073 
fxus64 klix 081721 
afdlix 


Area forecast discussion 
National Weather Service New Orleans la 
1121 am CST Thursday Jan 8 2009 


Update... 
..18z tafs... 


VFR conditions will be the rule at all taf sites through 12z 
Friday...as a broad ridge of high pressure at the 
surface...combined with strong subsidence and dry air aloft allow 
for continued clear skies. A weak inversion is expected to develop 
tonight...but the airmass is so dry that visibility restrictions 
are not expected. Winds will be variable through the period...as 
a weak back door cold front slips in tonight. Winds should shift 
from the west to the east by 02z...with a shift to the south after 
12z Friday as surface ridging begins to pull to the east of the 
region. 32 


&& 


Previous discussion... /issued 448 am CST Thursday Jan 8 2009/ 


Short term... 
middle/upper trough over eastern North America will shift east today 
through Friday with a return to zonal flow and much higher heights 
aloft/thicknesses expected along the Gulf Coast. Temperatures this 
morning will be starting out quite a bit higher than earlier 
forecast...and southwest winds early on will become west to 
northwest during the day as a weak west-east trough of low 
pressure moves into the forecast area this afternoon. These 
conditions combined with plentiful sunshine should cause 
temperatures to warm about 8 or 9 degrees warmer than 
yesterday...and have gone a few degrees above the mav guidance at 
most locations for highs today...and a degree or two above 
guidance tonight and Friday. Humidity will be increasing as south 
winds increase on Friday which will also bring a slight increase 
in cloud cover Friday afternoon. 


A positively tilted trough...a result of some phasing of 
shortwaves moving out of the northern plains and southern 
rockies...will push a cold front into northern and western 
sections of Mississippi and Louisiana late Friday night. Have 
maintained 20 to 30 percent rain chances after midnight Friday 
night. 


Long term... 
the middle/upper shortwave trough will move through the forecast 
area Saturday and Saturday night with the cold front pushing 
through most of the forecast area Saturday morning and the 
east/southeastern portions early Saturday afternoon. The GFS looks 
a bit fast...so have blended with the slower NAM/European model (ecmwf) solutions. 
Quantitative precipitation forecast amounts...generally a blend of the 00z GFS and European model (ecmwf)...are 
forecast to be in the .20 to .40 inch range...and since confidence 
in timing is pretty good...have raised the pop to the 50 to 60 
percent range for Saturday. Surface high pressure and dry and cool 
air will move into the area Saturday night into Sunday as the main 
shortwave trough moves towards the Atlantic coast. Low temperatures 
will drop into the 30s early Sunday morning...but should remain 
above freezing. 


A series of shortwave troughs are forecast to move south out of 
Canada into the Mississippi Valley Monday into early Tuesday with a 
reinforcing shot of Arctic air expected to invade much of the 
central and eastern Continental U.S.. there will be little moisture in our 
area...so no precipitation is expected Monday and Tuesday...however 
temperatures are expected to remain below normal with near 
freezing lows possible over the colder locations Monday through 
Wednesday mornings. The next chance of rain will be around Thursday 
as a modest increase in Gulf moisture interacts with frontal lift 
ahead of additional shortwaves in westerly flow. 22 


Aviation... 
surface high pressure is currently centered over the Gulf of Mexico. 
Pressure gradient has remained high enough to keep SW winds elevated 
overnight. Winds will gradually become more west and then northwest through 
the day. Vrb to calm winds expected overnight. Few to scattered high 
clouds will continue across the area. VFR conditions will prevail 
through the period. 


Meffer 


Marine... 
SW winds of 15 to 20 kts in the inner and outer coastals east of the 
miss are expected to continue into the afternoon...so added small 
craft exercise caution headline through 21z. Surface ridge will become 
center over the are this afternoon/evening and should result in decrease in 
winds later today. Onshore flow to return Thursday as high pressure 
shifts eastward. Southeast winds and seas begin increasing as press 
gradient tightens in response to approaching cold front. Will need 
to watch for SW winds ahead of the front for scy conditions. Slight 
discrepancy in timing of this boundary...but should move through 
the coastal waters Saturday afternoon. Small craft conditions are 
possible behind the front as brisk northwest winds will accompany the 
boundary but should be a relatively short event. Light winds and low 
seas sun evening through Monday. 


Meffer 


&& 


Preliminary point temps/pops... 
mcb 70 44 73 58 / 0 0 0 30 
btr 73 48 75 59 / 0 0 0 30 
msy 72 51 75 61 / 0 0 0 30 
gpt 73 47 68 61 / 0 0 0 20 


&& 


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


$$