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

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FXUS64 KLIX 210456
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1156 PM CDT Thu Jul 20 2017

.AVIATION...
VFR conditions outside what should be limited convection, though
some radar returns at this time over MS may hold together through
the night while moving west. This may portend better coverage
under the influence of extended trough axis aloft. 24/RR

&&

.PREV DISCUSSION... /issued 854 PM CDT Thu Jul 20 2017/

SOUNDING DISCUSSION...
There were not any problems with the upper air release this
evening. The 00Z sounding indicated an unstable, but overall
drier sounding. In particular, drier air was prevalent in the mid
and upper levels. The precipitable water value was down to 1.62
inches. A couple of weak inversions were present in the mid
levels. Mainly northeast to east northeast winds were observed
throughout much of the profile. 11

PREV DISCUSSION... /issued 337 PM CDT Thu Jul 20 2017/

DISCUSSION...

Latest surface analysis showed a broad 1020mb high over northwest
Gulf of Mexico to Tennessee valley. Upper air analysis revealed a
large anti- cyclonic circulation over the Central Plains with
an axis extending southeast to the Mid South and lower
Mississippi valley. A short wave was noted over Ohio Valley. In
addition, a closed cyclonic circulation was noted along the
Eastern Seaboard. The increase thickness layer over has warmed the
layer and suppressed most of the convection across the Louisiana
and Mississippi today.

Precipitable water values on a planer view showed values of around
1.5 inches over Mississippi, east half of Louisiana, Arkansas and
Tennessee. This feature initialized well but GFS initialized 2
inches over north Mississippi but NAM not showing this feature
until 18z today. Northerly flow on the front side of upper level
high and flow on the backside of the east coast low will advect
in mid layer moisture associated with the short wave over Ohio
Valley. Either way, deeper moisture will arrive from the northeast
around 18z on Friday. Weather remain relatively precip free til
Friday. With surface dewpoint in the upper 70s and surface heating
Friday morning, many locales will reach heat index values of 100
degrees between 10 and 11 am Friday morning and several points
reaching 106 degrees heat index by noon. Our office will be
monitored this heat event through Friday.

The closed upper level low is expected to push west over the
forecast area this weekend. Over the forecast area, 500mb temps of
-5C will decrease to -8C, 700 to 500mb lapse rates increasing to
 6.5c/km and PW values increasing back up to 2 inches Friday and
 over the weekend. As result, rain chances will go from nil today
 to scattered to numerous over the weekend, Friday will be the
 transition day. Upper level low will continue to push west and
 open next week and push north by mid layer drying from the gulf.
 This will slight shift will decrease our rain chances to slightly
 below normal for next week and dangerous heat index values will
 return with brief relief. 18

AVIATION...

VFR conditions will prevail at all of the terminals through tomorrow
afternoon.  Some scattered thunderstorm activity should develop from
late morning through the afternoon hours, and will include VCTS
wording to reflect this risk. 32

MARINE...

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 weak nocturnal coastal jet
associated with the seabreeze/landbreeze pattern is expected to
develop each night resulting in some westerly winds around 15 knots
each night.  Seas will generally range between 1 and 2 feet through
the period, but areas beneath the nocturnal jet could see a brief
period of seas up to 3 feet.  Overall, no significant impacts to
mariners are expected through the first half of next week. 32

DECISION SUPPORT...
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.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  76  93  74  88 /  10  40  40  50
BTR  77  93  75  89 /  10  40  40  50
ASD  77  92  76  90 /  20  40  40  50
MSY  78  91  77  89 /  20  40  20  40
GPT  79  91  78  88 /  20  40  20  40
PQL  77  91  77  88 /  20  40  20  40

&&

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

$$



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