Severe Thunderstorm Watch 409

Issued

Aug 6, 2021, 1:43 PM MDT (19:43 UTC)

Expired

Aug 6, 2021, 8:00 PM MDT

In force

6 hr

Issued by

the Storm Prediction Center

Largest hail expected

1 in

Strongest gust expected

60 kt

The Rapid City radar (KUDX), 126 km from the middle of the area, began a volume at 19:46 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.

Two or more tornadoes

5%

One or more EF2 to EF5 tornadoes

2%

Ten or more severe wind reports

40%

One or more gusts of 65 knots or more

20%

Ten or more severe hail reports

20%

One or more hailstones of 2 inches or more

5%

Six or more combined severe hail and wind reports

60%

• Mesoscale Discussion 1424 Severe potential...watch possibleAug 6, 12:39 PM MDT
• Mesoscale Discussion 1426 Severe thunderstorm watch 409Aug 6, 5:07 PM MDT

954 
WWUS20 KWNS 061941
SEL9  
SPC WW 061941
MTZ000-NEZ000-SDZ000-WYZ000-070200-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 409
NWS Storm Prediction Center Norman OK
140 PM MDT Fri Aug 6 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Extreme southeastern Montana
  The northwestern Nebraska Panhandle
  Western South Dakota
  Central and northeastern Wyoming

* Effective this Friday afternoon and evening from 140 PM until
  800 PM MDT.

* Primary threats include...
  Scattered damaging wind gusts to 70 mph possible
  Isolated large hail events to 1 inch in diameter possible

SUMMARY...Thunderstorms are expected to increase in coverage and
intensity this afternoon from central into northeastern Wyoming, and
storms will spread into the northwestern Nebraska Panhandle and
western South Dakota later this afternoon into this evening.  The
storm environment favors organized, high-based storm clusters with a
primary threat of damaging outflow winds to near 70 mph.  Isolated
supercells may also occur in central Wyoming, where isolated large
hail to near 1 inch diameter will be possible.

The severe thunderstorm watch area is approximately along and 125
statute miles east and west of a line from 85 miles northeast of
Gillette WY to 35 miles southwest of Douglas WY. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU9).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for 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. Severe thunderstorms can and occasionally do produce
tornadoes.

&&

AVIATION...A few severe thunderstorms with hail surface and aloft to
1 inch. Extreme turbulence and surface wind gusts to 60 knots. A few
cumulonimbi with maximum tops to 500. Mean storm motion vector
25035.

...Thompson

Severe Thunderstorm Watches in Wyoming, 2021Severe Thunderstorm Watches in South Dakota, 2021Severe Thunderstorm Watches in Nebraska, 2021Every severe thunderstorm watch in 2021

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.