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Area forecast discussion 
National Weather Service New Orleans la
720 am CST Wednesday Mar 4 2015

..sounding discussion...

The boundary layer is mostly saturated this morning leading to fog
to develop near the Mississippi Gulf Coast and around Lake
Pontchartrain. Much drier air is above 7200 feet. Winds are the
south-southwest at 20 knots in the low-levels...from the southwest
at 30 knots in the middle-levels and west-southwest in the upper
levels. A peak wind speed of 86 knots is located at 35500 feet.

12z balloon info: no issues with the flight this morning that
traveled 79 miles downrange from the office and reached a height
of 20.6 miles above the ground bursting northwest of Hurley MS.



Previous discussion... /issued 501 am CST Wednesday Mar 4 2015/


Surface weather map has a cold front extending from western
Tennessee southwestward across Arkansas into northwest Texas. A
broad and very strong upper level jetstream extends from southern
Baja California/northwest Mexico northeast across the central and Southern
Plains to the lower Great Lakes region...with 250 mb winds as high
as 100 knots extending south into northern Louisiana and north
Mississippi. Strong and digging middle/upper level troughs are noted in
water vapor imagery across both the northern and southern streams
from central Canada and the northern plains region to southwest of
the Baja California peninsula. A subtropical high over the southern/eastern
Gulf of Mexico and northwest Caribbean Sea is maintaining the warm
airmass over the Gulf Coast region for the time being.

Short term /today through Friday night/...

The shortwave over the northern plains will move southeast across
the lower Missouri Valley tonight. This will drive the Arctic cold
front southeast towards the extreme northwest portion of the
forecast area around midnight tonight and coastal areas around
daybreak to the early morning hours on Thursday. Ahead of the front
it will remain rather warm and humid with highs today expected to
reach the middle 70s to lower 80s. Isolated showers this morning may
become more scattered in coverage in some areas this
afternoon...however the bulk of the rain will hold off until tonight
and Thursday morning as the cold front approaches and moves through.
Rather limited instability is expected today due to poor middle level
lapse have removed mention of thunder from the forecast
through 6 PM. A few thunderstorms could mix in with showers after
sunset this evening as some slightly better forcing may initiate
some better elevated instability. No severe thunderstorms are

Regarding the threat of freezing precipitation...not much change in
thinking is noted from the previous forecast...except have
temperatures dropping to near freezing maybe an hour or two earlier
Thursday morning for a small portion of the area across northern and
western Wilkinson County. Otherwise...have kept the mention of rain
with a chance of light freezing rain or sleet just to the north of a
line from New Roads to McComb from 8 am to noon on Thursday.
Confidence is low to moderate...however expected impacts still
remain too low to go out with a winter weather or Freezing Rain
Advisory at this time. This will continue to be monitored on the day
shift today. It is likely the warm temperatures today and late
arrival of the cold air will not give the ground/near surface area
and even bridges sufficient time to drop to near freezing and allow
ice to develop...and any late morning light rain falling into near
freezing temperatures will be offset by the slight insolation of the
March sun through the clouds.

Rainfall is expected to taper off and end Thursday afternoon. While
the GFS and NAM keep some slight chance to low end chance probability of precipitation going
into Thursday night...the quantitative precipitation forecast is well to the south and mostly out in
the Gulf of have lowered the pop to less than 15 percent
in areas that are expected to see temperatures drop below 33 to 34
degrees in best agreement with the drier European model (ecmwf). Since southwest flow
can occasionally bring unexpected surges of moisture...this will
also have to be monitored as any precipitation that can move farther
inland Thursday night would likely fall as a wintery mix of
snow...sleet...and/or freezing rain.

It will be windy and cold on Friday into Friday night...but no
precipitation is expected.

Long term /Saturday through Tuesday night/...

Next shortwave trough should remain over northwest Mexico to near
extreme West Texas on the central Gulf Coast region
will remain under the influence of surface high pressure and a
shortwave ridge aloft. Have lowered the pop to slight chance range
for rain.

The active southern stream is expected to bring our next series of
disturbances and chances of rain Sunday through Tuesday. The models
have backed off on any substantial surface low development in the
Gulf of Mexico. Temperatures will gradually modify/warm through the
period but remain below the seasonal normals.

22/dew point


Prevailing LIFR and IFR ceilings of 200 to 1000 feet are in place at
most of the terminals. Only...kmsy and knew are still seeing MVFR
ceilings at this time. Expect these stations to see some IFR
ceilings by 12z. Some reduced visibilities of 1 to 3 miles are also
occurring at most terminals. However...kgpt and khum are seeing
some IFR and LIFR visibilities of less than one mile. The boundary
layer will quickly mix out by 15z...and expect to see ceilings
ranging from 2500 to 5000 feet from 18z through 00z. After 00z...a
band of light to moderate rain should develop over the terminals.
This band of rain will keep MVFR visibilities of 3 to 5 miles and
some lower stratus ranging from 1000 to 2500 feet in place over the
terminals through the night. 32


Onshore flow of 10 to 15 knots on the western periphery of a surface
ridge will continue through tonight. This onshore flow has allowed
for some advection fog to form over the cooler nearshore
waters...sounds...and tidal lakes this morning. The fog should
linger through middle-morning before lifting. Another round of fog will
be possible tonight before a cold front moves through.

This cold front will sweep through the waters early
Thursday...resulting in a period of strong offshore winds of 25 to
30 knots and seas of 6 to 9 feet in the open Gulf waters. These
Small Craft Advisory conditions will persist through Friday. Winds
will ease back into exercise caution range Friday night...and a
general northeast wind of 15 to 20 knots and seas of 3 to 5 feet
should linger into Saturday as a strong surface high continues to
settle over the Gulf south. The overall pressure gradient will ease
a bit on Saturday night...allowing fora brief break in exercise
caution flags. However...a low pressure system will begin to form
over the western Gulf on Sunday. This low will push the northeast
flow back into exercise caution and possibly advisory range in the
open Gulf waters Sunday night into Monday. 32

Decision support...

Activities...slurry support
dense fog threat this morning
threat of freezing rain and possibly sleet far northwest
Thursday morning.

Decision support services (dss) code legend
green = no weather impacts that require action
blue = long fused watch/warning/advisory in effect or high
visibility event
yellow = heightened impacts with short fused
watch/warning/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 to high risk severe
and/or direct tropical threats; events of National


Preliminary point temps/pops...
mcb 79 35 36 25 / 20 80 80 10
btr 81 38 39 27 / 30 80 70 10
asd 78 50 55 33 / 30 60 60 10
msy 80 49 57 35 / 30 60 60 20
gpt 76 55 59 33 / 30 60 60 20
pql 76 58 62 34 / 30 50 70 20


Lix watches/warnings/advisories...
la...dense fog advisory until 9 am Wednesday for the following zones:
lower Plaquemines...lower St. Bernard...Orleans...St.
Tammany...upper Plaquemines...and upper St. Bernard.

GM...dense fog advisory until 9 am Wednesday for the following zones:
Breton Sound...Chandeleur Sound...Lake Borgne...Lake
Pontchartrain and Lake Maurepas...and Mississippi Sound.

MS...dense fog advisory until 9 am Wednesday for the following zones:
Hancock...Harrison...and Jackson.

GM...dense fog advisory until 9 am Wednesday for the following zones:
Breton Sound...Chandeleur Sound...Lake Borgne...Lake
Pontchartrain and Lake Maurepas...and Mississippi Sound.



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