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Area forecast discussion 
National Weather Service New Orleans la
653 PM CST Sat Dec 20 2014

Sounding discussion...

Routine sounding terminated over Mississippi Highway 614 very
close to the Alabama-Mississippi State line. Flight terminated at
105.2k feet or close to 20 miles above the surface.

Sounding has dried out since this morning with a precipitable
water value of 0.81 inches...which is about 94 percent of normal.
The moisture is mainly below 800 mb...with rapid drying above that
level. Several inversions between 950 mb and 640 mb. Winds in the
lowest 5000 feet were generally out of the northeast...became
westerly just above 5000 feet and remained out of that direction
through 100 mb. Wind maximum 105 knots at 280 mb...32.5k feet.
Freezing level was at 13.3k feet and -20c level was at 22.2k feet. 35

&&

Previous discussion... /issued 342 PM CST Sat Dec 20 2014/

Short term...
cold front that moved through the area remains stalled well south of
the County Warning Area in the central Gulf of Mexico. Models appear to have backed
off on this boundary retrograding back north closer to the northern
Gulf Coast. So have pulled inland showers from the forecast...
leaving the coastal waters and adjacent la parishes as the only
areas to see rain overnight. Moving into Sunday there could be some
push further inland late in the day and evening hours as a weak
shortwave moves through. Once again the best chance for rain will be
along the coast but it may creep as far north as New Orleans by
Sunday aftn/evening. Cloud cover and elevated winds will keep
temperatures from falling too much overnight but should still see 40
to 45 for the northern half of the County Warning Area and 50 to 60 further south.

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. Model soundings show precipitation water values
steadily rising...passing 1 inch by midday. A few showers will be
possible so have kept probability of precipitation at 20 percent. A very amplified upper level
trough will be digging very deep into southern portions of the
country on Tuesday. Models show a surface low developing across the
County Warning Area in the afternoon and moving northeast. 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 them to around 60 percent but dont be
surprised to see that rise as the event nears. Definitely 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 pressure as the front approaching 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. Sorry
to anyone hoping for a rare white Christmas.

Meffer

Aviation...
IFR conditions continued to prevail at each of the terminals
this afternoon due to low ceilings. Visible satellite imagery showed the
clearing line approaching kmcb and kbtr from the north. Clouds will
likely scatter out at these locations for a time late this afternoon
and early this evening. Elsewhere...the clouds will hang on...
although ceilings may improve into the MVFR category. Lower ceilings
will continue tonight or redevelop again after 06z and persist into
Sunday morning with IFR to LIFR conditions forecast at most
locations. 11

Marine...
a surface low pressure area was broadening and transitioning into an
inverted open wave over the north central Gulf this afternoon. Low
level cold air advection has continued to result in Small Craft
Advisory conditions across the outer waters...so the Small Craft
Advisory has been extended until 6 PM today for the outer coastal
waters. Otherwise...exercise caution conditions will prevail for all
of the coastal waters tonight for areas beyond the lakes and sounds.
Winds will diminish somewhat Sunday and especially Sunday night into
Monday before picking up again from the south Monday night in
advance of the next cold front. A strong pressure gradient Tuesday
will result in near Small Craft Advisory conditions Tuesday as a
strong cold front approaches from the northwest. This front will
move across the coastal waters Tuesday night with upper end Small
Craft Advisory conditions or perhaps even gale conditions in its
wake late Tuesday night into Wednesday. The winds will diminish by
Thursday as high pressure settles over the region. 11

Decision support...
dss code...blue.
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 39 61 45 68 / 10 10 20 20
btr 43 64 48 70 / 10 10 20 20
asd 44 62 48 68 / 10 20 20 20
msy 50 62 53 69 / 10 20 20 20
gpt 47 62 51 67 / 10 30 30 20
pql 45 63 48 67 / 10 30 30 20

&&

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

$$

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