LIX issues Area Forecast Discussion (AFD) at Nov 18, 6:54 AM CST ...New AVIATION, MARINE...
009
FXUS64 KLIX 181254
AFDLIX
Area Forecast Discussion
National Weather Service New Orleans LA
654 AM CST Mon Nov 18 2024
...New AVIATION, MARINE...
.SHORT TERM...
(Today through Tuesday)
Issued at 515 AM CST Mon Nov 18 2024
Quiet night for the region with some patchy fog in a few areas
trying to develop and today will likely remain uneventful most of
the time but conditions could change rapidly late this afternoon
with numerous impacts tonight and into tomorrow morning. There is
a small risk of strong to severe storms but the great concern
looks to be locally heavy rain.
Currently we have the now remnants of Sara right along the Mexican
(western Yucatan) coast while a strong s/w is beginning to push
northeast across NM and west TX. Mid lvl ridge remains centered over
the eastern Gulf with the ridge axis extending NNW into the Mid MS
Valley. Aloft the sub-tropical jet is working across Mexico into TX
and the southern Plains. At the sfc high pressure was dominating
much of the eastern CONUS centered just offshore of SC/GA/FL. The
placement of the ridge both in the mid lvls and low lvls are already
starting to drive moisture north. GOES16 TPW product is quickly
showing PW racing north from Sara. At 3z GOES estimated TPW in the
central Gulf only at .9" but a little more than 100 miles south TPW
was already approaching 2". This will continue to race north as the
western TX s/w lifts to the NNE and the ridge remains just to the
east both which will help to drive deep moisture north into the
north-central Gulf. If this moisture does surge north as expected
then PWs this afternoon and evening could easily be over 2" and even
climb abv 2.25" (some models are even indicating PWs approaching
2.5). This would easily be a record value for today. Moisture is not
going to be a problem and locally heavy rain could easily become a
big problem however, does the environment tap into that potential
The s/w moving into the southern Plains is going to quickly lift
more north through the day and into the evening through the central
Plains and then into the Upper MS Valley over MN overnight tonight.
Overall that would generally suggest that most of the lift is going
to be well removed to the northwest and north from our but with the
ridge over the eastern Gulf we will likely see some of the mid and
low lvl remnants from Sara as well which could easily make up for
that and that is kind of what the models are showing with mid lvl
winds actually increasing this evening. The LL winds respond as
well. We will not necessarily have the greatest LL jet setup but
there will be a persistent southerly winds around 25-35 kts setting
up later today and through much of the night across the area and
well south into the Gulf. Aloft the sub-tropical jet will set up
from Mexico through the ARKLATEX and towards the Ohio Valley. This
doesn't quite put the area under the RRQ but it still looks like
overnight there will be decent upper lvl diffluence in place given
the jet placement and the ridge to the southeast. Given this
the dynamics are adequate and the kinematics are quite favorable.
As for the thermodynamics, instability will be a little lacking
however we will warm up into the 70s and lower 80s today along with
moisture increasing significantly and this will at the least keep the
region conditionally unstable with a moist adiabatic lapse rate this
evening and overnight. K Index values look to range from abv 36 to
near 40 and these values tend to suggest a heavy rain/efficient rain
scenario. The problem is that with the main s/w quickly lifting
almost due north today and tonight there is no real trough axis
pushing through the area and thus we remain conditionally unstable
all night. This is a double edge sword. First the lack of strong
forcing should limit the risk for severe but with no real push the
atmosphere won't get cleared out quickly leading to what storms
develop moving SW to NE and likely training over the same area. The
biggest drive east for storms would be cold pooling but given the
setup over the area cold pooling will not be favorable to develop.
The best chance for cold pooling would be in a line of storms
currently over western OK and TX can continue to develop and surge
east through the day and tonight. More on that in a little while.
The anomalous moisture expected over the region combining with
increasing but not overly strong mid lvl forcing (combination of the
s/w and some energy from Sara), an increasing LL wind field
providing some LL convergence (but not optimal) while under upper
lvl diffluence (not truly optimal either) with a conditionally
unstable environment all point to a decent potential for very
efficient rain leading to isolated to possibly scattered flash
flooding. Isolated to scattered light showers could begin late this
afternoon but we probably will remain mostly rain free until early
this evening as the forcing starts to increase. Everything looks to
really come together over the eastern or more so southeastern half
of the CWA during the late evening and especially overnight hours
where storms will likely begin to increase in coverage and intensity
while moving SW to NE with not much of a push east. If this does
occur storms will train over some areas with rain quickly adding up.
Widespread 1 to 4 inches of rain with locally higher amounts is
expected with the heaviest rain likely along and southeast of a line
from near Houma to Tylertown. There is a chance that we could see a
few bands of very heavy rain where rainfall totals go from under an
inch to 4 possibly 6 inches or more in a very short distance.
Exactly where that occurs can not be said at this time and likely
won't be known until we start seeing where storms initiate.
PWs abv 2.25 this time of the year is very concerning along with the
potential of this occuring overnight which would enhance the risk as
overnight flash flooding is the greatest risk due to lack of
recognition, especially for drivers. However, the question is will
we be able to truly tap into that as there are a few scenarios that
could completely derail the forecast.
One is probably the least likely is the cold pool scenario. The line
over TX is what we are watching, if that line can develop a decent
cold pool but not let the cold pool run out ahead of it today this
line could eventually approach the western portions of the CWA late
this afternoon/early evening and would have the best chance of
continuing to surge east during the evening and overnight hours.
That would be one of the better case scenario as it could push east
through the area keeping the risk of training down some and likely
not completely realizing the rain potential. This scenario is the
least likely to occur but one other scenario that could legitimately
develop and keep the impacts down considerably is, Gulf convection.
If storms develop over the Gulf and continue to increase in coverage
over the coastal waters that would greatly reduce the risk over the
land areas as it would cut off the moisture source and storms would
become anchored over the water. This has a shot of occurring and when
it does that is usually because the storms become anchored to the
better instability however that is usually because there is a big
difference in the amount of instability over the water vs land and
that may not quite be the case.
As for the severe risk. The biggest negative is the s/w lifting
out so far to the north with the area lacking a very strong punch.
The other issue is limited instability. Lapse rates will be very
shallow and with the timing over most of the convection expected
to be overnight, the risk for severe storms seems quite limited.
That said the slightly increasing winds at h85 will provide
adequate LL shear and there appears to be a lot of veering in the
LL. If any thunderstorm can tap into that potential and not be
disrupted by any other storm then we can not rule out a few
tornadoes. That said the greatest risk feels like the heavy rain
at this time.
Rain should move out tomorrow morning with the cold front finally
pushing through tomorrow afternoon. Drier air will initially
filter in behind the front but the cold air will still be lagging
back likely not moving in till Wednesday but it will move in
finally providing that Fall feeling. /CAB/
&&
.LONG TERM...
(Tuesday night through Sunday)
Issued at 515 AM CST Mon Nov 18 2024
Much of the forecast focus is on the first 36 hours of the fcst
but still need have some things to discuss in the long term as we
will finally get that real cold front. The models are in rather
good agreement with the cold front and fall finally showing its
face for the 2nd half of the week and through the weekend. NBM
looks too warm again for the morning lows with the deterministic
NBM running ATA the NBM75 for multiple days. With that we have
adjusted the morning lows for Thursday through Sunday down a few
degrees using a blend of the NBM and NBM50.
As mentioned earlier that front will move through late tomorrow with
dry air quickly moving in behind it but the colder air will not get
into the region till late Wednesday. We will see another push of
cooler air Friday as well. Winds will remain breezy Wednesday and
Thursday nights likely keeping the area from fully realizing that
cooling potential due to mixing but Friday night high pressure may
finally build in enough with winds slacking off, very dry air over
the region and probably clear skies. That seems to be the best night
for radiational cooling and could provide us our coolest morning of
the season with frost possible across the northern half of the cwa.
We begin to see temps moderate on Sunday and into Thanksgiving week
and possibly rain returning early to mid week. /CAB/
&&
.AVIATION...
(12Z TAFS)
Issued at 605 AM CST Mon Nov 18 2024
VFR conditions will continue through midday at least but after 18z
low cigs will likely begin to develop. This will occur as moisture
continue to stream in from the Gulf. Cigs will likely begin to
fall to around 2-3k ft this afternoon and then convection will
begin to develop probably around or after 00z with heavier rain
expected after 2z. The stronger storms will lead to IFR and
possibly LIFR vsbys due to heavy rain. Cigs could fall as low as
5-800 ft leading to IFR cigs. /CAB/
&&
.MARINE...
Issued at 605 AM CST Mon Nov 18 2024
Small craft advisory added to the waters east of the MS River as
winds will likely be stronger later today but especially
overnight. Front will move through tomorrow and winds will relax
as the front approaches and is initially on the light side as
winds come around to the northwest but once colder air moves in
Wednesday strong offshore winds will develop. /CAB/
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 81 67 80 52 / 0 80 60 10
BTR 86 70 84 57 / 20 90 40 0
ASD 82 71 82 57 / 10 90 90 10
MSY 83 73 82 61 / 30 100 80 10
GPT 79 71 78 59 / 10 100 90 10
PQL 84 72 81 59 / 10 100 90 20
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flood Watch from 6 PM CST this evening through Tuesday morning
for LAZ039-058>060-064>071-076>082-087>090.
Coastal Flood Advisory from 6 PM this evening to noon CST
Tuesday for LAZ058-060-066>070-076>078-080-082-084-086-087.
GM...Small Craft Advisory from 6 PM this evening to 6 AM CST Tuesday
for GMZ532-534-536-538-557.
Small Craft Advisory until 6 AM CST Tuesday for GMZ550-552-555-
570-572-575-577.
MS...Flood Watch from 6 PM CST this evening through Tuesday morning
for MSZ077-083>088.
Coastal Flood Advisory from 6 PM this evening to noon CST
Tuesday for MSZ086>088.
GM...Small Craft Advisory from 6 PM this evening to 6 AM CST Tuesday
for GMZ534-536-538-557.
Small Craft Advisory until 6 AM CST Tuesday for GMZ552-555-570-
572-575-577.
&&
$$
SHORT TERM...CAB
LONG TERM....CAB
AVIATION...CAB
MARINE...CAB
Source: LIX issues Area Forecast Discussion (AFD) at Nov 18, 6:54 AM CST ...New AVIATION, MARINE... (https://mesonet.agron.iastate.edu/p.php?pid=202411181254-KLIX-FXUS64-AFDLIX)
---------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!