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

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000
FXUS64 KLIX 290126
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
826 PM CDT Fri Apr 28 2017


.SOUNDING DISCUSSION...
There were no problems with the upper air release this evening.
The 00Z sounding indicated an unstable sounding with moisture
largely confined beneath a strong inversion in the 870 to 765 mb
layer. Dry air prevailed in the mid levels. The precipitable
water value was 1.52 inches. Southeast winds were observed near
the surface with southerly flow then up to 400 mb. Southwest winds
prevailed above that level. 11

&&

.PREV DISCUSSION... /issued 450 PM CDT Fri Apr 28 2017/

SYNOPSIS...

Latest surface analysis showed a 1022mb high off the Carolinas
coast with the ridge axis west to northwest Gulf of Mexico. In
addition, 997mb low/trough was noted over the Southern Plains.
Both features creating a tight pressure gradient of 10mb from
Houston to Mobile. South winds of 15 to 25 mph with frequent gusts
up to 30 mph were common this afternoon. Surface dewpoint readings
were mainly in the 70s across Louisiana and most of Mississippi.
Upper air analysis showed a high over Florida and deep cyclonic
low over the Four Corners Region. Isotach analysis at 250mb showed
a 160 knot jet max on the back side of low and 120 knot jet max on
the front side from Texas Panhandle to Great Lakes region. Sub-
tropical jet of 70 knots was present from South Texas to north
central Gulf of Mexico.

SHORT TERM...

This morning felt like July for areas. Winds did not decouple
over night and temperatures remain elevated especially around the
coast. Strong inversion from 4500 to 7000 feet will remain in play
through Saturday. However, surface heating in the mid to upper
80s may overcome this lid, the same as today but the system out
west will be closer Saturday afternoon. Maintained a chance of
convection across northwest zones. However, activity that do
develop will be isolated on Saturday.

Upper level low will press east over the Southern Plains tonight
through Saturday night. This system will create large wind field
across the Lower Mississippi Valley. Boundary layer winds around
25 knots are expected across Florida Parishes and Southwest
Mississippi and 20 knots over Mississippi coast by midday Saturday
but 25 to 30 knots south of tidal lakes. Higher values will be
present over northwest gulf and these values will shift over
coastal waters east of Mississippi River Saturday night.

There remains a high potential for widespread strong thunderstorms
with several of these becoming severe. Strong damaging wind
speeds look to be the most efficient component. This is due to the
addition of momentum transfer from thunderstorm activity to the
surface where there will already be winds around 25 mph. Any
thunderstorm will not have to produce more than a 25mph wind to
cause some fairly strong cumulative wind speeds.

Other modes of severe weather will not be left out. Precipitable
water values are expected to pool along the trough axis with
values up to 2.1 inches moving across the forecast area Sunday
morning through early Sunday evening. Total amounts during the
weekend event look to be between 2 to 4 inches with isolated
higher amounts. Goes without saying that if the majority of this
amount falls within a short period flooding would be possible.

Tides are up this afternoon. While only a few areas were affected
this afternoon. Stronger winds Saturday and Sunday will increase
tide levels especially during the high tide cycle each day. Levels
are expected to be half to 1 and half above normal Saturday and 1
to 2 feet above normal Sunday. Will maintain Coastal Flood
Advisory through Sunday evening and a few areas may be upgraded to
a warning if necessary.

LONG TERM...

Dry air will move in behind this front once it moves through the
area Sunday night into Monday. Tuesday night should find warm
front lifted northeast ahead of the next cold front. This feature
could be strongly forced depending on how deep the polar jet digs
over the gulf south, which would lead to a good bit of
thunderstorm activity once again from Wednesday through late
Thursday. The final push with cold air advection will occur next
Friday afternoon and likely dry for next weekend.

AVIATION...

Most terminals currently with MVFR to VFR ceilings, with a few
exceptions, KGPT currently has SCT-BKN009. Little change in
conditions through sunset, then expect MVFR conditions to
predominate through much of Saturday. Winds could be an issue
through the period, especially on east/west oriented runways with
gusts to 25-30 knots likely at most terminals during daytime hours.
Cannot rule out some isolated to scattered convection Saturday
afternoon, but threat not high enough at an individual terminal to
carry almost 24 hours out. 35

MARINE...

The pressure gradient will remain tight across the coastal waters through
the weekend. A deepening low pressure system over the Plains will
yield southerly winds of 20 to 30 knots through Sunday. Small
Craft Advisories are posted for the entire coastal waters through
Sunday morning as the waters will be hazardous all weekend. There
is also an outside chance that the Small Craft Advisory may have
to be upgraded to a Gale Warning, especially east of the
Mississippi River Saturday afternoon through early Sunday morning.
This will have to be watched as this system evolves. Gulf waters
due to these winds and seas of up to 7 feet. The tightening
pressure gradient will result in strong onshore winds of 25 to 30
knots impacting the coastal waters from Saturday afternoon through
Sunday evening. Very rough seas of up to 12 feet could also
impact the open Gulf waters during this period. Over the sounds
and lakes waves of up to 6 feet will be possible.

Winds will shift to the northwest late Sunday night and Monday in
the wake of the low pressure system and cold front. Winds should
remain elevated at around 20 knots through morning hours on Monday
and seas will remain rough. Conditions will begin to improve Monday
night and Tuesday as high pressure settles directly over the waters.
Winds will veer back to the east by Tuesday and decrease to between
10 and 15 knots. Seas should also fall back to 2 to 4 feet by
Tuesday morning.

DECISION SUPPORT...
DSS CODE...Blue.
DEPLOYED...None.
ACTIVATION...None.
ACTIVITIES...Monitoring severe potential for Sunday.

Decision Support Service (DSS) Code Legend:
GREEN  = No weather impacts that require action
BLUE   = Long fused Watch/Warning/Advisory in effect or high
         visibility event
YELLOW = Heightened impacts with short fused
         Watch/Warning/Advisory issuances; Radar support
ORANGE = High Impacts - Slight to Moderate risk of severe weather;
         Nearby tropical events, HAZMAT or other large episodes
RED    = Full engagement for moderate risk of severe weather; Direct
         tropical threats; events of national significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  72  88  73  78 /  10  30  20 100
BTR  74  89  75  78 /  10  30  20 100
ASD  74  86  75  80 /  10  20  20  80
MSY  76  87  75  82 /  10  20  10  90
GPT  75  84  76  79 /  10  20  20  70
PQL  72  84  74  81 /  10  20  20  50

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Wind Advisory from 6 AM to 10 PM CDT Saturday for LAZ034>037-039-
     040-046>050-056>072.

     Coastal Flood Advisory until midnight CDT Sunday night for
     LAZ040-050-058-060>064-066>070-072.

GM...Small Craft Advisory until 7 AM CDT Sunday for GMZ530-532-534-
     536-538-550-552-555-557-570-572-575-577.

MS...Wind Advisory from 6 AM to 10 PM CDT Saturday for MSZ068>071-077-
     080>082.

     Coastal Flood Advisory until midnight CDT Sunday night for
     MSZ080>082.

GM...Small Craft Advisory until 7 AM CDT Sunday for GMZ532-534-536-
     538-550-552-555-557-570-572-575-577.

&&

$$



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