Severe Thunderstorm Warning 265, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
314 PM CST Sat Dec 9 2023

...New SHORT TERM, LONG TERM, AVIATION, MARINE...

.SHORT TERM...
(This evening through Sunday night)
Issued at 233 PM CST Sat Dec 9 2023

A positively tilted longwave trough axis and an attendant cold
front will sweep through the forecast area tonight into tomorrow
morning. In advance of this trough, a broad region of increasing
upper level ascent and moderate instability will support the
continued development of scattered showers and isolated
thunderstorms through the early evening hours. Later this evening,
a more solid line of showers and thunderstorms will begin to move
into the forecast area in advance of the approaching cold front.
Fortunately, the severe potential associated with this line of
convection appears to be on the lower side as the best dynamics
remain well displaced to the north of the forecast area. Model
sounding analysis indicates that shear will maximize at between 35
and 40 knots within the effective inflow layer, and that
directional shear in the lowest 3km will peak around 125 m2/s2.
These values will support some modest updraft tilting and weak
mid- level rotation within the deepest convective cells, and a few
stronger storms with wind gusts of 40 mph could develop this
evening into the overnight hours. However, the prospect for severe
storms to develop looks very limited. PoP values near 90 percent
reflect the high potential for rainfall tonight.

By tomorrow morning, the front will be well offshore and well
east of the area as the parent upper level trough axis moves
through. Lingering post-frontal shower activity could impact the
Mississippi coast in the early morning hours, but a dry forecast
is in place from late tomorrow morning through Sunday night. Skies
will also rapidly clear late tomorrow morning into tomorrow
afternoon as strong negative vorticity and dry air advection takes
hold. A deep pool of much colder air will also advect into the
area from the north and west, and this will drive temperatures
well below normal tomorrow into tomorrow night. 925mb temperatures
will fall to between 30 and 35 degrees, and this will only support
daytime highs in the low to mid 50s over most of the area tomorrow
afternoon. Tomorrow night, temperatures will quickly cool as skies
clear and the airmass dries. The only inhibiting factor that will
prevent a more widespread freeze over parts of the area will be
continued strong boundary layer winds of 20 to 25 knots. These
winds will keep the boundary layer thermally mixed and prevent
temperatures from cooling as much. However, lows will still be
quite chilly in the 30s over inland areas and the low 40s south of
the lake and along the immediate Louisiana coast. Another light
freeze is likely to occur over parts of Coastal Mississippi, the
Northshore, and Southwest Mississippi, especially for inland areas
north of the I-10/12 corridor. This where the probabilities of
seeing freezing temperatures are highest at over 90 percent in the
NBM.

&&

.LONG TERM...
(Monday through Friday night)
Issued at 233 PM CST Sat Dec 9 2023

The start of the long term forecast should be relatively quiet as an
area of high pressure quickly builds in following the weekend's cold
front. This high pressure will gradually move through the area,
still holding enough on Tuesday to keep conditions calm. In terms of
temperatures highs remain in the 50s for Monday, but start to
recover by Tuesday warming into the low to mid 60s. Tuesday morning
lows will still be chilly, but a touch warmer than Monday morning
and only warming up more through the week.

Wednesday is when the forecast starts to ramp back up again, but the
globals are in large disagreement. The Euro exits the weekend front
all the way into the Caribbean, which keeps the next system further
into the Gulf and doesn't bring as much of an impact to us. The GFS
on the other hand does not take the front quite as far and as a
result, the next system in the form of a Gulf Low forms close enough
to bring impact to our area. This would be especially impactful for
our marine areas in the form of winds and waves. Depending on the
solution that plays out will greatly change the forecast. We will
have to continue to see how the models adjust as we get into early
next week.

&&

.AVIATION...
(18Z TAFS)
Issued at 233 PM CST Sat Dec 9 2023

Two areas of concern in the forecast for tonight. The first area
of concern will be the prospect of IFR ceilings and visibilities
persisting at GPT through the entire forecast period due to a
combination of advection stratus and fog through around 08z and
then from convective impacts and post-frontal stratus after 08z.
At the remainder of the terminals, the primary impacts will be
related to a band of convection expected to accompany the passage
of a cold front. This band of convection will produce a period of
IFR visibilities and ceilings as it passes through. The most
likely time period for convective impacts at BTR and MCB will be
between 02z and 06z. At MSY, HDC, HUM, NEW, and ASD, the most
likely time will be between 04z and 08z. At GPT, the most likely
time for convective impacts will be between 08z and 12z.
Conditions will improve rapidly at between 12z and 18z at nearly
all of the terminals as northerly flow ushers in a much drier
airmass. Even GPT will begin to see improvement as early as 18z
tomorrow.  PG

&&

.MARINE...
Issued at 233 PM CST Sat Dec 9 2023

Strong gradient flow behind a potent cold front will produce near
gale to gale force winds over the coastal waters starting late
tonight and continuing through the day tomorrow. Seas will quickly
respond to these strong northwest winds of 20 to 30 knots and
increase to between 6 and 10 feet in the offshore waters and 3 to
6 feet in the sounds and lakes. By tomorrow night, a gradual
decrease in the wind field is expected as a surface high builds
into the area. However, this respite in rough seas will be short-
lived as a low pressure system begins to form over the central
Gulf on Tuesday. An increasing pressure gradient over the waters
will push easterly winds back to between 15 and 25 knots from
Wednesday through Friday. Additionally, as the low intensifies
over the central and eastern Gulf later this week, a long period
swell train will develop and increase seas substantially. Swell of
5 to 7 feet on top of wind waves of up to 6 feet will push seas
to as high as 12 feet over the outer waters by Friday.
The other concern will be coastal flooding developing along east
facing shores from mid-week onward.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  44  53  29  56 /  90  20   0   0
BTR  48  55  33  58 /  90  10   0   0
ASD  49  56  32  58 /  80  30   0   0
MSY  52  56  41  55 /  90  20   0   0
GPT  50  58  35  56 /  80  40   0   0
PQL  51  61  32  59 /  80  50   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory from 3 AM Sunday to 6 AM CST Monday for
     GMZ530-532-534-536-538-555-557-575-577.

     Gale Warning from 3 AM to 3 PM CST Sunday for GMZ550-552-570-572.

     Small Craft Advisory from 3 PM Sunday to 6 AM CST Monday for
     GMZ550-552-570-572.

MS...None.
GM...Small Craft Advisory from 3 AM Sunday to 6 AM CST Monday for
     GMZ532-534-536-538-555-557-575-577.

     Gale Warning from 3 AM to 3 PM CST Sunday for GMZ552-570-572.

     Small Craft Advisory from 3 PM Sunday to 6 AM CST Monday for
     GMZ552-570-572.

&&

SHORT TERM...PG
LONG TERM....HL
AVIATION...PG
MARINE...PG

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>