Mesoscale Discussion 1547

Issued

Aug 17, 2021, 2:21 PM MDT (20:21 UTC)

Expired

Aug 17, 2021, 4:15 PM MDT

In force

114 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

The Billings radar (KBLX), 135 km from the middle of the area, began a volume at 20:21 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.

785 
ACUS11 KWNS 172021
SWOMCD
SPC MCD 172021 
MTZ000-WYZ000-IDZ000-172215-

Mesoscale Discussion 1547
NWS Storm Prediction Center Norman OK
0321 PM CDT Tue Aug 17 2021

Areas affected...Southern to Southwest Montana

Concerning...Severe potential...Watch unlikely 

Valid 172021Z - 172215Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated to scattered thunderstorms may be capable of
severe downburst winds across southwest to southern Montana this
afternoon and evening. However, this threat will most likely remain
too isolated to warrant a watch issuance.

DISCUSSION...A few deeper convective towers with occasional
lightning have emerged from a growing cumulus cluster over the
terrain of the ID/MT border over the past hour. This is likely the
result of increasing instability (MUCAPE values up to 1000 J/kg) and
strengthening lift over the region as a surface low slowly deepens
ahead of an approaching upper-level wave. As forcing for ascent and
instability continue to increase through the late afternoon
thunderstorm development will become more likely. Downstream of this
cluster, temperatures across southern MT have warmed into the upper
80s ahead of an approaching cold front. Additional boundary-layer
heating/mixing will help further steepen low-level lapse rates to
near 9 C/km, which may already be achieved at a few sites where
dewpoint depressions near 40 F are noted. Strong flow aloft may
support some initial storm organization, and the low-level
thermodynamic profiles will support a severe downburst potential
with any strong thunderstorm. Scattered storm coverage is possible,
but the combination of the approaching cold front and patchy cloud
cover may spatially limit favorable boundary-layer profiles and the
subsequent severe wind potential. Because of this limitation, a
watch is not expected at this time.

..Moore.. 08/17/2021

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

ATTN...WFO...BYZ...GGW...RIW...TFX...PIH...MSO...

LAT...LON   44891329 45401361 45921327 46921100 47470836 47440716
            47150647 46440652 45440717 45120810 44511151 44421218
            44531281 44891329

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.