Mesoscale Discussion 695

Issued

May 21, 2021, 2:52 PM MDT (20:52 UTC)

Expired

May 21, 2021, 5:15 PM MDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Sublette County, WY, Teton County, WY

The Riverton/Lander radar (KRIW), 166 km from the middle of the area, began a volume at 20:51 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.

965 
ACUS11 KWNS 212053
SWOMCD
SPC MCD 212052 
WYZ000-IDZ000-212315-

Mesoscale Discussion 0695
NWS Storm Prediction Center Norman OK
0352 PM CDT Fri May 21 2021

Areas affected...Parts of western Wyoming and adjacent southeastern
Idaho

Concerning...Severe potential...Watch unlikely 

Valid 212052Z - 212315Z

Probability of Watch Issuance...5 percent

SUMMARY...An isolated supercell or two could pose increasing severe
weather potential by 4-6 MDT, particularly near/west of the Big
Piney and Bondurant vicinities into the Jackson Hole area.

DISCUSSION...In the wake of early afternoon cloud cover and light
precipitation, breaks in the overcast may allow a corridor of weak
to modest boundary-layer destabilization to occur southwest of the
Wind River Range, particularly near the western slopes of the
Wyoming Range into the Tetons.  With the precipitation contributing
to at least some low-level moistening, steepening lapse rates, aided
by insolation beneath weak cold advection aloft, may contribute to
CAPE on the order of 250-500 J/kg.  As this occurs, large-scale
ascent, beneath difluent/divergent upper flow to northeast of the
broad and deep mid-level low centered to the east of the Sierra
Nevada, aided by orographic forcing, may contribute to the
initiation of isolated to widely scattered thunderstorms by 22-00Z.

While destabilization may be weak, deep-layer shear beneath 50-80+
kt southerly mid/upper flow is already strong, and NAM and Rapid
Refresh soundings have been suggestive that sizable, clockwise
curved low-level hodographs may develop across this region by late
afternoon.  Thus, it appears that one or two supercells could
evolve, accompanied by the potential to produce large hail, with
perhaps some risk for a brief tornado.

..Kerr/Guyer.. 05/21/2021

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

ATTN...WFO...RIW...PIH...

LAT...LON   43751121 44151036 42670954 42090989 41981033 42281060
            42641089 43751121

Mesoscale Discussions in Wyoming, 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.