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

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FXUS64 KLIX 252321
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
621 PM CDT Mon Mar 25 2024

...New AVIATION...

.SHORT TERM...
(This evening through Tuesday night)
Issued at 358 PM CDT Mon Mar 25 2024

Warm and WINDY day today. Deep sfc low moving through the central
Plains today combining with a large area of high pressure
dominating all of the eastern Seaboard and into the central Gulf
is leading to a rather impressive pressure gradient across the
region. Just across our CWA the pressure gradient is around 8mb
and that typically is more than sufficient to get windy
conditions. The winds being this strong has kept the airmass well
mixed and thus most places have only just now gotten into the mid
70s. Combine that with the broken to overcast skies and we are
just not warming up as much as we could. This is absolutely
hindering the instability and by 18z we still had only 500 J/kg
of CAPE or less. This is not expected to increase much as we move
into the evening however we will lose the CIN that has been over
the area so we won`t need much to work with.

Main focus in the forecast is really tonight and there are a lot of
questions about tonight. This event has somewhat of a high
ceiling/low probability feel to it. Confidence is not high that we
will get much in the way of severe but a few strong to severe storms
seems like a good shot. The problem is if we can get one or two
severe storms this evening and overnight along and north of the I-12
corridor in SELA, especially over southwest MS and the adjacent LA
parishes and they are able to get rather potent they will have
the potential to develop a tornado or two and could even be strong.

Synoptically L/W trough axis stretching south from Manitoba and
Saskatchewan Canada though the Plains and into the Baja of
California. A potent closed s/w embedded in the deeper flow is
moving through the Central Plains and is expected to move into the
Mid MS Valley tonight with a negative tilt s/w trough axis moving
through the ARKLATEX and the northern portions of the Lower MS
Valley. This does seem to suggest that the bulk of the strong deep
forcing will remain right along our northwest if not just north
of us. H5 hghts don`t really change much and even slightly rise
through the evening as the L/W trough does not move and the s/w
lifts northeast. Aloft the core of the 160kt jet will move from
eastern TX and into the TN Valley overnight along with slightly
weakening. Ridging over the eastern Gulf and into the southeastern
CONUS does provide some upper lvl diffluence this evening but as
we move into the overnight hours the diffluence is not as great.
At the sfc the sfc low currently moving over the NE/IA/MO border
will continue to lift northeast into Wisconsin by tomorrow
morning. The pulling farther way to the north and northeast could
really slow down things in the LL as the prefrontal trough slowly
moves into and across the area late this evening and overnight
thus allowing the weak cold front to catch up to it b/t 4-6z. This
may be the biggest influence tonight for the severe potential
which we will get into soon.

The dynamics seem to be some of the biggest questions. Like
mentioned earlier the h5 forcing may be too far to the north and
many even lead to timing issues when the best forcing is not
matching up with the instability and sfc support. As mentioned
earlier there is some small indications that the mid lvl hghts could
rise a touch but will likely remain steady all evening and not
actually drop until the early morning hours. The LL winds field if
you haven`t noticed already has been responding to the increase in
lift but as the bulk of the strong mid lvl punch move into the
northern portions of the Lower MS Valley, the LL jet that was
developing over the western Gulf and has aided in the convection
off to our west will quickly lift north into MS this evening and
by 4/5z we could be at the tale end of the LL jet with the core
all the way over western TN. This would actually promote LL
divergence as stronger southerly winds over southern MS remove the
air faster than the slightly weaker winds over SELA can replace
it. This is a common failure mode for us. That said we are not
saying nothing will develop because of this. There is a better
chance of not as much activity developing unless there is
something that can accommodate for the weakening LL convergence
which there may be a small window where we do have something. Even
though the bulk of the forcing is displaced to the north and we
don`t really get a good punch in the mid lvls, we will see mid
lvl flow strengthen through the night with h5 winds near 80kts
across southwest MS and adjacent LA parishes west of I-55. This
is very impressive mid lvl flow but broad lift wouldn`t promote
explosive development and more gradual increase in intensity.

Thermodynamics are not impressive at all but it will be more than
sufficient to support thunderstorms. We will have limited
instability to work with and the best instability may be only
immediately ahead of the line but MLCAPE may just inch over 1000
J/kg. The CIN has been decreasing through the afternoon and there
should be little to no CIN to overcome tonight and if there is some
the gradual increase in mid lvl flow and approaching front that
would be more than enough to overcome the lack of instability. Mid
lvl lapse rates steeper than 6.5 C/km are more than adequate.
Showalters of -3 to -4 are also more than enough to support robust
convection. So even as limited as the instability appeared to be
earlier it is still more than sufficient to support severe storms.

Shear is also not a problem. The wind field is very strong right now
and the shear is not missing at this time. The problem is that the
LL shear starts decrease as our LL jet lifts out but the deep layer
shear is expected to remain until the line moves through. 0-1 and 0-
3km SRH are currently around 300 and 500 respectively for most of the
area along and north of the 10/12 corridor. These will drop as the
h85 jet slowly pulls away but even at midnight the 0-1km should
still be between 200-300 m2/s2 and the 0-3km around 300-400 m2/s2.
But the shear appears to be more speed shear than directional shear.
Winds will be out of the south late this evening but by h75 may only
be out of the SSW a directional change of possibly only 20-30
degrees. The 0-6km bulk shear of 55-65kt should remain in play until
the line moves through. This type of bulk shear should promote
organized storms.

So there are a lot of positive features to work with to lead to a
severe weather threat but a lot are conditional on having enough of
a punch to really get a few storms ramping up. At this time the best
chance for the combination of everything looks to be between 03/04Z
and 8/9Z and maybe only from the Pearl River to about 20 miles west
of I-55 and north of I-12. The main culprit that could provide
enough of a punch is going to be the cold front catching up to the
prefrontal trough/weak convergent line which should be almost
bisecting the CWA around 4/5Z. This could lead to 2 concerning
issues. First is it would possibly  be enough to finally get a few
potent storms and with the environment in place that those storms
could finally tap into they could be quite severe with a few
tornadoes and possibly strong tornadoes. The other issue is that it
doesn`t look like we will have a solid QLCS like line and more so
broken cells. This would cut back on the number of people impacted
by possible severe weather but with maybe a few less storms these
storms would have a greater chance at becoming severe and even
tornadic as they could remain unimpacted by other storms.

So with that again high ceiling/impact but low probability seems to
be the mode we are looking at. That said leaning to fewer storms (a
broken line) and possibly a few severe with the greatest risk for
severe across southwest MS and perhaps right across the state line
into the LA parishes. Coastal MS is interesting as most if not all
CAMs showed the line quickly weakening again but many want to show
another uptick over Jackson county and this has historically
happened. If the line takes another uptick over Harrison and Jackson
counties this would likely occur around bus stop time and rush hour
traffic. /CAB/

&&

.LONG TERM...
(Wednesday through Sunday night)
Issued at 358 PM CDT Mon Mar 25 2024

The long term starts with high pressure spreading eastward across
the Missouri Ozarks and into the Ohio River Valley. This will
keep northeasterly flow across the region. Upper heights will be
relatively low as the H5 trough moves over the region. This should
help keep temperatures cool except for the MS Gulf Coast where
temperatures will be in the middle and upper 70s.

Going into late week, surface high pressure begins to settle into
the region and a dry northwesterly flow develops across the region.
Dry is the primary term needed to characterize the long term period
as POPs will be close to zero throughout. This means it will
primarily be a temperature forecast. So, in the spirit of a
temperatures forecast, it appears the long range will see a warming
trend, especially as a 591dam H5 ridge builds across the Bay of
Campeche and surface high pressure moves east over the Florida
peninsula initiating a return flow later this weekend. No foolin, by
Monday (Apr 1st if you didn`t catch that) temperatures will continue
to climb with a continuation of rising heights/thicknesses and
return flow. In fact, temperatures look to climb into the middle and
even upper 80s across the region with the coolest locations
remaining along the MS Gulf Coast where the onshore flow over the
cooler shelf waters will keep temperatures a bit lower. (Frye)

&&

.AVIATION...
(00Z TAFS)
Issued at 617 PM CDT Mon Mar 25 2024

A few showers are moving through now with a brief break before the
line of heavier showers and thunderstorms. No major changes made
to the tempo group at each site for the timing of the storms.
Thought that CIGS were be lower than they are right now but they
should still drop to around 1000 ft, maybe a little lower, as the
main line approaches. This would be the area of low confidence,
with timing of the line having moderate confidence. Could see
gusts a little stronger in thunderstorms.

&&

.MARINE...
Issued at 358 PM CDT Mon Mar 25 2024

Hazardous winds and seas over the coastal waters continue through
the night and into the morning tomorrow but should quickly subside
as the pressure gradient breaks down. There is no real good cold
air advection behind the line so the winds should quickly subside
tomorrow morning. High pressure than builds in with no headlines
expected tomorrow afternoon and through Wednesday. By later in the
week onshore flow will start to slowly increase and headlines may
be needed by the end of the week. /CAB/

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  57  77  46  69 / 100   0   0   0
BTR  61  80  51  75 /  90   0   0   0
ASD  62  82  52  76 /  90  20   0   0
MSY  63  79  57  74 /  90  20   0   0
GPT  62  79  54  76 /  90  60   0   0
PQL  63  83  52  79 /  80  80  10   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Wind Advisory until 4 AM CDT Tuesday for LAZ034>037-039-046>048-
     056>060-064>071-076>090.

     Coastal Flood Advisory until 4 AM CDT Tuesday for LAZ069-070-076-
     078.

GM...Gale Warning until 4 AM CDT Tuesday for GMZ530-532-534-536-538-
     550-552-555-557-570-572-575-577.

     Small Craft Advisory from 4 AM to 7 AM CDT Tuesday for GMZ530-
     532-534-536-538-550.

     Small Craft Advisory from 4 AM to noon CDT Tuesday for GMZ552-
     555-557-570-572-575-577.

MS...Wind Advisory until 4 AM CDT Tuesday for MSZ068>071-077-083>088.

     Coastal Flood Advisory until 4 AM CDT Tuesday for MSZ086.

GM...Gale Warning until 4 AM CDT Tuesday for GMZ532-534-536-538-550-
     552-555-557-570-572-575-577.

     Small Craft Advisory from 4 AM to 7 AM CDT Tuesday for GMZ532-
     534-536-538-550.

     Small Craft Advisory from 4 AM to noon CDT Tuesday for GMZ555-
     557-570-572-575-577.

&&

$$

SHORT TERM...CAB
LONG TERM....RDF
AVIATION...LN
MARINE...CAB


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