789 
fxus62 kilm 211314 
afdilm 


Area forecast discussion 
National Weather Service Wilmington NC 
814 am EST Sat Nov 21 2009 


Synopsis... 
increasing moisture from the Gulf of Mexico will enter the Carolinas 
Sunday into Monday with widespread rain expected. A brief warmup is 
expected Tuesday and Wednesday. A strong cold front Thursday will 
usher in some colder air for next weekend. 


&& 


Near term /through tonight/... 
as of 9 am Saturday...periods of multi-layered clouds will keep 
skies variably cloudy today with a cool northeast breeze in place. 
Low pressure developed overnight along a nearly stationary front 
well offshore. This led to an enhancement in the low-level northeast 
flow overnight. This low will move northeast and away from the area 
this afternoon...but new low pressure will develop late tonight 
along the eastern Gulf Coast. 


It appears enough dry air will remain entrenched in the sub-cloud 
layer to prevent measurable precipitation from developing across our 
area through daybreak Sunday. This is in agreement with the previous 
forecast and also the 06z runs of the NAM and GFS. The 06z NAM was 
notable in its depiction of a very deep dry sub-cloud layer moving 
in late tonight which could actually delay the onset of 
precipitation well into the day Sunday. We will revisit this 
potential with the afternoon forecast update. 


The incoming airmass is quite chilly and even with filtered sunshine 
we will only reach the lower to middle 60s this afternoon. The previous 
forecast remains in great shape and no significant changes were 
needed. 


&& 


Short term/Sunday through Monday night/... 
as of 3 am Saturday... 
moisture overrunning northeasterly surface flow associated with 
wedge of high pressure will bring plenty of cloudiness to start the 
period. Increasing isentropic upglide will also ramp up rain 
chances...ending up in the categorical range by evening. Quantitative precipitation forecast 
forecast is still a little uncertain as guidance has really backed 
off with rainfall when compared to previous days. Rain chances 
remain fairly high Sunday night as the weakening low jumps to the 
eastern side of The Wedge and ends up offshore. Soon thereafter rain 
chances should taper off from west to east early Monday. Clouds and 
possibly drizzle could linger into the morning hours. Might even see 
a trend towards overall slower progression which could mean drizzle 
and clouds linger most of the day. Have undercut guidance on Monday 
high temperatures. 


&& 


Long term/Tuesday through Friday/... 
as of 3 PM Saturday... 
a weak upper ridge manages to build on Tuesday and this should bring 
a mild afternoon. Wednesday may also bring highs in the low 70s 
ahead of what will end up being a pretty strong cold front on 
Thursday. Little to no moisture flow ahead of the front so its 
passage should be dry. The ecwmf has indicated otherwise for a few 
runs now but this model has been displaying a very wet bias for some 
time locally in such setups. Dry and cool weather for the rest of 
the period with highs struggling to low 60s by day and upper 30s at 
night. 


&& 


Aviation /12z Saturday through Wednesday/... 
weak low pressure will move along a stalled boundary just offshore 
today bringing middle level cloud cover to the coastal terminals. A 
more significant system developing in the Gulf of Mexico will cause 
gradually thickening high clouds at all terminals through the period. 


4sm visibility at lbt is only restriction this morning...and this will 
burn off quickly after sunrise leaving VFR all terminals. 11u-3.9u 
micron satellite is busy...with high level cirrus streaming across to 
the NE and MVFR/VFR stratus just offshore. With a moderate NE wind 
today at around 10 knots...expect some of this stratus to occasionally 
move onshore creating 5k foot ceilings at ilm/cre/myr. Do not believe 
any of this will get to Flo/lbt...but some afternoon cumulus may develop at 
those terminals around 4k feet. This cumulus will have very limited 
vertical extent due to the dry middle levels of the column. Model 
guidance has slowed in its progression of the Gulf of Mexico 
system...and have removed any vcsh to reflect this more delayed 
solution. VFR will be the rule all day with high level cirrus lowering 
to an as/ac deck around 12k feet by the end of the taf period as the 
column saturates from the top down. 


Extended outlook...potential IFR due to showers and low ceilings 
Sunday and Monday. Fog possible Tuesday morning. 


&& 


Marine... 
near term /through tonight/... 
as of 8 am Saturday...low pressure well off the South Carolina coast 
and high pressure over the Great Lakes are setting the stage for a 
sustained period of northeast winds lasting through the next several 
days. A pinched gradient developed overnight with wind gusts up to 
30 knots at the nearshore Wrightsville Beach buoy. Winds have 
diminished a little and we should drop to a relative lull in wind 
speeds this afternoon. Low pressure tonight will develop along the 
eastern Gulf Coast which will lead to an enhancement of the local 
pressure gradient late tonight. 


Seas are still running 7 feet at The Frying Pan Shoals buoy...and 5 feet 
at the nearshore Wrightsville Beach buoy. This matches very well 
with the local Swan wave model and no significant changes are needed 
to the previous forecast. 


Short term /Sunday through Monday night/... 
as of 3 am Saturday... 
surface high pressure wedge in control on Sunday to bring a moderate 
gradient wind. Small Craft Advisory from near term has been extended 
through Sunday for northern two zones as 6 feet seas affect the outer 
reaches along Frying Pan Shoals. Wave shadowing will probably 
preclude this over southern waters. A flat wave of low pressure will 
ride up the east side of The Wedge Sunday night into Monday. This 
will slightly taper the gradient and could lower the seas enough to 
drop any advisories. Wedge weakens but remains in place for the 
remainder of Monday and Monday night keeping winds with a northerly 
component. 


Long term /Tuesday through Wednesday/... 
as of 3 PM Saturday... 
looks like a fairly quiet pattern for most of the period. High 
pressure remains to the north Tuesday bringing a light northerly 
wind and seas in the 2 to 3 feet range. Changes may be underway come 
Wednesday as the high begins to lift out ahead of an approaching 
cold front. The timing of this front and the evolution of surface 
features associated with it is highly uncertain. 


&& 


Ilm watches/warnings/advisories... 
SC...none. 
NC...none. 
Marine...Small Craft Advisory until 7 am EST Sunday for amz256. 


Small Craft Advisory until 7 PM EST Sunday for amz250-252. 


&& 


$$ 


Synopsis...mbb/tra 
near term...tra 
short term...mbb 
long term...mbb 
aviation...jdw 

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