Alert archive / Idaho / Mesoscale Discussions in 2021

Mesoscale Discussion 1733

September 12, 20214 counties in Idaho; 4 counties in Utah; Lincoln County, Wyoming

The Storm Prediction Center issued this mesoscale discussion at Sep 12, 2021, 4:59 PM MDT for 4 counties in Idaho; 4 counties in Utah; Lincoln County, Wyoming. It was in force for 91 min.

The area

The outline as issued.

The facts

Issued
Sep 12, 2021, 4:59 PM MDT (22:59 UTC)
Expired
Sep 12, 2021, 6:30 PM MDT
In force
91 min
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
5%

Counties Bear Lake County, ID, Caribou County, ID, Franklin County, ID, Oneida County, ID, Box Elder County, UT, Cache County, UT, Rich County, UT, Weber County, UT, Lincoln County, WY

The radar

The Salt Lake City radar (KMTX), 111 km from the middle of the area, began a volume at 23:01 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, 11.0 hours before the alert went out and 150 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-pSkew-T log-p diagram, Salt Lake City I, UT at 12:00Z on 2021-09-12Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 108 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Salt Lake City I, UT at 12:00Z on 2021-09-12The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 76 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
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
108 J/kg
Mixed-layer CIN
-195 J/kg
Mixed-layer LCL
1716 m above ground
0-6 km bulk shear
32 kt
0-1 km storm-relative helicity
76 m²/s²
0-3 km storm-relative helicity
124 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

902 
ACUS11 KWNS 122259
SWOMCD
SPC MCD 122259 
WYZ000-IDZ000-UTZ000-130030-

Mesoscale Discussion 1733
NWS Storm Prediction Center Norman OK
0559 PM CDT Sun Sep 12 2021

Areas affected...far northern Utah...southeast Idaho...and western
Wyoming.

Concerning...Severe potential...Watch unlikely 

Valid 122259Z - 130030Z

Probability of Watch Issuance...5 percent

SUMMARY...An isolated large hail and severe wind threat is expected
through the evening.

DISCUSSION...An area of instability has developed ahead of a dryline
which is currently moving across southeast Idaho and northern Utah.
SPC mesoanalysis shows MLCAPE around 250 to 500 J/kg with some low
50s dewpoints in this region. A couple supercells have developed
along this dryline as it moves southeast. Effective shear is
increasing as mid-level flow strengthens from the Southwest ahead of
the mid-level shortwave trough across the Pacific Northwest. While
the threat should remain in a confined area, isolated large hail and
severe winds are possible with these storms as they move eastward
through the evening.

..Bentley/Grams.. 09/12/2021

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

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

LAT...LON   41971333 42821187 42991095 42861034 42621002 42031021
            41241149 41291281 41501342 41971333

Nearby

Mesoscale Discussions in Idaho, 2021Mesoscale Discussions in Utah, 2021Mesoscale Discussions in Wyoming, 2021Every 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.