Mesoscale Discussion 1321

Issued

Jul 23, 2020, 11:39 AM MDT (17:39 UTC)

Expired

Jul 23, 2020, 1:45 PM MDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

Counties Custer County, ID, Lemhi County, ID, Beaverhead County, MT, Broadwater County, MT, Deer Lodge County, MT, Gallatin County, MT, Granite County, MT, Jefferson County, MT, Lewis and Clark County, MT, Madison County, MT, Meagher County, MT, Powell County, MT, Ravalli County, MT, Silver Bow County, MT

The Missoula radar (KMSX), 192 km from the middle of the area, began a volume at 17:39 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 398Jul 23, 2:45 PM MDT

118 
ACUS11 KWNS 231739
SWOMCD
SPC MCD 231739 
MTZ000-IDZ000-231945-

Mesoscale Discussion 1321
NWS Storm Prediction Center Norman OK
1239 PM CDT Thu Jul 23 2020

Areas affected...northeast Idaho into southwest Montana

Concerning...Severe potential...Watch possible 

Valid 231739Z - 231945Z

Probability of Watch Issuance...40 percent

SUMMARY...Scattered thunderstorms developing over Idaho are expected
to gradually strengthen through the day. Storms may be capable of
producing strong winds and severe hail later in the afternoon, and a
watch is possible to cover these concerns.

DISCUSSION...Recent radar and satellite imagery shows a few weak
thunderstorms developing within a deformation band ahead of an
approaching shortwave trough from eastern OR into northeast ID.
Residual inhibition and weak deep layer shear are limiting the
strength and organization of convection at the moment, and should
continue to do so for the next hour or so. Heading into the mid and
late afternoon hours, modest daytime heating, coupled with steep
mid-level lapse rates observed in the BOI and TFX morning soundings,
should aid in further destabilization with MLCAPE values reaching
between 500-1000 J/kg. Winds aloft should increase with the approach
of the shortwave trough, and will help impose 30-35 knots of
effective shear over the region. These trends should lead to a
gradual intensification of ongoing storms, and help increase storm
coverage as broad lift is augmented by localized orographic ascent.
The main threats expected from these storms will be strong to severe
winds given steepening 0-3 km lapse rates, though instances of
severe hail are possible. Trends will be monitored over the coming
hours, and a watch is possible if convection begins to intensify as
expected.

..Moore/Hart.. 07/23/2020

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

ATTN...WFO...BYZ...TFX...PIH...MSO...BOI...

LAT...LON   45111507 45921442 46621370 47131246 47191118 46541071
            45791064 45011112 44461212 44151286 43931383 44421461
            44791507 45111507

Mesoscale Discussions in Montana, 2020Mesoscale Discussions in Idaho, 2020Every mesoscale discussion in 2020

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.