Alert archive / Wyoming / Mesoscale Discussions in 2021

Mesoscale Discussion 1424

August 6, 20214 counties in Wyoming

The Storm Prediction Center issued this mesoscale discussion at Aug 6, 2021, 12:39 PM MDT for 4 counties in Wyoming. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Aug 6, 2021, 12:39 PM MDT (18:39 UTC)
Expired: Aug 6, 2021, 2:45 PM MDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 60%

Counties Converse County, WY, Fremont County, WY, Natrona County, WY, Platte County, WY

The radar

The Riverton/Lander radar (KRIW), 158 km from the middle of the area, began a volume at 18:38 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.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 409Aug 6, 1:40 PM MDT

The nearest sounding before it

Riverton, WY (KRIW), launched 12:00Z, 6.7 hours before the alert went out and 152 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1589 m above ground
0-6 km bulk shear: 31 kt
0-1 km storm-relative helicity: 69 m²/s²
0-3 km storm-relative helicity: 150 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

433 
ACUS11 KWNS 061839
SWOMCD
SPC MCD 061839 
WYZ000-062045-

Mesoscale Discussion 1424
NWS Storm Prediction Center Norman OK
0139 PM CDT Fri Aug 06 2021

Areas affected...central and eastern WY

Concerning...Severe potential...Watch possible 

Valid 061839Z - 062045Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms will likely develop as convection moves from
a dry/deeply mixed boundary layer, located over south-central WY,
into greater moisture located farther east/northeast into parts of
central and eastern WY.  Severe gusts will probably accompany the
more intense downdrafts/outflow once storms mature later this
afternoon into the early evening.

DISCUSSION...Satellite imagery shows a potent mid-level shortwave
trough over ID moving into WY this afternoon.  Surface analysis
places a low near Casper.  To the east and north of the low, surface
dewpoints range from the lower 40s to lower 50s with temperatures
warming into the lower 80s over eastern WY.  Southwest of the
surface low, large temperature-dewpoint spreads are indicative of a
well-mixed boundary layer where the winds have veered to the
southwest.

As large-scale ascent strengthens over central WY this afternoon
while additional heating occurs, the erosion of MLCINH will lead to
isolated thunderstorms developing by mid afternoon.  Strong
southwesterly mid-level flow will aid in some storm organization,
mainly in the form of organized cells/clusters as they move into
greater moisture located over the eastern third of WY.  Severe gusts
and possibly large hail will accompany the stronger storms. 
Convective trends will be monitored for a possible severe
thunderstorm watch to include parts of central, eastern, and
northeastern WY and possibly the Black Hills.

..Smith/Thompson.. 08/06/2021

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

ATTN...WFO...UNR...CYS...RIW...

LAT...LON   41760544 42400687 42710843 43080864 43640841 43700632
            43220516 42070474 41760544

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 6, 1:43 PM MDT	Severe Thunderstorm Watch	SPC	Campbell, Converse, Crook, Fremont, Hot Springs, Johnson and 4 more	6 hr

Nearby

Mesoscale Discussions in Wyoming, 2021 Every mesoscale discussion in 2021

Sources

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.