Alert archive / California / Flash Flood Warnings in 2023

Flash Flood Warning 21, NWS Los Angeles, CA

August 20, 2023Ventura County, California

NWS Los Angeles, CA issued this flash flood warning at Aug 20, 2023, 4:20 PM PDT for Ventura County, California. It was in force for 3 hr. 4 reports 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 20, 2023, 4:20 PM PDT (23:20 UTC)
Expired: Aug 20, 2023, 7:45 PM PDT
In force: 3 hr
Issued by: NWS Los Angeles, CA
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Ventura County, CA

The radar

The Los Angeles radar (KVTX), 27 km from the middle of the area, began a volume at 23:23 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 20, 5:35 PM PDT	FLASH FLOOD	2 E Fillmore, CA	Roadway flooding on Highway 126 east of Fillmore.
Aug 20, 5:35 PM PDT	FLASH FLOOD	2 E Fillmore, CA	Roadway flooding on Highway 126 east of Fillmore.
Aug 20, 7:36 PM PDT	FLASH FLOOD	1 S Fillmore, CA	Swift water rescue in the Santa Clara River due to increased flows.
Aug 20, 7:36 PM PDT	FLASH FLOOD	1 S Fillmore, CA	Swift water rescue in the Santa Clara River due to increased flows.

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

The nearest sounding before it

Vandenberg AFB, CA (KVBG), launched 12:00Z, 11.3 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-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: 1 J/kg
Mixed-layer CIN: -194 J/kg
Mixed-layer LCL: 1646 m above ground
0-6 km bulk shear: 42 kt
0-1 km storm-relative helicity: 80 m²/s²
0-3 km storm-relative helicity: 128 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

774 
WGUS56 KLOX 202320
FFWLOX
CAC111-210245-
/O.NEW.KLOX.FF.W.0021.230820T2320Z-230821T0245Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Los Angeles/Oxnard CA
420 PM PDT Sun Aug 20 2023

The National Weather Service in Los Angeles/Oxnard has issued a

* Flash Flood Warning for...
  East Central Ventura County in southwestern California...

* Until 745 PM PDT.

* At 420 PM PDT, Doppler radar and automated rain gauges indicated 
  heavy rain falling across the warned area. Between 0.5 and 1.5 
  inches of rain have fallen. Flash flooding is already occurring, 
  with rock and mudslides on California 150.

  HAZARD...Life threatening flash flooding. Heavy rain producing
           flash flooding.

  SOURCE...Radar and automated gauges.

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

* Some locations that will experience flash flooding include...
  Fillmore, Ojai, Santa Paula, Topatopa Peak, and Piru.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

In hilly terrain there are hundreds of low water crossings which are 
potentially dangerous in heavy rain. Do not attempt to cross flooded 
roads. Find an alternate route.

&&

LAT...LON 3439 11868 3429 11911 3432 11920 3446 11926
      3451 11921 3457 11897 3459 11878 3458 11878
      3457 11878 3451 11875 3450 11874 3443 11870

FLASH FLOOD...RADAR AND GAUGE INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE

$$

Schoenfeld/Cohen

The office that day

Everything else NWS Los Angeles, CA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 19, 5:31 PM PDT	Special Weather Statement	LOX		29 min
Aug 20, 3:53 AM PDT	Small Craft Advisory	LOX		29 hr
Aug 20, 8:29 AM PDT	Areal Flood Advisory	LOX	Los Angeles	5 hr
Aug 20, 10:54 AM PDT	Flash Flood Warning Considerable damage threat	LOX	Los Angeles	8 hr
Aug 20, 11:48 AM PDT	Flash Flood Warning Considerable damage threat	LOX	Los Angeles, Ventura	8 hr
Aug 20, 12:44 PM PDT	Areal Flood Advisory	LOX	Ventura	8 hr
Aug 20, 3:10 PM PDT	Areal Flood Advisory	LOX	Los Angeles	6 hr

Nearby

Flash Flood Warnings in California, 2023 Every flash flood warning in 2023

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.