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fxus64 klix 161020 
afdlix

Area forecast discussion
National Weather Service New Orleans la
420 am CST Sat Dec 16 2017

Discussion...
the last bit of calm weather will take place today before a much
more active period starts late tonight and will last for the next
several days. High pressure will slide to the east today and allow
for return flow from the Gulf. This will set the stage for a
prolonged rainy period in the forecast. An upper level low will
eject out of northern Mexico and at the surface a low will develop
over the western Gulf of Mexico. This rapidly deepening low will
bring another cold front into the region and stall it over the
area for a few days. This will be the focus of shower and
thunderstorm development through early next week. This system will
also pull rich moisture into the forecast area Sunday and that
moisture will remain in place through midweek.

Precipitable water values for Sunday look to be well over 1.8
inches if the guidance is correct. This will put record amounts of
moisture in the forecast as the daily recorded Max for Sunday 12z
soundings at kasd is 1.64, and the recorded Max for Sunday
evening 0z soundings is 1.72. So we will be flirting with some
deep moisture over the region on Sunday into Monday. The weather
prediction center has the entire area outlooked in a marginal
risk for excessive rainfall on Sunday. Some flooding is possible
on Sunday. There is a shot that we could be outlooked again for
excessive rainfall again on Monday...as of now we are not but some
of the signals point to more heavy rainfall going into Monday as
well. We are expecting rainfall totals in the 2 to 4 inch range
for much of the area. Higher totals will certainly be possible if
any specific areas see multiple rounds of heavier storms. Some
localized ponding of water in low lying and poor drainage areas is
possible. Will have to monitor the flooding situation carefully
as this evolves into a multi-day type event with moisture rich
environment and a stalled front over the forecast area through at
least Tuesday.

One more note for this system as well...the Storm Prediction
Center has placed the area in a marginal risk for severe weather
on Sunday and Monday. Looking at the soundings the instability is
marginal but is sufficient enough to maintain some stronger
convection. There will be enough shear in the atmosphere also to
support convection. Main inhibiting factor will be whether the
convection is surface-based or not. Damaging wind appears to be the greatest
threat from any severe storms, but the higher shear means we can't
ignore the possibility of a tornado or two. Remember this is
winter and you do not need overly robust instability in the
atmosphere to cause a little bit of trouble. We will be watching
this close as well.

Guidance is in better agreement going into midweek. Another upper
low will eject out over the Southern Plains and another surface
low moves across the area. This will bring another round of
showers and thunderstorms to the region Wednesday morning. We
should be between systems Thursday...and guidance then also points
to another major system into the region next weekend. With that
being said have maintained a blend in the latter part of the
forecast period. 13/mh

&&

Aviation...
VFR category conditions will prevail at the terminals
through the day Saturday with mid and high levels clouds prevailing.
Ceilings will lower Saturday evening and night with MVFR conditions
expected to develop. Isolated to scattered showers will be possible
by late Saturday night...primarily for the western p/County Warning Area taf
locations. /11/

&&

Marine...
high pressure over the region will continue to slide east
today while cyclogenesis will begin over the southwestern Gulf. This
will send a warm front back across the region tonight. With that
winds will veer around today to easterly and then
southeasterly/onshore early Sunday after the front moves to the
north. The pressure gradient will also tighten across the region
with moderate to strong winds expected overnight tonight and more so
tomorrow. As the sfc low pulls away Monday the front will basically
stall over the region leading to lighter winds through Tuesday. A
lot of questions then arise for the remainder of the week. Another
sfc low is expected to traverse the lower MS valley which will bring
another weak cold front into and likely stalling over the region. By
the end of the week we should see a much stronger cold front with
strong offshore winds developing behind it. /Cab/

&&

Decision support...
dss code: green.
Deployed: none.
Activation: none.
Activities: none.

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.
Yellow = heightened impacts with short-fused watch, warning or
advisory issuances; radar support.
Orange = high impacts; slight to moderate risk severe; nearby tropical
events; hazmat or other large episodes.
Red = full engagement for moderate risk of severe and/or
direct tropical threats; events of National significance.

&&

Preliminary point temps/pops...
mcb 55 47 69 60 / 10 80 90 60
btr 57 50 71 61 / 10 80 90 50
asd 57 50 73 61 / 10 60 80 50
msy 57 53 73 63 / 10 60 80 50
gpt 56 50 70 62 / 10 50 80 60
pql 56 48 73 61 / 0 50 80 60

&&

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

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