-- Discussion containing changed information from previous version are highlighted. --
845
FXUS64 KLIX 282058
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
358 PM CDT Fri Jun 28 2024

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

.SHORT TERM...
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(This evening through Sunday night)
Issued at 356 PM CDT Fri Jun 28 2024

Convection has generally had a mind of its own for the past few
days now. It appears that even with warm mid lvl temps, poor LL
convergence, weak mid lvl flow, has not been enough top keep the
convection down across the northwest while the southeast has
scattered moderate showers with isolated storms at best and is
directly under the dissipating s/w. With 2.2 to 2.3 PWs over the
area it seems to be more than enough to overcome most of the
negatives as almost every outflow boundary is able to get at least
something to pop. Over the last few days outflow along with
sea/lake breeze boundaries really struggled to get much. Even
overnight convection which should be more marine based this time
of the year has not lived up to potential and convection instead
fired over lands areas from I-12 to just north of the coast. The
good thing with the convection today and associated loud cover is
it has tempered the temps and overall heat index potential. Most
of the area saw the heat index only rise to around 100-105 but
don`t look now as the heat potential is just going to ratchet up
over the next few days.

Trying to figure out how things handle tonight is tricky. Again
there is quite a bit more convection firing west and northwest of BR
which seems like it should be almost rain free. This convection will
not just completely dissipate like a puff of smoke at 00z like the
models try to show but this convection look almost exclusively
driven on diurnal fluctuations and once we begin to lose the
daytime heating those outflow boundaries should quickly stop
producing. Convection should at some point slack off over most of
the land areas becoming more coastal/marine based, however it would
not be out of the question again to see some redevelopment around
the tidal lakes and coastal Ms areas after 6z. This could provide
another heavy rain threat over isolated locations.

Saturday and Sunday...the impact is heat, the problem is convection.
When does convection develop, how much develops, and how fast does
it expand? All of these will play games with the temperature and
subsequent heat index problems. Early convection, say mid to late
morning hours, then little to no more afterwards will just be
miserable as these areas will still be able to heat up with peak
heating early afternoon. The added moisture from morning rain will
make it feel like a steam room and heat index readings would have
little issue getting to around 108 Saturday and possibly hotter
Sunday. Convection decides to hold off until late afternoon say 20z
or later, then those sites will have had all day to heat up and the
slight compressional heating and moisture pile up ahead of the
outflow boundaries from these storms will cause the heat indices to
ramps up with little to no problem of seeing heat index values in
the upper 100 to lower 110s. The sweet spot would be areas that have
convection occurring between 16 and 19/20z. That would mean
convection and cloud cover during peak heating and could impact just
long enough to keep those places from reaching their potential. So
the problem is what happens. The ridge is building east but doesn`t
look to be as stout as previously advertised at least for the
weekend. That said it will still build east and h5 temps are still
forecast to be in the -2 to -4C range. The weakness currently over
the area will continue to dissipate and should be all but
nonexistent by tomorrow evening but the ridge may be centered far
enough to our northwest leaving us on the periphery of its strongest
influence with the best subsidence possibly just northwest of the
area. With PWs still around 2.2-2.3 honestly see no reason the
southeastern half of the area won`t see convection but given the
overall lack of flow in the column not anticipating a robust
seabreeze to develop quickly which will allow for decent warming.
Convection likely begins around midday early afternoon and this
should lead to most of the area seeing heat index values around to
106 to 110 range. With that we have issued a heat advisory for
tomorrow.

As for Sunday this is more tricky. The ridge appears to continue to
build with some indications it could be around 598-599dm but it
would be centered over the Red river area possibly just far enough
to keep the CWA on the s/SE periphery. The places the area in a
tough spot where to our west and northwest little to no rain should
develop and to our east scattered to numerous afternoon storms will
be likely. The other interesting features is that moisture will
increase across the area. PWs could top out close to 2.5" with
increase LL moisture as well. The increase in LL moisture will make
for even more oppressive conditions as we heat up but with that much
moisture available to tap into it would take very little
lift/forcing to get convection to develop. Given the location of the
ridge and where we are the eastern to southeastern half of the CWA
seemed to have decent potential of seeing convection again where the
northwest will likely rely on convection from the east moving west
into these areas. Again given the lack of any substantial wind field
convection is going to be highly dictated by boundaries and their
interactions. The lack of a strong southerly LL winds field should
keep the seabreeze from activating early and then moving north very
fast. That is the convection how about the heat. Well we already
mentioned the increase in moisture and LL temps also try to inch up
but h925 temps right now look to only be around 25-26C and this is
typically lower to mid 90s. But the combination of mid 90s and very
humid conditions look to lead to heat index values climbing higher
on Sunday and could even top out around 112-114 in multiple
locations. This is very borderline to Excessive Heat Warning
criteria and if this was the only day with relief expected Monday
would likely hold off on any major decisions right now and allow
another forecast cycle or two to make a decision on heat products.
That said given that it is Friday and this is the weekend along with
what looks like a prolonged heat issue through much of the 4th of
July week we opted to get an Excessive Heat watch out now for most
of the area for Sunday. First off it is likely that some places in
the current watch will not reach 113 but where exactly is unknown
and if convection really struggles to develop then the heat index
values will likely be around 113 or higher across most of the area.
Right now to get the awareness out there about the potential along
with the likelihood of conditions being worse monday and Tuesday
next week we wanted to get the Watch out now and not wait until
tonight or tomorrow. /CAB/
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&&

.LONG TERM...
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(Sunday through Thursday night)
Issued at 356 PM CDT Fri Jun 28 2024

The northern stream upper level trough moves through the Great
Lakes Sunday evening and continue eastward into the Atlantic Ocean
Monday. The base of this trough doesn`t reach much farther south
than the Appalachian Mountains as it shifts offshore. This track
is why a weak backdoor front comes into the CWA from the northeast
just ahead of the trailing ridge. That upper ridge in the wake of
this trough will be sliding east across the entire Mississippi
Valley Monday afternoon into Tuesday. Global models have been
extremely consistent from run to run for a few days now showing a
596dm high will be centered near the Akrlatex region Monday
afternoon. Excluding rain potential, increasing 500mb heights will
bring already above normal weekend temps up even more. Guidance
spread through the forecast period is fairly minimal and as of 12z
runs, Monday has the potential to be the warmest with highs
mid/upper 90s to 100 degrees which is nearly 10 degrees above
normal. Convective coverage will probably be the bigger deciding
factor on max temps. That previously mentioned weak backdoor front
looks to stall near the Gulf Coast, which combined with forecast
temps, would support scattered to numerous showers and storms. If
convective initiation is early enough, heat indicies will get
knocked down quickly. However, if not too early, widespread upper
70 to 80 degree dewpoints with hot temps may bring heat indicies
into Excessive Heat Warning issuance. Tuesday will virtually
mirror with the same heat/convection timing challenges as the
center of the upper ridge will be progressing eastward fairly
slowly. As the rest of the week progresses, repeated northern
stream troughs/shortwaves will steadily flatten out the ridge
aloft and eventually cause it to retrograde to the west. As the
subsidence slowly fades from this upper level pattern change,
should eventually see some less extreme temps and more widespread
daily convection.

/MEFFER/
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&&

.AVIATION...
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(18Z TAFS)
Issued at 356 PM CDT Fri Jun 28 2024

Terminals completely at the whim of convection. Scattered
convection continues to develop mainly along and southeast of a
line from Thibodaux to just osuth of Poplarville and this
encapsulates all terminals but BTR, MCB and HDC. With that timing
storms and specific impacts is difficult but locations like ASD
and GPT should begin to see impacts in the next hour or two while
NEW and MSY should see conditions improve temporarily soon and for
a few hours before additional storms move in likely around 21/23z.
HUM probably will see the longest duration as storms continue to
fire back over that way and may do so through a good portion of
the afternoon. Overall the impacts have mostly been reductions to
vsbys to 3-4sm while MVFR cigs have lowered only to 2-3K otherwise
with the exception of 15-30 mins of IFR vsybys with the heavier
downpourts now other major restrictions. Only other thing to
mention is gusty winds with convection. /CAB/
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&&

.MARINE...
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Issued at 356 PM CDT Fri Jun 28 2024

High pressure will be in control through the weekend. This will
continue to provide mostly light winds across the coastal waters.
The biggest issues will be convection as decent coverage of
storms are possible in the morning hours over the coastal waters,
especially during the early morning hours. Very rich low level
moisture, light winds, and convection during the overnight/early
morning hours should lead to decent waterspout potential. /CAB/
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&&

.PRELIMINARY POINT TEMPS/POPS...
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MCB  74  92  74  94 /  10  70  20  60
BTR  79  96  78  97 /  10  70  10  50
ASD  78  93  78  95 /  40  70  10  50
MSY  80  92  80  95 /  40  70  10  50
GPT  78  91  78  95 /  60  60  20  60
PQL  78  94  77  97 /  50  60  20  60
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&&

.LIX WATCHES/WARNINGS/ADVISORIES...
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LA...Heat Advisory from 10 AM to 7 PM CDT Saturday for LAZ034>037-039-
     046>048-056>060-064-065-071-076>090.

     Excessive Heat Watch from Sunday morning through Sunday evening
     for LAZ034>037-039-046>048-056>060-064-065-071-076>090.

GM...None.
MS...Heat Advisory from 10 AM to 7 PM CDT Saturday for MSZ068>071-077-
     083>088.

     Excessive Heat Watch from Sunday morning through Sunday evening
     for MSZ068>071-077-083>088.

GM...None.
-- End Changed Discussion --
&&

$$

SHORT TERM...CAB
LONG TERM....ME
AVIATION...CAB
MARINE...CAB