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fxus64 klix 230118 
afdlix

Area forecast discussion
National Weather Service New Orleans la
818 PM CDT Mon may 22 2017

..sounding discussion...
Moisture is still up in the sounding this evening with precipitable water above
average at 1.8 inches. Winds are southwest at low levels then
become westerly by 500 mb. Instability is limited so much of the
rainfall overnight will be stratiform, though the possibility for
heavier rainfall remains across the la coast. Some areas of heavy
rain have developed just southwest of Lafayette, but the
strongest convection remains over the northern Gulf.

Krautmann

&&

Previous discussion... /issued 438 PM CDT Mon may 22 2017/

Discussion...

Large scale pattern will feature a longwave trough deepening from
the upper Mississippi Valley down to the Southern Plains and
western Gulf Coast region tonight through Tuesday night, with the
associated cold front meandering over the forecast area. The
frontal boundary will continue to occasionally act as a focus for
showers and thunderstorms as a series of minor shortwave troughs
and one or more weak surface lows/waves move through the forecast
area. This will also keep some upper level difluence over much of
the area, but generally shifting towards the coast, to the east
and offshore heading into Tuesday. The 12z GFS is fairly
aggressive lowering the precipitable water from the northwest
later tonight, and it may be a bit too aggressive, so have
compromised by blending in the European model (ecmwf) which keeps some heavier rain
a bit longer (between 1 and 7 am) tonight/Tuesday morning over
the far northwest. Current radar and pattern trends are indicating
the more concentrated thunderstorms and higher rainfall rates
should move across coastal regions and south of I-10 as we start
the evening with a more general moderate rainfall with embedded
thunderstorms over northern areas.

With this solution and the latest wpc quantitative precipitation forecast guidance, the Flash
Flood Watch ending time has been pushed back to 4 am tonight
across northwest areas from Metro Baton Rouge to Washington Parish
and points north. The remainder of the area now will have a noon
Tuesday expiration of the watch. While the dry air will cut back
on the average quantitative precipitation forecast amounts, there could still be occasional
scattered showers and thunderstorms going into Tuesday night as
the cold air advection reactivates the frontal boundary and pushes
it southeast. This will usher in the cooler and drier air
Wednesday into Wednesday night with highs expected to be mostly
in the 70s to near 80 with lows in the 50s to lower 60s.

Enjoy the pleasant conditions while you can as the airmass will
be quite transient with return flow already back over the region
early Friday morning. In fact the pattern is progressive enough
that it now looks like we could see some rain return next weekend,
but more likely Sunday into Sunday night with more isolated
activity Saturday. 22/dew point

Aviation...

Most convection well back to the southwest, between lch and lft at
this time, and threat of thunderstorms and rain in the short term is fairly low.
Ceilings primarily MVFR and anticipate that MVFR ceilings will
become prevailing condition at most terminals by sunset. Will carry
thunderstorms in the vicinity after about 03z at all terminals, but once location of primary
development becomes more apparent, amendments will be necessary to
beef up threat. Local IFR conditions will be likely in
thunderstorms. Thunderstorm threat will continue through 18z
Tuesday before diminishing from northwest to southeast. 35

Marine...

A cold front will remain stationary over near coastal areas
through Tuesday. Winds will increase some tonight as a low rides
along the front, and with that in mind have maintained exercise
caution headlines for most of the waters. A fairly strong late
may cold front may also bring some west to northwest winds over 15
knots during the late Wednesday to Wednesday night periods, but
models have been consistent keeping most areas below 20 knots. An
area of high pressure is then expected to move from west to east
across the north Gulf Wednesday night and Thursday which will
bring a return of moderate south winds Thursday night into Friday.
22

Decision support...
dss code...yellow.
Deployed...none.
Activation...none.
Activities...monitoring heavy rain potential/Flash Flood Watch
monitoring Mississippi River flooding

Decision support services (dss) code legend
green = no weather impacts that require action
blue = long fused watch/warning/advisory in effect or high
visibility event
yellow = heightened impacts with short fused
watch/warning/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 tonight risk severe
and/or direct tropical threats; events of National
significance

&&

Preliminary point temps/pops...
mcb 64 82 60 74 / 90 40 50 10
btr 68 82 62 75 / 90 50 40 10
asd 70 83 63 78 / 90 70 40 20
msy 73 83 66 77 / 90 80 50 20
gpt 73 81 67 78 / 90 80 50 30
pql 68 82 65 80 / 90 80 50 30

&&

Lix watches/warnings/advisories...
la...Flash Flood Watch through Tuesday morning for laz040-056>070.

Flash Flood Watch until 4 am CDT Tuesday for laz034>037-039-
046>050-071-072.

GM...none.
MS...Flash Flood Watch through Tuesday morning for msz077-080>082.

Flash Flood Watch until 4 am CDT Tuesday for msz068>071.

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