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

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FXUS64 KLIX 292020

Area Forecast Discussion
National Weather Service New Orleans LA
320 PM CDT Sat Apr 29 2017

The synoptic analysis remains the same as the previous forecast
package. GOES16 showing a mid level low pressure system near the
four corners with a wide open Gulf of Mexico feeding an excessive
rain event over portions of the midwest. High pressure centered
off the coast of the Carolinas will give way as the low moves
east to the TX panhandle by midnight, central KS noon Sunday, and
IA Monday morning. As the low moves east, it will drag a cold
front across the area Sunday.

12z sounding showed less of a cap compared to the previous run.
There is still a cap to limit convection through today. PW
measured at 1.32 inches with impressive low level winds of 40kt at
945mb, then weakens until 282mb with 43kt. A 3400 J/KG CAPE was
impressive on a 12Z sounding with lapse rates approaching 7C/km.
It will be tricky how much of the cap erodes Sunday ahead of a
strong line of thunderstorms forecast to move through during the
afternoon. This could highly impact the forecast timing of rain on
Sunday. Current thinking is most of the convection will be right
along the frontal boundary as a low level jet sets up tonight
with 50kt around 850mb. Looking at the GFS forecasted convective
parameters... 1500-2300 J/KG CAPE prominent along the front
with 0-3km bulk shear values at 20-30kt. Lapse rates progged
at 6C/km at 18z Sunday and 5C/km by 00z Monday. Taking all this
into account, expected impacts remain as previously thought.
Impact 1, heavy rain along the front can be expected with 2-4
inches of rain in a short period of time. Could be some local
flooding. 48 hour QPF used to compute river forecasts, with
sharp rises, but most at or below flood stage. Impact 2, winds
will continue to gust upwards 20 to 25 mph. As the front
approaches, winds will gust closer to the 30 to 35 mph range. This
poses a problem once convection nears as it would not take much
to push gusts to over 50 mph near the stronger storms. Shear is
not overly impressive, however there is always a chance of a quick
spinup tornado along the squall line Sunday afternoon into the
evening as the line moves eastward. Impact 3, dangerous lightning
could along the squall line poses a risk to outdoor activities
once thunderstorms arrive along the front. Impact 4, strong
persistent southeasterly flow is causing tides to elevate 1-2
feet above normal. This poses the greatest impact during high
tides around mid to late afternoon both Saturday and Sunday. Some
traditional roads that flood easy along the beach could experience
periods with 3-5 inches of water. These impacts pose of risk to
outdoor events and precautions should be taken. [KEG]

High pressure builds following the front Sunday bringing a brief
period of lower dew points. Return flow begins Wednesday with
rain again the forecast for Thursday. GFS is quite aggressive
with rain amounts on Thursday. Frontogenesis over OK and a
developing low pressure system by 12Z Thursday. The low is progged
over central AR by Fri at 00z and north AL Sat 12z. That track
brings a tight gradient over land areas towards the end of next
week which will bring strong winds over the region. Will have to
watch this system close for heavy rain and high winds. Both the
ECMWF and GFS continue this low to central FL at H240. [KEG]


Mid afternoon conditions split pretty evenly between MVFR and VFR
conditions with the lowest conditions at KGPT and KHUM, where
ceilings are near FL015. Expect MVFR ceilings to return within a few
hours of sunset where they aren`t already in place. Will introduce
TSRA for western portions of the area late Sunday morning, including
KMCB, KBTR and KHDC. The 00z package will spread the mention of
storms across the remaining terminals between 18z Sunday and 00z
Monday, although storms could linger beyond that at KGPT.

Winds will be a factor during the daylight hours with gusts to 30
knots or higher likely at most terminals. This will especially be a
problem for east-west oriented runways. Winds may lose some of their
gustiness during the overnight hours, but should quickly return
around 14-15z Sunday. Expect winds to diminish after the passage of
the front. 35


The strong pressure gradient continues over the coastal waters
this weekend.  Low pressure continues to deepen over the four
corners area and will bring a strong cold front and associated
squall over the coastal waters Sunday afternoon through the
evening. Winds will increase to 20 to 30 kt Sunday. A Small Craft
Advisory has been posted for all our marine areas as winds and
seas will create hazardous if not dangerous conditions at times.
Waves near 6 feet in larger lakes, near 7 feet in the coastal
waters, and 9 to 12 feet in the open Gulf of Mexico can be
expected ahead of the front. Once the front moves through, winds
will shift to the northwest last Sunday night into Monday. Winds
will remain high post front at around 20 knots and waters will
still be rough. Expect improving conditions by Tuesday as high
pressure builds and seas begin to calm. Another low pressure
system is expected to impact the coast towards Thursday and Friday
of next week. [KEG]



DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Emergency Management emails
            Monitoring convective threats for Sunday.

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  73  78  52  80 /  20 100  50  10
BTR  75  78  53  80 /  30 100  30  10
ASD  75  80  60  79 /  10 100  70  10
MSY  75  82  61  79 /  20 100  60  10
GPT  76  79  62  77 /  10 100  80  10
PQL  74  81  63  78 /  10 100  90  10


LA...Wind Advisory until 10 PM CDT this evening for LAZ034>037-039-

     Coastal Flood Advisory until midnight CDT Sunday night for

GM...Small Craft Advisory until midnight CDT Sunday night for GMZ530-

MS...Wind Advisory until 10 PM CDT this evening for MSZ068>071-077-

     Coastal Flood Advisory until midnight CDT Sunday night for

GM...Small Craft Advisory until midnight CDT Sunday night for GMZ532-


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