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afdlix

Area forecast discussion
National Weather Service New Orleans la
507 am CDT Mon Oct 21 2019

Short term...

Latest upper air analysis showed a cyclonic circulation over
eastern Nebraska and southwest flow over mid and lower
Mississippi Valley. In addition, a disturbance was located over
south Texas in the southern stream. Isotach analysis at 250mb
showed the jet Max of 150kts on the back side of the trough over
the northern rockies, 120kts on the front side of the trough from
NE Oklahoma to southeast Iowa, and southern jet from Big Bend Texas to
northern Alabama.

Surface analysis showed a deep 998mb low underneath the upper
level low...eastern Nebraska. An associated frontal boundary
extended south and southwest into central Texas. A moisture axis
with 70 dewpoint readings were from Texas and Louisiana coasts to
east half of Arkansas on south winds.

Vertically stacked low will continue to push east. However, jet
Max on the back side of the trough will dive southeast and
continue to pool moisture ahead of the trough axis. Convection is
ongoing and becoming more linear as the storms push southeast but
individual cells are possible. Surface base cape values of 300 to
700 j/kg will be available along the front. In addition, 0-3
helicity hovers between 125 and 200 M/S ahead of the front but 200
to 350 M/S over the coastal waters ahead of the southern stream
wave. Ergo, any storms that become severe will contain damaging
winds and a few isolated weak tornadoes are possible today. Storm Prediction Center
has the entire forecast area in a slight risk due to an
approaching wave in the southern stream/west Gulf and the main
trough axis. There is a possibility that the southern stream wave
could be the main threat of severe weather across the south half
of the forecast area today. Any storms that become severe will
contain damaging winds and a few isolated weak tornadoes are
possible today.

Long term...

Associated cold front will push through tonight with strong cold
air advection. Both GFS and Euro show a 40 to 50m drop across the
area from this evening to Tuesday morning. Cold air advection
will continue through Wednesday with an addition 30 to 400m drop.
Ergo, a few areas will drop into the 40s Wednesday and Thursday
mornings. Another system will yield showers and a few isolated
thunderstorms across the forecast area Thursday into Friday and
bring another cold front through the area Friday into Saturday.
However, the models do diverge with timing and strength with this
system.

&&

Aviation...
expect primarily VFR conditions through early morning as
winds are keeping dewpoint depressions at around 5 degrees.
Conditions will deteriorate after 13z as a disturbance moves out the
northwest Gulf and brings an area of showers and storms out ahead of
an approaching cold front bringing terminals down to MVFR and
briefly IFR through this afternoon. The main line of storms moving
from northwest Louisiana will merge with the disturbance and keep showers
and storms in the forecast through the afternoon hours bringing the
potential for strong gusty winds, reduced visibilities, and heavy
rain. Conditions will improve by mid afternoon in western terminals
such as btr, late afternoon at msy, and finally by early evening
at gpt as the squall line passes through and eventually east of the
forecast area. Winds will be from the south and southwest during the
daytime hours and then west and eventually northwest by tonight
after 03z across the terminals. Winds will be gusty behind the cold
front tonight with winds possibly gusting to 25 mph at knew and 20
to 25 at kmsy by late tonight and early tomorrow morning.

&&

Marine...
exercise caution headlines are inserted for today for outer
waters. Winds may decrease a tad as the front approaches this
evening, shift and increase with the frontal passage tonight
after midnight. Small craft advisories will be necessary after
midnight tonight or by sunrise Tuesday, continuing into Wednesday.
Another round of headlines likely with the next front Friday
night or Saturday.

&&

Decision support...

Dss code: yellow.
Deployed: National Weather Service office support city of New Orleans for
building collapse.
Activation: none.
Activities: forecast support to New Orleans for building collapse.
Convective threats for Monday.



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 78 54 73 47 / 100 50 10 0
btr 78 56 74 50 / 100 50 10 0
asd 82 58 76 48 / 90 60 10 0
msy 82 63 76 58 / 90 60 10 0
gpt 79 60 75 52 / 90 60 10 0
pql 82 60 76 47 / 80 80 10 0

&&

Lix watches/warnings/advisories...
la...none.
GM...none.
MS...none.

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