Alert archive / Louisiana / Special Weather Statements in 2021

Special Weather Statement, NWS New Orleans, LA

May 12, 2021Saint Charles Parish, Louisiana

NWS New Orleans, LA issued this special weather statement at May 12, 2021, 12:33 AM CDT for Saint Charles Parish, Louisiana. It was in force for 42 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
May 12, 2021, 12:33 AM CDT (05:33 UTC)
Expired
May 12, 2021, 1:15 AM CDT
In force
42 min
Issued by
NWS New Orleans, LA

County Saint Charles Parish, LA

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 5.6 hours before the alert went out and 75 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-pSkew-T log-p diagram, Slidell Radar S, LA at 00:00Z on 2021-05-12Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 618 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Slidell Radar S, LA at 00:00Z on 2021-05-12The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 135 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
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
618 J/kg
Mixed-layer CIN
-59 J/kg
Mixed-layer LCL
924 m above ground
0-6 km bulk shear
32 kt
0-1 km storm-relative helicity
135 m²/s²
0-3 km storm-relative helicity
212 m²/s²
Significant tornado parameter
0.3
Supercell composite
4.7

Open this sounding in Storm Lab

The text

As transmitted.

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What forecasters said that day

The local office's own words before this special weather statement 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 special weather statement went out at May 11, 11:53 PM CDT, 40 minutes earlier.

Area forecast discussion, May 11, 11:53 PM CDT, 40 minutes before
Area Forecast Discussion
National Weather Service New Orleans LA
1153 PM CDT Tue May 11 2021

.AVIATION (06Z TAF package)...

Quite a mix of conditions at press time with about half of the
terminals VFR and the rest MVFR to IFR. Convection scattered
across the area with only KMCB being directly impacted at present.
Convective threat to continue through the nighttime hours at most
terminals with occasional IFR conditions. Prevailing conditions
will be MVFR for most of the forecast period, with at least some
threat of TSRA for most of the day as well. Will be carrying VCTS
and amend as necessary for direct impacts (IFR or lower
ceilings/visibilities). 35

&&

.PREV DISCUSSION... /issued 250 PM CDT Tue May 11 2021/

SHORT TERM...
Biggest forecast concern in the short term is the ongoing heavy
rain. Current rainfall totals have been widespread amounts of
4-5 inches and with swaths of 8-10 inches especially on the south
shore. Unfortunately, we already have high PW with our 12z
sounding showing 1.8 inches which looking at SPC's sounding
climatology is very moist for this time of year. Moist air
advection will continue and the environment continues to be
favorable for thunderstorm development with plenty of CAPE. A
stalled boundary has been draped right along the Louisiana coast.
Storms have been firing off on this boundary. We currently are in
a lull in terms of rainfall but expect more rounds later tonight
and tomorrow. Because of the potential for flash flooding, will
be keeping the current flash flood watch through tomorrow 18z.
Depending on how the evolution of the thunderstorm development
goes Wednesday morning, an extension into Thursday may be needed.
This wet period should begin to taper off on land Thursday as the
boundary pushes offshore.

LONG TERM (Friday and beyond)...
Once we get out of the short term, we get a break from all the
rain Friday and Saturday and offshore flow will help flush some of
the excess rain out.   An upper level low will close off around
northern California and slowly trek southeastward and a shortwave.
Rain will return to the area starting Monday of next week.
Guidance mostly agrees on decent PoPs Monday through Wednesday but
the agreement diverges on exact timing and potential amounts so
left the NBM for now.

MARINE... Onshore flow of around 10 knots will remain through
tomorrow then will switch over to offshore. Showers and
thunderstorms will be possible with strong and erratic winds
possible in the strongest thunderstorms. Once the front clears the
nearshore coastal waters, winds will remain relatively light
until late Thursday into Friday then bump up to around 15 knots.
It will then begin to slack again and move back to southeasterly
flow.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  65  74  57  75 /  70  70  40  10
BTR  67  77  60  77 /  70  80  30  10
ASD  67  79  62  77 /  80  80  50  20
MSY  71  79  67  77 /  70  80  50  20
GPT  67  79  62  75 /  70  70  60  30
PQL  66  79  61  75 /  70  70  60  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch through Wednesday afternoon for LAZ034>037-039-
     046>050-056>061-063>072-075>078.

GM...None.

MS...Flash Flood Watch through Wednesday afternoon for MSZ068>071-077-
     080>082.

GM...None.

&&

In the hours before

Special weather statement, May 11, 9:24 PM CDT, 3 hours 9 minutes before
Special Weather Statement
National Weather Service New Orleans LA
924 PM CDT Tue May 11 2021

LAZ046-049-056-057-120315-
Iberville-Ascension-Assumption-St. James-
924 PM CDT Tue May 11 2021

...A STRONG THUNDERSTORM WILL AFFECT SOUTHWESTERN ASCENSION...
NORTHWESTERN ST. JAMES...SOUTHEASTERN IBERVILLE AND NORTHWESTERN
ASSUMPTION PARISHES...

At 924 PM CDT, a strong thunderstorm was located over Pierre Part, or
7 miles north of Belle River, moving northeast at 20 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Donaldsonville, St. Gabriel, White Castle, Paincourtville, Geismar,
Carville and Belle Rose.

LAT...LON 3025 9109 3008 9084 2986 9120 2990 9121
      2992 9123 2993 9123 2997 9126 3000 9126
      3000 9123 3004 9122 3003 9124 3006 9127
      3006 9133
TIME...MOT...LOC 0224Z 224DEG 17KT 2999 9117

LN
Special weather statement, May 11, 10:15 PM CDT, 2 hours 18 minutes before
Special Weather Statement
National Weather Service New Orleans LA
1015 PM CDT Tue May 11 2021

LAZ046-049-056-057-120345-
Iberville-Ascension-Assumption-St. James-
1015 PM CDT Tue May 11 2021

...A STRONG THUNDERSTORM WILL AFFECT ASCENSION...NORTHWESTERN ST.
JAMES...SOUTHEASTERN IBERVILLE AND NORTHEASTERN ASSUMPTION
PARISHES...

At 1015 PM CDT, a strong thunderstorm was located over Belle Rose, or
near Donaldsonville, moving northeast at 20 mph.

Winds in excess of 40 mph and penny size hail are possible with this
storm.

Locations impacted include...
Gonzales, Donaldsonville, Napoleonville, St. Gabriel, Sorrento,
Paincourtville, Geismar and Belle Rose.

This includes Interstate 10 in Louisiana between mile markers 172 and
189.

LAT...LON 2992 9103 3005 9122 3031 9102 3017 9074
TIME...MOT...LOC 0315Z 219DEG 19KT 3005 9103

LN
Special weather statement, May 11, 10:35 PM CDT, 1 hour 58 minutes before
Special Weather Statement
National Weather Service New Orleans LA
1035 PM CDT Tue May 11 2021

LAZ046-049-050-056>058-120415-
Livingston-Iberville-Ascension-Assumption-St. John The Baptist-St.
James-
1035 PM CDT Tue May 11 2021

...AN AREA OF STRONG THUNDERSTORMS WILL AFFECT WEST CENTRAL ST. JOHN
THE BAPTIST...ASCENSION...CENTRAL ST. JAMES...SOUTHWESTERN
LIVINGSTON...SOUTHEASTERN IBERVILLE AND NORTHERN ASSUMPTION
PARISHES...

At 1035 PM CDT, strong thunderstorms were clustered over Pierre Part,
or 7 miles north of Belle River, moving northeast at 30 mph.

Wind gusts up to 50 mph and penny size hail are possible with this
storm.

Locations impacted include...
Gonzales, Donaldsonville, Napoleonville, St. Gabriel, Gramercy,
Lutcher, White Castle, Sorrento, Port Vincent, Paincourtville,
Geismar, Convent, Prairieville, Carville, Belle Rose and Garyville.

This includes Interstate 10 in Louisiana between mile markers 171 and
197.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 3035 9092 3034 9090 3037 9088 3010 9062
      2984 9115 2986 9120 2990 9121 2997 9126
      3000 9126 3000 9123 3004 9122 3003 9124
      3006 9127 3006 9136 3007 9137
TIME...MOT...LOC 0335Z 236DEG 26KT 2999 9118

LN
Special weather statement, May 12, 12:18 AM CDT, 15 minutes before
Special Weather Statement
National Weather Service New Orleans LA
1218 AM CDT Wed May 12 2021

LAZ056-057-059-065-066-120545-
Lower Terrebonne-Upper Terrebonne-Assumption-St. James-Upper
Lafourche-
1218 AM CDT Wed May 12 2021

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHERN ST. JAMES...
NORTHWESTERN TERREBONNE...NORTHWESTERN LAFOURCHE AND ASSUMPTION
PARISHES...

At 1217 AM CDT, radar indicated strong thunderstorms were located
along a line extending from near Bayou Geneve to near Stephensville
to 14 miles south of Patterson. Movement was east at 30 mph.

Winds in excess of 40 mph are possible with these storms.

Locations impacted include...
Thibodaux, Napoleonville, Schriever, Supreme, Gray, Chackbay,
Labadieville, North Vacherie and South Vacherie.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 2954 9127 2956 9123 2960 9119 2959 9116
      2963 9108 2965 9111 2981 9110 2985 9118
      2994 9118 3004 9071 2977 9071 2939 9101
      2940 9122 2943 9121 2945 9126 2948 9128
TIME...MOT...LOC 0517Z 266DEG 25KT 2988 9109 2975 9109 2949 9130
Special weather statement, May 12, 12:33 AM CDT, 0 minutes before
Special Weather Statement
National Weather Service New Orleans LA
1233 AM CDT Wed May 12 2021

LAZ057>060-120615-
St. Charles-St. John The Baptist-St. James-Upper Lafourche-
1233 AM CDT Wed May 12 2021

...A STRONG THUNDERSTORM WILL AFFECT ST. JOHN THE BAPTIST...
SOUTHEASTERN ST. JAMES...NORTHERN ST. CHARLES AND NORTHWESTERN
LAFOURCHE PARISHES...

At 1232 AM CDT, a strong thunderstorm was located near Edgard, or 7
miles south of Reserve, moving east at 25 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Reserve, Hahnville, Laplace, Killona, Norco, Paradis, Montz, Edgard,
Luling, Garyville, Boutte, Wallace, Ama, Destrehan, Taft, New Sarpy,
St. Rose, South Vacherie and Bayou Gauche.

This includes the following Interstates...
 Interstate 10 in Louisiana between mile markers 201 and 213, and
between mile markers 215 and 221.
 Interstate 55 in Louisiana between mile markers 1 and 3.
 Interstate 310 between mile markers 1 and 11.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

LAT...LON 2987 9068 3011 9067 3013 9043 3009 9041
      3006 9038 3005 9028 2993 9028 2990 9027
      2988 9024 2986 9024
TIME...MOT...LOC 0532Z 271DEG 21KT 2998 9059

The office that day

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

IssuedProductOfficeCountiesLasted
May 11, 8:49 PM CDTRiver Flood WarningLIXSaint Tammany14 hr
May 11, 9:24 PM CDTSpecial Weather StatementLIXAssumption51 min
May 11, 10:15 PM CDTSpecial Weather StatementLIXAscension30 min
May 11, 10:35 PM CDTSpecial Weather StatementLIXAscension, Assumption, Saint James40 min
May 11, 10:37 PM CDTSevere Thunderstorm WarningLIXAscension, Assumption, Iberville, Saint James30 min
May 11, 10:38 PM CDTFlash Flood WarningLIXAscension, Assumption, Iberville, Saint James3 hr
May 11, 11:05 PM CDTSevere Thunderstorm WarningLIXAscension, Assumption, Lafourche, Saint James, Saint John the Baptist40 min
May 11, 11:41 PM CDTSevere Thunderstorm WarningLIXAscension, Assumption, Lafourche, Saint Charles, Saint James, Saint John the Baptist64 min
May 12, 12:18 AM CDTSpecial Weather StatementLIXAssumption27 min
May 12, 12:31 AM CDTAreal Flood AdvisoryLIXAssumption, Jefferson, Lafourche, Saint Charles, Saint James, Saint John the Baptist2 hr
May 12, 12:48 AM CDTSpecial Weather StatementLIXLafourche57 min
May 12, 1:12 AM CDTSpecial Weather StatementLIXSaint Charles33 min
May 12, 1:41 AM CDTSpecial Weather StatementLIXLafourche, Orleans, Saint Charles, Saint Tammany49 min
May 12, 1:46 AM CDTSpecial Marine WarningLIX44 min
May 12, 1:58 AM CDTAreal Flood AdvisoryLIXJefferson, Orleans, Plaquemines, Saint Bernard, Saint Charles81 min
May 12, 1:58 AM CDTSevere Thunderstorm WarningLIXJefferson, Orleans, Plaquemines, Saint Bernard, Saint Charles32 min
May 12, 2:08 AM CDTTornado WarningLIXJefferson, Orleans, Plaquemines, Saint Bernard12 min
May 12, 2:30 AM CDTSpecial Marine WarningLIX46 min
May 12, 2:47 AM CDTSpecial Marine WarningLIX43 min
May 12, 3:14 AM CDTSpecial Marine WarningLIX108 min
May 12, 4:25 AM CDTSpecial Marine WarningLIX65 min
May 11, 9:08 PM CDTRiver Flood WarningLIXHarrison4 days
May 11, 9:10 PM CDTRiver Flood WarningLIXHarrison60 hr
May 11, 10:31 PM CDTFlash Flood WarningLIXAmite, Wilkinson3 hr
May 12, 12:16 AM CDTFlash Flood WarningLIXPike3 hr
May 12, 2:53 AM CDTSevere Thunderstorm WarningLIXHancock24 min
May 12, 3:26 AM CDTAreal Flood AdvisoryLIXHancock, Harrison, Jackson11 min
May 12, 3:37 AM CDTFlash Flood WarningLIXHarrison, Jackson71 min
May 12, 9:24 AM CDTRiver Flood WarningLIXPike, Walthall45 hr

Nearby

Special Weather Statements in Louisiana, 2021Every special weather statement 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.