386 
fxus64 klix 200915 
afdlix 


Area forecast discussion 
National Weather Service New Orleans la 
415 am CDT Sat Mar 20 2010 


Short term... 


A rapidly deepening upper level trough currently over the southern 
rockies will continue to pull to the east tonight into tomorrow. 
As the upper level trough moves to the east...a strong surface low 
will develop over the Southern Plains and move into the middle- 
misissippi valley by Saturday evening. As the upper level system 
deepens...cold air over the northern plains will be drawn 
southward into the Southern Plains and Texas. The upper level 
system will begin to take on a more negative tilt tomorrow 
night...allowing the surface cold front to rapidly sweep eastward 
across the forecast area. The upper level low and surface low 
should become vertically stacked by this point. 


Thunderstorm development is expected along the front...but an 
overall lack of low level instability will greatly limit the 
chances for severe weather tomorrow night. After looking at the 
latest model soundings...the best lapse rates will be found above 
850mb. This would support the development of hail...but the risk 
of strong winds and tornadoes will be greatly limited. 


In the wake of the front...the vertically stacked and slowly 
moving upper level low will continue to bring clouds and scattered 
showers to the northern half of the County Warning Area through Sunday night. 
However...strong cold air advection associated wtih the upper 
level trough will drop temperatures a good 20 degrees below normal 
Sunday into Sunday night. Overall...1000-500mb thicknesses are 
expected to drop to around 5400 meters as far south as the New 
Orleans area on Sunday. Fortunately...surface temperatures will 
be warm enough to keep all precipitation in the liquid form. 
Thicknesses will begin to increase late Sunday night into Monday 
as the main upper level low pulls into the Middle-Atlantic States. In 
addition to the colder than normal temperatures...strong winds 
aloft should mix down Saturday night into Sunday. These strong 
winds could lead to a possible Wind Advisory for Sunday. 


Long term... 


Heading into the remainder of next week...a broad upper level 
ridge is expected to build in Monday night into Tuesday and remain 
in place through Wednesday. This strong upper level ridging will 
allow for clear skies and a return to more normal tempeature 
readings. However...another upper level trough is expected to 
affect the region Thursday into Thursday. Both the GFS and European model (ecmwf) 
are in good agreement on the timing and strength of this next 
system...and have fairly decent confidence with this event. This 
system will be more Pacific in nature...with little in the way of 
cold air advection expected behind the front Thursday night. In 
addition...with less overall forcing...expect less precipitation 
coverage. The upper level pattern should turn more zonal after 
this upper level trough moves...with near normal temperatures and 
dry conditions expected Friday and Saturday. 


&& 


Aviation...overall not expecting much in the way of problems for 
the taf sites but reduced visbies could occur during the early 
morning hours. Winds should start to increase mainly just above the surface 
and this will likely keep things mixed well enough to keep visbies 
from dropping below MVFR if they even fall that far. By this evn 
things will begin to change as increasing moisture and the approach 
of a strong cold front will lead to lowering ceilings and eventually 
rain showers and isolated thunderstorms and rain. Winds will also be on the increase...especially 
after the frontal passage which will occur across the County Warning Area b/T 3z and 
9z sun. /Cab/ 


&& 


Marine...things will begin to change quickly today. As the Western 
Plains disturbance drops into the Southern Plains and deepens. This will 
aid in cyclogenesis occurring across the lower MS valley today and 
this will start to tighten the pressure gradient this afternoon across 
the area. This will cause srly winds to increase to around 15-20kt 
so we will start scs headlines around midday. The main surface low will 
develop over NE Arkansas and this will push a strong cold front through 
the area rather quickly tonight and should be completely through the 
coastal waters no later than 9z. On the back side of the front winds 
will veer around to the west-northwest and with surface pressure rises on the order 
of 4-6mb in 6 hours winds will quickly ramp up. Add in rather strong 
cold air advection in the ll along with winds quickly becoming unidirectional from 
the surface to 850 mb we will have the recipe for very strong winds during 
the early morning hours and through much of the day sun. Models are 
suggesting winds of 35 to 50kts around h925 and 850 mb and these winds 
should have no problem mixing down to the surface as gusts. With 
frequent gusts(possibly even sustained winds at times) at and above 
35kts we will go ahead with a gale watch from 9z Sun morning till 
21z sun. This watch will likely need to be upgraded to a warning 
today and may even need to be extended into the evn hours sun. Winds 
will then begin to slack off Sun night and more so on Monday as the 
broad surface low lifts off to the east-northeast and high pressure builds back 
into the Gulf. Seas will of course also be an issue and the outer 
waters could see seas around 9-11ft during the early morning and 
midday hours sun. The tidal lakes could need a Gale Warning but at 
this time we will stick with a scy from 9z sun through 12z Monday. On 
another note...the very strong winds we saw Mar 1st associated with 
a wake low...we are not expecting the same thing to occur. There 
wont be a rapidly deepening surface low moving across the coast or a 
decent area of deep convection moving across southeastern la which aided in 
that developing but those types of mesoscale features are very hard 
if not near impossible to completely predict. That said winds will 
be rather gusty across the entire area...land included on sun. /Cab/ 


&& 




Preliminary point temps/pops... 
mcb 71 39 49 33 / 20 80 30 30 
btr 74 39 52 35 / 20 80 20 20 
asd 71 43 53 35 / 10 80 20 20 
msy 71 42 54 40 / 10 80 10 10 
gpt 69 45 55 38 / 10 80 20 20 
pql 70 52 56 37 / 10 80 20 20 


&& 


Lix watches/warnings/advisories... 
la...none. 
GM...Small Craft Advisory from 7 PM Saturday to 4 am Sunday 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. 


Gale watch from 4 am Sunday to 4 PM Sunday 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. 


Small Craft Advisory from 4 PM Sunday 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. 


Small Craft Advisory from 4 am Sunday to 7 am Monday for the 
following zones: and Lake Pontchartrain and Lake Maurepas. 


MS...none. 
GM...Small Craft Advisory from 4 am Sunday to 7 am Monday for the 
following zones: and Lake Pontchartrain and Lake Maurepas. 


Gale watch from 4 am Sunday to 4 PM Sunday 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. 


Small Craft Advisory from 7 PM Saturday to 4 am Sunday 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. 


Small Craft Advisory from 4 PM Sunday 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. 


&& 


$$ 


32 

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