Scientific Forecaster Discussion
fxus64 klix 230951
Area forecast discussion
National Weather Service New Orleans la
451 am CDT Fri Aug 23 2019
Short term (today through sunday)...
Infrared satellite imagery shows a broad mid level low over the west
to northwest Gulf of Mexico that is moving north. This has already
brought a surge of deep tropical moisture into southeast Louisiana
and south Mississippi with precipitable water (pw) values running
high in the 2 to 2.25 inch range. The models remain in decent
agreement taking this low/trough north today across the northwest
Gulf towards the mouth of the Sabine River tonight and Saturday.
This will maintain the deep tropical moisture over the forecast area
today, so have maintained the high rain chances from the previous
forecast, especially given the fact that there is so much
scattered shower activity already during the overnight to early
morning hours. While the rain chances are high, most locations
should see rainfall amounts in the half inch to one inch range
today since the showers and thunderstorms should be moving at a
decent pace. The weather prediction center has mainly coastal
areas of Louisiana in a marginal risk of excessive rainfall today
where more repetitive convection could occur. With much less
sunshine expected today, most locations should see high
temperatures staying below 90 degrees. Most of the rain should
diminish this evening but then redevelop again offshore overnight
and impact at least southwest portions of the area around south
On Saturday, deep tropical moisture will persist and support high
rain chances again along with locally heavy rainfall. The heaviest
rainfall amounts are expected along the southwest and south central
Louisiana coastline where there is a slight risk of excessive
rainfall, and the marginal risk extends across most inland portions
of south Louisiana. At this time, a Flash Flood Watch is not
warranted, however that could change if rainfall amounts exceed
what is expected.
A potent shortwave trough will be moving southeast from the central
and Southern Plains into the lower Mississippi Valley Sunday. This
will help pick up and phase in the mid level trough over the western
Gulf Coast region and pull it east across south Louisiana. Once
again, this will maintain deep tropical moisture and a favorable
environment for fairly widespread rainfall and a threat of locally
very heavy downpours from heavier showers and thunderstorms. The
entire forecast area is in a marginal risk of excessive rainfall on
Sunday and Sunday night. At this time, the average rainfall amounts
for the three days today through Sunday night are mostly in the 1 to
2 inch range, however this pattern will likely support some higher
totals in the 3 to 5 inch range, particularly south of I-10 in
Long term (monday through thursday)...
This system should finally start to exit the region on Monday as the
mid level trough moves east, however there will still be deep
tropical moisture over the region to support scattered to numerous
showers and thunderstorms. In fact, it should remain a fairly wet
pattern Tuesday into Wednesday as a frontal boundary will start to
approach the region from the north as a fairly potent series of
shortwave troughs carve out a broader mid/upper level trough across
the upper to mid Mississippi Valley and Great Lakes region. The
European model (ecmwf) is stronger pushing the cold front through the forecast area
on Thursday and Thursday night while the GFS keeps the boundary
mostly north of the forecast area. Have indicated a bit of a
drying trend for Thursday, but confidence is low at this time.
All terminals currently VFR. Radar is showing an area of showers
moving onshore between kbve and khum. If they hold together, likely
to reach knew and kmsy prior to 10z. Have already added early
morning thunderstorms in the vicinity to those, and may need to do the same for khdc and
kasd. Likely to see MVFR ceilings and IFR visibilities with these
Should see more daytime areal coverage of rain showers/thunderstorms and rain than yesterday,
with significant areal coverage during the afternoon hours. Will
carry prevailing rain showers beyond 17-18z with thunderstorms in the vicinity. Expect a diminishing
trend around 00z, with the cycle likely to repeat 24 hours from now.
No significant issues with prevailing light onshore winds and low
seas outside of convection, which is blossoming this morning. The
air mass will become increasingly more conducive for tropical funnel
and waterspout formation in the near shore waters, near shore
marshes and tidal lakes/bays through at least the weekend. 24/35
dss code: yellow.
Activities: marginal risk excessive rainfall today/Sunday.
Marginal to slight risk Saturday.
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
Preliminary point temps/pops...
mcb 88 71 89 71 / 60 20 70 30
btr 87 74 88 74 / 70 20 70 30
asd 89 73 90 73 / 60 20 60 20
msy 88 77 89 76 / 70 20 60 30
gpt 86 74 88 74 / 60 20 50 40
pql 89 73 91 73 / 60 30 50 40