816 
fxus62 kilm 211343 
afdilm 


Area forecast discussion 
National Weather Service Wilmington NC 
942 am EDT sun Mar 21 2010 


Synopsis... 
a strong cold front will approach from the southwest today and move 
across and offshore around daybreak Monday. An upper level low will 
move across the area Monday night and early Tuesday...keeping some 
clouds across the area with below normal temperatures. Dry high 
pressure will finally build into the area late Tuesday and prevail 
through Thursday. A chance of rain will return for Friday ahead of 
the next frontal system. 


&& 


Near term /through tonight/... 
as of 9:40 am Sunday...regional radar loops showing a broad area of 
showers with little or no lightning embedded over most of Georgia 
struggling to move northward into South Carolina. This area is being 
forced primarily by difluence aloft and with dewpoints in the 50s in 
these areas...there is little or no instability to work with. This 
area will continue to move north through the day but I have trimmed 
back probability of precipitation and delayed them across the board by a couple of hours. 
Still expecting much of South Carolina to measure by 0000 UTC...but 
with light amounts. Further north...confidence is lower on 
measurable rain...but will hold on to a slight chance at least for 
now. 


0600 UTC models remain consistent with scenario for tonight as the 
GFS/NAM show a narrow band of of surface based cape moving across the 
area between 0600 and 1200 UTC. This...when combined with 0-3 km above ground level 
helicity approaching 500ms/s2 could still spell some trouble for the 
area. The latest Storm Prediction Center day one outlook has expanded the two percent tornado 
area inland coinciding with these higher helicity values. 


One last thing...trimmed back high temperatures a degree or two 
today based on the latest guidance and the thick cloud cover now 
moving in from the south. 
&& 


Short term /Monday through Tuesday/... 
as of 3 am Sunday...precipitation chances under a strong closed upper low 
will be the main question in this period. Our best shot at rain 
from this event will be associated with a low-level jet that is 
prognosticated to just be exiting the northeastern corner of the ilm County Warning Area 
by 12z Monday. Therefore will initialize with high chance probability of precipitation in 
the coastal NC counties...and taper down to slight chance in SC. 
Impressive dry slot will wrap in by midday with precipitable water 
dropping to about a half inch. However...there will be one more 
window of opportunity for precipitation Monday evening with another vorticity 
lobe pinwheeling around the upper low. Lack of deep moisture will 
be the limiting factor...and have gone for a low chance/low quantitative precipitation forecast 
event. 


Temperatures will run slightly below normal both days...and are pretty 
well in line with MOS guidance as both GFS MOS and NAM MOS agree 
closely. 


&& 


Long term /Tuesday night through Saturday/... 
as of 3 am Sunday...ridging both at the surface and aloft will 
bring sunshine and warmer/seasonable weather through the midweek 
period. Not much confidence regarding a progressive system 
advertised by the GFS for Friday. For now will carry slight or low 
chance probability of precipitation mainly for Friday...but timing is certainly subject to 
change. In the absence of any significant cold air advection 
temperature deviations from climatology will probably only end up 
being a function of cloud cover. 


&& 


Aviation /12z Sunday through Thursday/... 
as of 12z...11u-3.9u satellite indicates some lower clouds 
developing near the coastal terminals but skies are remaining 
mostly scattered. Infrared satellite loops indicate high level 
cloudiness quickly spreading southwest to northeast. 


Some fog developed earlier at cre which dropped visibilities to 
MVFR/IFR and MVFR at times at ilm. Surface winds have now increased 
so confidence is high that fog will not redevelop. 


Winds today will be southeast around 10 knots with some 15-20 knot 
gusts possible by afternoon. Low clouds around 2500 feet will 
develop this morning...but per time height forecasts it looks as if low- 
level lift is minimal so do not expect these to constitute a 
ceiling. Confidence is moderate to high that VFR will continue at 
the terminals through 18z. Middle-level ceilings and some light rain 
will spread into the flow terminal by afternoon and to near lbt and 
myr/cre by middle-late afternoon. Since precipitation is expected to be 
light do not expect any adverse effects at the Airport. 
Confidence is moderate to high of VFR continuing through the 
afternoon. 


Flight conditions will decrease this evening as a cold front 
approaches. Confidence is high that MVFR conditions associated with 
shower activity can be expect to develop from southwest to northeast 
across the terminals ahead of the front. Right along the front 
itself there is moderate confidence there will be a band of 
heavier showers and isolated thunderstorms with associated IFR 
conditions. As the front passes conditions will improve to VFR 
with precipitation ending and winds shifting to the southwest. 
This will occur just after midnight (at flow 


Extended outlook...VFR. 


&& 


Marine... 
near term /through tonight/... 
as of 9:40 am...still very tranquil across the waters this morning 
with eight knots at 41013 with seas 2.3 feet. Gradient increases 
through the afternoon hours warranting the increase in the forecast 
to 10-15 knots. Seas ranging from 2-4 feet will suffice nicely for 
the afternoon hours. 


Short term /Monday through Tuesday/... 
as of 3 am Sunday...will begin Monday with winds diminishing and 
shifting from south to southwest as the low-level jet translates 
east of the waters. Tight gradient but only so much mixing...so 
wind speeds will generally run around 15 to occasionally 20 knots. 
Seas will start off in the 5-7 feet range thanks to the strong 
onshore flow Sunday night...with a very slow subsiding trend as 
the day progresses. Expect seas to drop below Small Craft Advisory thresholds late 
Monday morning across the southern waters...and late afternoon 
along Frying Pan Shoals. Therefore have set the expiration time on 
the advisory at 18z Monday for the SC waters...and 00z Tuesday for the NC 
waters. 


Winds finally come around to due west late Monday night and deep 
mixing will help maintain 15-20 knots on Tuesday. Seas just below 
advisory criteria along Frying Pan Shoals...but offshore 
trajectory will limit seas to 2-3 feet near shore. 


Long term /Tuesday night through Thursday/... 
as of 3 am Sunday...westerly gradient will relax Tuesday night as 
high pressure builds in. Look for winds around 10 knots and seas 2-3 
feet from Wednesday afternoon Onward. 


&& 


Ilm watches/warnings/advisories... 
SC...none. 
NC...none. 
Marine...Small Craft Advisory from 9 PM this evening to 2 PM EDT Monday 
for amz254-256. 


Small Craft Advisory from 9 PM this evening to 8 PM EDT Monday 
for amz250-252. 


&& 


$$ 


Near term...shk 
short term...Ras 
long term...mbb/Ras 
aviation...mrr 

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