Alert archive / Louisiana / Flash Flood Warnings in 2021

Flash Flood Warning 75, NWS New Orleans, LA

July 20, 2021Saint Tammany Parish, Louisiana

NWS New Orleans, LA issued this flash flood warning at Jul 20, 2021, 12:58 AM CDT for Saint Tammany Parish, Louisiana. It was in force for 3 hr. 3 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: Jul 20, 2021, 12:58 AM CDT (05:58 UTC)
Expired: Jul 20, 2021, 3:45 AM CDT
In force: 3 hr
Issued by: NWS New Orleans, LA
Area: Storm-based polygon
Damage threat: Considerable
Flood severity: None

County Saint Tammany Parish, LA

What was reported inside it

Time	Report	Where	Remark
Jul 20, 2:19 AM CDT	FLASH FLOOD	2 Nne Mandeville, LA	WATER ENTERING SEVERAL HOMES. MANY ROADS IMPASSABLE AND BARRICADED.
Jul 20, 3:15 AM CDT	FLASH FLOOD	2 N Mandeville, LA	A SOCIAL MEDIA VIDEO SHOWED AT LEAST A DOZEN FLOODED CARS IN AN APARTMENT COMPLEX IN MANDEVILLE. A LARGE DUMPSTER WAS ALSO FLOATING.
Jul 20, 3:30 AM CDT	FLASH FLOOD	2 Nnw Mandeville, LA	PUBLIC REPORTED IMPASSABLE SERVICE ROAD IN MANDEVILLE DUE TO HIGH WATER.

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

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 6.0 hours before the alert went out and 40 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: 866 J/kg
Mixed-layer CIN: -23 J/kg
Mixed-layer LCL: 872 m above ground
0-6 km bulk shear: 24 kt
0-1 km storm-relative helicity: 56 m²/s²
0-3 km storm-relative helicity: 69 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.7

Open this sounding in Storm Lab

The text

As transmitted.

460 
WGUS54 KLIX 200558
FFWLIX
LAC103-200845-
/O.NEW.KLIX.FF.W.0075.210720T0558Z-210720T0845Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service New Orleans LA
1258 AM CDT Tue Jul 20 2021

The National Weather Service in New Orleans has issued a

* Flash Flood Warning for...
  Southwestern St. Tammany Parish in southeastern Louisiana...

* Until 345 AM CDT.

* At 1258 AM CDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 2 and 4 inches of rain 
  have fallen. The expected rainfall rate is 2 to 4 inches in 1 
  hour. Additional rainfall amounts of 3 to 5 inches are possible in 
  the warned area. Flash flooding is ongoing or expected to begin 
  shortly.

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

  SOURCE...Radar.

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

* Some locations that will experience flash flooding include...
  mainly rural areas of Southwestern St. Tammany Parish

This includes the following Interstates...
	Interstate 12 between mile markers 65 and 67.

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.

&&

LAT...LON 3040 9014 3044 9004 3038 9001 3036 9008
      3036 9009 3037 9010 3037 9011

FLASH FLOOD...RADAR INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL...2-4 INCHES IN 1 HOUR

$$

TE

The office that day

Everything else NWS New Orleans, LA issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 20, 12:41 AM CDT	Areal Flood Advisory	LIX	Saint Tammany	17 min
Jul 20, 1:55 AM CDT	Areal Flood Advisory	LIX	Saint Tammany	3 hr
Jul 20, 4:02 AM CDT	Special Marine Warning	LIX		58 min
Jul 20, 5:24 AM CDT	Areal Flood Advisory	LIX	East Feliciana, Saint Helena, West Feliciana	3 hr
Jul 20, 5:44 AM CDT	Special Marine Warning	LIX		31 min
Jul 20, 6:23 AM CDT	Areal Flood Advisory	LIX	East Feliciana, Saint Helena, Tangipahoa, Washington	3 hr
Jul 20, 6:33 AM CDT	Flash Flood Warning	LIX	Saint Tammany	4 hr
Jul 20, 6:46 AM CDT	Flash Flood Warning	LIX	Saint Helena, Tangipahoa, Washington	3 hr
Jul 20, 6:55 AM CDT	Special Weather Statement	LIX	Saint Tammany	50 min
Jul 20, 8:28 AM CDT	Special Marine Warning	LIX		62 min
Jul 20, 9:19 AM CDT	Areal Flood Warning	LIX	Saint Tammany	3 hr
Jul 20, 10:29 AM CDT	Areal Flood Warning	LIX	Saint Tammany	2 hr
Jul 20, 2:50 PM CDT	River Flood Warning	LIX	Saint Tammany	43 hr

Nearby

Flash Flood Warnings in Louisiana, 2021 Every flash flood warning 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive.