Alert archive / Utah / Flash Flood Warnings in 2020

Flash Flood Warning 21, NWS Salt Lake City, UT

August 23, 2020Washington County, Utah

NWS Salt Lake City, UT issued this flash flood warning at Aug 23, 2020, 9:52 PM MDT for Washington County, Utah. It was in force for 3 hr. 1 report came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Aug 23, 2020, 9:52 PM MDT (03:52 UTC)
Expired: Aug 24, 2020, 12:45 AM MDT
In force: 3 hr
Issued by: NWS Salt Lake City, UT
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Washington County, UT

The radar

The Cedar City radar (KICX), 80 km from the middle of the area, began a volume at 03:53 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 was reported inside it

Time	Report	Where	Remark
Aug 23, 10:08 PM MDT	FLASH FLOOD	St George, UT	LAW ENFORCEMENT REPORTED MULTIPLE ROAD CLOSURES DUE TO 1 TO 3 FEET OF WATER ACROSS ROADWAYS. STALLED VEHICLES, ROCKS AND OTHER DEBRIS HAVE BEEN REPORTED IN ROADWAYS.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Las Vegas, NV (KVEF), launched 00:00Z, 3.9 hours before the alert went out and 195 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: 935 J/kg
Mixed-layer CIN: -118 J/kg
Mixed-layer LCL: 2851 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: 14 m²/s²
0-3 km storm-relative helicity: 25 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

871 
WGUS55 KSLC 240352
FFWSLC
UTC053-240645-
/O.NEW.KSLC.FF.W.0021.200824T0352Z-200824T0645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Salt Lake City UT
952 PM MDT Sun Aug 23 2020

The National Weather Service in Salt Lake City has issued a

* Flash Flood Warning for...
  South Central Washington County in southwestern Utah...

* Until 1245 AM MDT.

* At 952 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 0.75 and 1.75 inches of 
  rain have fallen. Flash flooding is ongoing or expected to begin 
  shortly.

  HAZARD...Life threatening flash flooding. Thunderstorms
           producing flash flooding.

  SOURCE...Doppler radar.

  IMPACT...Life threatening flash flooding of creeks and streams,
           urban areas, highways, streets and underpasses.

* Some locations that will experience flash flooding include...
  St George, Washington, Hurricane, Santa Clara, Ivins, Bloomington 
  and Snow Canyon State Park.

This includes the following highways...
	Interstate 15 between mile markers 3 and 16.
	Utah Route 18 between mile markers 0 and 8.

Additional rainfall amounts of 0.25 to 0.75 inches are possible in 
the warned area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

Excessive runoff from heavy rainfall will cause flooding of small 
creeks and streams, urban areas, highways, streets and underpasses 
as well as other drainage areas and low lying spots.

&&

LAT...LON 3713 11370 3703 11363 3703 11351 3709 11345
      3713 11343 3717 11344 3719 11352 3715 11354
      3714 11360 3720 11362

FLASH FLOOD...RADAR INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL...0.5-1 INCH IN 1 HOUR 

$$

Church

2 follow-up statements

936 
WGUS75 KSLC 240412
FFSSLC

Flash Flood Statement
National Weather Service Salt Lake City UT
1012 PM MDT Sun Aug 23 2020

UTC053-240645-
/O.CON.KSLC.FF.W.0021.000000T0000Z-200824T0645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Washington UT-
1012 PM MDT Sun Aug 23 2020

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1245 AM MDT MONDAY 
FOR SOUTH CENTRAL WASHINGTON COUNTY...

At 1012 PM MDT, local law enforcement reported thunderstorms 
producing heavy rain across the warned area. Between 1 and 2 inches 
of rain have fallen. Flash flooding is ongoing, with multiple road 
closures across St. George, 1 to 3 feet of water reported on several 
roadways and cars stalled and stuck in flood waters.

HAZARD...Life threatening flash flooding. Thunderstorms producing
         flash flooding.

SOURCE...Law enforcement.

IMPACT...Life threatening flash flooding of creeks and streams,
         urban areas, highways, streets and underpasses.

Some locations that will experience flash flooding include...
  St George, Washington, Hurricane, Santa Clara, Ivins, Bloomington 
  and Snow Canyon State Park.

This includes the following highways...
	Interstate 15 between mile markers 3 and 16.
	Utah Route 18 between mile markers 0 and 8.

Additional rainfall amounts of 0.25 to 0.5 inches are possible in 
the warned area.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

Be especially cautious at night when it is harder to recognize the 
dangers of flooding.

Excessive runoff from heavy rainfall will cause flooding of small 
creeks and streams, urban areas, highways, streets and underpasses 
as well as other drainage areas and low lying spots.

&&

LAT...LON 3713 11370 3703 11363 3703 11351 3709 11345
      3713 11343 3717 11344 3719 11352 3715 11354
      3714 11360 3720 11362

FLASH FLOOD...OBSERVED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

Church

562 
WGUS75 KSLC 240646
FFSSLC

Flash Flood Statement
National Weather Service Salt Lake City UT
1246 AM MDT Mon Aug 24 2020

UTC053-240654-
/O.EXP.KSLC.FF.W.0021.000000T0000Z-200824T0645Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Washington UT-
1246 AM MDT Mon Aug 24 2020

...THE FLASH FLOOD WARNING FOR SOUTH CENTRAL WASHINGTON COUNTY WILL
EXPIRE AT 1245 AM MDT...

The earlier heavy rain has moved north of the warned area. 
Additional flash flooding is no longer expected to pose a threat.

LAT...LON 3713 11370 3703 11363 3703 11351 3709 11345
      3713 11343 3717 11344 3719 11352 3715 11354
      3714 11360 3720 11362

$$

Conger

The office that day

Everything else NWS Salt Lake City, UT issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 23, 7:22 PM MDT	Special Weather Statement	SLC	Washington	38 min
Aug 23, 9:05 PM MDT	Special Weather Statement	SLC	Washington	40 min
Aug 23, 9:15 PM MDT	Areal Flood Advisory	SLC	Washington	37 min
Aug 24, 5:45 PM MDT	Special Weather Statement	SLC		60 min

Nearby

Flash Flood Warnings in Utah, 2020 Every flash flood warning in 2020

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.