Mesoscale Discussion 1152

Issued

Jul 4, 2021, 6:11 PM MDT (00:11 UTC)

Expired

Jul 4, 2021, 8:15 PM MDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Carter County, MT, Powder River County, MT, Harding County, SD, Crook County, WY, Sheridan County, WY

The Rapid City radar (KUDX), 221 km from the middle of the area, began a volume at 00:11 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.

383 
ACUS11 KWNS 050012
SWOMCD
SPC MCD 050011 
SDZ000-NDZ000-MTZ000-WYZ000-050215-

Mesoscale Discussion 1152
NWS Storm Prediction Center Norman OK
0711 PM CDT Sun Jul 04 2021

Areas affected...Southeast Montana...far Northeast Wyoming...and far
Northwest South Dakota

Concerning...Severe potential...Watch unlikely 

Valid 050011Z - 050215Z

Probability of Watch Issuance...5 percent

SUMMARY...Storms may become more organized this evening, posing an
isolated wind/hail threat. Watch issuance unlikely.

DISCUSSION...Regional radar shows a cluster of somewhat disorganized
but marginally intense storms over southeast portions of Montana.
Strong diabatic heating has resulting in hot surface temperatures
into the mid 90s F, yielding strong low-level lapse rates. Weak
easterly/upslope flow has allowed surface dew point temperatures to
rise to near 50 F in proximity to the ongoing convection. The large
temperature/dew point spread is resulting in inverted-v soundings,
with weak instability (MLCAPE approaching 500 J/kg).

Despite the weak low-level easterly flow, amid marginal westerly
flow aloft, deep-layer shear remains rather weak (effective shear
perhaps near 20 kt). However, forecast soundings indicate some
potential for an increase in effective shear throughout the evening,
perhaps approaching 30-35 kt by 03z, as low-level southeasterly flow
increases. Thus, the ongoing convection may become a bit more
organized if it can persist for a few more hours. Should this occur,
storms will pose a threat for strong outflow wind gusts and severe
hail. At this time, the threat is expected to remain fairly
isolated/brief, and thus, watch issuance is not expected.

..Karstens/Hart.. 07/05/2021

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

ATTN...WFO...BIS...UNR...BYZ...RIW...

LAT...LON   44020469 44340601 44720729 45620728 46140637 46210441
            45760324 44670362 44020469

Mesoscale Discussions in Montana, 2021Mesoscale Discussions in Wyoming, 2021Mesoscale Discussions in South Dakota, 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.