Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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658
FXUS64 KLIX 161300
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
800 AM CDT Wed Aug 16 2017

...SOUNDING DISCUSSION...
The sounding this morning still indicates a moist profile with
plenty of instability. PW is above average at 2.3 inches and mixed
layer CAPE is 1850 J/KG. Winds are southwest at about 15 kts
through 700 mb then become easterly above 400 mb. Scattered storms
are expected to develop midday and some could be strong with
locally heavy rain.

Krautmann

&&


.PREV DISCUSSION... /issued 338 AM CDT Wed Aug 16 2017/

SHORT TERM...
Some rapid changes coming over the next 3 days. Today will be more
of the same but the change will be the supressive ridging that
will begin to move into the southern half of the area by late
today and tonight forcing the weakness northward. Heavy rainfall
will continue to be an issue but we will need to add one more item
to the problem list...isolated severe thunderstorms. Downburst
numbers are peaking today over the southern half of the area due
to the ridge trying to nudge into the area. This will add enough
dry air starting at 800mb early in the day then at 700mb by
afternoon. So with dry air being entrained at 800mb, thunderstorms
will be capable of 30-40mph wind speeds but as dry air moves in
at 700mb around noon or shortly thereafter, downburst wind speeds
of 50 to 60mph could become an issue. This is not expected to be
widespread. The next 3 days show the possibility of isolated
severe. But as the stacked supressive ridge digs into the area
Thursday with strong capping, there should be very few if any
sh/ts that are capable of developing, with somewhat of an
exception near Baton Rouge. If under these conditions, a
thunderstorm is able to get going, the potential would be
heightened to produce severity since it will be able to take
advantage of a lot of energy. The main issue with Thursday will be
the heat as cloud cover and rain will be at a premium. Heat index
values will definitely make it feel like summer and may reach
108+ during the hottest part of the day. This would normally not
be too much of a worry if conditions had been this hot already,
but this will seem like a sudden onset of hot conditions that
could prove to be an issue with outdoor activities.

Friday, we will see the trough(weakness) move back toward the
south displacing the stacked ridge and providing deep moisture
once again. Where these two air masses battle, will provide once
again the possibility of severe thunderstorms as dry air will be
entrained into the thunderstorms that develop as they move south
into and through the area. Most of this activity should be found
over the northern half of the area Friday and downburst numbers
are showing this as well as they peak in the mid 30s. Rather
not specify any particular area in products and simply include
the entire area in the risk of isolated severe thunderstorms
through Friday.

Once the deep moisture moves back into the area, we will move from
severe possibilities to heavy rainfall once again and the heat
will settle to what we have been used to. Saturday looks to be
quite wet but Sunday looks to be the wettest of the weekend. Most
of these thunderstorms over the weekend will be backbuilding and
this could lead to some flooding of streets and low lying areas.

LONG TERM...
The deep moisture stays with us through much of next week keeping
the chance of rain at or just above average.

AVIATION...
Most terminals currently VFR, but KMCB has had SCT-BKN004 for the
last several hours, so they can be LIFR-IFR on occasion until
shortly after sunrise. KGPT went to MVFR briefly as a SHRA passed
by.

Convection appears to be a little more vigorously moving onshore
between Morgan City and Lafayette this morning. It`s possible
convection could see a little earlier start than the last few
mornings.

Lower level convective cloud development today along with scattered
SHRA/TSRA are expected to produce the areas of MVFR category
CIGS/VSBYS, and brief occurrences of IFR/LIFR under the heavier
cores of the cells. Will not carry the lower conditions at this time
due to usual uncertainty of the timing, but have a general trend
towards mention of -SHRA and VCTS as the morning progresses towards
midday. TEMPO TSRA may end up being more appropriate for the
afternoon, will continue to assess. 22/35

MARINE...
Normal August doldrums pattern will hold as high pressure will
remain in place and diurnal fluctuations will be the main driver
of winds. With most nights look for a weak enhanced jet over the
waters east of the MS delta where winds could bump up to 10-15
knots at times. Seas will remain in the 2-3 ft range or less.

DECISION SUPPORT...
DSS code: Yellow.
Deployed: NOHSEP.
Activation: None.
Activities: DSS support for NOHSEP; Monitoring Convective trends and
            River Flooding.

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  89  74  93  74 /  80  10  20  10
BTR  90  75  94  76 /  70  10  20  10
ASD  91  76  95  76 /  60  10  20  10
MSY  90  77  94  77 /  60  10  20  10
GPT  89  76  91  77 /  60  10  20  20
PQL  90  75  93  75 /  50  10  20  20

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

$$



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