Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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FXUS64 KLIX 280330
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
930 PM CST Sun Nov 27 2022

...New UPDATE...

.UPDATE...
Issued at 913 PM CST Sun Nov 27 2022

Overnight forecast may not be quite as straightforward as one
might think tonight. Temperatures have been slower to fall off
this evening than what was in the original grid forecast. Have
already adjusted those to fit current trends.

There is a shortwave moving across Oklahoma and Texas this
evening, and there`s been enough moisture getting advected
northeastward from the Gulf of Mexico to produce some clouds
around 3,000 feet over the Gulf, which produced some brief
ceilings along the Louisiana coast just after sunset.

Right now, it`s the battle of 2 scenarios. The first, would be if
winds decouple completely in the next few hours and the clouds
over the Gulf stay offshore. That sets us up for a radiation fog
event which appears to maximize near the Interstate 10/12 corridor
as temperatures chill, probably after 4 AM CST. The second
scenario would be the clouds move in off of the Gulf, restrict fog
development, and keep temperatures warmer than currently
forecast.

At this point, forecast is leaning toward scenario number two, but
we`ll need to maintain a lookout for fog development overnight.

&&

.SHORT TERM...
(This evening through Monday night)
Issued at 347 PM CST Sun Nov 27 2022

The upper level low that brought yesterdays showers and
thunderstorms is now over the Ohio River Valley and racing
northeast. Post frontal high pressure is building in and lending to
today`s spectacular weather. Skies remain clear and temps are quite
temperate. Although temps would typically fall behind a cold front,
overnight lows will be modified by a cirrus deck that`s expected to
move in across the region from the southwest.

A weak shortwave trough will swing through the Mississippi Valley on
Monday. There`s not going to be any moisture return before this
system moves through as winds remain offshore up until its arrival.
Temps remain the same with highs near normal for this time of year.

&&

.LONG TERM...
(Tuesday through Saturday night)
Issued at 347 PM CST Sun Nov 27 2022

The primary headline to monitor beyond Monday is severe weather and
excessive rainfall potential associated with the next frontal system
on Tuesday night into Wednesday followed by cooler temperatures
behind the front. A gradual warmup can be expected thereafter into
the weekend with only slight rain chances as winds flip and moisture
returns on Friday night into Saturday across the western CWA.

The synoptic pattern setting up over CONUS preceding the severe
weather potential on Tuesday evening is characterized by a deep
positively tilted trough ejecting out of the central rockies which
reaches its peak depth over the central plains Tuesday evening
before lifting out into the Ohio Valley on Wednesday. This trough
will initiate lee cyclogenesis off the rockies where a deepening
surface low develops over southwest Kansas and propagates quickly
east-northeastward during the day Tuesday. Strengthening of the
pressure gradient over the southern plains will thus enhance low-
level moisture return out of the Gulf of Mexico and provide more a
more favorable thermodynamic profile (MLCAPE 1000-1800 j/kg) for
severe weather up into the Ark-La-Tex region by Tuesday afternoon.
With time, these more favorable thermo profiles will continue north
and eastward with the surface low as it tracks toward the Great
Lakes. Kinematically, wind profiles will be most favorable for
discrete convective activity in the warm sector as storms initiate
on Tuesday afternoon north and west of our CWA, but exact placement
and timing of any prefrontal boundaries and corridors for more
favorable convective development are out of range of CAM/HREF
guidance at this time. As we move into the evening and overnight
hours, the surface low begins to speed off to the northeast leaving
behind less favorable, unidirectional wind profiles that favor more
linear convective modes which would still be capable of carrying a
severe wind threat for the northwest half of the CWA as the frontal
boundary encroaches on the CWA. Forced convection along the boundary
through the overnight hours and into Wednesday morning appear to
still have favorable enough thermodynamic profiles (MLCAPE ~1000
j/kg) to sustain deeper updrafts and the severe weather risk does
appear to extend through this period while not explicitly outlooked
yet. As of now, the Wednesday portion of how this event pans out
will be highly dependent on the evolution of warm sector convection
through the day Tuesday.

Excessive rainfall will be the other side of this event with
moisture return amping PWAT values to near the climatological daily
maximum of 1.8-2" on Tuesday night into Wednesday which coupled with
ample forcing and more widespread convective activity could cause
locally heavy rainfall over areas already saturated from this past
weekend. One silver lining, however, is that these storms should be
relatively progressive in motion which could ease a more substantial
flash flood threat with this event.

After the cold front on Wednesday afternoon, temperatures will fall
to slightly below average into Thursday before gradually rebounding
back toward more seasonable temperatures by the weekend. A weak
shortwave on Friday in addition to winds switching back and enabling
moisture return could enhance slight chances for showers Friday
night into Saturday, but coverage appears to be fairly sparse.

&&

.AVIATION...
(00Z TAFS)
Issued at 530 PM CST Sun Nov 27 2022

Primarily a VFR forecast for this package. Would note that there
are indications in guidance for radiation fog around sunrise,
especially near the Interstate 10/12 corridor terminals. Will
carry some restrictions in the 11z-14z window, but not a high
confidence forecast. Beyond 15z, no restrictions during the
daytime hours, and probably not until after 06z Tuesday.

&&

.MARINE...
Issued at 347 PM CST Sun Nov 27 2022

Relatively light winds and relaxed seas expected through Monday as
surface ridge moves in and continues to weaken the wind field. It`s
not until Tuesday that more impactful conditions develop. A surface
low will develop on the leeside of the Rockies Monday night and
track northeastward across the northern Mississippi River Valley
Tuesday and to the Great Lakes thereafter. In doing so, the local
pressure gradient will tighten and bring onshore winds well up into
Exercise Caution category. They`ll remain there until the frontal
passage Wednesday afternoon. Strong Small Craft Advisory conditions
are likely to develop post-frontal. Looking at boundary layer winds,
there`s at least some chance for Gale conditions, at least in
coastal waters west of the Mississippi River Wednesday
afternoon/evening. Otherwise, 20Kts+ expected through Thursday
before relaxing as we go into the weekend with surface ridge moving
in.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  46  69  52  74 /   0   0   0  80
BTR  50  71  56  78 /   0   0   0  90
ASD  53  73  56  77 /   0   0   0  80
MSY  59  71  60  77 /  10   0  10  80
GPT  56  71  58  74 /   0   0   0  70
PQL  55  71  55  74 /   0   0   0  60

&&

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

$$

SHORT TERM...ME
LONG TERM....TJS
AVIATION/UPDATE...RW
MARINE...ME


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