Severe Thunderstorm Warning 58, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
1230 PM CDT Sat May 26 2018

.AVIATION...

Scattered to broken convection this afternoon near all terminals.
These will be slow moving storms and propagating more than moving.
Will carry VCTS or TEMPO through the afternoon hours before most
convection dissipates. Mainly VFR conditions, although likely MVFR
to IFR when convection directly impacts a terminal. Convection
likely to re-initiate by mid-morning on Sunday. More movement of
convection from east to west on Sunday. 35

&&

.PREV DISCUSSION... /issued 813 AM CDT Sat May 26 2018/

SOUNDING DISCUSSION...

Routine sounding terminated over Mississippi Sound south of Ocean
Springs at a height of 110,000 feet or 20.8 miles above the
surface.

Airmass remains moist and unstable with a precipitable water value
of 1.82 inches, and a MU CAPE of 2764 J/kg. Lifted index of the MU
parcel was -8. Lapse rates above the surface were about 6.5C/km.
Freezing level was near 13,000 feet and -20C level at 24,400 feet.

Shear almost non-existent in the lower levels this morning. Winds
lighter than 10 knots until 400 mb, mainly out of the south.
Winds became west to northwest above 200 mb through 75 mb. Max
wind of 37 knots near 46,000 feet. 35

PREV DISCUSSION... /issued 512 AM CDT Sat May 26 2018/

SHORT TERM...
Unsettled weather continues across the CWA. The combination of
minimized subsidence, ample moisture in place (PW's near average
max for this time of year), and daytime heating will once again
produce numerous showers and thunderstorms across the area.
Localized 2 to 4" will be possible with such high PWs. The flash
flood watch remains in effect for this reason and expanded north
to account for development there. Coverage the last few days has
been well above guidance. With no changes in the air mass today,
bumped up POPs into the 70 to 90% range. Thunderstorm movement
will be dominated by outflow boundaries.

LONG TERM...
Potentially even more impactful weather still looks to be the
case over this Memorial Day weekend due to Alberto. Global models
have come into much better agreement on the track of this tropical
system. After days of the GFS being the eastern solution and the
ECMWF being the western one, they have since swapped. The official
NHC track is roughly an average of those, and of course tropical
model solutions. It's not much different than previous forecasts
which means expected local impacts remain the same. The biggest
focus will be rainfall totals. There will quite a gradient from
west to east across the CWA. Based on the current forecast track,
areas west of Lake Pontchartrain will see the least amount of
rain, probably not much more than inch or so. Therefore, will
likely be removing many of those parishes from the Flash Flood
Watch. East of the Lake is where well several inches to possibly
isolated amounts over a foot will be possible. The greatest
concern in along the Mississippi Coast as it will be closest to
the center, mainly in the late Sunday through late Monday
timeframe.

Building ridge west/southwest of the area and weak trough racing
across the upper Mississippi Valley will force the tropical
moisture northeast and out of the region around the middle of next
week. Temperatures will bounce back into the lower to mid 90s.

MEFFER

MARINE...
Winds will remain in and around the 10-15kt range over open waters
and even lighter in protected waters. Winds should start to respond
today Alberto. Models are much more agreeable with the eventual
path of the storm.

TPC started advisories yesterday and these will be headlined in all
waters along and east of the Miss River. There will still be the
possibility of small craft advisory headlines for waters west of
Port Fourchon. But these winds do not take place until Sunday night
or Monday. If winds do not meet criteria, sea heights surely will as
swell should be around 4 to 6 feet and wind waves on top of that
should make a total sea of around 8 feet or better.

AVIATION...
Most if not all terminals will experience sh/ts again today. Storm
motion will be very slow. This will begin to change into Sunday as
sh/ts will begin to move from east to west within the outer flow of
Alberto otherwise VFR outside thunderstorms.

DECISION SUPPORT...
DSS code: ORANGE.
Deployed: None.
Activation: Tropical desk; 6 hourly upper air special releases
Activities: Tropical cyclone briefings; potential flood
            monitoring.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  87  71  86  73 /  80  50  50  30
BTR  88  72  88  75 /  80  50  50  30
ASD  86  71  81  74 /  70  40  70  60
MSY  87  75  83  77 /  70  40  70  60
GPT  85  73  80  76 /  70  40  80  70
PQL  84  71  80  75 /  70  40  90  90

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Tropical Storm Watch for LAZ040-049-050-057-058-060>064-068>070-
     072.

     Flash Flood Watch through Tuesday evening for LAZ037-039-040-
     046>050-056>072.

     Coastal Flood Advisory until 7 AM CDT Tuesday for LAZ040-050-058-
     060-061-072.

GM...Tropical Storm Watch for GMZ530-532-534-536-538-552-555-557-572-
     575-577.

MS...Tropical Storm Watch for MSZ080>082.

     Flash Flood Watch through Tuesday evening for MSZ070-071-077-
     080>082.

GM...Tropical Storm Watch for GMZ532-534-536-538-552-555-557-572-575-
     577.

&&

Hazardous Weather Outlook
National Weather Service New Orleans LA
1117 AM CDT Sat May 26 2018

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>082-270430-
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-
1117 AM CDT Sat May 26 2018

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

.DAY ONE...This Afternoon and Tonight

A Flash Flood Watch is in effect for most of southeast Louisiana
and coastal Mississippi for slow moving showers and thunderstorms
that may produce a quick 1 to 3 inches of rain.

A Tropical Storm Watch remains in effect for areas east of Grand
Isle including Lakes Pontchartrain and Maurepas as well as the
Mississippi Gulf Coast.

A Storm Surge Watch is in effect from the Mouth of the
Mississippi River eastward to include the entire Mississippi
coast. A Coastal Flood Advisory is in effect for the Louisiana
tidal lakes.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Tropical Storm conditions are expected for portions of the
outlook area generally from Lake Pontchartrain eastward through
coastal Mississippi Sunday through early Tuesday. Refer to the
latest tropical cyclone products issued by our office and the
National Hurricane Center for details.

Flash flooding will be a significant concern for multiple inches
of rainfall through early next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is requested for flood monitoring and
eventually for tropical storm support Sunday through late Monday
or early Tuesday. Additional flood monitoring may be required
Tuesday through Thursday.

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Special Weather Statement
National Weather Service New Orleans LA
224 PM CDT SAT MAY 26 2018

LAZ034-262000-
Pointe Coupee-
224 PM CDT SAT MAY 26 2018

...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN POINTE COUPEE
PARISH...

At 224 PM CDT, a strong thunderstorm was located near New Roads,
moving northwest at 5 mph.

Wind gusts up to 50 mph are possible with this storm.

Locations impacted include...
New Roads, Livonia and Fordoche.

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.

LAT...LON 3073 9141 3062 9133 3059 9136 3051 9150
      3066 9168
TIME...MOT...LOC 1924Z 147DEG 5KT 3062 9146