LIX issues Area Forecast Discussion (AFD) at Dec 25, 11:43 PM CST ...New UPDATE, AVIATION...758
FXUS64 KLIX 260543
AFDLIX
Area Forecast Discussion
National Weather Service New Orleans LA
1143 PM CST Wed Dec 25 2024
...New UPDATE, AVIATION...
.UPDATE...
Issued at 1126 PM CST Wed Dec 25 2024
Concern increasing somewhat regarding potential for overnight fog
development across at least southern and western portions of the
area. Day shift indicated that lack of fog development was
predicated on boundary winds remaining strong enough to hinder fog
development. Surface winds across southwestern portions of the
CWA have dropped to about 5 mph or so, and that may not be strong
enough to preclude fog development. We've seen some fog on traffic
cameras in the Houma area over the last 45 minutes or so, and
observations to the west in the Lafayette and Patterson areas are
also showing fog. If trends continue, midnight shift may need to
issue a Fog Advisory pretty early in the shift.
&&
.UPDATE...
Issued at 800 PM CST Wed Dec 25 2024
Sharp shortwave notable on water vapor imagery along Interstate 55
is pushing organized convection out of our coastal waters. Any
precipitation the remainder of the night should be limited to a
few patches of light rain showers. Temperatures are unlikely to
move very much from where they are at right now in the upper 50s
and lower 60s. Likely to do an update shortly after 9 PM CST,
along with the CWF evening update to lower rain chances
overnight.
&&
.SHORT TERM...
(This evening through Friday night)
Issued at 250 PM CST Wed Dec 25 2024
A very progressive 500mb pattern will remain in place through
Friday night, and this will result in a series of fast moving
shortwave troughs passing through the region. The first of these
features is currently sliding through the Gulf South and will
continue to produce a band of showers and thunderstorms.
Fortunately, the risk of severe weather and heavy rainfall is
diminishing with this system, and most of the rainfall should be
dissipated by this evening. At most, some light scattered rain
showers will persist through the overnight hours. This is
reflected by overnight PoP values of 20 to 30 percent. East-
southeast flow will persist and some weak decoupling of the
boundary layer will allow for largely overcast skies to persist
through the overnight hours. However, boundary layer winds should
remain just high enough to keep much in the way of fog from
developing later tonight into tomorrow morning. With high
dewpoints still in place, temperatures will also not cool much
with readings only dipping into the upper 50s and lower 60s.
Tomorrow will see a weak shortwave ridge and a slight increase in
upper level subsidence pass through the area. The end result will
be continued lower rain chances of 20 to 30 percent through the
day. Deep layer east-southeast flow will continue to advect in a
warm and humid airmass and this will allow temperatures to be a
good 15 degrees above average in the low to mid 70s. These warm
and humid conditions will persist into tomorrow night resulting in
lows only dipping into the low to mid 60s. Boundary layer winds of
20 to 25 knots will keep most dense fog once again at bay, but
cloudy skies and some reduced visibilities due to lighter fog are
expected tomorrow night into early Friday morning.
The next fast moving shortwave trough will move in on Friday. This
system will begin to take on a negative tilt as it passes through
the Lower Mississippi Valley, but the latest guidance suggests
that the best forcing will remain displaced to the north of the
forecast area. Thermodynamic support is questionable due to weak
mid-level lapse rates of around 5.5C/km, so it would take a
substantial amount of deep layer forcing to overcome these
limitations and produce strong to severe storms on Friday. At this
time, it looks like that forcing will more situated along and
north of the I-20 corridor. Across our forecast area, a weaker
convective line of showers and thunderstorms is expected to impact
the area. The strongest convection would be across portions of
southwest Mississippi and inland portions of the Florida Parishes
where gusty winds and small hail could occur. Surface temperatures
will remain warmer than average as southeast flow persists with
highs easily rising into the mid to upper 70s and lows only
dipping into the lower 60s. Again, low stratus is more likely than
fog at this point in time given the strong boundary layer flow of
25 knots currently expected to be in place.
&&
.LONG TERM...
(Saturday through Tuesday night)
Issued at 250 PM CST Wed Dec 25 2024
No big changes in the overall progressive 500mb pattern are
expected through the long term period. A stronger shortwave trough
axis will sweep through the region on Saturday, and a review of
both thermodynamic and dynamic parameters indicate that this will
be the most likely day to see strong to severe thunderstorm
activity impact the region. The area will be in a region of strong
upper level difluence and very favorable jet dynamics, and the end
result is that effective bulk shear will be in the 40 to 50 knot
range. This will combine with higher MLCAPE values of around 1000
to 1500 J/KG Saturday afternoon to produce a line of thunderstorms
along a surface based cold front that is expected to form in
conjunction with the trough axis as it moves through Texas and
into Louisiana. The main concerns will be hail and strong damaging
winds on Saturday, but enough helicity will be in place to support
an isolated tornado threat. Highs will climb into the low to mid
70s on Saturday before the front moves through and bring cooler
and more stable air to the region for Sunday and Monday. However,
little in the way of cool air advection will accompany this
frontal passage and values will remain 5 to 10 degrees above
average.
The next feature is expected to slip through the region on
Tuesday, but this is currently expected to be a very shallow
trough that will only bring an isolated threat of showers to the
area due to a lack of sufficient moisture return and limited
forcing. Temperatures will be little changed with readings still
averaging 5 to 10 degrees warmer than average.
&&
.AVIATION...
(06Z TAFS)
Issued at 1126 PM CST Wed Dec 25 2024
In the near term, concerns will be with low ceilings and/or
visibilities, with most terminals already reporting IFR ceilings.
KHUM currently near field minima, with traffic cams around the
Houma area showing patches of fog as well. Main question is
whether boundary layer winds will mix enough to keep a low stratus
deck in, rather than dense fog. Expect IFR or lower conditions
through mid to late morning at most or all terminals, with at
least some threat of conditions at field minima. Even if fog
doesn't occur, don't anticipate conditions improving to even MVFR
until 16z or so.
Second concern will be the potential for TSRA toward the very end
of the forecast period. Some convection allowing models are
showing potential for a line of TSRA over western Louisiana in the
00z-06z Friday time frame, with storms weakening as they approach
our western terminals around 06z. If storms hold together longer
than expected, the 12z TAF package will need to address that for
at least KBTR and KHUM.
&&
.MARINE...
Issued at 250 PM CST Wed Dec 25 2024
Prevailing onshore flow will continue through Saturday with winds
generally remaining in the 10 to 15 knot range. However, periods
of stronger winds are expected to develop both tonight and
tomorrow night over portions of the outer Gulf waters. These
stronger winds will prompt the issuance of small craft exercise
caution headlines. A weak front will slip through Saturday night,
and winds will briefly shift offshore Sunday into Sunday night.
However, winds will turn back to an onshore component on Monday as
a surface ridge slides to the east.
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 55 68 61 73 / 40 30 70 80
BTR 60 72 64 75 / 30 30 60 70
ASD 58 70 61 75 / 60 30 40 60
MSY 60 71 64 76 / 50 20 30 50
GPT 55 66 61 70 / 70 20 40 50
PQL 54 67 60 72 / 70 20 30 50
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&
$$
SHORT TERM...PG
LONG TERM....PG
AVIATION/UPDATES...RW
MARINE...PG
Source:
LIX issues Area Forecast Discussion (AFD) at Dec 25, 11:43 PM CST ...New UPDATE, AVIATION...---------------
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