Alert archive / Utah / Mesoscale Discussions in 2021
Mesoscale Discussion 1767
The Storm Prediction Center issued this mesoscale discussion at Sep 18, 2021, 10:59 AM MST for Coconino County, Arizona; 12 counties in Utah. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 18, 2021, 10:59 AM MST (17:59 UTC)
- Expired
- Sep 18, 2021, 1:00 PM MST
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
Counties Coconino County, AZ, Carbon County, UT, Duchesne County, UT, Emery County, UT, Garfield County, UT, Kane County, UT, Piute County, UT, Sanpete County, UT, Sevier County, UT, Summit County, UT, Utah County, UT, Wasatch County, UT, Wayne County, UT
The radar
The Cedar City radar (KICX), 183 km from the middle of the area, began a volume at 18:00 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
Grand Junction, CO (KGJT), launched 12:00Z, 6.0 hours before the alert went out and 237 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.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 3697 m above ground
- 0-6 km bulk shear
- 31 kt
- 0-1 km storm-relative helicity
- 52 m²/s²
- 0-3 km storm-relative helicity
- 64 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
182
ACUS11 KWNS 181800
SWOMCD
SPC MCD 181759
UTZ000-AZZ000-182000-
Mesoscale Discussion 1767
NWS Storm Prediction Center Norman OK
1259 PM CDT Sat Sep 18 2021
Areas affected...Far northern Arizona into northern Utah
Concerning...Severe potential...Watch unlikely
Valid 181759Z - 182000Z
Probability of Watch Issuance...5 percent
SUMMARY...A couple strong to severe gusts and perhaps an instance of
large hail may occur with one of the stronger storms. A WW issuance
is not expected given the relatively brief, localized nature of the
severe threat.
DISCUSSION...Current visible satellite imagery depicts some breaks
in the clouds across portions of the Lower Colorado River Basin,
promoting modest insolation and associated increasing buoyancy.
Clusters of ongoing thunderstorms along the AZ/UT border have
recently supported surface gusts up to 40 kts within the past hour,
and these storms are poised to move through the aforementioned axis
of surface heating through the afternoon. The 12Z SLC observed
sounding showed up to 8 C/km lapse rates within the 700-500 mb
layer, and with surface temperatures warming through the 70s F (per
latest METAR observations), widespread 7.5-8.5 surface-500 mb lapse
rates will result (as already shown by 17Z mesoanalysis). These
steep lapse rates will contribute to 500 J/kg amid 45 kts of 500 mb
flow, which may efficiently mix downward within the deep, dry
boundary layer to support strong to briefly severe wind gusts. A
brief instance or two of large hail also cannot be ruled out.
However, the severe threat is expected to remain sparse and brief,
and a WW issuance appears unlikely.
..Squitieri/Hart.. 09/18/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GJT...FGZ...SLC...VEF...
LAT...LON 35581309 38741246 40461186 40921154 40951049 40550999
39910975 38750973 37560982 37001007 35571126 35581309Nearby
Mesoscale Discussions in Utah, 2021Mesoscale Discussions in Arizona, 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.