Special Weather Statement, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
1133 PM CDT Wed Apr 14 2021

.Updated for the 6Z TAF issuance...

.AVIATION...
Widespread showers and thunderstorms continue across all
terminals. Lower CIGS and visibility restrictions are still
expected through the night as these showers and storms move
through the area. Another round of showers and thunderstorms will
affect most terminals in the morning through midday tomorrow.
MVFR ceilings should return by late Thursday afternoon as we
finally get breaks in cloud cover. /TDB/

&&

.PREV DISCUSSION... /issued 647 PM CDT Wed Apr 14 2021/

AVIATION...
IFR/MVFR ceilings continue as bands of showers and thunderstorms
have moved through the area. Ceilings are expected to lower to
LIFR for most terminals mainly north and then IFR everywhere else;
as showers and thunderstorms redevelop overnight. The most
thunderstorm coverage is expected in the early morning  hours as
elevated instability increases.MVFR ceilings should return for
most terminals by noon as we finally get some breaks in cloud
cover. CIGs and visibility restrictions should continue to improve
through the remainder of the TAF cycle. /TDB/

PREV DISCUSSION... /issued 415 PM CDT Wed Apr 14 2021/

SHORT TERM...(through Saturday)
Another MCS embedded in the zonal flow aloft is currently moving
through the Lower MS region this afternoon. The back end of the
convective activity that is currently over the northern half of
the forecast area has been 50-75 miles farther north and a bit
more organized than what was depicted by 12Z CAMs and in our
forecast this morning. Luckily this activity is progressing fast
enough to the east to limit the threat of flash flooding across
the North Shore of LA and coastal MS. PoPs decrease from NW to SE
across the region this evening when a relative lull in
precipitation is expected.

Yet another MCS is expected to pass nearby just to our north (Mid
South states) late tonight into Thursday morning. With a frontal
boundary stalled along the Gulf coast and low-level flow backing
out of the southwest ahead of the MCS, isentropic lift will lead
to additional showers and storms developing overnight. The
highest PoPs will be during the morning hours on Thursday. The
severe threat looks limited with convection predominately elevated
and modest on the cool side of the boundary. The main threat with
this round of storms will be locally heavy rainfall. An additional
1-2 inches of rainfall is expected with this next round with
locally higher amounts to 3" possible. The Flash Flood Watch will
remain in effect for the entire area through noon Thursday.
There's still some uncertainty regarding exactly where the
heaviest rain falls Thursday morning as the guidance has been
wavering north-south somewhere between the SE LA-S MS and coast

There looks to be another relative lull in the precipitation
Thursday afternoon (especially late) through at least Friday
morning. Then the last round of potentially heavy rainfall appears
to be late Friday afternoon through Saturday morning. Depending on
how much rainfall occurs early Thursday (and where), a more
targeted Flash Flood Watch may be needed for Friday night.

LONG TERM (Saturday night through Wednesday)...

The boundary that has been parked over the area for much of the
week will finally progress south and east of the region Saturday
night. This will allow us to finally dry out by Sunday after the
recent wet spell. A broad area of high pressure will build over
the Southern Plains and Gulf Coast region through much of the
week, which should keep the area mainly dry during the long term.
The one exception may be coastal LA depending on exactly how close
the aforementioned frontal boundary drifts back northward toward
the coast Sunday- Wednesday. Temperatures will generally be 5-10
degrees below normal owing to a northerly component to the winds
on the cool side of the front.

AVIATION...
Conditions so far this afternoon have generally been MVFR or IFR
with showers and storms and VFR outside of precip. The greatest
coverage of TSRA through about 20-21Z will be north of BTR-HDC,
east of ASD, and from the NOLA terminals especially southward.
The trend will be for this activity to weaken and drift southward
toward the LA coast. While a break in the convection is
anticipated this evening, CIGs looks to gradually lower to MVFR
and IFR with northerly flow and stratus developing on the cool
side of the front.

Showers and storms are expected to redevelop tonight toward C LA
and move southward across the area overnight and into the early
morning hours. Thunderstorm coverage should be limited initially
during the overnight, but increase (scattered coverage) in the
morning as elevated instability increases. Mainly IFR or low-end
MVFR CIGs should be prevailing through the morning hours. CIGs may
improve gradually in the afternoon with some breaks in the cloud
cover that allow for modest daytime mixing. N-NE winds 5-15 kt are
expected.

MARINE...
A SCA has been expanded this afternoon to include the MS sound
and coastal waters. Latest marine observations show an enhanced SE
wind just offshore with winds 20-25 kt, gusting to 30 kt. The
onshore surge is expected to rather short lived and weaken toward
sunset. Accordingly, the SCA is only in effect through 7 PM.
Additionally, the SCA for the LA coastal waters was extended
until midnight. Although the stronger winds were slow to develop
today, the have over the past few hours. While there were some
gusts of 35-40 kt a few miles off the SE LA coast, this looked to
be convectively driven with N-NE winds caused by an outflow
boundary from earlier thunderstorms. However, S-SE winds are
expected to strengthen this evening to around 20 kt.

Winds and seas should remain below SCA criteria Thursday through
the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  59  73  54  68 /  80  60  40  70
BTR  62  75  58  71 /  70  70  30  70
ASD  64  76  58  72 /  80  90  20  70
MSY  67  75  64  74 /  80  80  20  60
GPT  64  75  57  71 /  90  80  20  60
PQL  63  75  57  71 /  90  80  10  60

&&

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

GM...Small Craft Advisory until 4 AM CDT Thursday for GMZ550-552-555-
     570-572-575.

     Flash Flood Watch through Thursday morning for GMZ530.

MS...Flash Flood Watch through Thursday morning for MSZ068>071-077-
     080>082.

GM...Small Craft Advisory until 4 AM CDT Thursday for GMZ552-555-570-
     572-575.

&&

Special Weather Statement
National Weather Service New Orleans LA
1224 AM CDT Thu Apr 15 2021

LAZ075-076-150645-
Southeast St. Tammany-Northwest St. Tammany-
1224 AM CDT Thu Apr 15 2021

...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN ST. TAMMANY
PARISH...

At 1224 AM CDT, a strong thunderstorm was located over Lacombe, or 11
miles west of Slidell, moving east at 20 mph.

Penny size hail is possible with this storm.

Locations impacted include...
Slidell, Pearl River, Lacombe, Pearlington and Slidell 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 3044 8968 3040 8968 3036 8966 3034 8963
      3029 8964 3025 8963 3021 8960 3021 8979
      3022 8985 3025 8987 3026 8998 3030 8999
      3035 9006 3039 9005 3050 8974
TIME...MOT...LOC 0524Z 267DEG 17KT 3032 8997

CAB

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Special Weather Statement
National Weather Service New Orleans LA
244 AM CDT Thu Apr 15 2021

LAZ075-MSZ077-080-150845-
Northwest St. Tammany-Hancock-Pearl River-
244 AM CDT Thu Apr 15 2021

...A STRONG THUNDERSTORM WILL AFFECT CENTRAL ST. TAMMANY PARISH...
NORTHERN HANCOCK AND SOUTHERN PEARL RIVER COUNTIES...

At 244 AM CDT, a strong thunderstorm was located over Picayune,
moving east at 25 mph.

Half inch hail is possible with this storm.

Locations impacted include...
Picayune and Mcneil.

LAT...LON 3087 8934 3050 8934 3046 8980 3063 8980
      3088 8935
TIME...MOT...LOC 0744Z 264DEG 23KT 3056 8972

CAB