Special Marine Warning 372, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
355 AM CDT Tue Jun 22 2021

.SYNOPSIS...

A weak frontal or outflow boundary appears to be rather close to
the Interstate 10 corridor early this morning. At least pressure
fields appear to support that idea. Really not much difference in
surface conditions on either side of the front with temperatures
and dew points in the 70s. Water vapor loops indicate a shortwave
from the Great Lakes states southward into Arkansas and north
Texas. Radar indicates one complex of thunderstorms exiting our
eastern coastal waters and the next one near the Sabine River
basin.

&&

.SHORT TERM...

Airmass near and south of the boundary remains extremely moist, as
the 00z LIX sounding showed a precipitable water value of 2.05
inches. Looking at the forecast NAM BUFR soundings from the 00z
run for New Orleans (and supported by 00z GFS BUFR soundings),
precipitable water values will remain in the 2.0-2.2 inch range
during the afternoon hours both today and Wednesday, before
dropping below 2 inches for Thursday.

The tail end of the shortwave in Arkansas and Texas is expected to
impact this moist airmass today, with scattered to numerous
showers and storms anticipated, primarily to the south of the
boundary. While it doesn't appear that widespread heavy rain will
occur, much of the area in the current Flash Flood Watch will have
problems with any prolonged period of heavy rain, and will leave
the watch in place.

On Wednesday, while the very moist airmass remains in place,
there's not really any significant lifting mechanism to trigger
organized convection. Convection on Wednesday is more likely to be
diurnally driven than anything else, and expect areal coverage to
be more limited, with a pulse type life cycle. Will not extend the
Flash Flood Watch into Wednesday at this time.

As noted above, precipitable water values drop off somewhat beyond
tomorrow. No strong lifting mechanism on Thursday, either, and for
the first time in quite a few days, precipitation chances will
fall below 60 percent areawide.

High temperatures have been running above guidance, even with all
the rainfall the last few days, and will trend forecast highs
toward the upper end of the guidance envelope in the short term,
bumping up the NBM values by a degree or two. 35

&&

.LONG TERM (Friday and beyond)...

A gradual drying trend will take hold of the area by the latter part
of the week as a cold frontal boundary washes out over the area and
an upper level ridge over Texas inches its way eastward by Friday.
Another shortwave trough over the northern plains swings down with
an associated cold front into the southern plains.  Meanwhile a weak
disturbance over the gulf will merge with the cold front bringing
increased rain chances by Sunday. Front will stall over the area
bringing scattered to numerous showers and thunderstorms into the
area for the rest of the forecast period. Temperatures will rebound
into the lower 90s by the end of the week as upper level ridging
builds into our west.

&&

.AVIATION (12z TAF package)...

Most terminals with VFR conditions at this time. The exceptions
are KBTR and KHDC, where IFR ceilings have developed in the last
hour or so. Don't really expect widespread IFR conditions this
morning, but most terminals will likely develop MVFR ceilings by
mid-morning. Convection should get going prior to 18z, and will
try to time highest threat with a couple hours of TEMPO TSRA,
carrying SHRA and/or VCTS otherwise. Likely to see IFR
visibilities and possible gusts to 30 knots or so with any TSRA
that directly impact a terminal. Should see a diminishing trend
of convection toward 00z, with most all terminals returning to
MVFR/VFR shortly after 00z. 35

&&

.MARINE...

Main marine concern over the next few days will be the threat of
thunderstorms. It's possible that the outer open waters could see
sustained winds around 15 knots this afternoon, but not really
anticipating any wind-related headlines over the coastal waters
beyond today through the end of the week. 35

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  85  72  88  72 /  60  20  50  10
BTR  87  74  90  74 /  80  30  70  10
ASD  87  74  90  74 /  90  40  70  20
MSY  88  78  90  77 /  90  30  70  20
GPT  86  75  87  75 /  90  40  70  30
PQL  85  73  87  73 /  90  40  70  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch through this evening for LAZ056>061-063>070-
     075>078.

GM...None.
MS...Flash Flood Watch through this evening for MSZ077-080>082.

GM...None.
&&