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

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FXUS64 KLIX 181316

Area Forecast Discussion
National Weather Service New Orleans LA
816 AM CDT Fri Aug 18 2017

The sounding this morning indicates slightly less influence from
the passing high pressure aloft. PW is up to 2.0 inches and the
subtle low level subsidence inversion from yesterday is reduced.
Mixed layer CAPE is at 1300 J/KG. The low level temperature
profile is warm, about 90% in the climatology, and will mix down
to hot surface conditions today. It will take again until late
this afternoon for scattered showers and storms to develop.
Coverage is expected to be low. Winds are light and westerly
through 400 mb then variable above.



.PREV DISCUSSION... /issued 336 AM CDT Fri Aug 18 2017/

Today will be the end of a short period of lower pops and the return
to a more typical wet mid August regime. This pattern will persist
through at least this weekend and possibly into next week. An upper
level ridge that was centered near the northern Gulf of Mexico has
been suppressed by a trough thats moving across the Mid-Mississippi
and Ohio River Valleys. Strong daytime heating and decreased
subsidence will allow for afternoon thunderstorms to develop, with
higher coverage in northern portions of the forecast area that are
closer to the trough. Model soundings indicate an inverted-V profile
in the lower levels which suggests that the main threat with storms
will be downburst winds. Some could produce marginally severe winds.
Propagation in general should be NW to SE but outflow dominated
cells could have movements outside of that main direction for that

From a temperature standpoint, did consider a heat advisory. Daytime
highs should be similar to yesterday, 90 to 95, and dewpoints in the
mid 70s. Those numbers didn`t quite yield 108+ Heat Index Advisory
criteria and likely will have enough mixing to keep dewpoints low
enough during peak heating. Although an isolated location may touch
criteria, the overall impacted areas should be too few to justify an

A secondary trough will dip out of Canada into the Northern Plains
tonight and cross the Great Lakes Saturday. This feature will track
on a more west to east direction than the previous which will limit
subsidence over the area. Meanwhile, a Tutt low (currently seen
moving west across the Bahamas) will be tracking west across the
GOM. This feature in combination with trough to the north will
enhance daytime convection and allow for numerous showers and
thunderstorms to develop Saturday and Sunday. Coverage should easily
be in the 50%ish range.

An upper ridge building from the east and try to extend towards the
CWA during the first half of next week. The aforementioned Tutt low
will be slowly progressing westward towards the NW Gulf. Moisture
drawn onshore will keep rain chances higher through Tuesday. Moving
into mid week, models indicate a broad long wave trough will send a
frontal boundary towards the region. This will keep the CWA in an
enhanced pop development pattern.


AVIATION...TSRA to start for sites over the northern half of
the area on and off through the day. Development to start during the
afternoon for the southern half of the area. Wind gusts could be
strong with some of this activity as well. Ceilings generally SCT-BKN
at 030 to 040 north this morning and south during the afternoon. VFR
conditions expected outside convective locations.

MARINE...No changes as high pressure remains the dominant
factor over the northern gulf. Diurnal fluctuations will remain 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.

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

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.


MCB  92  74  91  74 /  40  10  60  10
BTR  92  76  92  75 /  20  10  50  10
ASD  94  77  92  76 /  30  10  50  10
MSY  93  77  92  78 /  20  10  50  20
GPT  91  77  90  77 /  40  20  40  20
PQL  93  76  92  75 /  40  20  30  20



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