Mesoscale Discussion 1200

Issued

Jul 8, 2021, 1:15 PM MDT (19:15 UTC)

Expired

Jul 8, 2021, 2:15 PM MDT

In force

60 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

60%

Counties Daniels County, MT, Dawson County, MT, McCone County, MT, Phillips County, MT, Prairie County, MT, Richland County, MT, Roosevelt County, MT, Valley County, MT

The Glasgow radar (KGGW), 29 km from the middle of the area, began a volume at 19:14 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 352Jul 8, 1:35 PM MDT

033 
ACUS11 KWNS 081916
SWOMCD
SPC MCD 081915 
MTZ000-082015-

Mesoscale Discussion 1200
NWS Storm Prediction Center Norman OK
0215 PM CDT Thu Jul 08 2021

Areas affected...portions of north-central and eastern Montana

Concerning...Severe potential...Watch possible 

Valid 081915Z - 082015Z

Probability of Watch Issuance...60 percent

SUMMARY...A supercell has recently evolved across Montana and severe
weather appears possible with this storm as it move to the east
southeast. Additional development and a greater severe risk later in
the day appears likely. A watch is possible but uncertain in the
short term, with greater confidence in the need for a watch later
this afternoon.

DISCUSSION...A lone supercell in Phillips County, MT has intensified
over the last half hour as it continues to track into destabilizing
airmass across central and eastern Montana. Ahead of a progressive
mid-level vort max, forcing for ascent and insolation will continue
to remove mixed-layer inhibition over the next several hours,
setting the stage for additional thunderstorm development. With
continued destabilization, spc mesoanalysis and RAP forecast
soundings show 1500-2000 J/kg of MLCAPE developing by late
afternoon. As this cell, and potentially others, track eastward into
the instability corridor, additional strengthening appears possible.


Ahead of the vort max, mid-level shear profiles are robust, with
45-55 kts of effective shear supporting a supercellular storm mode.
Mid-level lapse rates near 8 C/km will support large to very large
hail. Damaging wind gusts also appear to be a significant threat,
given temperature dewpoint spreads near 30 F. While a tornado cannot
be ruled out given a favorable storm mode, it does not appear likely
with higher LCLs and weaker low-level shear profiles.

Th severe threat posed by the current storm will most likely remain
isolated over the next several hours given, casting doubt on the
need for a weather watch in the short term. However, additional
storm development appears probable later this afternoon/evening as
the main vort max continues to eject eastward. Hi-res guidance
signals continue to suggest a more widespread severe weather threat
developing across the region this evening where a watch would likely
be needed. Convective trends Will continue to be monitored.

..Lyons/Guyer.. 07/08/2021

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

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

LAT...LON   47410708 47530771 47850853 48620870 49050817 49070759
            49090635 49080571 49020526 48610463 48170426 47460423
            46940444 46630507 47010608 47410708

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.