509 
fxus64 klix 042128 
afdlix 


Area forecast discussion 
National Weather Service New Orleans la 
328 PM CST Thursday Dec 4 2008 


Synopsis... 
the cold front has moved through the majority of the area and 
temperatures have been falling throughout the afternoon as 
forecast. Only isolated showers remain over the coastal waters 
east of the Mississippi River. Thick clouds still covering the 
area...but the clearing line is starting to approach the 
northwest portion of the area. 


&& 


Short term... 
skies should begin to clear this evening and will continue to 
clear overnight tonight as high pressure builds into the area. 
With guidance pretty tightly clustered through the short 
term...didn/T see a reason to stray very far from the temperatures 
forecast in the models. Generally expecting middle to upper 30s 
across the northern half of the area and low 40s across the 
southern half tonight. Temperatures should rebound into the middle 50s 
during the afternoon hours Friday. 


A second upper trough will move through the region Saturday 
evening pushing a reinforcing high into the area which will keep 
cool and dry weather in the forecast through the weekend. 


Long term... 
models begin to diverge significantly Monday. The GFS and European model (ecmwf) 
continue to flip flop with each other almost every model run. 
Given the uncertainty...have made few changes to the extended 
period as the inherited forecast appears to be in fairly good 
agreement with the HPC forecasts and is a close match to the GFS. 


As a surface low develops over eastern Oklahoma...a warm front is 
expected to lift through the region Monday evening and into Monday 
night. Have increased probability of precipitation into the chance category for this time 
period and will indicate thunder along and the expected frontal 
boundary. 


By Tuesday...the southerly flow is expected to increase as a low 
level jet takes strengthens over the region. This should lead to 
an influx of very moist and unstable air into the region...which 
is expected to be smack dab in the middle of the warm sector by 
this time. Will carry high end chance probability of precipitation for Tuesday...but will 
need to watch future model runs as the forecasts evolve and get a 
better handle on the situation. The way the GFS forecast stands 
now...moderate instability should be in place with Li values of -2 
to -5 and cape values in the 500 to 1200 j/kg range across much of 
the area. However...with pretty good cloud cover in place...the 
main question will be whether we get enough heating to destabilize 
at the surface. All in all it looks to be a very dynamic system 
at this time and we will certainly be watching it as the model 
forecasts evolve over the next few days. 


The cold front is currently forecast to clear the area Tuesday 
night with high pressure building into the area for the second 
half of the week. 


&& 


Aviation... 
/00z tafs/ 
at 21z Thursday...back edge of cloud deck was approaching Jackson and 
Natchez and progression to the south was slow. Clearing may occur at 
mcb and btr 00z to 02z Friday...msy 04 to 06z and gpt 06 to 08z. Low 
clouds of 5 to 15kft will cover these sites with a few breaks. In 
addition...north winds with brief gusts 15-20 knots are possible at 
all four sites through the remainder of the afternoon and remain 
strong at msy this evening and overnight. VFR conditions are 
expected after o6z Friday at all four sites. 


&& 


Marine... 
moderate north winds are expected tonight and tapering off Friday 
late morning and 1000 to 700mb thickness layers will drop 30m 
overnight and cold air advection will become neutral Friday through early Saturday. 
Another cold front will push through the area Saturday night. The 
main trough will remain across the east Continental U.S. Maintain northwest 
flow across the marine area Saturday and Saturday night. Finally...a 
very dynamic system will move east across the lower Mississippi 
Valley late Tuesday night...producing a strong low level jet across 
the extreme north Gulf Monday night into Tuesday. Strong winds are 
expected to behind the frontal passage Tuesday night and strong 
winds possibly continuing through next Thursday. 


&& 


Preliminary point temps/pops... 
mcb 33 53 29 58 / 0 0 10 10 
btr 36 55 31 58 / 0 0 10 10 
msy 42 56 38 59 / 0 0 10 10 
gpt 37 56 33 57 / 0 0 10 10 


&& 


Lix watches/warnings/advisories... 
la...none. 
GM...Small Craft Advisory from 6 PM this evening to 9 am CST Friday 
for gmz530-550-555-570-575. 


MS...none. 
GM...Small Craft Advisory from 6 PM this evening to 9 am CST Friday 
for gmz550-555-570-575. 


&& 


$$ 


Aviation/marine...18 
rest of discussion...95/dm