Alert archive / Montana / Severe Thunderstorm Warnings in 2002

Severe Thunderstorm Warning 4, NWS Great Falls, MT

May 21, 2002Hill County, Montana

NWS Great Falls, MT issued this severe thunderstorm warning at May 21, 2002, 6:35 PM MDT for Hill County, Montana. It was in force for 40 min. 1 report came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: May 21, 2002, 6:35 PM MDT (00:35 UTC)
Expired: May 21, 2002, 7:15 PM MDT
In force: 40 min
Issued by: NWS Great Falls, MT
Area: Counties, with a storm outline in the text

County Hill County, MT

The radar

The Great Falls radar (KTFX), 140 km from the middle of the area, began a volume at 00:34 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.

What was reported inside it

Time	Report	Where	Remark
May 21, 7:00 PM MDT	Hail 0.75	Kremlin, MT	A severe thunderstorm produced 0.75 inch hail near Kremlin.

NCEI Storm Data entries that began inside the alert's area while it was in force. Before 2003 the local storm report archive is thin, so this is the record of what happened rather than what was phoned in.

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 21, 3:45 PM MDT	Tornado Watch	SPC	5 hr

The nearest sounding before it

Great_falls, MT (KTFX), launched 00:00Z, 0.6 hours before the alert went out and 120 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: 829 m above ground
0-6 km bulk shear: 60 kt
0-1 km storm-relative helicity: 110 m²/s²
0-3 km storm-relative helicity: 328 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

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

000 
WUUS55 KTFX 220035
SVRGTF
MTC041-220115-

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE GREAT FALLS MT
635 PM MDT TUE MAY 21 2002

THE NATIONAL WEATHER SERVICE IN GREAT FALLS HAS ISSUED A

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

* UNTIL 715 PM MDT

* AT 635 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
  A SEVERE THUNDERSTORM 24 MILES SOUTHEAST OF GILDFORD...MOVING
  NORTH AT 45 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...
KREMLIN...GILDFORD AND HINGHAM BY 650 PM MDT

A TORNADO WATCH REMAINS IN EFFECT UNTIL 900 PM MDT TUESDAY EVENING
FOR NORTH CENTRAL MONTANA.

VERY LARGE HAIL...INTENSE RAIN AND STRONG DAMAGING WINDS ARE LIKELY 
WITH THIS STORM. TAKE COVER IN A SUBSTANTIAL SHELTER UNTIL THE STORM 
PASSES.

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 4832 11076 4832 10981 4882 10979 4885 11075

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 21, 2:40 PM MDT, 3 hours 55 minutes earlier.

Area forecast discussion, May 21, 2:40 PM MDT, 3 hours 55 minutes before

SOUTHWEST AND NORTH CENTRAL MONTANA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
240 PM MDT TUE MAY 21 2002

.SHORT TERM...A LOW PRESSURE TROF OVER THE PACIFIC NORTHWEST IS
MOVING SLOWLY EAST WITH A LARGE AREA OF DIFLUENCE DEVELOPING
OVER THE CWA. TEMPS ARE RELATIVELY COOL BUT CAA ALOFT...MAINLY
SOUTH...CONTINUES TO KEEP THE AIRMASS UNSTABLE. THE 7H LOW MOVES OVER
SE MT BY 18Z WED WITH A TROF EXTENDING NE TOWARDS FCA. RH IS HIGH AND
PRECIP SHOULD EXTEND ACROSS MOST OF THE CWA...WITH SNOW LEVELS
DROPPING BELOW 6000 FEET AFTER MIDNIGHT OVER THE NORTHERN ROCKIES. A
COLDER AIRMASS MOVES SOUTH OUT OF CANADA EARLY WEDNESDAY AND SNOW
SHOULD DEVELOP OVER THE NORTHERN CWA DURING THE MORNING...SPREADING
TO THE SOUTHERN CWA BY LATE AFTERNOON. SNOW AMOUNTS WILL BE TRICKY
WITH RAIN/SNOW MIX AS WELL AS WARM GROUND A FACTOR ON WEDNESDAY...
BUT WILL ASSUME ALL SNOW OVERNIGHT. WINTER STORM WARNING WILL BE
NECESSARY REGARDLESS DUE TO HIGH QPF AND STRONG WINDS ON WEDNESDAY.
AIRMASS DRIES QUICKLY FROM THE NORTH THURSDAY MORNING. HIGH
PRESSURE ALOFT ALSO BEGINS TO REBUILD THURSDAY...HOWEVER NORTHWEST
FLOW CONTINUES ALOFT AND AIRMASS MAY ALLOW FOR SOME ADDTIONAL
SCATTERED SHOWERS. ANOTHER SHORT WAVE MOVES ONSHORE OVER THE PACIFIC
NORTHWEST ON SATURDAY BUT THE LOCAL AREA WILL REMAIN UNDER THE
INFLUENCE OF THE HIGH. ZELZER

.EXTENDED....SW FLOW ALOFT IS EXPECTED OVER THE FORECAST AREA LATE
IN THE WEEKEND THROUGH EARLY NEXT WEEK. MODELS DIFFER ON SAT WITH
12Z TUE RUN OF THE UKMET AND 12Z MON RUN OF THE ECMWF SHOWING NW
FLOW ALOFT FOR SAT. DO NOT FORESEE ANY MODERATE OR STRONG SHORTWAVES
DURING THE PERIOD. ALTHOUGH THERE COULD BE ISOLATED SHOWERS OVER THE
PLAINS DURING THE PERIOD DUE TO THE PASSAGE OF WEAK SHORTWAVES...FOR
CONTINUITIES SAKE WILL CONTINUE DRY FORECAST OVER THE PLAINS. LATEST
AVN AND AVN EXTENSION DOES HAVE SOME QPF OVER SW MT FOR SUN THROUGH
TUE SO WILL GO WITH A SLIGHT CHANCE OF SHOWERS. BLANK

.CCF NUMBERS
GTF SW 044/047 030/045 030 13++7
    BBBBB 062/040 068/042 070/042 070/042 070 31111111111
CTB SW 040/043 026/044 030 13++6
    BEBBB 058/040 064/040 065/040 065/040 065 31111111111
HLN SW 045/049 034/052 034 13++7
    BBEEE 065/043 070/045 071/045 071/045 071 31111222222
BZN SW 042/048 030/050 030 13+97
    BBEEE 060/038 065/040 066/040 066/040 066 31111222222
WEY SW 033/043 025/038 022 13+97
    BBEEE 050/028 060/033 060/033 060/033 060 31111222222
DLN SW 038/045 032/047 030 13886
    BBEEE 060/038 065/040 066/040 066/040 066 31111222222
HVR SW 047/051 030/046 033 13++7
    BBBBB 060/040 070/042 071/042 071/042 071 31111111111
LWT SW 044/050 030/043 030 13++7
    BBBBB 059/038 068/040 068/040 068/040 068 31111111111=

.TFX...WINTER STORM WARNING FOR ROCKY MOUNTAIN FRONT TUESDAY
       NIGHT THROUGH WEDNESDAY NIGHT
    ...WINTER STORM WARNING FOR AREAS OF SOUTHWEST MONTANA TUESDAY
       NIGHT THROUGH WEDNESDAY NIGHT
    ...WINTER STORM WARNING NORTH CENTRAL MONTANA WEDNESDAY AND
       WEDNESDAY NIGHT.
    ...FLOOD WATCH FOR THE DEARBORN RIVER THROUGH WEDNESDAY

The office that day

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

Issued	Product	Office	Counties	Lasted
May 21, 6:23 PM MDT	Severe Thunderstorm Warning	TFX	Fergus	37 min
May 21, 7:15 PM MDT	Severe Thunderstorm Warning	TFX	Hill	45 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; verification from NCEI's Storm Data; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.