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Area forecast discussion
National Weather Service New Orleans la
406 am CDT Fri Oct 18 2019

Short term...potential tropical cyclone 16 will move through the
northeast Gulf of Mexico today and tonight. Breezy conditions and
some coastal rain showers can be expected today. Further inland,
overcast skies and cooler than average temperatures will persist.
Highs should only warm to around 70 degrees this afternoon. Strong
easterly flow of around 20 knots should also support some minor
coastal flooding issues, especially along east facing shores.
Temperatures should once again cool into the upper 50s and lower
60s tonight as the low starts moving toward the Florida Panhandle.

In the wake of the departing low tomorrow, strong subsidence and
dry air advection will take hold as high pressure builds into the
region. Clearing skies, lower humidity, and somewhat warmer
temperatures near 80 degrees can be expected. The clear skies and
dry air will allow for strong radiational cooling tomorrow night
with lows dipping back into the upper 50s and lower 60s.

The region will find itself in the right entrance region of an
upper level jet Max by Sunday afternoon. Increased Omega values
combined with an increased onshore flow and weak moisture
advection could promote increased cloud development and possibly
some isolated convection along the Atchafalaya basin Sunday
afternoon. Temperatures should also continue to modify with highs
climbing into the low to mid 80s.

Long term...little change in thinking heading into next week. All
of the model guidance remains in good agreement that a strong cold
front will sweep through the region on Monday. Have kept in high
pop values, and fully expect to see a line of thunderstorms sweep
through during the afternoon and evening hours across southeast
Louisiana and southern Mississippi. This is supported by both
favorable thermodynamic and dynamic support. Cape values should
climb to around 2000 j/kg by the afternoon hours, and lifted index
values of -4 to -7 are expected. The region will also remain in
the right entrance of a strong jet streak and this will support
the development of deeper convection. Helicity values are not
expected to excessive, but effective shear in excess of 50 knots
will support a quasi-linear convective system type of severe
weather event with bowing segments and straight line wind damage
being the main concern.

The front and line of thunderstorms should quickly sweep offshore
Monday night and strong dry air and cold air advection will take
hold by Tuesday. Expect to see clearing skies and decreasing rain
chances from the northwest part of the County Warning Area to the southeast part
of the County Warning Area through the night Sunday night. Some severe convection
could still be impacting parts of coastal Mississippi and coastal
Louisiana as well as the Gulf waters in the evening, but these
thunderstorms should push out of the County Warning Area by Tuesday morning.
Temperatures will be cooler on Tuesday with highs falling back
into the lower 70s and lows dropping into the 50s at most
locations Tuesday night. The cool and dry conditions will persist
into Wednesday as the high pressure settles over the region.

By Thursday, a broad region of positive vorticity advection and
increased Omega will overspread the forecast area in advance of
another longwave trough moving in from the west. Warm-frontal
processes will take over, and an increase in cloud cover and rain
chances can be expected Thursday into Thursday night. Elevated
convection looks possible as cape values at 850mb would support
thunderstorm activity. However, a cooler and more stable airmass
will remain in place at the surface with highs in the middle 70s
and lows in the 50s and low 60s.

The longwave trough and an associated cold front will sweep
through the area on Friday, and have pop values in high end chance
range. Instability values look less favorable for severe
thunderstorm development on Friday at this time. Highs should
remain cooler than average in the low to mid 70s.

&&

Aviation...VFR conditions will continue at all of the terminals
through the early morning hours. Winds should gradually increase
from the northeast as a low pressure system approaches from the
southwest. At kgpt, knew, kmsy, and khum a period of MVFR ceilings
and visibilities may develop after 18z as some light rain develops
on the northwest side of the low pressure system. Winds will also
be quite gusty from the north-northeast at 20 to 30 knots in the
afternoon and early evening hours. Improving conditions back into
VFR range are expected to take hold at nearly all of the terminals
after 00z as the low tracks further to the east.

&&

Marine...potential tropical cyclone 16 will affect the Gulf
waters and sounds today and tonight with strong winds and high
seas. The tidal lakes will see Small Craft Advisory conditions
today as the low pressure system passes by. As the low pulls away
tomorrow improving conditions can be expected with decreasing
winds and subsiding seas. The next significant round of marine
impacts will occur Monday night into Tuesday in the wake of a
passing cold front. Small Craft Advisory conditions are expected
to redevelop over the coastal waters as a cooler and drier airmass
advects in from the north.

&&

Decision support...

Dss code: Orange.
Deployed: forecaster deployed to support city of New Orleans for
building collapse.
Activation: none.
Activities: forecast support to New Orleans for building collapse.
Monitoring possible tropical development in Gulf.

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 70 54 79 58 / 10 10 10 0
btr 72 57 79 62 / 10 10 10 0
asd 70 57 81 60 / 30 20 10 0
msy 73 62 81 66 / 30 20 10 0
gpt 69 59 79 62 / 40 30 10 0
pql 68 58 80 60 / 50 40 20 10

&&

Lix watches/warnings/advisories...
la...Tropical Storm Warning for laz068>070.

Coastal flood advisory until 9 am CDT Saturday for laz040-050-
058-060>064-067>070-072.

GM...Tropical Storm Warning for gmz532-534-536-538-550-552-555-557-
570-572-575-577.

Small Craft Advisory from 7 am this morning to 10 PM CDT this
evening for gmz530.

MS...coastal flood advisory until 9 am CDT Saturday for msz080>082.

GM...Tropical Storm Warning for gmz534-536-538-550-552-555-557-570-
572-575-577.

&&

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