666
FXUS64 KLIX 130003
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
703 PM CDT Sun May 12 2024

...New AVIATION...

.SHORT TERM...
(This evening through Monday night)
Issued at 300 PM CDT Sun May 12 2024

Tonight through Tuesday morning, multiple rounds of showers and
storms will move through the area. There is still quite a bit of
uncertainty in the models regarding the timing of the bulk of the
rainfall. But in general, a round of showers and storms will move
through the northernmost areas overnight tonight into early
Monday. These storms could be strong to severe. The risk of
severe weather is a low confidence forecast, however. A lot will
depend on the eventual mode of the storms and storm motion. The
main threats, however, will be gusty winds 30-60mph and large
hail. Flash flooding will be a concern with these storms
overnight, especially for the S MS areas and northern Southeast
Louisiana parishes. This area is outlooked in a Slight Risk of
Excessive Rainfall (level 2 out of 4) through 7AM. While
antecedent conditions are fairly dry overall, the rainfall rates
are forecast to be quite high 2-3 inches per hour. The PWs are
around 2.0 inches, which is approaching the daily max for SPC
Sounding Climatology. A Flood Watch is in effect for our northern
half of our CWA (north of I-10/12) starting tonight through 10AM
Tuesday. So with these storm overnight tonight into Monday
morning, the main threat will be flash flooding with a limited
risk of severe weather in the form of strong winds (30-60mph) and
large hail. A tornado or two cannot be ruled out for our
northernmost areas.

After 7AM tomorrow, scattered showers and storms will be likely
during the morning hours across the area ahead of a strong line
of storms that is expected to move into the area Monday night into
Tuesday morning. The timing of the storms is still unusually
uncertain as model consensus has been quite lacking between the
CAMs and global models, and also from the model to model runs
individually. The main timing for the line of storms for the
morning model consensus was mainly from midnight through 8am.
Recent trends in a few of the mid-day CAMs are indicating that the
line could approach our area as early as 00z (7pm Monday night).
We hesitate to put all our eggs in that basket unless the 00Z runs
also show an earlier timing on the line. For now, we would say the
main timing is generally 10pm to 7am on Monday night into Tuesday
morning for our area with the potential for the system to be
earlier than forecast.

Regardless of the timing of the line, there will be an all-day
threat for severe weather and especially for flash flooding. With
decent lapse rates during the daytime hours tomorrow, good
instability, decent shear, there could be some damaging winds and
large hail possible inside of scattered storms during the daytime
hours. The main question for the daytime storms (but not for the
line) will be whether there is enough forcing for severe storms.
The main severe weather threat with the line tomorrow night will
be damaging winds, hail, and an embedded tornado or two cannot be
ruled out. We are outlooked in a Slight Risk of Severe Weather
tomorrow through 7AM Tuesday for our entire area. To summarize,
inside of storm development there will be the potential for
damaging winds and large hail and a tornado cannot be ruled out,
especially inside the line(s) of storms. For areas north of
I-10/12, this risk will be in place from tonight through Tuesday
morning and for areas south of I-10/12, this risk will be in place
from Monday morning ~7AM through Tuesday morning.

Regarding the flash flooding threat, there will be abundant
moisture, good instability, deep atmospheric moisture column, and
warm rain processes in the model soundings. PW values are 2.0-2.1
inches, which is approaching the daily max for SPC sounding
climatology for our area. As a result, the rainfall will be highly
efficient with rainfall rates estimated to be around 2-3 inches
per hour. This will be the case for the scattered storms as well
as the line of storms. The other concern related to the flash
flooding risk will be if storms occur over the same area
repetitively, which is possible. We are outlooked in a Moderate
Risk (3 out of 4) of Flash Flooding for the majority of our area.
Generally, we are expecting 3-5 inches of rainfall for the total
event with locally higher amounts in excess of 6 inches possible. And
a Flood Watch is in effect for our northernmost areas tonight
through 10AM Tuesday morning and for our southernmost areas
(I-10/12 and south) from 7AM Monday through 10AM Tuesday. All this
to say... There will be the chance for flash flooding inside of
shower/storm activity from tonight through Tuesday morning. The
most vulnerable areas and areas with the greatest potential for
flash flooding will be places that see multiple rounds of rainfall
as well as urban areas (New Orleans metro, Baton Rouge, Coastal
MS). Be prepared in case a warning is issued, and stay alert to
the weather. If you encounter flooded roadways, turn around, don`t
drown.

In Summary, severe weather and flash flooding are likely tonight
through Tuesday morning. Flash flooding is the larger concern,
especially Monday morning through Tuesday with 3-5 inches of
rainfall total for the event forecast with locally higher amounts
in excess of 6 inches possible and rainfall rates of 2-3 inches
per hour expected. But the severe threat potential will be there
inside any storm activity with the main threats being damaging
winds and large hail, especially inside the line(s) of storms. A
tornado or two cannot be ruled out. Stay weather aware over the
next 24-36 hours, and have multiple ways to receive warnings,
especially overnight. And if you encounter flooded roadways,
especially at nighttime with the limited visibility, turn around,
don`t drown. MSW

&&

.LONG TERM...
(Tuesday through Saturday night)
Issued at 300 PM CDT Sun May 12 2024

By sunrise Tuesday, a cold front should be pushing east of the local
CWA, although we may still have some lingering precipitation during
the morning hours. The associated upper system will be moving
through the Ohio River Valley during the day on Tuesday, toward the
Virginia coast by late Wednesday. Drier air will be moving into the
area briefly, but surface winds will regain a southerly component
Thursday morning with moisture rebounding quickly. For instance,
forecast soundings at Baton Rouge will be around 1 inch at 12z
Thursday and increase to 1.8 by Thursday evening. Southwesterly
upper flow will bring another shortwave across the area Thursday
night into Friday morning. That will produce another round of
showers and thunderstorms. Considering the moisture availability, if
we see another round of 2+ inch rainfalls across the area, there
will be potential for hydrologic issues, especially if the short
term forecast amounts verify. Beyond Friday morning, forecast
confidence decreases, as the global models come into disagreement
regarding which stream, north or south becomes the predominant
trough. The ECMWF focuses energy in the northern stream, while the
GFS is on the southern stream. This will mean the GFS operational
run brings another area of thunderstorms and heavy rainfall across
the area Saturday, while the ECMWF operational is much drier. Will
note that the 00z ECMWF ensemble numbers support the 12z ECMWF
global PoPs. Will ride the NBM PoPs for the weekend for now, and
acknowledge limited confidence int eh weekend forecast.

Won`t make significant changes to NBM max/min numbers. The days with
no precipitation will likely see high temperatures near 90 degrees.
Overnight lows will continue to be near to above normal.

RW

&&

.AVIATION...
(00Z TAFS)
Issued at 634 PM CDT Sun May 12 2024

Most terminals reporting VFR at issuance time. Convection has been
weakening as it moves into our area over the last hour or two.
With lightning activity diminishing, have removed it from KBTR in
the near term, but will hold VCTS in KHDC and KMCB. Expect
ceilings to fall into the MVFR range at most terminals beyond 06z,
and perhaps the upper end of IFR. Quite a bit of uncertainty
regarding convective development overnight, both in location and
timing, but there is likely a warm front north of Interstate 10,
with convection primarily on or north of the front. Expecting
amendments will be necessary during the evening hours as
convective processes reveal themselves. Least likely terminals for
convection tonight into Monday morning will be KNEW/KMSY/KHUM. At
this time the second round of organized convection will occur
beyond 00z Tuesday, and may be addressed more fully in the 06z
forecast issuances.

&&

.MARINE...
Issued at 300 PM CDT Sun May 12 2024

A system bring multiple rounds of rain and storms will be moving
through the area tonight through Tuesday morning, which will cause
strong (15-25kts) southerly winds and higher seas through
Wednesday morning. Exercise Caution headlines are in effect
through at least tomorrow and will likely need to be extended in
time. Winds will ease shift northerly Wednesday into early
Thursday behind the system. Another system will likely move
through the area Thursday through Saturday morning, which will
strengthen the southerly winds (15-20kts) and bring higher seas.
MSW

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  65  82  65  84 /  80  90  90  40
BTR  71  89  69  89 /  80  80  80  30
ASD  71  87  68  88 /  70  90  90  60
MSY  75  88  72  87 /  70  90  90  60
GPT  70  85  69  87 /  80  90 100  70
PQL  69  86  68  87 /  70  90 100  80

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flood Watch through Tuesday morning for LAZ034>037-039-046>048-
     071-076-079>086.

     Flood Watch from Monday morning through Tuesday morning for
     LAZ056>060-064>070-077-078-087>090.

GM...None.
MS...Flood Watch through Tuesday morning for MSZ068>071-077-083>088.

GM...None.
&&

$$

SHORT TERM...MSW
LONG TERM....RW
AVIATION...RW
MARINE...MSW