FXUS64 KLIX 202046

Area Forecast Discussion
National Weather Service New Orleans LA
346 PM CDT Fri Oct 20 2017


Not a significant change in thinking from the previous forecast. A
potent upper level trough and associated surface low and cold
front will impact the area through the weekend. Lingering coastal
showers will persist into the overnight hours tonight, but most of
the area will remain fairly dry throughout the night. Increasing
dewpoints through the night will keep overnight lows higher than
average in the upper 60s and lower 70s.

Tomorrow will see increasing positive vorticity advection and
omega values overspread the forecast area. As a result, expect to
see greater convective coverage through the day with the highest
POP values occurring in the afternoon hours. It still looks like
the greatest risk of shower and thunderstorm activity will be
closer to the Atchafalaya Basin or west of the I-55 corridor where
likely POP of 60 percent is in the forecast. The farther east, the
lower the rain chances as moisture convergence and overall forcing
looks to be lower. This is noted by a lower 20 to 30 percent rain
chance along the Mississippi Coast. This risk of severe weather is
limited tomorrow due to fairly low wind shear values, but a few
stronger thunderstorms producing lightning strikes and locally
heavy downpours cannot be ruled out. Temperatures will remain mild
with highs easily rising back into the lower to middle 80s. The
convective coverage should decrease a bit Saturday night as
temperatures cool back into the upper 60s and lower 70s, but still
expect to see scattered shower and thunderstorm activity persist
through the night. This will mainly be due to a continuation of
higher omega values and related forcing in the mid and upper
levels associated with the approaching longwave trough axis.

The biggest change in thinking for Sunday is a reduction in the
threat of severe weather. The reason for this reduction is a
slightly warmer air mid-level airmass than previously thought. It
looks like wet bulb zero heights should be closer to 13000 feet
now, and mid-level lapse rates will be slightly weaker. This
decreases the overall MLCAPE values to less than 1000 J/KG, and
this will result in weaker updraft strength than thought the last
few days. Speed shear values will also remain limited with 0-3km
shear not exceeding 30 knots and helicity values tending to
remain at 100 m2/s2 or less. Given these parameters, some stronger
thunderstorms could develop on Sunday, but the prospect for severe
thunderstorms will be greatly limited. At worst, an isolated
severe thunderstorm may try to form over the northern third of the
CWA where shear values and lapse rates will be most conducive.
Otherwise, it still looks like a band of showers and thunderstorms
will develop along a pre-frontal trough late Sunday morning over
central Louisiana and then spread eastward across the entire CWA
Sunday afternoon into Sunday evening. Confidence in this occurring
is fairly high and have categorical POP in excess of 80 percent in
the forecast for Sunday. Temperatures will be near average in the
upper 70s and lower 80s on Sunday.

The main cold front and associated neutral tilted upper level
trough axis should push through the forecast area Sunday night.
Still expect to see likely POP of 60 to 80 percent across the
Mississippi coast Sunday evening, but lower POP of 20 to 50
percent is expected across Southwest Mississippi and Southeast
Louisiana as the cold front moves through. Later Sunday night,
skies should begin clearing and rain come to an end over the
western third of the forecast area. Along the Mississippi Coast,
only scattered showers and isolated elevated thunderstorms are
expected late Sunday night in the wake of the passing cold front
and trough axis. Temperatures will also see a gradient with lows
in the upper 50s and lower 60s north and west and middle to upper
60s in the southern and eastern parts of the forecast area.


Next week will see a largely dry and stable weather pattern take
hold of the forecast area. Deep layer northwest flow aloft and
strong ridging in the low levels will result in strong negative
vorticity, dry air, and cold air advection into the region through
the week. However, there will be some initial shower activity
Monday morning as this airmass builds in and trough impacting the
area this weekend departs. Skies will clear and rain chances will
come to an end through the afternoon hours. By Monday night,
clear skies, low humidity, and cool temperatures will be firmly in
control. Temperatures on Monday will be significantly cooler due
to the cold air advection with highs only climbing into the lower
to middle 70s and lows dipping into the 50s Monday night.

A reinforcing shortwave feature in the upper levels along with an
attendant cold front will sweep through on Tuesday. This front
will advect in an even colder airmass, and expect to see lows
Wednesday night drop into the middle to upper 40s over inland
areas and the lower 50s along the coast. Although skies will be
sunny, low 925mb temps of around 45 degrees should translate to
surface temperatures in the middle to upper 60s Wednesday
afternoon. Some modification in temperatures is expected Thursday
and Friday as the ridge axis shifts to the east and southerly
winds develop. By Friday, temperatures should warm back to more
seasonal temperatures with highs in the upper 70s and lows middle
to upper 50s.



A high cloud deck will linger over the area through the entire
forecast period, but prevailing VFR conditions are expected. There
could be a brief period of lower ceilings and possibly some light
fog at KBTR around 12z tomorrow, but any MVFR ceiling and
visibility impacts will be very short-lived. After 12-13z
tomorrow, some widely scattered convection could develop. Have
included PROB30 wording to reflect this low chance of showers and
thunderstorms tomorrow morning. 32



Moderate to occasionally strong easterly flow will continue across
the coastal waters through Saturday. This will result in exercise
caution conditions through tonight and small craft advisory criteria
east of the Mississippi river Saturday morning through late
Saturday night. Will issue a small craft advisory east of river
through this time. Winds are expected to ease a tad before a cold
front pushes through the coastal waters late Sunday night. Moderate
to strong offshore flow will develop in the wake of this
front that will persist as a another stronger cold front expected
Tuesday afternoon. 18



DSS code: Green.
Deployed: None.
Activation: None.
Activities: None.

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 66 83 69 78 / 10 40 40 90
BTR 69 85 70 80 / 10 50 50 90
ASD 68 84 70 81 / 10 50 40 90
MSY 72 84 73 82 / 10 50 50 90
GPT 69 83 71 80 / 10 30 30 90
PQL 67 83 69 80 / 10 20 30 90


GM...Small Craft Advisory from 7 AM Saturday to 7 AM CDT Sunday for

GM...Small Craft Advisory from 7 AM Saturday to 7 AM CDT Sunday for



Back to Main Forecast Discussion Page