River Flood Warning 110, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
343 PM CDT Mon Aug 26 2019

.SHORT TERM...A upper level low centered over south Louisiana
will continue to support scattered convective activity through
tomorrow as it slowly transits eastward along the northern Gulf
coast. This upper level low will bring increased vorticity and
resultant upper level lift to the area, and this will provide a
more conducive environment for thunderstorm development.

A typical seabreeze cycle is expected to remain in place in the
low levels, and this will be the main driver of where convection
develops over the next 36 hours. Ongoing convection will gradually
diminish in intensity through the evening hours, and have mainly
dry weather in the forecast by late evening. However, the
convective activity will increase in coverage across the coastal
waters as a weak landbreeze serves as a focus for convective
development. The seabreeze should begin to form by mid- morning
tomorrow, and convection will gradually develop further and
further inland through the late morning and afternoon hours
tomorrow. Have a near average 30 to 40 percent chance of rain in
the forecast for tomorrow to reflect this risk. The temperature
profile will also be closer to normal as highs climb back into the
lower 90s.

A vigorous cold front for late August will sweep into the region
on Wednesday. Strong low level convergence along the front along
with continued higher than average omega aloft will support
thunderstorm development along and ahead of the frontal boundary.
Some of the thunderstorms could be on the stronger side as
temperatures aloft begin to cool, lapse rates increase, and some
drier air entrains into the deeper updrafts. Strong wind gusts
would be the primary concern from any deeper convective cells that
develop Wednesday afternoon. By Wednesday night, strong dry air
advection and increasing subsidence aloft will begin to take hold
of the area. Precipitable water values will fall below 2 inches,
and the main threat of convection will shift into the offshore
waters.

.LONG TERM...Dry air advection will continue to feed into the area
on the back of deep layer northerly flow on Thursday and Friday,
and expect to see mostly clear skies and very low convective risk
of less than 20 percent. Precipitable water values will be well
below average at an inch or less. With clear skies and lower
dewpoints in place, a larger than average diurnal range can be
expected. Overnight lows are forecast to dip into the middle to
upper 60s across the northern half of the forecast area
Friday morning and in the upper 60s on Saturday morning. Highs
will warm into the upper 80s and lower 90s, but the low humidity
values will allow for cooler heat index readings only rising into
the middle to upper 90s. Given the time year, a couple of fairly
pleasant days are on tap.

The respite from normal August weather will be brief as a return
to deep layer easterly flow and more normal precipitable water
values in excess of 2 inches are expected by Saturday afternoon.
These conditions will persist through Monday as a weak inverted
trough axis slides through the Gulf of Mexico. Seabreeze cycle
dominated convection will be possible each day with offshore
convection developing in the overnight and early morning
hours spreading inland with the seabreeze during the late morning
and afternoon hours each day. As the inverted trough passes
directly over the area on Sunday, a surge of deeper tropical
moisture and higher precipitable water values should lead to
slightly more convective development than expected on Saturday and
Monday. Have went with higher than climatological average POP of
50 to 60 percent for Sunday. Otherwise, POP of 30 to 50 percent is
expected on both Saturday and Monday. Temperatures will generally
be near average with highs near 90 and lows in the middle to
upper 70s.

&&

.AVIATION...VCTS wording is in place at all of the terminals
through around 00z to reflect the ongoing risk of scattered
thunderstorms that could pass near the terminals. MVFR ceilings
ranging from 2000 to 3000 feet can be expected through the evening
hours. Most of the terminals will have prevailing VFR conditions
during the overnight hours, but KMCB and KHDC could see ceiling
fall into IFR range. At KMCB, some patchy fog may also push
visibilities into MVFR range around daybreak tomorrow. By 15z, a
mix of scattered to broken ceilings ranging from 2000 to 3000 feet
should develop at all of the terminals as convection begins to
redevelop.

&&

.MARINE...South to southwest winds of 10 to 15 knots and seas of 1
to 3 feet will persist over the coastal waters through tomorrow
night as a broad high pressure system remains parked over the
eastern Gulf. A cold front is expected to then move through the
waters Wednesday into Wednesday night, and winds will shift to the
northwest and then the north at 10 to 15 knots. Winds should
continue to veer to the northeast and then the east from Thursday
through Saturday, and seas of 1 to 3 feet will persist. The risk
of thunderstorms will also decrease on Thursday and Friday as
weak high pressure builds in from the north.

&&

.DECISION SUPPORT...

DSS code: Yellow.
Deployed: None.
Activation: None.
Activities: Marginal to Slight risk of excessive rainfall.

Decision Support Services (DSS) Code Legend
Green  = No weather impacts that require action.
Blue   = Long-fused watch, warning, or advisory in effect or high
         visibility event; Marginal risk severe or excessive rain.
Yellow = Heightened impacts with short-fused watch, warning or
         advisory issuances; radar support for slight risk severe
         or excessive rain.
Orange = High Impacts; Enhanced risk severe; nearby tropical
         events; HazMat or other large episodes.
Red    = Full engagement for Moderate to high risk of severe and/or
         excessive rainfall, or direct tropical threats; Events of
         National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  72  92  73  89 /  20  30  30  60
BTR  75  92  75  91 /  10  40  30  70
ASD  75  92  75  91 /  30  30  30  60
MSY  77  92  78  91 /  20  40  30  60
GPT  76  89  76  90 /  40  30  30  60
PQL  74  90  74  92 /  50  30  30  60

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

PG

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