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

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FXUS64 KLIX 221739
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
1239 PM CDT Mon Apr 22 2019

.UPDATE...
Updated for 18z aviation discussion

&&

.AVIATION...
VFR conditions are expected to continue through Tuesday morning.
Lower level clouds in the southerly low level winds across
southwest Louisiana will likely develop eastward into portions of
southeast Louisiana on Tuesday, but have not indicated any MVFR
CIGS at this time since most of the lower clouds should remain
scattered Tuesday morning. Brief, patchy ground fog could occur
at an airport or two late tonight/early Tuesday morning, but
confidence is too low for inclusion at this time. 22/TD

&&

.PREV DISCUSSION... /issued 411 AM CDT Mon Apr 22 2019/

SHORT TERM...It was another nice quiet night. Clear skies and
light winds have allowed the region to cool and by 8z most of the
region ranged from the upper 40s to mid 50s. Still a few more hours
for temps to drop another degree or two before sunrise. Still looks
like our main forecast problem is the system coming through
Thursday.

Forecast remains quiet today and through Wednesday. We will remain
under the influence of a broad ridge which will keep the region dry
and allow temps to continue to moderate. H925 temps climb to around
17-18C and this should lead to most of the region reaching the
upper 70s to near 80. As for tonight one more night of decent
radiational cooling conditions should be in place however with LL
winds out of the southeast moisture will slowly be creeping up and
thus lows should be a little warmer tomorrow morning.

Heading into Tuesday the ridge axis will slide east; at the same
time the nose of the upper jet will begin to push into the region.
Both of these would allow upper level moisture to stream over the
area with a blanket of cirrus likely moving in. H925 temps will
increase a little more but thanks to these high clouds, afternoon
highs will likely be similar to todays.

Again Wednesday is the transition day. The antagonist will only
just be moving into western TX late Wednesday morning and may
actually locally amplify the ridge across the southeast CONUS. This
would keep the area on the warm and dry side of the forecast. /CAB/

LONG TERM...Model consistency and continuity continue to be great
in the medium range. Confidence continues to increase in the
forecast but there are still some questions with coverage and
intensity of convection Thursday.

Wednesday night we will finally begin to see some impacts from our
approaching system. As the closed low moves towards the ARKLATEX
Wednesday night lift will increase across the region. An organized
area of showers and thunderstorms will likely be ongoing across TX
and move into LA overnight. It may begin to approach the
northwestern portions of the CWA during the early morning hours but
should weaken as runs into the ridge and ahead of the better
dynamics. Conditions should improve Thursday for convection to
become re-invigorated around midday as the system approaches the
Lower MS Valley and another impulse moves into the region. There
continues to be some concern on the coverage and intensity
Thursday and Thursday evening. It is beginning to look like a
large area of convection will either move along the LA coast or
develop along the central and southeast LA coast and in the Gulf.
This looks to coincide with a surge in the H85 theta e air and a
mid level jet streak. If this does occur then there is a good
chance that half of the CWA will get cut off from significant
rain. Also multiple models are suggesting another blob of
convection could track across the northern 3rd of the CWA or
perhaps just north of the area. This area would have more support
to work with in the forms of a LL jet, the upper level jet (LFQ
or perhaps even a possible coupled jet region shown by the ECMWF),
and more lift. With this would not be surprised to see a stretch
of minimum rainfall bisecting our CWA and will try to show this in
the weather and pop grids for Thursday. Convection will continue
to work to the east overnight Thursday night and may actually
taper off completely before sunrise.

As for the severe and heavy rain threat there is still some concern.
The strong to severe potential is still there however the kinematic
field is marginal and instability is just adequate (nothing seems to
really jump out). If convection doesn`t develop over the Gulf and
rob half of the CWA of moisture, it would allow the region to
become a little more unstable things may become more favorable.
As for the heavy rain threat this may be a little more likely.
Very rich moisture will be in place. Combine that with some
instability to work with and favorable jet dynamics aloft and
thunderstorms will be efficient. The location where the heaviest
rain may occur looks to be across the northwestern portions of the
CWA, close to the same locations as last Thursdays system.

Friday we will still have the upper low/tough over the region and
the cooler mid levels temps will be in place. As the region heats up
we could see scattered afternoon convection once. This should be
diurnally driven and likely confined to of very close to the land.
This activity will quickly come to an end as the sun goes down.

Another quiet weekend is in store but don`t look for the cool down
that we saw this weekend. This system is coming from the desert
southwest and will not be associated with any surge of cooler and
drier air. LL temps really don`t drop and dewpoints only drop a
little. /CAB/

AVIATION...Expect VFR conditions for all area terminals through the
entire forecast period. For today, some thin high-level cirrus will
try to press east across central LA at around 20-25kft. With a
surface high pressure system centered now to the northeast across GA
and the Carolinas, onshore flow will persist today. Only minor
hazard to speak of will be a wind shift later this morning/early
afternoon at and near coastal TAF sites from a northward surging
seabreeze boundary, with a sudden change to a southerly wind
direction and gusts 08 to 12 knots. Otherwise, no additional impacts
or hazards are expected. KLG

MARINE...A surface high pressure system to the northeast of the
northern Gulf will continue to promote onshore winds through mid-
week, ranging roughly from the ESE to SE. Winds will be on the light
side throughout this time frame, but may gust to around gentle to
moderate breeze at times, especially for outer marine zones. A storm
system is due to approach the area on Thursday, with all long-range
model guidance in good agreement on timing and confidence with this
system. ATTM, a cold front will send showers and thunderstorms
quickly across the northern Gulf coast late Thursday morning through
Thursday evening. Some of these storms may be strong to possibly
severe, with main marine hazards from these storms being strong
gusty winds to gale force or higher, waterspouts and perhaps small
hail in any stronger storm. This storm system will be slow to want
to exit the area on Friday, with a lingering surface low pressing
south and east across coastal MS/AL and into northern Gulf waters.
While widespread strong winds appear not to be an issue during this
time frame, transitioning winds to more from the NW will accompany
marine areas as this low passes. Long-range guidance also supports
the idea of any wrap-around precipitation to be confined more to
land areas, which should keep marine zones dry through this period,
followed by a continued drying trend through the weekend. KLG

DECISION SUPPORT...

DSS code: Blue.
Deployed: None.
Activation: None.
Activities: River flood warnings

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, or direct tropical threats; Events of
         National Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  80  53  79  57 /   0   0   0   0
BTR  81  57  81  60 /   0   0   0   0
ASD  78  56  79  59 /   0   0   0   0
MSY  78  60  79  63 /   0   0   0   0
GPT  75  57  76  61 /   0   0   0   0
PQL  78  54  79  58 /   0   0   0   0

&&

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

$$



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