LIX issues Area Forecast Discussion (AFD) at Sep 5, 6:54 PM CDT ...New AVIATION...392
FXUS64 KLIX 052354
AFDLIX
Area Forecast Discussion
National Weather Service New Orleans LA
654 PM CDT Thu Sep 5 2024
...New AVIATION...
.SHORT TERM...
(This evening through Friday night)
Issued at 338 PM CDT Thu Sep 5 2024
Heavy rain fell over much of the Flash Flood Watch today with some
locations seeing 3 to almost 5 inches of rain during the morning
hours. Most of the heavy rain fell in the watch area as well and
lighter amounts were on the outside. With that we will not make
any adjustments to the current watch in area or length.
BLUF - We are not done yet. We are currently in a lull but it
appears likely additional heavy rain will impact much of the
region over the next 36 hours. Locally heavy rain would begin to
move back into the area as early as a few hours after 5/6z with
heavy rain expected to impact both the Baton Rouge and New Orleans
metros around rush hour tomorrow morning. Depending on how things
play out there could be significant impacts if the amount of rain
some models keep wanting to advertise occur and occur in the wrong
areas.
Now there are some rather large discrepancies leading to some
questions and thus not as high of confidence in the forecast as we
would like. Many of the CAMs are just about sold on coastal
convection with a sharp gradient south to north. Problem is with
the CAMs they can often get convection going and then it takes
control of everything the convection dictates what else will
develop and ignore some or more of the synoptic influence. Global
models and other mesoscale models are not quite as locked in on
coastal convection and have a band of much heavier rain from
southwest to northeast across the middle of the CWA. Honestly this
appears to be a better solution and looking at track record with
what has occurred over the last 2-3 days, we adjusted the
forecast and heavily blended the GFS with the NBM.
Biggest feature that looks like will dictate how things evolve is
the deep and digging L/W trough over the Hudson Bay with the
trough axis through the Upper MS Valley and into the central
Plains. Even though most of this will stay well north and move
east of the area as it digs into the Great Lakes and OH Valley
and towards the Mid Atlantic and Northeast Atlantic coasts.
However the massive ridge to the west will amplify with the ridge
axis well north through western Canada. In response there will be
piece of energy that breaks off the trough and surges due south
across the Plains and towards the southern Plains and northwestern
Gulf coast. This is going to provide quite a bit of support to our
northwestern Gulf low. At the same time the jet stream will also
intensify across the Lower MS and TN Valleys and this will provide
a very strong and enhanced outflow channel to the northeast. This
is all likely going to help deepen the sfc low over the Gulf. All
that said this is what we would see in late November through
March, an extra-tropical system and that is what this is going to
likely act like. So the typical tropical characteristics that we
see likely won't happen and the synoptic features should have a
much greater say in the rainfall production and placement and that
is leading to a blend of the GFS and NBM.
Most ingredients remain in play. Moisture obviously is still well
entrenched over the region with PWs from 2.35 to 2.6". We already
have some diffluence and good divergence aloft, and LL and
moisture convergence is expected to increase overnight.
As the sfc low slowly works east overnight and tomorrow we expect
convection to impact the area once again associated with the
inverted trough stretching to the northeast from the sfc low. As
the support dives into the backside this sfc low may slow down
even more and this could prolong the rain potential into Saturday
as there may not be anything to kick this system out. With that
the inverted trough will slowly move across the region tomorrow
and this could provide a slow moving and rather heavy band of rain
across the region. If the sfc low is able to stay much closer the
coast it may still deepen considerably but could be far enough
east to kick out a little faster but this would likely lead to
another band of even heavier rain along and just to the north of
the track of the sfc low. This could lead to a rather extreme rain
even over coastal portions of the CWA if the sfc low is along or
even just north of the coast. /CAB/
&&
.LONG TERM...
(Saturday through Wednesday night)
Issued at 338 PM CDT Thu Sep 5 2024
Well advertised cold front will push southward but will stall near
or over the coastal waters. Depending on where exactly the boundary
stalls, showers and storms should mostly be confined to the coastal
waters. Thanks to the drier continental air being pushed by the
front, dew points will get into the 60s. So in particular, low
temperatures will be below average this weekend with lows being in
the low to mid 60s possible especially as you move further north
inland. Temperatures will still be warm during the daytime hours
with highs in the 80s but will have a slight warming trend as we get
into early next week. -BL
&&
.AVIATION...
(00Z TAFS)
Issued at 637 PM CDT Thu Sep 5 2024
Low pressure continues over the western Gulf of Mexico this
evening. Bands of rain wrapping around the circulation continue to
affect most terminals, although areal coverage has diminished a
bit over the last few hours. There's been very little lightning
over the last 3 hours anywhere near the area, and am not
initializing terminals with mention of thunder at any site. Did
not include any mention of thunder until mid-morning Friday, and
even that may be too soon. That's not to say we won't have any
impacts. There is a bit of dry air in the mid levels, so in most
cases, ceilings will either be somewhere around FL010 or near
FL100. So rapid changes between VFR and IFR can be encountered.
Trend during the overnight hours should be to see the lower
conditions become predominant. At this point, it appears the heavy
rain threat, and more consistent low visibilities, may hold off
until mid-morning Friday. Generally, low conditions expected to
continue through at least Friday evening.
&&
.MARINE...
Issued at 338 PM CDT Thu Sep 5 2024
Small craft headlines has been extended for all zones through the
night, mainly for frequent gusts. The sfc low continues to slowly
take shape in the northwestern Gulf and depending on how it
evolves will the impacts and severity of impacts. If the sfc low
deepens and moves more east to east-northeast the pressure
gradient will tighten and winds will increase once again tomorrow.
As it moves east strong winds will move in out of the north and
northwest behind this with moderate to high end small craft
advisory conditions developing. If the low takes more of a
southeast motion and/or doesn't deepen as much then the winds will
continue to slack off tomorrow but strong offshore winds could
still impact western portions of the coastal waters Saturday.
Minor coastal flooding continues along east facing shores and even
the western portions of lakes Maurepas and Pontchartrain.
Waters will remain unsettled with numerous showers and storms
through Saturday morning and will result in locally higher winds
and seas. A frontal passage will bring more offshore winds by the
weekend and potential headline criteria again. /CAB/
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 70 77 66 83 / 90 90 30 10
BTR 74 81 70 86 / 100 100 40 20
ASD 72 79 69 83 / 90 100 70 30
MSY 74 81 71 82 / 90 100 70 40
GPT 73 79 68 82 / 80 100 70 40
PQL 73 83 69 85 / 80 100 70 40
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Small Craft Advisory until 7 AM CDT Friday for LAZ068.
Flood Watch through Saturday morning for LAZ046>048-056>060-
064>070-076>090.
Coastal Flood Advisory until 7 AM CDT Friday for LAZ058-069-070-
076-078-084.
GM...Small Craft Advisory until 7 AM CDT Friday for GMZ530-532-534-
536-538-550-552-555-557-570-572-575-577.
MS...Flood Watch through Saturday morning for MSZ083>088.
Coastal Flood Advisory until 7 AM CDT Friday for MSZ086.
GM...Small Craft Advisory until 7 AM CDT Friday for GMZ532-534-536-
538-550-552-555-557-570-572-575-577.
&&
$$
SHORT TERM...CAB
LONG TERM....BL
AVIATION...RW
MARINE...CAB
Source:
LIX issues Area Forecast Discussion (AFD) at Sep 5, 6:54 PM CDT ...New AVIATION...---------------
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