Special Weather Statement, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
413 PM CDT Sat Aug 19 2017

.SHORT TERM...
Unsettled air mass in place near the col aloft between ridge axis
running from Texas to north Florida and a trough axis from a long
wave to the north and large TUTT circulation over the east Gulf.
Flow pattern is essentially from the north-northeast for much of
the column allowing for continental heat induced storms to move
into and along axis of deeper low level moisture off the gulf.
Storms have been maintaining steady motions around 15 kt but may
become erratic with outflow interactions the remainder of the
afternoon, including what may become slow movers over the New
Orleans metro area shortly. Outside of rain areas, apparent
temperatures have reached 110-112F ranges but rain cooled areas
drop into the lower 80s. Downburst potential has been rather high
in this environment with some indications on radar of close to 50
kt at times, hence the warnings. Sunday can be a similar situation
with only slow changes to the air mass. The TUTT low will be
moving into the middle Gulf and place the area on the wetter
inflow side, and dragging the col center pretty much over the
forecast area. This will allow for short-lived convection but also
slow moving cells that will tend to be more influenced by
outflows. Temperature forecast is a consensus blend throughout the
forecast package. Monday's diurnal curve was altered for a
flatter, even 1-2 hours of slightly cooler, temperature trend
during the eclipse passage, but still ample daylight to recover to
max temperatures after eclipse ends. Essentially shaved 2 degrees
for the noon hour, 3-4 degrees for 1 pm, then start recovery after
2 pm to get back on typical diurnal trend.

.LONG TERM...
Main feature will be frontal zone that drops from the north but
only gets so far to place the deep south in a compressional
heating and high moisture content situation for higher than normal
rain chances Wednesday through Friday. Temperatures held closer to
climatological normals. 24/RR

&&

.AVIATION...
VFR conditions will prevail at all of the terminals through the
forecast period. Any lingering convection this evening should
quickly die off by 02z.  Tomorrow, another round of showers and
thunderstorms should develop in the afternoon hours.  Will add VCTS
wording into the forecast to reflect the risk of convective activity
tomorrow. 32

&&

.MARINE...
A persistence forecast remains in place for the coastal waters. The
seabreeze cycle will dominate the local wind field as a broad ridge
of high pressure remains parked over the northern Gulf of Mexico. As
a result, light and variable winds are expected through the day with
an offshore component in the morning shifting to an onshore
component in the afternoon and evening hours.  Seas will be fairly
calm at 1 to 2 feet through the period.  There will be some
thunderstorm activity each day that will produce locally higher
winds and waves for brief periods of time. 32

&&

.DECISION SUPPORT...
DSS code: Blue.
Deployed: None.
Activation: None.
Activities: DSS support for NOHSEP.

Decision Support Services (DSS) Code Legend
Green  = No weather impacts that require action.
Blue   = Long-fused watch, warning, or advisory in effect or high
         visibility event.
Yellow = Heightened impacts with short-fused watch, warning or
         advisory issuances; radar support.
Orange = High Impacts; Slight to Moderate risk severe; nearby
         tropical events; HazMat or other large episodes.
Red =    Full engagement for Moderate risk of severe and/or direct
         tropical threats; Events of National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  74  92  73  91 /  20  30  20  40
BTR  75  92  75  91 /  20  30  10  40
ASD  75  92  75  91 /  10  30  10  30
MSY  77  92  77  90 /  20  30  10  30
GPT  76  91  77  89 /  10  30  10  30
PQL  74  93  75  90 /  10  30  20  30

&&

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

Hazardous Weather Outlook
National Weather Service New Orleans LA
1103 AM CDT Sat Aug 19 2017

GMZ530-532-534-536-538-550-552-555-557-570-572-575-577-LAZ034>037-
039-040-046>050-056>072-MSZ068>071-077-080>082-200415-
Lake Pontchartrain and Lake Maurepas-Mississippi Sound-
Lake Borgne-Chandeleur Sound-Breton Sound-
Coastal Waters from Port Fourchon LA to Lower Atchafalaya River
LA out 20 nm-
Coastal waters from the Southwest Pass of the Mississippi River
to Port Fourchon Louisiana out 20 NM-
Coastal Waters from Boothville LA to Southwest Pass of the
Mississippi River out 20 nm-
Coastal waters from Pascagoula Mississippi to Stake Island out
20 NM-
Coastal waters from Port Fourchon Louisiana to Lower Atchafalaya
River LA from 20 to 60 NM-
Coastal waters from Southwest Pass of the Mississippi River to
Port Fourchon Louisiana from 20 to 60 NM-
Coastal Waters from Stake Island LA to Southwest Pass of the
Mississippi River from 20 to 60 nm-
Coastal waters from Pascagoula Mississippi to Stake Island
Louisiana out 20 to 60 NM-Pointe Coupee-West Feliciana-
East Feliciana-St. Helena-Washington-St. Tammany-Iberville-
West Baton Rouge-East Baton Rouge-Ascension-Livingston-Assumption-
St. James-St. John The Baptist-Upper Lafourche-St. Charles-
Upper Jefferson-Orleans-Upper Plaquemines-Upper St. Bernard-
Upper Terrebonne-Lower Terrebonne-Lower Lafourche-Lower Jefferson-
Lower Plaquemines-Lower St. Bernard-Northern Tangipahoa-
Southern Tangipahoa-Wilkinson-Amite-Pike-Walthall-Pearl River-
Hancock-Harrison-Jackson-
1103 AM CDT Sat Aug 19 2017

This Hazardous Weather Outlook is for portions of Southeast
Louisiana...South Mississippi and the adjacent coastal waters.

.DAY ONE...This Afternoon and Tonight

Afternoon showers and thunderstorms are expected. A few could be
strong to possibly severe with damaging downburst winds. Frequent
lightning and heavy downpours with localized flooding are a
potential as well.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Daily afternoon thunderstorms are expected through next week. A
few of the storms each day could become strong, producing gusty
winds, frequent lightning and heavy downpours that could result
in localized street flooding.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

32

Special Weather Statement
National Weather Service New Orleans LA
344 PM CDT SAT AUG 19 2017

MSZ068>070-192130-
Pike-Wilkinson-Amite-
344 PM CDT SAT AUG 19 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHERN PIKE...
WILKINSON AND AMITE COUNTIES...

At 344 PM CDT, radar indicated strong thunderstorms were located
along a line extending from 6 miles south of Jonesville to Slocum to
6 miles west of Gloster to 7 miles southwest of Mccomb. Movement was
southeast at 15 mph.

Winds in excess of 30 mph are possible with these storms.

Locations impacted include...
Liberty, Magnolia, Centreville, Woodville, Gloster, Osyka, Gillsberg
and Mccomb Airport.

Torrential rainfall is also occurring with these storms, 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.

LAT...LON 3124 9116 3126 9053 3100 9026 3100 9117
      3106 9152 3116 9160 3124 9156 3122 9153
      3123 9149 3126 9148 3128 9150 3130 9147
TIME...MOT...LOC 2044Z 329DEG 14KT 3154 9186 3128 9167 3118 9112 3120
9057

32

Special Weather Statement
National Weather Service New Orleans LA
402 PM CDT SAT AUG 19 2017

LAZ036-037-048-050-071-072-192130-
Livingston-St. Helena-Northern Tangipahoa-East Feliciana-Southern
Tangipahoa-East Baton Rouge-
402 PM CDT SAT AUG 19 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT SOUTHERN ST. HELENA...
NORTHERN LIVINGSTON...SOUTHEASTERN EAST FELICIANA...WEST CENTRAL
TANGIPAHOA AND NORTHEASTERN EAST BATON ROUGE PARISHES...

At 401 PM CDT, radar indicated strong thunderstorms were located
along a line extending from 8 miles northeast of Pride to Roseland.
Movement was south at 10 mph.

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

Locations impacted include...
Greensburg, Amite, Amite City, Independence, Roseland, Montpelier,
Pride, Watson, Greenwell Spring, Natalbany and Tickfaw.

Torrential rainfall is also occurring with these storms, 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.

LAT...LON 3056 9107 3055 9041 3082 9044 3082 9093
TIME...MOT...LOC 2101Z 010DEG 8KT 3076 9087 3076 9054

32

Special Weather Statement
National Weather Service New Orleans LA
405 PM CDT SAT AUG 19 2017

LAZ056-059-065-066-192200-
Lower Terrebonne-Upper Terrebonne-Assumption-Upper Lafourche-
405 PM CDT SAT AUG 19 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT CENTRAL TERREBONNE AND
SOUTHEASTERN ASSUMPTION PARISHES...

At 405 PM CDT, radar indicated strong thunderstorms were located
along a line extending from Labadieville to 9 miles west of Dulac to
13 miles east of Cocodrie. Movement was southwest at 10 mph.

Winds in excess of 30 mph are possible with these storms.

Locations impacted include...
Morgan City, Supreme, Dulac, Labadieville, Cocodrie, Tambour Bay Buoy
and Lumcon Center Buoy.

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 2916 9094 2926 9088 2926 9099 2924 9101
      2922 9091 2917 9094 2917 9099 2929 9103
      2973 9111 2996 9097 2947 9082 2929 9051
      2920 9055 2919 9061 2924 9064 2918 9061
      2911 9071 2912 9071 2909 9086
TIME...MOT...LOC 2105Z 023DEG 10KT 2983 9098 2941 9085 2918 9046

32

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Special Weather Statement
National Weather Service New Orleans LA
449 PM CDT SAT AUG 19 2017

LAZ059-060-192215-
St. Charles-Upper Lafourche-
449 PM CDT SAT AUG 19 2017

...A STRONG THUNDERSTORM WILL AFFECT SOUTHERN ST. CHARLES AND NORTH
CENTRAL LAFOURCHE PARISHES...

At 448 PM CDT, a strong thunderstorm was located near Luling, or 9
miles southwest of Avondale, moving west at 5 mph.

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

Locations impacted include...
Bayou Gauche, Paradis, Des Allemands, Luling and Boutte.

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 2987 9025 2975 9025 2967 9047 2994 9047
TIME...MOT...LOC 2148Z 089DEG 6KT 2981 9031

32

Special Weather Statement
National Weather Service New Orleans LA
452 PM CDT SAT AUG 19 2017

LAZ046>050-057-058-192245-
Livingston-Iberville-Ascension-St. John The Baptist-West Baton
Rouge-St. James-East Baton Rouge-
452 PM CDT SAT AUG 19 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT WEST CENTRAL ST. JOHN
THE BAPTIST...ASCENSION...ST. JAMES...SOUTHEASTERN WEST BATON
ROUGE...SOUTHWESTERN LIVINGSTON...SOUTHEASTERN IBERVILLE AND
SOUTHWESTERN EAST BATON ROUGE PARISHES...

At 452 PM CDT, radar indicated strong thunderstorms were located
along a line extending from Old Jefferson to Sorrento to Laplace.
Movement was southwest at 10 mph.

Winds in excess of 40 mph and pea size hail are possible with these
storms.

Locations impacted include...
Baton Rouge, Denham Springs, Gonzales, Donaldsonville, Plaquemine,
Reserve, Oak Hills Place, Laplace, St. Gabriel, Gramercy, Addis,
Lutcher, Brusly, White Castle, Sorrento, Westminster, Geismer,
Garyville, Shenandoah and Old Jefferson.

Torrential rainfall is also occurring with these storms, 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.

LAT...LON 3047 9094 3021 9078 3012 9048 2995 9071
      3004 9096 3007 9096 3009 9112 3041 9131
TIME...MOT...LOC 2152Z 067DEG 9KT 3038 9098 3019 9086 3010 9047

32