Alert archive / Montana / Special Weather Statements in 2021

Special Weather Statement, NWS Great Falls, MT

August 21, 2021Cascade County, Montana

NWS Great Falls, MT issued this special weather statement at Aug 21, 2021, 2:59 PM MDT for Cascade County, Montana. It was in force for 31 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: Aug 21, 2021, 2:59 PM MDT (20:59 UTC)
Expired: Aug 21, 2021, 3:30 PM MDT
In force: 31 min
Issued by: NWS Great Falls, MT
Hail: 0.00 in
Wind: 30

County Cascade County, MT

The radar

The Great Falls radar (KTFX), 28 km from the middle of the area, began a volume at 21:02 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.

The nearest sounding before it

Great_falls, MT (KTFX), launched 12:00Z, 9.0 hours before the alert went out and 86 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: 1318 m above ground
0-6 km bulk shear: 33 kt
0-1 km storm-relative helicity: 8 m²/s²
0-3 km storm-relative helicity: 102 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

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What forecasters said that day

The local office's own words before this special weather statement 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 special weather statement went out at Aug 21, 10:16 AM MDT, 4 hours 43 minutes earlier.

Area forecast discussion, Aug 21, 10:16 AM MDT, 4 hours 43 minutes before

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        The site you requested is temporarily down for maintenance or an unexpected outage.
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In the hours before

Special weather statement, Aug 21, 1:39 PM MDT, 1 hour 20 minutes before

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  <main class="wrap">
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      <h1 id="headline">This service is currently unavailable.</h1>
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        The site you requested is temporarily down for maintenance or an unexpected outage.
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Special weather statement, Aug 21, 2:10 PM MDT, 49 minutes before

Special Weather Statement
National Weather Service Great Falls MT
210 PM MDT Sat Aug 21 2021

MTZ012-014-048-052>054-212045-
Broadwater MT-Cascade MT-Southern Rocky Mountain Front MT-
Jefferson MT-Central and Southern Lewis and Clark MT-Meagher MT-
210 PM MDT Sat Aug 21 2021

...Strong thunderstorms will impact portions of southeastern Lewis
and Clark, northwestern Broadwater, northwestern Meagher,
northeastern Jefferson and southwestern Cascade Counties through 245
PM MDT...

At 208 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 13 miles east of Lincoln to 9 miles southeast
of Wolf Creek to near Montana City. Movement was northeast at 40 mph.

HAZARD...Winds in excess of 30 mph and a period of heavy rainfall.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. The heavy rainfall will make roads slick
         with some ponding of water, so beware of hydroplaning if
         driving on roadways.

Locations impacted include...
Helena, Cascade, East Helena, Wolf Creek, Montana City, Bowmans
Corner, Tower Rock State Park, York, Craig and Black Sandy State
Park.

This includes the following highways...
 Interstate 15 between mile markers 198 and 263.
 Highway 200 between mile markers 80 and 124.
 Highway 12 between mile markers 47 and 62.
 Highway 287 between mile markers 1  and 25.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Heavy rainfall may lead to localized flooding of low lying areas. Do
not drive your vehicle through flooded roadways.

&&

LAT...LON 4750 11213 4733 11148 4682 11113 4640 11186
      4675 11206 4695 11255
TIME...MOT...LOC 2008Z 215DEG 36KT 4699 11240 4689 11196 4653 11183

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH

SC

Special weather statement, Aug 21, 2:55 PM MDT, 4 minutes before

Special Weather Statement
National Weather Service Great Falls MT
255 PM MDT Sat Aug 21 2021

MTZ012-014-054-212130-
Cascade MT-Central and Southern Lewis and Clark MT-Meagher MT-
255 PM MDT Sat Aug 21 2021

...A strong thunderstorm will impact portions of southeastern Lewis
and Clark, northwestern Meagher and south central Cascade Counties
through 330 PM MDT...

At 254 PM MDT, Doppler radar was tracking a strong thunderstorm 23
miles southeast of Cascade, moving northeast at 30 mph.

HAZARD...Winds in excess of 40 mph and pea size hail. A period of
         brief heavy rain is also expected.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

This storm will remain over mainly rural areas of southeastern Lewis
and Clark, northwestern Meagher and south central Cascade Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Heavy rainfall may lead to localized flooding of low lying areas. Do
not drive your vehicle through flooded roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4680 11156 4703 11172 4727 11117 4694 11096
TIME...MOT...LOC 2054Z 242DEG 27KT 4696 11151

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

SC

Special weather statement, Aug 21, 2:59 PM MDT, 0 minutes before

Special Weather Statement
National Weather Service Great Falls MT
259 PM MDT Sat Aug 21 2021

MTZ012-014-048-049-212130-
Cascade MT-Southern Rocky Mountain Front MT-Eastern Teton MT-
Central and Southern Lewis and Clark MT-
259 PM MDT Sat Aug 21 2021

...An area of heavy showers with isolated thunderstorms will impact
portions of central Lewis and Clark, southeastern Teton,
southwestern Chouteau and northern Cascade Counties through 330 PM
MDT...

At 257 PM MDT, Doppler radar was tracking an area of heavy rain
shower with isolated thunderstorms along a line extending from 15
miles southeast of Augusta to 12 miles south of Cascade. Movement
was northeast at 40 mph.

HAZARD...Winds in excess of 30 mph and a period of heavy rain.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Locations impacted include...
Great Falls, Cascade, Fairfield, Belt, Black Eagle, Fort  Shaw, Fort
Shaw, Power, Eden, Malmstrom Afb, Stockett, Tracy, Vaughn, First
Peoples Buffalo Jump State Park, Centerville, Sun River, Bowmans
Corner, Tower Rock State Park, Ulm and Sand Coulee.

This includes the following highways...
 Interstate 15 between mile markers 239 and 306.
 Highway 200 between mile markers 105 and 139.
 Highway 287 between mile markers 13 and 28.
 Highway 89 between mile markers 9 and 35, and between mile markers
74 and 8.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Heavy rainfall may lead to localized flooding of streets and low
lying areas. Do not drive your vehicle through flooded roadways.

&&

LAT...LON 4786 11206 4770 11141 4741 11087 4703 11172
      4730 11233
TIME...MOT...LOC 2057Z 222DEG 34KT 4737 11211 4710 11162

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...30 MPH

SC

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 21, 1:39 PM MDT	Special Weather Statement	TFX	Lewis and Clark	36 min
Aug 21, 2:10 PM MDT	Special Weather Statement	TFX	Lewis and Clark	35 min
Aug 21, 2:55 PM MDT	Special Weather Statement	TFX	Cascade	35 min
Aug 21, 3:44 PM MDT	Special Weather Statement	TFX	Cascade	31 min
Aug 21, 3:49 PM MDT	Special Weather Statement	TFX	Cascade	26 min
Aug 21, 5:31 PM MDT	Special Weather Statement	TFX	Beaverhead	44 min
Aug 21, 5:37 PM MDT	Special Weather Statement	TFX	Chouteau, Hill, Liberty	38 min

Nearby

Special Weather Statements in Montana, 2021 Every special weather statement in 2021

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.