774 
fxus64 klix 200435 
afdlix 


Area forecast discussion 
National Weather Service New Orleans la 
1135 PM CDT Friday Mar 19 2010 


Aviation... 
VFR conditions will prevail at each of the taf sites through 00z 
Sunday...with the possible exception of some MVFR visibilities due 
to light fog around sunrise Saturday. Ceilings will lower into the 
MVFR category after 00z Sunday as a cold front approaches and 
moves across the forecast area. Widespread showers and 
thunderstorms area expected with this system...with the majority 
of the precipitation being Post frontal. 11 


&& 


Previous discussion... /issued 944 PM CDT Friday Mar 19 2010/ 


Marine... 
with the issuance of the evening update to the coastal waters 
forecast package...a Small Craft Advisory has been issued for the 
Gulf coastal waters for the period from Saturday evening through 
early Monday morning. Small Craft Advisory conditions are 
expected in the wake of a cold front that will push across the 
north Gulf Saturday night. Gale force wind gusts will also be 
possible at times from late Saturday night through Sunday. 11 


Previous discussion... /issued 753 PM CDT Friday Mar 19 2010/ 


Update... 
sounding discussion... 


The atmosphere is stable and very dry above 800 mb...precipitable 
water value is 0.46 inches and is expected to begin increasing. An 
inversion is present near 8000 feet along with southerly winds in 
the lower levels and westerly winds aloft. 


Previous discussion... /issued 312 PM CDT Friday Mar 19 2010/ 


Synopsis... 
high pressure centered just southeast of Boothville this 
afternoon. Light gradient winds and plenty of sunshine providing 
differential heating...so the first real lakebreeze/seabreeze has 
kicked in this afternoon. Satellite shows the cloud shadow very 
well...probably about 15 miles inland at 19z. Temperatures 
generally in the upper 60s at mid-afternoon. 


Short term... 
upper trough will exit the southern rockies this afternoon. Surface 
low will develop over south Texas tonight and move toward the area 
Saturday. All models have low pressure moving through western 
Louisiana into southeast Arkansas overnight Saturday night...with 
a cold front moving through the area between 00z and 08z Saturday 
evening. Moisture return will be weaker than normal...with dew 
points only reaching the middle to upper 50s ahead of the front. 
Forecast convective available potential energy only 100-200 and lifted indices do not go into the 
negative across most of the area. Steepest low level lapse rates 
lift north of our area well before the boundary reaches the area. 
Wind fields are conducive for severe weather...but not the 
thermodynamics. Will continue mention of thunder in the 
forecast...mainly for Saturday night...but will not play up too 
much in the severe weather potential statement. Small probability of precipitation for Saturday...categorical Saturday 
night...small probability of precipitation Sunday morning...other periods dry. 


Guidance temperatures for overnight lows have worked well the last 
2 nights...and see no reason to contradict them for tonight. 
Saturday temperatures fine as well. Will use met 3 hourly temperatures 
for Saturday night temperatures...expecting temperatures to remain 
elevated until frontal passage then drop rapidly to near 40. Any 
recovery in temperatures Sunday will be rather slow. Temperatures 
Sunday night may approach freezing in the extreme northern 
portions of the area. Monday to remain about 10 degrees below 
normal before the surface high moves off to the east. 35 


Long term... 
main change in the long term portion of the forecast is to push 
precipitation back about 24 hours near the end of the forecast 
period. This dries out the Wednesday forecast...and carries the 
best chance of precipitation Thursday night and Friday. This is in 
agreement with GFS and European model (ecmwf) solutions. Temperatures slightly 
below normal for Tuesday through Wednesday morning...then near to 
slightly above normal for Wednesday afternoon through Friday. 35 


Aviation... 
Gulf Breeze convective cloud deck between 050-065 noted in satellite 
imagery with flow becoming more onshore oriented. This cloud deck 
will dissipate shortly after sunset around 01z for prevailing VFR 
ceiling and visibility OK condtions at all terminals through at least 18z Saturday. 
Convective cloudiness expected after 18z in advance of approaching 
cold front to lower ceilings to around 030-035 with tempo lower MVFR 
in receiver station/thunderstorms and rain pre-frontal. Frontal passage at kbtr and kmcb projected around 
210300z...kmsy around 210500...kgpt around 210630z. 24/rr 


Marine... 
onshore flow to steadily increase to moderate levels in response to 
low pressure system swinging into middle Mississippi Valley Saturday 
afternoon. Associated cold front to move across the coastal waters 
Saturday evening and overnight will result in strong cold air 
advection and momentum tranport from very dry air aloft to produce 
very windy westerly winds Sunday. Conditions appear certain for high 
end Small Craft Advisory criteria and possibly a duration of minimal 
Gale Warning conditions due primarily to frequent gusts in the 35-45 
knots range. Winds and seas should subside steadily Monday as high 
pressure becomes settled over the Gulf states by Monday night. 24/rr 


&& 


Preliminary point temps/pops... 
mcb 44 71 39 50 / 10 20 80 20 
btr 47 74 42 54 / 10 30 80 20 
asd 45 71 44 56 / 10 20 80 20 
msy 53 73 46 53 / 10 20 80 20 
gpt 47 70 46 58 / 10 20 80 30 
pql 46 71 53 60 / 10 10 80 30 


&& 


Lix watches/warnings/advisories... 
la...none. 
GM...Small Craft Advisory from 7 PM Saturday to 7 am Monday for the 
following zones: coastal waters from Pascagoula MS to the 
Southwest Pass of the Mississippi River from 20 to 60 
nm...coastal waters from Pascagoula MS to the Southwest 
Pass of the Mississippi River out 20 nm...coastal waters 
from the Southwest Pass of the Mississippi River to lower 
Atchafalaya River la from 20 to 60 nm...and coastal waters 
from the Southwest Pass of the Mississippi River to lower 
Atchafalaya River la out 20 nm. 


MS...none. 
GM...Small Craft Advisory from 7 PM Saturday to 7 am Monday for the 
following zones: coastal waters from Pascagoula MS to the 
Southwest Pass of the Mississippi River from 20 to 60 
nm...coastal waters from Pascagoula MS to the Southwest 
Pass of the Mississippi River out 20 nm...coastal waters 
from the Southwest Pass of the Mississippi River to lower 
Atchafalaya River la from 20 to 60 nm...and coastal waters 
from the Southwest Pass of the Mississippi River to lower 
Atchafalaya River la out 20 nm. 


&& 


$$ 

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