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

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FXUS64 KLIX 242107

Area Forecast Discussion
National Weather Service New Orleans LA
407 PM CDT Sun Sep 24 2017


A broad area of low pressure in the upper levels will linger over
the area through Tuesday while also gradually weakening over the
next couple of days. The main impact from this upper level low
will be continued deep moisture transport into the forecast area
as noted by precipitable water values of around 2 inches both
today and tomorrow. The increase in upper level lift associated
with the low over the region, and the increase in available
moisture will allow for higher than normal rain chances through
tomorrow afternoon. The highest rain chances tonight will tend to
be in the eastern coastal waters and along the immediate
Mississippi coast where the deepest pool of moisture, greatest
instability, and strongest omega values are expected to reside.
Given these parameters, have likely POP of 60 to 70 percent in the
forecast for the eastern coastal waters tonight. Tomorrow will see
a similar pattern as seen today with showers and thunderstorms
spreading onto the coast in the morning and then developing over
inland areas during the afternoon hours. Have similar POP values
for tomorrow afternoon as those today with POP of 40 to 50 percent
in the forecast. The convection tomorrow should tend to develop
along outflow boundaries that push further inland through the day.
Temperatures will remain above average with highs in the upper 80s
and lower 90s tomorrow afternoon, and lows only cooling into the
upper 60s and lower 70s.

Tuesday will see a bit less convective coverage as the upper level
low begins to weaken dramatically. A resultant decrease in upper
level forcing should result in less overall convective potential
Tuesday, but continued high precipitable water values of around 2
inches should keep a risk of at least scattered showers and
thunderstorms in the forecast for Tuesday. The pattern will be
similar to Monday with offshore convection moving inland on the
back of outflow boundaries through the morning and afternoon
hours. Temperatures will remain well above average with highs near
90 and lows in the upper 60s and lower 70s.


The upper level low will completely dissipate by Wednesday and a
strong shortwave ridge will develop over the area. This strong
ridge will remain in control of the area through Thursday. With
increased subsidence and dry air advection taking hold, a strong
capping inversion in the mid-levels will develop. This strong cap
will effectively suppress any convective potential both Wednesday
and Thursday, and do not have any mention of POP higher than 10
percent in the forecast. At most, some scattered fair weather
cumulus clouds could form beneath the mid-level cap. The increase
in subsidence throughout the column will allow temperatures to
further warm into the lower to possibly middle 90s both Wednesday
and Thursday afternoons.

A shortwave trough sliding through the Midwest and toward the
eastern seaboard on Friday will suppress the upper level ridge
over the Gulf South, and also allow for a weak front passage and
subsequent northeast flow regime to develop over the forecast
area. This front will tend to be moisture starved with low
precipitable water values lingering over the region on Friday, and
expect only a slight increase in cloud cover as the front moves
through. Weak cold air advection should develop on the back of the
northeast flow pattern by Friday evening, and expect to see lows
Friday night dip into the middle 60s at most locations.

Over the upcoming weekend, the models indicate that another fast
moving shortwave trough axis should move through the Lower
Mississippi Valley. However, the exact timing of this system and
the strength of said system has some discrepancies between the
models. At this point, have opted to use a blend of the model
solutions for the weekend. This results in a slight chance of
showers and thunderstorms developing in advance of the approaching
shortwave feature by Sunday. Temperatures will remain closer to
average over the weekend with highs in the middle 80s and lows in
the lower to middle 60s both Saturday and Sunday.



Prevailing VFR conditions can be expected at all of the terminals
through the forecast period. However, scattered convection could
briefly impact the terminals especially from 15z through 00z
tomorrow. Have included VCTS wording to reflect this risk. If
convection moves over a terminal, a brief period of MVFR
visibilities and ceilings could take hold. 32



Benign weather conditions are expected over the coastal waters
away from any thunderstorm activity that forms over the next
couple of days. A prevailing east-southeast wind of less than 10
knots and seas of less than 2 feet can be expected through
Thursday. A weak front should slide through on Friday resulting in
a shift to a more northeast wind, and an increase in winds to 10
to 15 knots. Seas could also increase to around 3 feet in the open
Gulf waters as these stronger offshore winds develop. 32



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.


MCB  68  88  68  89 /  20  30  20  30
BTR  69  88  70  89 /  20  40  20  30
ASD  69  87  69  87 /  40  50  30  30
MSY  74  86  74  87 /  30  50  30  40
GPT  70  85  71  87 /  50  50  30  30
PQL  68  86  68  88 /  50  50  30  30




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