVR WR 048/075 045/049 028 13257
    WBBBB 044/042 060/043 068/043 070/043 070 74311111111
LWT WR 048/068 039/052 030 13257
    WBBBB 044/040 060/042 065/042 067/042 067 74311111111

.TFX...NONE

The office that day

Everything else NWS Great Falls, MT issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 21, 4:26 PM MDT	Severe Thunderstorm Warning	TFX	Judith Basin	34 min

Nearby

Severe Thunderstorm Warnings in Montana, 2002 Every severe thunderstorm warning 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.