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

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FXUS64 KLIX 250502
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1202 AM CDT Tue Jul 25 2017

.UPDATE...

Updated for 06z Aviation Discussion.

&&

.AVIATION...

Scattered SHRA/few TSRA just started developing in the last hour
to hour and a half over east central/south central Louisiana and
extreme southwest Mississippi. Current movement will take
activity in and near KBTR, KMCB & KHDC through 08z, and possibly
other airports mainly near and north of Lake Pontchartrain into
south Mississippi later tonight into Tuesday. Will have to adjust
the timing and impacts with lower conditions as the amount of
coverage and intensity is determined over the next few hours. Away
from the SHRA/TSRA, mostly VFR will prevail. 22/TD

&&


.PREV DISCUSSION... /issued 802 PM CDT Mon Jul 24 2017/

UPDATE...

Radar indicated most of the showers have dissipated with the
exception being near a portion of the southeast Louisiana coast and
coastal waters. Updated the tonight portion of the forecast to
account for these trends, and most locations should remain dry this
evening. There remains a moisture gradient across the forecast area
with the deeper moisture over the northern and eastern portions of
the forecast area. This deeper moisture area will also interact with
a mid level shortwave trough that sweep through the region later
tonight and Tuesday morning. This should lead to redevelopment of
scattered convection towards or shortly after midnight and
continuing into at least Tuesday morning. A few of the thunderstorms
could once again produce torrential downpours, possibly repeating
over some areas like late last night and today leading to localized
flash flooding. The flash flood watch will remain in effect for
areas north of metro Baton Rouge to north of Lake Pontchartrain, and
across south Mississippi. 22/TD

AVIATION...

Conditions have become prevailing VFR with the SHRA/TSRA having
dissipated. Conditions remain favorable for redevelopment of
SHRA/TSRA mainly at or after 06Z to possibly impact KMCB, KGPT,
KBXA and KPQL. Away from convection, some periodic lower CIGS
and BR could result in MVFR conditions towards 12z. Any MVFR early
Tuesday morning should improve back to VFR by 15z or so and remain
so through the day with the exception being during isolated to
scattered SHRA/TSRA. 22/TD

SOUNDING DISCUSSION...

Some significant changes in the atmosphere since the 12z sounding
mainly due to a surge of drier air advecting into the mid-levels.
This drier air has resulted in a much larger T/Td spread below
500mb, and warmer mid-level temperatures. This warming has
resulted in less instability in the atmosphere as lapse rates
weaken in the mid-levels. This is most noted by the drop in 0-3km
lapse rates below 6.0C/km, and mixed layer CAPE falling to 855
J/KG. The warming of the mid-levels is also noted by the increase
in freezing levels from 15,400 feet to 16,200 feet from 12z to
00z. The drier air has also reduced atmospheric moisture content
as noted by precipitable water values dropping a third of an inch
sand mean mixing ratios falling by 1.5 g/kg since the 12z
sounding. Overall, all of these parameters point to a more stable
atmosphere developing between the morning and evening soundings.
32

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  73  88  72  92 /  50  50  10  10
BTR  74  91  74  93 /  40  30  10  10
ASD  76  92  76  93 /  50  50  10  20
MSY  77  91  77  92 /  30  40  10  10
GPT  77  90  76  91 /  50  60  20  20
PQL  75  89  75  92 /  50  70  20  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch through Tuesday evening for LAZ035>037-039-040-
     071-072.

GM...None.
MS...Flash Flood Watch through Tuesday evening for MSZ068>071-077-
     080>082.

GM...None.
&&

$$


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