Alert archive / Louisiana / Flash Flood Warnings in 2021

Flash Flood Warning 77, NWS New Orleans, LA

July 20, 2021Saint Helena Parish, Tangipahoa Parish, Washington Parish, Louisiana; Amite County, Pike County, Walthall County, Mississippi

NWS New Orleans, LA issued this flash flood warning at Jul 20, 2021, 6:46 AM CDT for Saint Helena Parish, Tangipahoa Parish, Washington Parish, Louisiana; Amite County, Pike County, Walthall County, Mississippi. It was in force for 3 hr. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Jul 20, 2021, 6:46 AM CDT (11:46 UTC)
Expired: Jul 20, 2021, 9:45 AM CDT
In force: 3 hr
Issued by: NWS New Orleans, LA
Area: Storm-based polygon
Flood severity: None

Counties Saint Helena Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Amite County, MS, Pike County, MS, Walthall County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 11.8 hours before the alert went out and 102 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.

065 
WGUS54 KLIX 201146
FFWLIX
LAC091-105-117-MSC005-113-147-201445-
/O.NEW.KLIX.FF.W.0077.210720T1146Z-210720T1445Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

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

The National Weather Service in New Orleans has issued a

* Flash Flood Warning for...
  Northeastern St. Helena Parish in southeastern Louisiana...
  Northern Tangipahoa Parish in southeastern Louisiana...
  Northwestern Washington Parish in southeastern Louisiana...
  Southeastern Amite County in southern Mississippi...
  Southern Pike County in southern Mississippi...
  Southwestern Walthall County in southern Mississippi...

* Until 945 AM CDT.

* At 646 AM CDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 1 and 2 inches of rain 
  have fallen. The expected rainfall rate is 2 to 3 inches in 1 
  hour. Additional rainfall amounts of 2 to 4 inches are possible in 
  the warned area. Flash flooding is ongoing or expected to begin 
  shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar.

  IMPACT...Flash flooding of small creeks and streams, urban
           areas, highways, streets and underpasses as well as
           other poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Franklinton, Magnolia, Kentwood, Tylertown, Osyka, Mount Herman 
  and Mccomb Airport.

This includes the following Interstates...
	Interstate 55 in Louisiana between mile markers 60 and 66.
	Interstate 55 in Mississippi between mile markers 1 and 12.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Be aware of your surroundings and do not drive on flooded roads.

&&

LAT...LON 3120 9046 3116 9026 3110 9000 3100 9003
      3078 9011 3081 9029 3083 9040 3100 9066

FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL...2-3 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, 12:58 AM CDT	Flash Flood Warning Considerable damage threat	LIX	Saint Tammany	3 hr
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, 6:55 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
Jul 20, 4:01 AM CDT	Special Weather Statement	LIX	Hancock	44 min
Jul 20, 11:12 AM CDT	Special Weather Statement	LIX	Jackson	48 min
Jul 20, 2:46 PM CDT	Special Weather Statement	LIX	Hancock	44 min
Jul 20, 3:18 PM CDT	Special Weather Statement	LIX	Pearl River	42 min
Jul 20, 5:50 PM CDT	Areal Flood Advisory	LIX	Pearl River	115 min

Nearby

Flash Flood Warnings in Louisiana, 2021 Flash Flood Warnings in Mississippi, 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; the sounding from the Mesonet's radiosonde archive.