Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New Orleans la
700 PM CST sun Dec 21 2014

Sounding discussion...

Routine flight terminated over the Alabama-Mississippi State line
east of Lucedale Mississippi at a height of 106.4k feet or 20.15
miles in altitude.

Sounding was a little more moist than this morning with a
precipitable water value of 0.91 inches...which is 105 percent of
the climatological normal for the day. One moist layer was between
650 and 750 mb...and another between 300 and 450 mb. Variable
winds below 900 mb quickly became southwest above that and
continued through 100 mb. Wind field in the upper levels was
rather strong...with a maximum wind from the southwest at 128 knots
just below 40k feet. Freezing level was just below 11k feet and
the -20c level was 20.2k feet. 35

&&

Previous discussion... /issued 339 PM CST sun Dec 21 2014/

Short term...
a frontal boundary remains stalled across the the central Gulf of
Mexico. Water vapor imagery shows abundant middle level Pacific
moisture streaming northeast across the northern Gulf to the
southeastern US. A weak shortwave will be moving along this swath of
moisture and provide just enough lift to spark shower development.
Radar images over the last few hours show increasing showers moving
across the off shore coastal waters south of the mouth of the
Mississippi River. Some of this activity is expected to nudge
northward into the coastal parishes and eastern MS counties this
evening and overnight. For now have kept the rain out of New Orleans
but a few stray showers could reach that far north. Regardless...
extensive cloud cover overnight should keep temperatures from
falling too much. Have kept forecast lows on the warm side of guidance
with temperatures likely not dropping below 50 degrees for anyone by
northern portions of the County Warning Area.

Long term...
onshore flow will begin to pump moisture back into the area Monday
as a deepening surface trough northwest of the area tightens the pressure
gradient over the region and surface ridge north of the area lifts
northeast. Model soundings show precipitation water values steadily
rising...passing 1 inch by midday Monday. A few showers will be
possible through the day so have kept probability of precipitation at 20 percent. On Tuesday an
upper level trough moving into the Central Plains will be amplifying
and digging deep into the Southern Plains and Texas. Models show a
surface low developing along the Texas coast and racing northeast
across the County Warning Area in the afternoon. Meanwhile...an associated cold
front will be marching towards the area and swinging through during
the evening and overnight hours. Showers and thunderstorms will
develop out well ahead of this feature with highest probability of precipitation during the
day on Tuesday. Have increased even more today to around 80 percent.
Definitely still have some concern for severe weather with this
system. At this time...there appears to be ample instability with warming
low level temperatures and middle level cooling Tuesday. Cape values could top
1000 j/kg. A 100+kt 250mb jet will be passing over the County Warning Area midday as
well. This combined with plenty of lift from falling pressures as the
front approaches could be quite conducive for strong to severe
storms with all modes of severe weather possible.

Only going to be a couple days of reprieve as progressive pattern
brings in another cold front Friday night into Saturday. Showers
could begin as early as Friday. The good news is that Christmas day
should be rain and cloud free with temperatures near normal.

Meffer

Aviation...
MVFR ceilings have persisted this afternoon at knew...kmsy and khum.
At the remainder of the terminals...VFR to occasionally MVFR
conditions due to ceilings have been observed. This trend will
continue through the remainder of the afternoon and into the
evening. Ceilings will lower later tonight...after 06z...into the
LIFR category with areas of light fog also possible at times. These
conditions will persist into the morning hours Monday before some
improvement after 16z. 11

Marine...
generally light northeast to east flow this afternoon will shift to
the southeast tonight as a ridge of high pressure over the eastern
U.S. Shifts east. Onshore flow will increase Monday and Monday night
as the pressure gradient tightens in response to developing low
pressure over the central Continental U.S.. by Tuesday...winds will likely
flirt with Small Craft Advisory criteria across parts of the coastal
waters. A strong cold front will approach the western coastal waters
late in the day Tuesday and then move across the coastal waters
Tuesday night. Strong offshore flow will develop in the wake of the
front late Tuesday night and Wednesday with upper end Small Craft
Advisory to possibly gale conditions possible. The winds will ease
Thursday as high pressure settles over the region. 11

Decision support...
dss code...green.
Deployed...none.
Activation...none.
Activities...slurry support

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
significance.

&&

Preliminary point temps/pops...
mcb 48 70 61 71 / 10 20 50 80
btr 52 72 61 73 / 10 20 50 80
asd 53 73 63 72 / 10 20 50 80
msy 55 74 63 73 / 10 20 50 80
gpt 54 71 63 70 / 10 20 50 80
pql 53 73 63 72 / 20 30 50 80

&&

Lix watches/warnings/advisories...
la...none.
GM...none.
MS...none.
GM...none.
&&

$$

National Weather Service Glossary of Abbreviations