Alert archive / Utah / Mesoscale Discussions in 2021

Mesoscale Discussion 1556

August 18, 20219 counties in Utah

The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2021, 2:35 PM MDT for 9 counties in Utah. It was in force for 115 min.

The area

The outline as issued.

The facts

Issued: Aug 18, 2021, 2:35 PM MDT (20:35 UTC)
Expired: Aug 18, 2021, 4:30 PM MDT
In force: 115 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 448

Counties Beaver County, UT, Emery County, UT, Garfield County, UT, Grand County, UT, Iron County, UT, Piute County, UT, Sanpete County, UT, Sevier County, UT, Wayne County, UT

The radar

The Cedar City radar (KICX), 120 km from the middle of the area, began a volume at 20:34 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 nearest sounding before it

Salt Lake City I, UT (KSLC), launched 12:00Z, 8.6 hours before the alert went out and 265 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: 7 J/kg
Mixed-layer CIN: -398 J/kg
Mixed-layer LCL: 1192 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: -6 m²/s²
0-3 km storm-relative helicity: 17 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

929 
ACUS11 KWNS 182036
SWOMCD
SPC MCD 182035 
UTZ000-NVZ000-182230-

Mesoscale Discussion 1556
NWS Storm Prediction Center Norman OK
0335 PM CDT Wed Aug 18 2021

Areas affected...Central Utah

Concerning...Severe Thunderstorm Watch 448...

Valid 182035Z - 182230Z

The severe weather threat for Severe Thunderstorm Watch 448
continues.

SUMMARY...The severe wind potential continues across WW 448 as
thunderstorms continue to increase in coverage.

DISCUSSION...Radar trends over the past hour have shown an increase
in thunderstorm coverage across central to southern Utah along and
ahead of a cold front that is slowly migrating to the
south/southeast. While most storms have been transient in nature, a
few have shown signs of organization with strong downdrafts, and a
53 mph wind gust was recently noted in central UT associated with a
strong thunderstorm. The overall thermodynamic and kinematic
environment remains supportive for transient organized convection,
and low-level lapse rates have steepened to near 10 C/km (per recent
mesoanalysis estimates) across west and east-central UT where
temperatures have warmed into the upper 80s. Favorable lift will
remain over the region heading into the evening hours, so the severe
wind potential will continue - especially across the aforementioned
areas with the steepest boundary-layer lapse rates.

..Moore.. 08/18/2021

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

ATTN...WFO...GJT...SLC...VEF...

LAT...LON   38611409 38811328 39361197 39631090 39530962 39130927
            38480939 38050999 37591090 37431153 37391269 37491337
            37731401 38111423 38611409

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 18, 11:34 AM MDT	Mesoscale Discussion	SPC	Beaver, Carbon, Duchesne, Emery, Garfield, Iron and 8 more	86 min
Aug 18, 12:14 PM MDT	Severe Thunderstorm Watch	SPC	Beaver, Carbon, Daggett, Duchesne, Emery, Garfield and 15 more	8 hr

Nearby

Mesoscale Discussions in Utah, 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.