Tornado in Louisiana, December 27, 2024

Area Forecast Discussion...UPDATED
National Weather Service New Orleans LA
548 AM CST Fri Dec 27 2024

...NEW UPDATE, AVIATION...

.UPDATE...
Issued at 539 AM CST Fri Dec 27 2024

It appears that we are finally starting to decouple this morning
and winds have largely decreased across much of the region. This
may become a slight problem with the lower wind speeds in terms of
stratus build down fog potential. In fact, the last hour MSY
winds have dropped below 10kts and visibilities have dropped to
2SM. Furthermore, over the past half hour here at ASD the winds
have dropped to around 05kt and visibilities have dropped from
10SM to now 2SM, partly due because showers, but likely also from
stratus build down. We'll keep monitoring, but a short fused
dense fog advisory may be needed if more widespread dense fog is
apparent through the morning. (Frye)

&&

.SHORT TERM...
(Today through Saturday Night)
Issued at 301 AM CST Fri Dec 27 2024

A band of convection developed last evening across central and
southwest Louisiana along or just slightly a head of an advancing
cold frontal boundary. This convection has started to weaken quite
considerably over the last hour or two as the upper level trough
begins to lift out taking much of the upper forcing along with it.
Out ahead of this front the surface flow has actually remained
quite moderate as the surface has yet to decouple. This is helping
with moisture return and in some instances allowed the surface
from cooling much. A low stratus deck continues to reside over the
area and some stratus build down fog, if you will, has developed,
especially over the lake. Hazy conditions haven't become too
consequential this morning as again the moderate low level flow
is keeping visibilities at the surface in good shape.

The surface frontal boundary is forecast to stall over/near the
central Gulf Coast today. Despite the loss of some upper support
we cannot rule out additional showers and storms, however,
intensity and coverage appear to be limited. Later today and
especially tonight we'll begin to monitor an amplifying shortwave
over the high plains. As the trough begins to amplify the residual
surface front will begin to lift northward as a warm front. Along
the front and with dynamic support from a perfectly timed H3 jet
arrival, some showers and storms will develop along this
boundary. The boundary will surge northward quickly allowing the
warm sector to overspread the region by around noon. There is at
least some severe weather potential initially with the warm front
depending on timing of the upper forcing. Initially north of the
front, elevated hailers would be the primary focus, however,
right along the boundary, surface based instability will allow for
at least a lower-end tornado potential early on as the front
surges northward.

Going into Saturday afternoon, guidance is a little murky in
terms of what to expect. CAMs coming into range tell a very
different story depending on the model. The key here is that
moderate surface based instability should be around. With the
surface low developing over the Delta Region, expect surface winds
to back slightly adding at least some element of curvature to the
low level hodograph. SRH looks to increase to around 200-300
M2/S2 as the LLJ begins to increase later in the afternoon. A line
or broken line of storms should develop along the advancing
frontal boundary. Any storm would have the potential to become
severe with strong damaging wind gusts, hail, and a tornado
potential would also be present. A stronger tornado or two cannot
be ruled out over SW Mississippi and generally north of I12 in
Louisiana where the higher instability and strongest wind shear
will reside. Ahead of the line (or lines) of storms, we'll have to
monitor any cells that develop. Supercells wouldn't be out of the
question, especially in the unstable highly sheared environment.
There are still some questions and potential limitations such as
early convection disrupting low level thermals limiting
instability, but this could be compensated for with such a strong
moisture rich low level flow.

Eventually, the front rolls through during the overnight hours
Saturday taking the convection east of our region by Sunday
morning. As for temperatures, with the strong southerly or
southeasterly low level flow, above average is anticipated through
the short term with temperatures climbing into the 70s for most
both today and Saturday and some locations may end up close to 80F
(looking at BTR). (Frye)

&&

.LONG TERM...
(Sunday through Thursday)
Issued at 301 AM CST Fri Dec 27 2024

Dry west-northwesterly flow sets up behind the passing short wave
and frontal boundary. Without much of a plunge in terms of a
larger scale trough, temperatures will not change very much...just
a little reduced humidity early in the long term. Overall, the
pattern evolves to about more of the same...zonal/progressive to
start the new workweek. Surface high pressure will see to it that
we stay quiet at least Monday. Another upper level impulse begins
to amplify over the cornbelt early to midweek next week, however,
this feature stays well to our north. Although it does help drag a
cold front through the region Tuesday or early Wednesday. Surface
high pressure then makes its way east out of Texas and Oklahoma
again keeping the weather on the quiet side and it is then that we
will have another cool down as the large scale upper trough
amplifies east of the Rockies. (Frye)

&&

.AVIATION...
(12Z TAFS)
Issued at 539 AM CST Fri Dec 27 2024

Overall, IFR conditions expected through much of this cycle for
most of the local terminals. There could be some exceptions here
or there in terms of slightly better (MVFR/VFR briefly) or
slightly worse respectively. Showers and perhaps a thunderstorm or
two will be possible. Tried to nailed down timing and confidence
with PROBs and TEMPOs again respectively. More low stratus/VIS
issues by the end of the cycle with some improvement for MSY
between the 24-30 hour window. (Frye)

&&

.MARINE...
Issued at 301 AM CST Fri Dec 27 2024

Marine fog over the lakes this morning will continue. Also,
surface winds remain in the cautionary headline range at least for
the next few hours before winds begin to subside. Going into the
weekend southerly winds and seas should stay rather benign. A few
showers and thunderstorms will be possible through Saturday night
as a cold front moves through the region. This will shift winds to
a more northerly direction briefly before returning to a more
southerly/onshore flow by the start of the new workweek. (Frye)

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  73  60  72  56 /  70  20  90  80
BTR  78  64  78  59 /  70  20  90  70
ASD  77  62  76  59 /  60  30  80  80
MSY  78  64  76  61 /  50  20  80  70
GPT  71  61  72  60 /  70  40  70  90
PQL  76  62  77  60 /  80  50  70  90

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Dense Fog Advisory until 10 AM CST this morning for GMZ530-534.

MS...None.
GM...Dense Fog Advisory until 10 AM CST this morning for GMZ534.

&&

UPDATE...RDF
SHORT TERM...RDF
LONG TERM....RDF
AVIATION...RDF
MARINE...RDF