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

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368
FXUS64 KLIX 230928
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
328 AM CST Wed Jan 23 2019

.SHORT TERM...A positively tilted upper level trough axis will
take on a more neutral tilt as it moves through the forecast area
today. This morning, the combination of strong positive vorticity
advection, favorable jet dynamics, and ample moisture will allow
for scattered to numerous showers and a few thunderstorms to begin
developing. By late morning and early afternoon, a strong cold
front associated with this approaching trough axis will push
across the forecast area, and expect to see a band of heavier
showers and thunderstorms impact the region. After reviewing model
soundings, it looks like the set-up will be our fairly typical
high shear and low CAPE event. Ample shear is in place with 0-6km
speed shear values around 50 knots and storm relative helicity
values in excess of 200m2/s2. However, instability is fairly
limited with marginal lapse rates of around 6.0C/km, and MLCAPE
values of 400 J/KG or less. If a severe thunderstorm manages to
develop today, the primary threats will be damaging wind gusts and
tornadoes. Due to the weak lapse rates, hail should not be a
threat with any severe storms today. After the front moves past an
area today, a quick drop in temperatures from the 60s into the 50s
and then the 40s by late this afternoon can be expected. Strong
subsidence and dry air advection in the wake of the front and
upper level trough axis will also lead to rapidly clearing skies
through the evening hours. By tomorrow morning, clear skies,
breezy conditions, and cold temperatures in the 30s can be
expected.

Deep layer northwest flow in the mid and upper levels will then
dominate the forecast area through Friday. In the low levels, a
strong high pressure system will settle over the area. A very dry
and very stable airmass will remain in place, and have clear skies
and colder than average temperatures in the forecast. Overnight
lows will drop into the 30s both Thursday and Friday nights, and
daytime highs will only warm into the middle 50s.

.LONG TERM...The northwest flow pattern and a strong surface high
will remain in firm control of the forecast area through Monday.
Some modification in temperatures is expected over the weekend as
cold air advection wanes. Daytime highs should warm back to more
normal readings in the low to mid 60s from Saturday through Monday
and overnight lows will be closer to average in the upper 30s and
lower 40s.

A reinforcing front will sweep through the region late Monday
night and early Tuesday. This front should be moisture starved,
and only have a slight chance of showers in the forecast mainly
due to the fairly strong forcing anticipated along the front
itself. By Tuesday evening, the front should be in the Gulf and a
drier, colder, and more stable airmass should begin to advect back
into the area for Tuesday night and Wednesday.

&&

.AVIATION...Most terminals will have ceilings remain at OVC060. There is a
possibility that a few sites could have TEMPO decks move through at
OVC003 ahead of the front and this could cause some vis reduction
this morning. Wind shift from southerly to NW with fropa roughly
around 15z at BTR, 18z MSY, and 20z GPT. The front will carry mainly
SHRA inland while some TSRA will be found along and near coastal
locations Wed. There is also a slight chance that a light wintry mix
will move through at some northern terminal locations just as the
precip is moving out this evening, but even if this occurs, it is
not expected to cause any impacts.

&&

.MARINE...As the front passes winds will become NW and rapidly rise to around
25kt today. This will include all protected waters as well. Wind
speeds are not being handled well by any raw model guidance and
therefore the model averages are also having trouble with this. 1kft
winds are already fairly strong behind the front and it shouldn`t be
difficult to bring the majority of those speeds to the sfc. It would
not be surprising to observe sustained winds up to 25kt with a
few gusts possibly to gale force on the lake and definitely over
open waters. Wind speeds will only back off a little before the
northerly winds are reinforced by another cold front moving
through Friday. Southerly winds will be back by late Saturday
ahead of the next front moving through Saturday night into Sunday
of next weekend with another set of strong winds.

&&

.DECISION SUPPORT...

DSS code: Yellow
Deployed: None
Activation: None
Activities: small craft advisory and slight risk severe wx
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 rain; direct tropical threats; Events of National
         Significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  64  31  54  30 / 100  40   0   0
BTR  64  32  55  32 / 100  30   0   0
ASD  68  33  56  31 / 100  70   0   0
MSY  69  37  54  37 / 100  60   0   0
GPT  67  35  55  34 / 100  80   0   0
PQL  71  37  56  32 / 100  80   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 6 AM CST Thursday for GMZ536-538-550-
     552-555-557-570-572-575-577.

     Small Craft Advisory from noon today to 6 AM CST Thursday for
     GMZ530-532-534.

MS...Coastal Flood Advisory until 6 AM CST early this morning for
     MSZ080.

GM...Small Craft Advisory until 6 AM CST Thursday for GMZ538-550-552-
     555-557-570-572-575-577.

     Small Craft Advisory from noon today to 6 AM CST Thursday for
     GMZ532-534.

&&

$$

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