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

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FXUS64 KLIX 211743

Area Forecast Discussion
National Weather Service New Orleans LA
1243 PM CDT Fri Jul 21 2017

Showers and thunderstorms are starting to develop over the area.
Expect VFR to MVFR conditions to prevail throughout the afternoon.
VCTS will remain in the forecast for all sites this afternoon and
storms should diminish after sunset. Nocturnal convection will
also be a possibility especially south of Lake Pontchartrain
later on in the night. Otherwise expect VFR conditions with
afternoon convection once again for Saturday. 13/MH


.PREV DISCUSSION... /issued 1021 AM CDT Fri Jul 21 2017/

Area radars indicated isolated showers and thunderstorms were
confined to the coastal waters with the more recent development
occurring in Chandeleur Sound and the coastal waters to the east
and southeast. Interaction of outflows from this convection and
prevailing northeast winds along the Mississippi Gulf coast and
near the tidal lakes in southeast Louisiana should allow for rapid
development of isolated to scattered showers and thunderstorms
during the remainder of the morning to around midday since the
convective temperature will have been reached or exceeded. Main
update was to the hourly Pop and weather to account for these
trends. Otherwise, the forecast for scattered afternoon showers
and thunderstorms across most land areas is still is on track for
today. Also raised the high temperatures by a degree or two mainly
over the more inland areas where convection and associated clouds
will arrive later in the day. 22/TD

PREV DISCUSSION... /issued 805 AM CDT Fri Jul 21 2017/

The sounding this morning depicts more easterly flow at upper
levels. 500 mb heights have dropped some to 591 dm as well,
indicating the upper ridge has weakened a bit and shifted north.
There is still a strong subsidence inversion at 600 mb and another
near 500 mb, though plenty of instability with mixed layer CAPE at
1900 J/KG. A few more storms are expected this afternoon, though
mainly over cities and near the lake/sea breeze boundary.


PREV DISCUSSION... /issued 412 AM CDT Fri Jul 21 2017/

Oppressive heat continues but with some cloud cover expected
along with a few more sh/ts around, heat index numbers should
remain very warm but not heat advisory criteria. Regardless of
advisories, this heat is still dangerous for prolonged outdoor
activities. Even better cloud coverage should keep these numbers
from getting out of control through the weekend. But this will
change as we move through next week.

Two upper lows to the east. The first is near Tallahassee this
morning which will affect our area tonight and Saturday as it
moves west. The other is near the Bahamas and will move north
eventually. This one will allow deep layered dry air to its east
to move quickly through the Florida Straits while it develops a
strong sfc high which will be stacked up to 700mb. This will be
the sfc high that will move in behind the upper low Sunday night
into Monday as it moves away from the area. This will all but
shut down the development of sh/ts over most of the area starting
Monday and may last through much of next week. It will also
increase optical depth causing a very efficient heating process.
And by the mid to latter part of next week, we could see some of
the warmest temps so far this season. A surge of moisture from the
east is then advertised by global models to finally bring some
relief in the form of sh/ts by Saturday.

With such strong heating, when thunderstorms develop, they can
become strong or even severe on any given day as they will be able
to take full advantage of the heating without much competition.
The best chances of a severe thunderstorm occurring will be
Saturday(tomorrow) and again next Saturday. Winds and hail would
be the two most notable factors associated with this activity if
capable of occurring.

VFR conditions expected through this cycle outside any convective
activity. Some sh/ts activity may affect terminals along and south
of a line from ASD to HDC as early as this morning.

A rather benign weather regime will persist over the coastal waters
through early next week as the region remains on the western
periphery of broad surface high. A rather strong sfc high will
move into the northern gulf Sunday night into Monday causing a
nearshore jet to set up. This feature will be stronger during the
overnight hours easing somewhat during the daylight hours. Overall,
no significant impacts are expected through the first half of
next week.

DSS code: Green.
Deployed: None.
Activation: None.
Activities: Monitoring Convective trends

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  74  88  73  88 /  30  40  20  60
BTR  75  89  75  88 /  30  40  20  60
ASD  76  90  77  88 /  30  40  20  60
MSY  77  89  77  88 /  30  40  20  60
GPT  78  88  78  87 /  30  40  20  50
PQL  77  88  76  87 /  20  40  20  50



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