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

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FXUS64 KLIX 252056
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
356 PM CDT Wed Apr 25 2018

.SYNOPSIS...

Latest surface analysis showed a 1018mb high over northwest Gulf
of Mexico and a cold front from the Ohio Valley to Arklatex
Region to central Texas. Surface winds over the area were
generally northerly around the high and surface dewpoint readings
were in the 50s this afternoon. Upper air analysis showed a low
over north oklahoma with the associated trough axis positively
tilted to west Texas. Southwest flow ahead of the trough axis has
increased moisture over east Texas and Arkansas. Precipitable
water values were 0.8 inch over Louisiana and 1.25 inches over
central Texas at 12z. Another trough axis was noted over Montana.

18
&&

.DISCUSSION...

The upper level trough over the Southern Plains will dive
southeast tonight and Thursday. This wave will bring its own
moisture or the moisture ahead of the trough. Precipitable water
values will increase up to 1.4 inches late tonight. The trough
will reach the Lower Mississippi Valley Thursday morning becoming
neutrally tilted Thursday morning and becoming negatively tilted
over Alabama Thursday afternoon, north and east of our forecast
area.

This is a cold core system will have a core temp of -21F well
north of the area. Models have backed off with the cooler temps
at 5h sweeping across our north zones, now projecting -12F to -14F
over the north zones. Will maintain convection and coverage late
tonight with a slight decrease in coverage as the system becomes
neutrally tilted toward noon Thursday. Then dry air will behind
exiting trough will decrease rain chances Thursday afternoon.
Severe weather is not anticipated as stronger dynamics will remain
north of the area on late tonight through Thursday afternoon.

The next system will quickly dive southeast over the forecast on
Friday. We talked about moisture remaining limited for several
runs and GFS show a little swath of 1 inch precipitable water
value at 18z across the north zones, 0.2 higher than previous
runs. Model consensus show web bulb zero around 8kft over the
forecast area Friday, less time for melting hail stones if
present. Mid layer lapse rates 7h to 5h off of GFS, NAM12 and Euro
showed values of 6.8 to 7.5 C/km, need around 7 C/km or greater.
In addition, MUCAPE value between BTR and ASD at 18z is projected
around 1000 J/kg, 1000 J/kg is need for any hail formation. Flow
will be northwesterly throughout the sounding at 18Z. With no deep
sheer, growth of hail will be difficult but sub- severe small
hail is possible on Friday and Hazardous Weather Outlook has it
covered for now. Conditions will improve Friday night with a
pleasant dry weekend expected with seasonal temperatures. Next
chance of rain will be mid next week.

18
&&

.MARINE...
A relatively weak cold front slide through Thursday morning as a
weak upper trough tracks across the southeast. A surge of drier air
behind this front could push winds back to around 15 knots Thursday
morning and early afternoon. Its borderline whether an exercise
caution headline will be needed. Very progressive upper level
pattern will bring yet another frontal boundary through the coastal
waters Friday. This will push winds back to 15 knots over the open
Gulf waters for Friday evening through early Saturday. Surface high
pressure will track from west to east across the southeastern CONUS
this weekend. This will cause winds to rotate around from NW to SE.
Onshore flow regime will settle in for the first half of next week.
Wind speeds will gradually increase due to tightening pressure
gradient.

MEFFER
&&

.AVIATION...
VFR conditions will dominate through the rest of this afternoon with
little in the way of cloud cover. A fast moving frontal system will
move into the region overnight. Showers with a few storm possible
will pass through from west to east from after 06z tonight and
ending during the mid to late morning hours. The main impact will be
lower ceilings, which could fall below 1kft.

MEFFER
&&

.DECISION SUPPORT...
DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Sandhill Crane NWR Outreach Support
            New Orleans Navy Week Support

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; Marginal risk severe or excessive rain.
Yellow = Heightened impacts with short-fused watch, warning or
         advisory issuances; radar support for Slight risk severe or
         excessive rain.
Orange = High Impacts; Enhanced risk severe; nearby tropical events;
         HazMat or other large episodes.
Red    = Full engagement for Moderate to high risk of severe and/or
         excessive rainfall; direct tropical threats; Events of
         National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  57  70  51  74 /  60  20  10  30
BTR  58  72  53  75 /  50  20  10  30
ASD  59  73  53  75 /  30  40  10  30
MSY  63  73  57  75 /  30  40  10  30
GPT  64  74  55  73 /  20  50  10  20
PQL  64  74  52  75 /  20  50  10  20

&&

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

$$



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