Widespread heavy thunderstorms developing and training along outflow boundaries led to heavy rainfall which caused flash flooding mainly across the Southshore of southeastern Louisiana.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LIX wrote it up.
Widespread heavy thunderstorms developing and training along outflow boundaries led to heavy rainfall which caused flash flooding mainly across the Southshore of southeastern Louisiana.
The local office's own words before the first event, 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 the first event at Jul 4, 2:11 PM CST, 23 hours earlier.
Area Forecast Discussion National Weather Service New Orleans LA 311 PM CDT Sat Jul 4 2020 .SHORT TERM... Tonight through Monday...convection from this afternoon will continue into the evening...models hint at some westward and southerly propagation along the outflows into the New Orleans Metro and towards Baton Rouge by late afternoon/early evening. After loss of heating as we approach sunset would likely see the convection start to wane across the area. Inside any thunderstorms may be very heavy rainfall with slow moving storms and PWATS at or just over 2 inches...rainfall rates of 4-5inches per hour are being seen at this time along with 25-30kt wind gusts. Frontal boundary and weak low will remain near the region through the short term period with mainly more diurnally driven convection each day...some lingering showers and isolated thunderstorms possible overnight but smaller chances for sure..may have overdone chances for rainfall overnight. Evening crew can follow radar and mesoanalysis trends to adjust if so tonight...possible tomorrow night and Monday night as well as no real indication of significant driver of the convection but daytime heating even with the boundary in place. Overall, high forecast certainty for storms during the afternoon and evening...much lesser certainty for late night into early morning. Afternoon high temps a bit lower than seasonal due to the cloud cover, overnight lows may be a bit higher because of the same cloud cover from daytime storms. ABS .LONG TERM... Tuesday through Saturday...Frontal boundary remains to start the long term portion of the forecast before some indication that upper level ridging to the west and south pushes the boundary and the weak low out of the area mid week into Thursday. Mostly diurnally driven storms and showers with locally heavy rainfall Tuesday and Wednesday. Drying out Thursday into the weekend for the most part...some uncertainty exists exactly how the ridge sets up and that can have a huge role in precip chances late next week into the weekend. If the ridge is slightly further west and/or north then we could see "ring of fire" storm development as easterly flow pushes moist gulf air into the region...if the ridge moves a bit further east then it could stifle any chance for storms and temps could become quite hot into the middle 90s at least by Friday or Saturday and into the weekend. Alot at play for the far end of the extended forecast. ABS && .AVIATION... 18Z TAFS... VFR conditions will dominate the period...but with convection developing this afternoon and continuing into the evening will look for possible tempo periods of MVFR and IFR at most sites. Have used VCTS with CB for now to show this potential and will watch radar trends for updates to TAFs across the area. Light winds will continue through the period outside of the storms...with the possibility of minor drops in visibility to 5-6sm in the early morning hours. Didn't fully embrace that in TAFs as some of that I believe is predicated on how much rainfall occurs today/tonight and if clearing of the skies can occur. ABS && .MARINE... Winds will be light (<15 knots) and westerly through Monday morning. Monday evening through Friday morning, winds will be light (<15 knots) and southwesterly to southerly. Friday evening through Saturday, winds will be light (<15 knots) and westerly. Wave heights will correspond with the wind speeds. MSW && .PRELIMINARY POINT TEMPS/POPS... MCB 73 88 74 85 / 60 80 60 90 BTR 74 88 74 85 / 60 70 60 90 ASD 72 89 74 87 / 60 80 70 90 MSY 75 87 76 86 / 60 70 70 80 GPT 75 86 76 85 / 60 80 70 90 PQL 72 89 73 87 / 60 80 70 90 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...None. GM...None. MS...None. GM...None. &&
The national radar mosaic for the moment the first event began.
2 flash flood, 1 flood. Local standard time, as filed.
Water of 3 to 4 inches deep at U.S. Highway 90 and Stumpf Blvd in Gretna.
Destrehan pumping station measured 6.89 inches. Luling pumping station 3.91 inches. Rest of parish between 2 and 3 inches. Numerous streets flooded and several homes inundated.
Several streets flooded with some impassable in downtown Slidell. Hasswood area 1.48 inches, Fremaux area 3.5 inches, ham radio reports Heritage Estates street flooding and Independence/Patriot drive area impassable.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Louisiana in 2020Every state in 2020This day in weather historyWarnings in Louisiana, July 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-10-01. Each event’s entry at NCEI: 911900, 911902, 911907.