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

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FXUS64 KLIX 232031
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
331 PM CDT Sat Sep 23 2017

.SHORT TERM...

Very little change in thinking with the latest forecast update.
Latest water vapor imagery shows a broad upper level low pushing
west toward the area this afternoon, and this low is still
expected to become centered over the region by tomorrow. The upper
level low should then linger over the area through Monday. An
increase in upper level omega and mid-level moisture into the
region should allow for greater convective activity over the next
couple of days. Precipitable water values will increase from
around 1.5 inches today to around 2 inches by Monday. Fully expect
to see POP ranging around 30 to 40 percent tomorrow, and then
increasing to around 50 to 60 percent by Monday. With an increase
in cloud development and convection, temperatures should cool back
to more normal levels for late September with highs in the middle
to upper 80s and lows in the upper 60s and lower 70s.

.LONG TERM...

The upper level low will begin to weaken and shift back to the
east of the area on Tuesday. A decrease in forcing aloft and a
slight reduction in precipitable water values and available
moisture will result in less overall convective potential Tuesday
afternoon. Have POP values of 20 to 30 percent in the forecast on
Tuesday, and expect to see slightly warmer temperatures climbing
back near 90 degrees in the afternoon.

Wednesday and Thursday will see the area dominated by deep layer
ridging and strong subsidence. With a sinking airmass in place
over the region, cloud development will be suppressed and
temperatures will warm considerably. Do not expect to see much in
the way of convective activity due to the subsidence and a strong
mid-level cap, and only have a POP of 5 to 10 percent in the
forecast each day. Highs should easily climb into the lower to
middle 90s both Wednesday and Thursday. The drier airmass and
clear skies should allow for a larger diurnal temperature range,
so overnight lows should be closer to average in the middle to
upper 60s.

The ridge should break down Thursday night and Friday as a strong
long wave trough dives into the Midwest. This trough will send an
attendant cold front through the area Friday into Friday night.
This front looks to be fairly moisture starved as northerly flow
and lower precipitable water values linger over the region. As
a result, have a mostly dry forecast in place for Friday. At most,
some isolated showers and thunderstorm may try to develop along
the Louisiana coast and offshore as the front moves through. By
Saturday, the front should be well offshore allowing a cool, dry,
and very stable airmass to advect in from the north. Temperatures
should fall into the lower to middle 80s by Saturday afternoon,
and overnight lows could even dip into the upper 50s across the
northern third of the CWA Saturday night.

&&

.AVIATION...

VFR conditions are expected to prevail at most terminals through
Friday. A weak temperature inversion around 12z this morning could
produce some MVFR visibility restrictions at KMCB, KHUM and possibly
KBTR for a couple of hours as patchy fog develops. Any fog should
quickly burn off after 14z allowing for a return to VFR conditions.
Southeast flow will increase moisture and increase rain chances to
30 percent around most taf sites. Will maintain PROB30 most sites
except KMCB. 18

&&

.MARINE...

No significant changes in thinking from the previous forecast. Ridge
of high pressure will build just to the east of the coastal waters
through the forecast period. This will result in  persistent
southeast flow of 10 knots and seas of 3 feet or less during this
period. 18

&&

.DECISION SUPPORT...

DSS code: Green.
Deployed: None.
Activation: None.
Activities: None.

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  68  89  68  89 /  10  40  20  40
BTR  70  91  69  91 /  10  30  20  40
ASD  70  89  70  89 /  20  40  30  50
MSY  75  89  74  89 /  20  40  30  50
GPT  72  87  71  87 /  20  50  40  50
PQL  69  87  69  89 /  30  50  40  50

&&

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

$$

32


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