905 
fxus64 klix 041505 
afdlix 


Area forecast discussion 
National Weather Service New Orleans la 
905 am CST Thursday Dec 4 2008 


Update... 
did a quick update to clear probability of precipitation out faster than previously 
forecast. The back end of the rain is quickly moving eastward 
and should clear most of the area before noon. Decided to leave a 
slight chance in for this afternoon across the southeastern 
portion of the area to cover any showers that may linger behind 
the boundary. Otherwise...this morning/S forecast package appears 
to be on track and no additional updates are anticipated before 
the afternoon package. 95/dm 


&& 


Previous discussion... /issued 624 am CST Thursday Dec 4 2008/ 


Aviation... 
/12z tafs/ 
band of rain/rain showers accelerating through the area with no more ts 
expected. Back edge of rain will clear kmcb-kbtr shortly followed 
by wind shift to north with brief gusts 15-20 knots possible. Rain 
will move through kmsy 12-15z and kgpt 13-16z with occasional MVFR 
conditions. IFR category ceilings will follow the cold frontal 
passage for 3-6 hours...with brief LIFR conditions possible 
at kmcb and kbtr through 15z. Low clouds should clear kmcb-kbtr 
around 00z...but clearing line looks to slow down tonight...so 
have held MVFR category ceilings in kgpt-kmsy through 05/12z. 


22 


Previous discussion... /issued 400 am CST Thursday Dec 4 2008/ 


Synopsis... 
cold front over central Louisiana will move across the Atchafalaya 
River in the next hour or two. Band of rain and thunderstorms 
accompany front...along with some wind gusts around 30 knots. 
Temperatures generally in the 60s ahead of the front. 


Short term... 
most of the forecast problem is in the first period of the forecast. 
For verification purposes...basically trying to forecast location of 
cold front at 12z. It should be east of btr at that point and just 
about on top of mcb. Based on movement of precipitation...front 
should be through most or all of our area by 18z. Will go with 
likely probability of precipitation ahead of front...with chance behind it for this 
morning...then slight chance all areas for the afternoon...to 
account for the few showers behind the front. Temperatures at 12z 
may be the maximum for the daytime hours behind the front...depending on 
whether clearing occurs behind the front. NAM rather bullish on 
holding clouds in...but will trend toward GFS solution...which will 
diminish clouds during the afternoon. 


After the first period...going forecast looks good. In fact...mav 
guidance in very good agreement with what we already had in 
forecast...so little change needed at this time. Only fly in the 
ointment could be a small chance of precipitation late Friday or on 
Saturday as next shortwave moves by to the north. Current solutions 
have precipitation remaining offshore...but this will need to be 
monitored. 35 


Long term... 
both GFS and European model (ecmwf) solutions have issues with handling portions of 
the forecast. European model (ecmwf) has upper low moving through the southwest 
Sunday and Monday...where GFS has a ridge. GFS has issues with the 
strength of upper vortex...being 4sd below normal heights to 
Pennsylvania by midweek. HPC not really supporting details of either 
solution with their early morning medium range discussion. 


Considering this is my first midnight shift of this set...not 
comfortable with the lack of model continuity. Will not make 
significant changes to the extended forecast at this time. 35 


Marine... pressure gradient will continue to support south to 
southwest winds 15 to 20 knots and seas up to 6 feet in advance of 
cold front over warmer waters...except lower over cool near shore 
waters. Small craft should exercise caution today. Numerous 
showers and scattered thunderstorms will move across the tidal 
lakes this morning...and the coastal waters by middle morning into 
early afternoon. Behind the cold front...northerly winds should 
increase to around 20 knots. A Small Craft Advisory will likely be 
required tonight into Friday morning. Winds will decrease Friday 
afternoon into Saturday...then increase a bit Saturday night into 
Sunday as reinforcement of cool high pressure moves into the 
marine area. 22 


&& 


Preliminary point temps/pops... 
mcb 58 33 53 32 / 70 0 0 10 
btr 61 36 55 33 / 30 0 0 10 
msy 66 42 56 39 / 70 0 0 10 
gpt 66 37 56 35 / 80 0 0 10 


&& 


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


$$