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

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FXUS64 KLIX 161635

Area Forecast Discussion
National Weather Service New Orleans LA
1035 AM CST Tue Jan 16 2018

Made updates this morning to bring up POPs this afternoon and
evening and better clarify rain to freezing rain to snow switch.
As of 1030am a light wintry mix has been reported in West
Feliciana and West Baton Rouge Parish with temps at 30-32.



.PREV DISCUSSION... /issued 830 AM CST Tue Jan 16 2018/

12z sounding is already obsolete since the cold front passed
through about an hour after the balloon launch. Surface
observations indicate low level winds have already shifted to the
northwest, and expect cold air advection to begin shortly. We will
do a special launch at 18z to gauge wintry precipitation
potential this afternoon and evening. 95/DM

PREV DISCUSSION... /issued 311 AM CST Tue Jan 16 2018/


Today through this evening will be the main focus of the short
term discussion. A strong arctic cold front is currently pushing
across northern Louisiana, and will move through the forecast area
during the morning hours. Before this front moves in, a surge of
warmer air has started to advect in from the west. This has
resulting in rising temperatures early this morning, and now
expect to see temperatures around daybreak in the upper 30s and
lower 40s at most locations. As a result, the initial
precipitation that moves will be in the form of rain.

By late morning and early afternoon, a transition over to light
sleet and snow should occur across the northern half of the
CWA...mainly along and north of the I-12 corridor. Fortunately,
precip amounts will be very light as moisture divergence is still
expected to occur over Southeast Louisiana today. Currently
forecasting not much more than a dusting of snow across Southwest
Mississippi and the Florida Parishes of Southeast Louisiana by
this evening. Below the I-10 corridor, a transition from light
rain to light sleet and snow should occur in the late afternoon or
early evening hours. Again, any precipitation will be very light,
and little to no accumulation is expected. However, the risk of
some black ice forming on a few bridges has prompted the extension
of the Winter Weather Advisory to include Baton Rouge, New
Orleans, the River Parishes, and Houma.

Temperatures will quickly drop in the afternoon and evening
hours, and still expect to see lows middle to upper teens north of
I-12 and the lower to middle 20s elsewhere. Hard Freeze and
Freeze warnings remain in effect for the region. Additionally,
strong north winds of 15 to 20 mph combined with the cold
temperatures will push wind chills into the single digits and
teens late tonight and tomorrow morning. A wind chill advisory
also remains in effect for the area due to these bone chilling

The heart of the 925mb cold pool will be over the forecast area
tomorrow, and temperatures should only climb into the middle to
upper 30s at most locations. Wind chills will make it feel like
the 20s throughout the day. Winds should finally begin to decrease
tomorrow night as a surface high settles over the region, and
clear skies and low humidity values will allow temperatures to
fall back into the upper teens and lower 20s north of I-10
corridor, and the middle to upper 20s closer to the Louisiana

A more zonal flow regime will develop on Thursday as the upper
level trough and main heart of the arctic cold pool lift to the
northeast of the region. Temperatures will modify a bit, and
expect to see highs warm into the middle to upper 40s. A dry
airmass will linger over the area, so skies should remain mostly
clear. Temperatures Thursday night will fall back below freezing
for the northern half of the CWA, but only a light to moderate
freeze is expected.


A weakening shortwave trough over Texas will push through the
forecast area Friday night into Saturday. Increasing high level
cloud cover is expected on Friday, but the low to mid levels
should remain relatively dry. As a result, a dry forecast is in
place for Friday. Temperatures will also continue to modify, and
expect to see highs in the middle to upper 50s. Weak moisture
advection in advance of the shearing out shortwave trough will
allow for isolated to widely scattered shower development Saturday
into Saturday evening. Fortunately, lapse rates on Saturday remain
very weak, so no thunderstorm activity is expected. Temperatures
will continue to warm, and expect to see highs in the upper 60s
and lower 70s Saturday afternoon.

Saturday night appears to be the most favorable time for a
possible sea fog event to develop. Onshore flow will continue to
advect in a warm and humid airmass through the night. The
temperature and dewpoint spread compared to the nearshore water
temperatures looks favorable for sea fog to form. Additionally,
weak shortwave ridging aloft will also assist in suppressing
boundary layer turbulence. With less boundary layer turbulence and
mixing in place, fog formation is more likely. Temperatures should
only dip into the middle to upper 50s Saturday night.

Sunday should start off foggy, but increasing positive vorticity
advection in advance of an approaching shortwave trough axis and
front should result in the fog lifting by mid-day. Onshore flow
should also increase in advance of this upper level trough and a
deepening surface low in the Midwest. As temperatures warm into
the lower to middle 70s, instability should also increase. Model
soundings suggest some marginal instability with CAPE of 500-1000
J/KG, and this should support the development of scattered
thunderstorms Sunday afternoon into Sunday evening. A veering wind
profile from the surface into the mid-levels should support some
directional shear, and this is noted by storm relative helicity
values of around 300 M2/S2. Thus, a high shear/low CAPE
environment appears to be in place for Sunday. Severe
thunderstorms could develop, and this will need to be monitored
over the coming days.

Increasing subsidence and negative vorticity advection will take
hold in the wake of the passing front on Monday and Tuesday.
Temperatures will cool a bit behind the front, but a Pacific based
airmass will be advecting in. As a result, highs should only dip
down to the lower 60s, and overnight lows should only cool to near
40 degrees at night. These temperatures are near seasonal averages
for mid-January.


Low clouds will begin to build over the area today ahead of a cold
front expected to quickly surge through during the late morning
hours and should be through all of the terminals by 18z. MVFR cigs
will begin to develop from northwest to southeast beginning around
15/16z by MCB and BTR. Precip should begin to slowly develop and
fall over the area also from northwest to southeast and should begin
as either light rain, maybe even light freezing rain but more likely
as sleet at BTR and MCB and then likely quickly switching to snow at
MCB between 18-20z and likely around 19-21z at BTR. All terminals
will likely show some frozen precip by this afternoon and into the
evening hours. All precip will be out of the area by midnight but if
icing conditions develop, it could remain until after we warm above
freezing Wednesday. This would occur on mainly protruding and
elevated structures.


Strong offshore winds will develop in the wake of a strong arctic
cold front with small craft advisory conditions forecast by
afternoon across all coastal waters. Will keep headlines as is for
now as sustained winds should be in the mid to upper portion of
advisory criteria but there will definitely be gale force gusts
occurring with this system. Winds will remain elevated into
Wednesday night before easing on Thursday as strong high pressure
builds into the region. The high will shift to the east by the end
of the week as the next system begins to approach the area from
the western gulf.


DSS code: Yellow.
Deployed: None.
Activation: None.
Activities: Winter weather threats today/tonight
            Hard freeze threat tonight and Wednesday night
            Dangerous wind chills tonight/Wednesday morning

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  37  16  37  18 /  80  30   0   0
BTR  40  18  39  20 /  80  30   0   0
ASD  42  20  40  21 /  30  60   0   0
MSY  43  23  38  26 /  30  60   0   0
GPT  45  22  39  23 /  30  60   0   0
PQL  50  22  40  21 /  30  60   0   0


LA...Freeze Warning from 6 PM this evening to noon CST Wednesday for

     Wind Chill Advisory from 9 PM this evening to 11 AM CST
     Wednesday for LAZ034>037-039-040-046>050-056>072.

     Hard Freeze Warning from 6 PM this evening to noon CST Wednesday
     for LAZ034>037-039-040-046>050-056>065-071-072.

     Winter Weather Advisory from 2 PM this afternoon to midnight CST
     tonight for LAZ039-040-056>065.

     Winter Weather Advisory until midnight CST tonight for

GM...Small Craft Advisory until 6 PM CST Wednesday for GMZ536-538-550-

     Small Craft Advisory until midnight CST Wednesday night for

     Small Craft Advisory until noon CST Wednesday for GMZ530-532-534.

MS...Wind Chill Advisory from 9 PM this evening to 11 AM CST
     Wednesday for MSZ068>071-077-080>082.

     Hard Freeze Warning from 6 PM this evening to noon CST Wednesday
     for MSZ068>071-077-080>082.

     Winter Weather Advisory from 2 PM this afternoon to midnight CST
     tonight for MSZ071-077-080>082.

     Winter Weather Advisory until midnight CST tonight for

GM...Small Craft Advisory until 6 PM CST Wednesday for GMZ538-550-552-

     Small Craft Advisory until midnight CST Wednesday night for

     Small Craft Advisory until noon CST Wednesday for GMZ532-534.


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