Severe Thunderstorm Warning 94, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
413 PM CDT Wed Jul 18 2018

.SHORT TERM...

A mid/upper level high remains situated over the southwest CONUS
into the southern plains while a mid/upper level trough extended
from the Great Lakes into the much of the eastern third of the
CONUS today. This will continue to expose the central Gulf coast
to shortwave troughs/MCV features and the associated flare ups of
MCS/clusters of showers and thunderstorms that move from northwest
and north to southeast and south into Thursday. Like today,
confidence in the both the areas that receive the more widespread
and heaviest rainfall and the timing will be very difficult to say
much in advance, however the general forecast of slightly higher
PoPs in eastern/coastal areas will continue through Thursday
before rain chances drop substantially on Friday as the mid/upper
level high pressure builds in from the west. Temperatures will
start to rise on Thursday with some locations likely seeing some
heat indices nearing heat advisory criteria, however the higher
rain coverage should make any higher heat indices more brief. That
will change on Friday, as the advertised heat indices approaching
110 in many areas still looks like a good bet. Will not issue a
heat advisory at this time since it is in the fourth forecast
period, however that issuance will likely be required late
tonight or Thursday.

.LONG TERM...

The building ridge from the west is likely to keep hot and humid
conditions that will likely be in heat advisory criteria again
Saturday and Sunday. The initial shortwave trough over the
eastern CONUS will move east into the Atlantic Ocean while another
digging and potent shortwave trough moves into the upper
Mississippi Valley/Great Lakes and Ohio Valley to southeast states
late in the week into the weekend. The upper trough axis should
be unseasonably sharp and deep into Florida and the south Atlantic
coast late in the weekend and early next week, and there the 12z
GFS/ECMWF models are now indicating a broad closed mid/upper low
embedded in the trough will get nudged southwest by a westerly
expanding high over the western Atlantic. This low is now forecast
to move over or near the forecast area Tuesday or Wednesday. While
the confidence in this solution is low since the models just made
this shift, have trended the forecast in the the direction of a
return towards more seasonal temperatures and higher rain chances.
22/TD

&&

.AVIATION...

Generally VFR conditions across the terminals at present. Threat
for scattered TSRA will continue through the afternoon hours into
the early evening. If convection is expected to directly impact a
terminal, it will likely cause IFR or lower visibilities and MVFR
to IFR ceilings, as well as wind gusts around 30 knots. Will amend
as necessary. Most convection will dissipate by 03z with VFR
conditions overnight, but terminals near the coast could again
see convection as early as 10z or so. One more day with a
significant convective threat on Thursday, with terminals possibly
impacted as early as 14-15z. 35

&&

.MARINE...

A large ridge of high pressure will prevail across most of the
central to southern Gulf of Mexico through the weekend, however a
slow moving and weakening cold front will be pushing south
through the mid to deep south region tonight. While this front
will remain well north of the north Gulf coast, the pressure
gradient will tighten which will support periodic westerly winds
up near 15 knots through Thursday. Seas will be mostly 1 to 3
feet, but a few 4 footers will be possible over some offshore
waters through Thursday. Winds and seas are expected to
ease/diminish a bit on Friday as the pressure gradient slackens.
Scattered to numerous thunderstorms will continue to produce
periodic higher winds and seas not reflected in the general
forecast through Friday. An upper level disturbance moving
southeast and south from the lower Great Lakes/Ohio valley region
late in the weekend and early next week will cause lower surface
pressure to develop just inland from the central and eastern Gulf
coast starting Saturday night into Sunday night which is now
expected to produce stronger westerly winds either in 15 to 20
knots or possibly a bit over 20 knots over at least eastern
coastal waters, and seas will likely respond to more hazardous
levels for small craft. 22/TD

&&

.DECISION SUPPORT...
SS code: Green.
Deployed: None.
Activation: None.
Activities: Monitoring issuance of Heat Advisory that will likely
be required starting Friday.

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; Marginal risk severe or excessive rain.
Yellow = Heightened impacts with short-fused watch, warning or
         advisory issuances; radar support for slight risk severe or
         excessive rain.
Orange = High Impacts; Enhanced risk severe; nearby tropical events;
         HazMat or other large episodes.
Red    = Full engagement for Moderate to high risk of severe and/or
         excessive rainfall, or direct tropical threats; Events of
         National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  73  94  74  96 /  40  30  20  10
BTR  76  94  78  96 /  30  30  20  10
ASD  76  93  77  95 /  50  60  20  20
MSY  77  93  78  96 /  40  60  20  20
GPT  75  92  78  94 /  40  50  30  20
PQL  74  93  75  96 /  40  50  30  20

&&

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

Hazardous Weather Outlook
National Weather Service New Orleans LA
449 PM CDT Wed Jul 18 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>082-191400-
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-
449 PM CDT Wed Jul 18 2018

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

.DAY ONE...Tonight

Scattered showers and thunderstorms are expected tonight, especially
during the evening hours. No severe weather is expected; however, a
few storms could produce frequent lightning, gusty winds, and
locally heavy rainfall.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Isolated to scattered showers and thunderstorms are expected each
day through the period, with the best chances on Thursday. A few
storms could become strong and produce frequent lightning, gusty
winds, and locally heavy rainfall.

Heat index readings may approach 110 degrees starting Friday
and lasting into early next week. People sensitive to heat
related illnesses should be prepared to take precautions during
the heat of the day during this period.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

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Special Weather Statement
National Weather Service New Orleans LA
400 PM CDT WED JUL 18 2018

MSZ081-182145-
Harrison-
400 PM CDT WED JUL 18 2018

...A STRONG THUNDERSTORM WILL AFFECT SOUTHERN HARRISON COUNTY...

At 359 PM CDT, a strong thunderstorm was located near Lyman, or near
Long Beach, moving west at 15 mph.

Winds in excess of 30 mph are possible with this storm.

Locations impacted include...
Gulfport, Biloxi, Long Beach, D'iberville, Lyman and Gulfport
Airport.

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 3038 8907 3036 8909 3032 8922 3045 8928
      3050 8913 3055 8892 3042 8889 3043 8893
      3042 8894 3043 8899 3042 8901 3041 8888
      3039 8888
TIME...MOT...LOC 2059Z 081DEG 14KT 3044 8917

KLG

Special Weather Statement
National Weather Service New Orleans LA
406 PM CDT WED JUL 18 2018

LAZ037-MSZ069-182130-
St. Helena-Amite-
406 PM CDT WED JUL 18 2018

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN ST. HELENA PARISH
IN SOUTHEASTERN LOUISIANA AND SOUTHEASTERN AMITE COUNTIES...

At 405 PM CDT, a strong thunderstorm was located near Liberty, moving
southeast at 15 mph.

Winds in excess of 40 mph are possible with this storm.

Locations impacted include...
Liberty, Darlington, Gillsberg and Easleyville.

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 3101 9054 3100 9055 3100 9057 3098 9057
      3085 9079 3096 9085 3099 9084 3100 9083
      3100 9087 3110 9093 3120 9075
TIME...MOT...LOC 2105Z 325DEG 12KT 3109 9079

KLG

Special Weather Statement
National Weather Service New Orleans LA
436 PM CDT WED JUL 18 2018

LAZ039-071-MSZ070-182200-
Washington-Northern Tangipahoa-Pike-
436 PM CDT WED JUL 18 2018

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN TANGIPAHOA...
NORTHWESTERN WASHINGTON PARISHES IN SOUTHEASTERN LOUISIANA AND SOUTH
CENTRAL PIKE COUNTIES...

At 435 PM CDT, a strong thunderstorm was located near Osyka, or 16
miles north of Amite, moving southeast at 20 mph.

Winds in excess of 30 mph are possible with this storm.

Locations impacted include...
Franklinton, Kentwood, Osyka, Mount Herman and Wilmer.

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 3080 9013 3068 9039 3068 9041 3097 9054
      3106 9036
TIME...MOT...LOC 2135Z 330DEG 17KT 3095 9041

11