Alert archive / Louisiana / Flash Flood Warnings in 2020

Flash Flood Warning 26, NWS New Orleans, LA

August 12, 2020Jefferson Parish, Orleans Parish, Louisiana

NWS New Orleans, LA issued this flash flood warning at Aug 12, 2020, 2:45 PM CDT for Jefferson Parish, Orleans Parish, Louisiana. It was in force for 39 min. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Aug 12, 2020, 2:45 PM CDT (19:45 UTC)
Expired: Aug 12, 2020, 3:24 PM CDT
In force: 39 min
Issued by: NWS New Orleans, LA
Area: Storm-based polygon
Flood severity: None

Counties Jefferson Parish, LA, Orleans Parish, LA

Did it verify

Not verified. The Iowa Environmental Mesonet's Cow found no qualifying storm report inside this flash flood warning while it was in force. That is not proof nothing happened: reports are thin where few people live.

Cow counts a report within 15 km of the polygon while the warning was in force: a tornado for a tornado warning; hail of 1 inch or more, a gust of 58 mph or more or wind damage for a severe thunderstorm warning; a flash flood report for a flash flood warning.

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 7.8 hours before the alert went out and 54 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: 2468 J/kg
Mixed-layer CIN: -16 J/kg
Mixed-layer LCL: 701 m above ground
0-6 km bulk shear: 14 kt
0-1 km storm-relative helicity: 4 m²/s²
0-3 km storm-relative helicity: -16 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

231 
WGUS54 KLIX 121945
FFWLIX
LAC051-071-122145-
/O.NEW.KLIX.FF.W.0026.200812T1945Z-200812T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service New Orleans LA
Issued by National Weather Service Mobile AL
245 PM CDT Wed Aug 12 2020

The National Weather Service in New Orleans has issued a

* Flash Flood Warning for...
  North Central Jefferson Parish in southeastern Louisiana...
  Southwestern Orleans Parish in southeastern Louisiana...

* Until 445 PM CDT.

* At 245 PM CDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 1 and 1.5 inches of 
  rain have fallen. Flash flooding is ongoing or expected to begin 
  shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Doppler radar.

  IMPACT...Flooding of small creeks and streams, urban areas,
           highways, streets and underpasses as well as other
           drainage and low lying areas.

* Some locations that will experience flash flooding include...
  New Orleans, Marrero, Harvey, Timberlane, Avondale, Metairie, 
  Belle Chasse, Jefferson, Gretna, Harahan, Westwego, Bridge City, 
  Estelle, Woodmere, Terrytown and Elmwood.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 2997 9019 2997 9017 2998 9010 2997 9007
      2996 9004 2989 9001 2987 9002 2985 9004
      2984 9011 2986 9018 2989 9019

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL...1-1.5 INCHES IN 1 HOUR 

$$

BB

1 follow-up statement

748 
WGUS74 KLIX 122024
FFSLIX

Flash Flood Statement
National Weather Service New Orleans LA
Issued by National Weather Service Mobile AL
324 PM CDT Wed Aug 12 2020

LAC051-071-122034-
/O.CAN.KLIX.FF.W.0026.000000T0000Z-200812T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Jefferson LA-Orleans LA-
324 PM CDT Wed Aug 12 2020

...FLASH FLOOD WARNING IS CANCELLED FOR NORTH CENTRAL JEFFERSON AND 
SOUTHWESTERN ORLEANS PARISHES...

The heavy rain has ended. Minor street flooding may continue until 
water recedes but heavy rainfall threat has ended. Please continue 
to heed remaining road closures.

LAT...LON 2997 9019 2997 9017 2998 9010 2997 9007
      2996 9004 2989 9001 2987 9002 2985 9004
      2984 9011 2986 9018 2989 9019

$$

BB

What forecasters said that day

The local office's own words before this flash flood warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS New Orleans, LA wrote its last area forecast discussion before this flash flood warning went out at Aug 12, 1:03 PM CDT, 1 hour 42 minutes earlier.

Area forecast discussion, Aug 12, 1:03 PM CDT, 1 hour 42 minutes before

Area Forecast Discussion...UPDATED
National Weather Service New Orleans LA
Issued by National Weather Service Mobile AL
103 PM CDT Wed Aug 12 2020

.18Z AVIATION UPDATE...

Scattered to occasional broken low cloud deck will continue to
impact the TAF sites, while showers and thunderstorms currently
developing expand in coverage throughout the afternoon. VFR
conditions will prevail through much of the forecast, except near
thunderstorms when visibilities and ceilings could drop to MVFR
or IFR criteria. Wind gusts of 15-25 knots are possible near
thunderstorms this afternoon. Storms should diminish by 02z or so.
Storms will re-develop over the Gulf and near the coast early
tomorrow. /22

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  93  76  91  75 /  10  10  70  10
BTR  95  77  93  76 /  10   0  70  10
ASD  95  76  92  75 /  30   0  80  20
MSY  93  79  92  78 /  20   0  70  20
GPT  92  78  90  77 /  20   0  70  30
PQL  95  75  92  76 /  30   0  70  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

In the hours before

Special weather statement, Aug 12, 1:53 PM CDT, 52 minutes before

Special Weather Statement
National Weather Service New Orleans LA
Issued by National Weather Service Mobile AL
153 PM CDT Wed Aug 12 2020

LAZ060>062-121930-
Orleans LA-St. Charles LA-Upper Jefferson LA-
153 PM CDT Wed Aug 12 2020

...A STRONG THUNDERSTORM WILL AFFECT THE FOLLOWING COUNTIES...CENTRAL
ST. CHARLES...SOUTHWESTERN ORLEANS AND NORTHWESTERN JEFFERSON
PARISHES UNTIL 230 PM CDT...

At 152 PM CDT...the strong thunderstorm was located over Luling, or
7 miles southeast of Hahnville, moving southeast at 5 mph.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
New Orleans, Avondale, Marrero, Harvey, Timberlane, Metairie,
Hahnville, Jefferson, Gretna, Harahan, Westwego, Luling, River Ridge,
Boutte, Ama, Destrehan, Estelle, St. Rose, Woodmere and Paradis.

LAT...LON 2991 9048 3002 9026 2992 8998 2992 8999
      2979 9014 2977 9037
TIME...MOT...LOC 1852Z 320DEG 5KT 2992 9032

Black

Special weather statement, Aug 12, 2:30 PM CDT, 15 minutes before

Special Weather Statement
National Weather Service New Orleans LA
Issued by National Weather Service Mobile AL
230 PM CDT Wed Aug 12 2020

LAZ060>063-122015-
Orleans LA-St. Charles LA-Upper Plaquemines LA-Upper Jefferson LA-
230 PM CDT Wed Aug 12 2020

...A STRONG THUNDERSTORM WILL AFFECT THE FOLLOWING COUNTIES...
SOUTHEASTERN ST. CHARLES...SOUTHWESTERN ORLEANS...NORTHWESTERN
JEFFERSON AND NORTHWESTERN PLAQUEMINES PARISHES UNTIL 315 PM CDT...

At 229 PM CDT...the strong thunderstorm was located over Westwego,
or over Avondale, moving east at 10 mph.

Wind gusts up to 50 mph will be possible with this storm.

Locations impacted include...
New Orleans, Marrero, Harvey, Avondale, Timberlane, Metairie, Belle
Chasse, Jefferson, Gretna, Harahan, Westwego, Jean Lafitte, Woodmere,
Elmwood, Terrytown, Bridge City, River Ridge, Estelle, Waggaman and
Ama.

LAT...LON 2981 9039 3001 9024 2995 9001 2994 9000
      2979 9004 2972 9019
TIME...MOT...LOC 1929Z 291DEG 7KT 2990 9016

Black

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 11, 7:05 PM CDT	Special Weather Statement	LIX	Orleans	25 min
Aug 11, 8:06 PM CDT	Special Weather Statement	LIX	Saint John the Baptist	24 min
Aug 11, 8:27 PM CDT	Areal Flood Advisory	LIX	Saint Tammany, Tangipahoa	47 min
Aug 11, 8:42 PM CDT	Special Weather Statement	LIX	Saint Tammany	33 min
Aug 11, 8:52 PM CDT	Special Marine Warning	LIX		23 min
Aug 11, 9:08 PM CDT	Special Marine Warning	LIX		67 min
Aug 11, 9:20 PM CDT	Special Weather Statement	LIX	Orleans, Saint Charles, Saint John the Baptist	25 min
Aug 11, 9:35 PM CDT	Special Marine Warning	LIX		25 min
Aug 11, 9:57 PM CDT	Special Weather Statement	LIX	Saint Charles	33 min
Aug 11, 10:09 PM CDT	Special Marine Warning	LIX		66 min
Aug 11, 11:14 PM CDT	Special Marine Warning	LIX		61 min
Aug 11, 11:56 PM CDT	Special Marine Warning	LIX		64 min
Aug 12, 12:55 AM CDT	Special Marine Warning	LIX		65 min
Aug 12, 1:13 AM CDT	Special Marine Warning	LIX		47 min
Aug 12, 2:48 AM CDT	Special Marine Warning	LIX		57 min
Aug 12, 10:51 AM CDT	Special Marine Warning	LIX		41 min
Aug 12, 1:53 PM CDT	Special Weather Statement	LIX	Saint Charles	37 min
Aug 12, 2:02 PM CDT	Areal Flood Advisory	LIX	Jefferson, Orleans, Plaquemines, Saint Bernard, Saint Charles	118 min
Aug 12, 2:30 PM CDT	Special Weather Statement	LIX	Saint Charles	45 min
Aug 12, 3:15 PM CDT	Special Weather Statement	LIX	Saint Tammany	45 min
Aug 12, 4:20 PM CDT	Special Weather Statement	LIX	Terrebonne	25 min

Nearby

Flash Flood Warnings in Louisiana, 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; the sounding from the Mesonet's radiosonde archive.