Mesoscale Discussion 1183

Issued

Jul 7, 2021, 2:03 PM MDT (20:03 UTC)

Expired

Jul 7, 2021, 4:00 PM MDT

In force

117 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

60%

Counties Broadwater County, MT, Cascade County, MT, Custer County, MT, Fergus County, MT, Garfield County, MT, Golden Valley County, MT, Judith Basin County, MT, McCone County, MT, Meagher County, MT, Musselshell County, MT, Park County, MT, Petroleum County, MT, Prairie County, MT, Rosebud County, MT, Stillwater County, MT, Sweet Grass County, MT, Treasure County, MT, Wheatland County, MT, Yellowstone County, MT

The Billings radar (KBLX), 104 km from the middle of the area, began a volume at 20:04 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.

• Severe Thunderstorm Watch 346Jul 7, 3:05 PM MDT

786 
ACUS11 KWNS 072004
SWOMCD
SPC MCD 072003 
MTZ000-072200-

Mesoscale Discussion 1183
NWS Storm Prediction Center Norman OK
0303 PM CDT Wed Jul 07 2021

Areas affected...south central Montana

Concerning...Severe potential...Watch possible 

Valid 072003Z - 072200Z

Probability of Watch Issuance...60 percent

SUMMARY...Severe storms, including a few supercells, are forecast to
develop north of a warm front with a risk for damaging winds and
hail into this evening. A weather watch may be needed.

DISCUSSION...Downstream of a shortwave trough across the Pacific
Northwest, showers and a few thunderstorms have developed across
portions of western Montana and eastern Idaho. As additional
lift/destabilization develops ahead of the approaching trough,
convective coverage/intensity should increase late this afternoon
and early this evening. Warm and moist surface conditions with T/TDs
in the 80s/50s F respectively are contributing to between 500 and
1000 J/kg of MLCAPE across much of Montana. While some inhibition
remains, it should reach diurnal minimum over the next couple of
hours coincident with increased forcing for ascent from the trough
aloft. Additional storm development appears increasingly likely by
21-23z within a moderately sheared airmass (effective shear 40-50
kts). Supercells and short line segments appear to be the dominant
storm mode as high-based convection moves out of the mountains into
deeper moisture and becomes better organized. With steep low and
mid-level lapse rates in place, damaging wind gusts and severe hail
will be the primary threats. Later this evening, upscale growth into
one or two convective clusters/line segments may present an enhanced
corridor of wind damage potential downstream across portions for
central and eastern Montana. Here, greater vertical shear may
support a more organized storm mode capable of strong wind gusts, a
few of which could be significant. 

Convective trends are being monitored for a possible weather watch 
around the 22-00z time frame.

..Lyons/Guyer.. 07/07/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BYZ...GGW...TFX...

LAT...LON   46020538 45490735 45480892 45371062 45401092 46021187
            47021189 47571091 47830964 47980739 47980715 47920674
            47640573 47300534 46640513 46020538

Mesoscale Discussions in Montana, 2021Every mesoscale discussion 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.