Alert archive / Utah / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 448
The Storm Prediction Center issued this severe thunderstorm watch at Aug 18, 2021, 12:14 PM MDT for 21 counties in Utah. It was in force for 8 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 18, 2021, 12:14 PM MDT (18:14 UTC)
- Expired
- Aug 18, 2021, 8:00 PM MDT
- In force
- 8 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 21 counties
Beaver County, UT, Carbon County, UT, Daggett County, UT, Duchesne County, UT, Emery County, UT, Garfield County, UT, Grand County, UT, Iron County, UT, Juab County, UT, Kane County, UT, Millard County, UT, Piute County, UT, Salt Lake County, UT, Sanpete County, UT, Sevier County, UT, Summit County, UT, Uintah County, UT, Utah County, UT, Wasatch County, UT, Washington County, UT, Wayne County, UT
The radar
The Cedar City radar (KICX), 221 km from the middle of the area, began a volume at 18:13 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 40%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 30%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
13 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 18, 12:34 PM MDT | Severe Thunderstorm Warning | SLC | Juab, Tooele | 56 min |
| Aug 18, 1:05 PM MDT | Flash Flood Warning | SLC | Wayne | 3 hr |
| Aug 18, 1:12 PM MDT | Flash Flood Warning | SLC | Garfield | 2 hr |
| Aug 18, 1:24 PM MDT | Severe Thunderstorm Warning | SLC | Juab, Tooele, Utah | 81 min |
| Aug 18, 1:39 PM MDT | Flash Flood Warning | SLC | Kane, Washington | 3 hr |
| Aug 18, 2:27 PM MDT | Flash Flood Warning | SLC | Utah | 3 hr |
| Aug 18, 2:37 PM MDT | Flash Flood Warning | SLC | Utah | 113 min |
| Aug 18, 3:25 PM MDT | Flash Flood Warning | SLC | Utah | 3 hr |
| Aug 18, 3:46 PM MDT | Flash Flood Warning | SLC | Emery, Wayne | 3 hr |
| Aug 18, 4:22 PM MDT | Flash Flood Warning | SLC | Garfield | 3 hr |
| Aug 18, 4:36 PM MDT | Severe Thunderstorm Warning | GJT | Grand, San Juan | 24 min |
| Aug 18, 4:57 PM MDT | Severe Thunderstorm Warning | GJT | Grand, San Juan | 33 min |
| Aug 18, 7:43 PM MDT | Flash Flood Warning | SLC | Kane | 4 hr |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Salt Lake City I, UT (KSLC), launched 12:00Z, 6.2 hours before the alert went out and 215 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
- 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
The text
As transmitted.
723 WWUS20 KWNS 181810 SEL8 SPC WW 181810 UTZ000-190200- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 448 NWS Storm Prediction Center Norman OK 1210 PM MDT Wed Aug 18 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Utah * Effective this Wednesday afternoon and evening from 1210 PM until 800 PM MDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...Scattered storms including a few supercells will become capable of producing damaging wind and a few instances of large hail this afternoon into the early evening. The severe thunderstorm watch area is approximately along and 105 statute miles north and south of a line from 20 miles east southeast of Vernal UT to 40 miles west of Cedar City UT. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU8). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 447... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 24035. ...Dial
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, 2:35 PM MDT | Mesoscale Discussion | SPC | Beaver, Emery, Garfield, Grand, Iron, Piute and 3 more | 115 min |
Nearby
Severe Thunderstorm Watches in Utah, 2021Every severe thunderstorm watch 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.