228
FXUS64 KLIX 172036
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
336 PM CDT Sat Aug 17 2024

...NEW SHORT TERM, LONG TERM, MARINE...

.SHORT TERM...
(This evening through Monday Night)
Issued at 336 PM CDT Sat Aug 17 2024

Another hot day across the CWFA with most if not all sites running
at heat advisory criteria this afternoon. And if they haven`t
gotten there they will...outside of maybe MCB? Those lucky ones
are far and few...(although this forecaster questions whether or
not 105 degree heat index values is really lucky vs 108+?). After
a few low topped showers earlier today, a mostly dry scan on
KHDC. This will gradually change later this evening as a few
isolated to scattered showers and thunderstorms develop, which
will provide at least a few of us with some heat relief closer to
sunset or perhaps even shortly after. The best potential for
activity will be along and north of the I10 corridor with the main
focus on interior south MS and MS Gulf Coast...closer to a
surface boundary we will be following going through much of the
short term period and into the start of the long term. Think most
of this activity will remain rather benign outside of the typical
summer time convection, however, DCAPE is running at or above 1000
J/kg. SBcape from an instability side of things looks to also be
moderate or around 2500 J/kg. Although for this time of year
instability could be better. That said, a more robust updraft may
have the potential to end with a strong wind gust or two out
there...again best potential MS both interior and Gulf Coast
through this evening.

Going into Sunday, surprise surprise another hot one. As I
mentioned there will be a surface boundary or a backdoor cold
front that will try to move into the region with the upper level
flow mostly from the north. Along and ahead of this feature, low
level moisture pooling will be able to counter and BL mixing from
strong surface heating...meaning dew points will remain very high.
With that, temperatures are forecast to increase back into the
upper 90s to even above 100 in some places which will result in
heat index values exceeding the 113 degree heat index criteria for
an Excessive Heat Warning...so covered the region with this
headline for Sunday. Now, similar there will be a shot of showers
and storms on Sunday, but again more isolated to scattered in
variety and once again the best chances will be across south MS
and the Florida Parishes later in the evening. Now the difference
in today and Sunday will simply be the higher instability (almost
double that of today with a bit cooler air working into the upper
levels) as well as a slight uptick in wind shear as well, which
is very "interesting" for this time of year. Nonetheless, the
parameters along with robust DCAPE suggest the potential for a
severe wind gusts or hailstone or two in the strongest activity.
Again, coverage appears to still be limited to isolated/scattered.
SPC has delineated a marginal risk but a categorical upgrade to
slight will not be impossible for the far north and eastern
portions of the CWFA if parameters continue to reflect a slightly
higher damaging wind and hail potential respectively.

Quickly, for the short term relied heavily on CAMs. Global QPF
signals have been running relatively high, which is causing
consensus models to over compensate with POP/QPF forecasts. Kept
POPs and QPF manageable based on verification over the last cycle
or two and again weighted today and tomorrow heavily on mesoscale
model data.

By Monday, the surface backdoor cold front will have moved south
across the northern Gulf waters and stretching NW and eventually N
crossing through the middle of Louisiana. The dry northerly flow
will keep the eastern two-thirds of the forecast areas dry aloft
and even some help from mixing some of the drier conditions to the
surface. However, along the boundary out close to the
Atchafalaya, conditions will remain more on the moist side. An
impulse or two on the eastern periphery of the ridge center well
to our west will work with the diurnal cycle as well as the
surface boundary that is stalled under the mean upper level flow.
So, this is enough evidence to keep at least some mention of
convection with again winds and perhaps a small hailstone or two
looking possible in the wider updrafts. Otherwise, heat index
values along and north of 10 look to be below headline
criteria...sadly along and south look to required heat headlines
along with locations closer to surface boundary since those areas
again will hold onto low level moisture a bit longer. (Frye)


&&

.LONG TERM...
(Tuesday through Friday night)
Issued at 336 PM CDT Sat Aug 17 2024

The region will reside under a mostly northerly or northeasterly
flow to start the long term period. The old backdoor front that
stalled out north to south of the center part of Louisiana will
eventually move west as a stronger upper level impulse moves
southward and advances the boundary further away from the region.
Much drier air at the surface can be expected. Although surface
temperatures will still be well above average, the dry surface
conditions will help make things slightly more comfortable. Rain
chances will mostly be offshore closer the stalled surface
trough/boundary so rain chances midweek will be tough to find.
Going into the 2nd half of the week, a mid/upper level low begins
to pinch off from the east coast trough. A weak surface trough
develops and both move west. At the surface our winds will
transition to a more east or southeast direction with time helping
low level moisture creep back into the region. With the proximity
to the upper low and surface trough, POPs will begin to creep
back up as well late in the period. Temperatures late in the
period will remain hot, but there is a bit of a confidence factor
in there depending on timing of convective initiation, which is
unclear at this range. (Frye)

&&

.AVIATION...
(18Z TAFS)
Issued at 1216 PM CDT Sat Aug 17 2024

VFR conditions are largely expected through the cycle. Cannot rule
out some evening convection this evening generally before 06z and
the best potential being for terminals along and north of I10.
Outside of convection, MCB may have limited VIS around sunrise,
especially if rain occurs. Otherwise, light and variable winds
expected. (Frye)

&&

.MARINE...
Issued at 336 PM CDT Sat Aug 17 2024

Overall favorable marine conditions this weekend outside of any
potential nocturnal showers or storms. Naturally, convection will
increase winds and seas locally. Otherwise, a surface front will
eventually push into the local waters to start the new workweek.
Outside of the chance of additional shower and thunderstorm
activity, winds will turn more to the north or northeast Monday
and into Tuesday. Cautionary headlines will be possible early next
week, especially for the MS Sound areas. High pressure will
eventually take back over late in the period and allow winds to
shift back to a more southeasterly direction. (Frye)

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  75  99  74  92 /  20  10  30  30
BTR  80 101  80  96 /  20  10  20  30
ASD  77 100  79  96 /  20  10  30  30
MSY  80  98  80  95 /  10  10  20  30
GPT  78  97  79  96 /  30  10  30  30
PQL  77 101  78  98 /  30  20  40  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Heat Advisory until 7 PM CDT this evening for LAZ034>037-039-
     046>048-056>060-064>071-076>090.

     Excessive Heat Warning from 10 AM to 7 PM CDT Sunday for
     LAZ034>037-039-046>048-056>060-064>071-076>090.

GM...None.
MS...Heat Advisory until 7 PM CDT this evening for MSZ068>071-077-
     083>088.

     Excessive Heat Warning from 10 AM to 7 PM CDT Sunday for
     MSZ068>071-077-083>088.

GM...None.
&&

$$

SHORT TERM...RDF
LONG TERM....RDF
AVIATION...RDF
MARINE...RDF