Severe Thunderstorm Warning 90, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
110 PM CDT Wed Aug 17 2022

.AVIATION...18Z TAF Package...Terminals are generally in VFR
status but if the cu is directly over the ASOS a few sites may
report MVFR cigs around 2k ft butit trully ius scattered out
there. Convetion will likely hold off most of the day and may
start to impact the region later afternoon or more so early
evening. Outside of convection VFR conditions should persist for
most terminals but can't rule out some tempo MVFR cigs around 2-3k
ft. MCB again has the potential for reduced vsbys between 10-13z
and low cigs. /CAB/

&&

.PREV DISCUSSION... /issued 615 AM CDT Wed Aug 17 2022/

AVIATION (12z TAFs)...
VFR conditions will be the prevail condition at all terminals
through this taf cycle. There could be some convection that forms
near MCB after 00z, and PROB30 groups have been used with timing
of when this activity should occur for each site.

PREV DISCUSSION... /issued 400 AM CDT Wed Aug 17 2022/

SHORT TERM (Now through Thursday Night)...

After some earlier convection over Plaquemines Parish and adjacent
waters, mostly quiet conditions have evolved this morning. The
overall current pattern is fairly interesting across the Lower
Mississippi River Valley. A surface "frontal" boundary resides
generally along and north of the I20 corridor. The front has
become parallel to the H5 northwesterly flow, which typically is
dry. Indeed, the 00z LIX RAOB does show quite a bit of mid and
upper level dry air. However, this time of year impulses along
this flow often utilize any boundary layer moisture available.
That is what we are currently seeing with a thunderstorm complex
riding down the front and courtesy of an upper level impulse
within the northwesterly flow from north Arkansas. This feature in
particular likely will not have any impacts on our region as
guidance suggests it should weaken as it approaches later this
morning or early afternoon. However, the outflow may help nudge
the surface boundary a bit closer to our region late this
afternoon or early evening allowing for convective development to
occur, especially north and east of a line from Woodville to
Hammond to Shell Beach. Timing certainly seems a bit later than
normal. Surface winds should help keep the sea breeze pinned along
the coast so no early afternoon convection expected along I10 in
MS. Likewise the westerly flow over the LA Parishes looks to limit
at least slightly the propagation of the Lake breeze. So, as the
outflow from the early morning complex moves in, the atmosphere
could be prime (no overturning) to allow for some at least
isolated more robust convection to develop. Especially if these
surface features collide. A strong to severe storm or two cannot
be ruled out with strong winds and perhaps a few small hailstones
or two not completely out of the question, especially along the MS
Gulf Coast.

With the sea breeze getting pinned closer to the MS Gulf Coast,
expect little in the way of relief from heat this afternoon...at
least until convection develops closer to evening. Because of this
went ahead and placed portions of the MS Gulf Coast Counties in
heat advisories. Max ApT's drop off the further west you go so
held off for SE LA, but a short fused NPW cannot be ruled out for
heat during the mid/late AM update.

As the front (again motivated to move closer to our CWFA thanks to
stronger outflow propagation from convection) there will be an
enhancement of shower and thunderstorm activity through the
remainder of the short term period. The front aided by modest H5
impulses from time to time will help generate a few opportunities
for rainfall with the best potential aligned with the diurnal
cycle. Of course hydro concerns will be possible, especially in
the urban or more flood prone areas that get multiple storms in a
short time. (Frye-28)

LONG TERM (Friday through Tuesday)...

Going into the upcoming weekend the upper level synoptic pattern
still remains interesting. The subtropical high over the western
Atlantic tries to nose into the region setting up an active
southwesterly flow aloft. Upstream over the central United States
a positively tilted trough will begin to dig southward in the the
lower Missouri River Valley by late Friday and into Saturday.
Locally, rain chances look to remain elevated especially during
max insolation across the land based zones. Again, any ripple in
the mid levels within the flow will hep enhance coverage for
thunderstorms (again hydro concerns possible in those flood prone
areas cannot be ruled out). At the surface, the residual front
pretty much remains in place into the weekend. Eyes tend to catch
the tropical features NHC is highlighting in the latest TWOs as
it moves northwest into the Bay of Campeche and eventually toward
the Rio Grande Valley. Globals vary on what exactly happens to
this feature. One thing they tend to agree on is it appears to be
very weak so any development should be limited. The ECM takes
much of the moisture northwest into northern Mexico and into TX.
The latest runs of the GFS brings the tropical moisture plume
northward...is absorbed by the front/parent upper trough spreading
southward out of the lower MO or Mid MS River Valley and carries
the moisture north and eastward within the southwest flow aloft
across much of the southeast. Confidence is low in terms of where
this moisture will end up, however, taking out the disturbance
altogether and there remains higher-end climo POPs given the
active upper flow regime. The Subtropical ridge again tries to
spread westward across the northern Gulf, but models are trending
more and more south with this feature over time, which places our
region on the wetter side again within that active western
periphery.

AVIATION (06z TAFs)...

VFR conditions will prevail at all
of the terminals through the entire forecast period. There could
be some convection that forms near MCB after 03z, and VCTS wording
has been put in the forecast to reflect this risk. However,
confidence is too low to add a PROB30 or TEMPO group at this time.
PG

MARINE...

A cold front will move southward and stall over or near our local
waters through the rest of the week. Light to moderate winds will
vary in direction from a southerly to a westerly and then
eventually a northerly direction (through more erratic winds will
be possible in and around convection that develops). In the
strongest activity expect locally higher winds and seas along
with frequent cloud-to-water lightning, waterspouts, and brief
heavy rainfall. (Frye-28)

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  71  85  69  85 /  60 100  80  80
BTR  75  89  73  87 /  40 100  90  90
ASD  75  90  73  88 /  50  90  80  90
MSY  77  90  76  88 /  20  90  80  90
GPT  75  89  74  87 /  50  90  80  90
PQL  74  90  73  87 /  50  80  80  90

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...Heat Advisory until 6 PM CDT this evening for MSZ077-080>082.

GM...None.
&&

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