Area forecast discussion 
National Weather Service Mount Holly New Jersey 
424 am EST Friday Dec 19 2014 


Synopsis... 
high pressure over the northern Great Lakes will move into the Ohio 
Valley this morning. Low pressure is expected to form over the Gulf 
states late tonight and track across Georgia Saturday. A strong low 
pressure system and cold front may move through the eastern Seaboard on 
Christmas evening. 


&& 


Near term /until 6 PM this evening/... 
surface high continues to slide closer to the region today. However, 
like last week, there appears to be abundant moisture below the 
inversion, so despite the synoptic scale subsidence, should still 
see quite a bit of cloud cover. With little change in the air mass, 
expect highs near maximum temperatures yesterday which are near or just below 
normals. 


&& 


Short term /6 PM this evening through 6 am Saturday/... 
the biggest change tonight from the last few nights is that with the 
high inching closer and thus the pressure gradient across the region 
decreasing, winds should be light. Though we would typically expect 
to see clearing skies in this pattern, with the low level moisture 
likely still in place, could still see quite a bit of cloud cover, 
especially over the northern half of the region. 


&& 


Long term /Saturday through Thursday/... 
middle-level flow the next couple of days is rather flat though a 
change to that pattern appears likely by the end of the weekend. A 
deep trough emerges across the central U.S. By Tuesday as multiple 
Pacific northwest waves round the base of the trough and across our 
region...we are heading for a very unsettled period by early next 
week. 


Saturday - Sunday...looks mostly dry both days with high pressure 
anchored to our northeast. There is some northern stream energy to 
contend with late Saturday night with the help of a weak inverted 
trough offshore. This combination could touch off a few showers as 
along the northeastern New Jersey coast but will be of little 
consequence. Onshore flow will help to keep ample low-level moisture 
streaming into the region, under the subsidence inversion. Saturday 
could be the sunnier day than Sunday, but each day the convective 
temperatures look to be reached so it may be short lived. 


Monday - Tuesday...once the aforementioned system above departs 
another, better defined system moves off the Carolina coast and out 
to sea on Tuesday. Weak baroclinic zone off the middle-Atlantic coast 
will allow for ample moisture to advect in from the south. As the 
wave of low pressure moves by it will tap into the moisture feed 
allowing for better chances of precipitation. Continued onshore flow 
ahead of the system will allow for a warming low-level thermal 
profile so any precipitation will be liquid with some mixing 
possible in the far northwestern zones. It is entirely possible that 
a weak cad setup occurs late Monday night with a northerly boundary 
layer ageostrophic wind component. Models have been known to warm 
the surface layer too fast with a rather large New England high 
pressure in place, or they push the high out faster allowing a 
southeast return flow. Either way it could be a messy Tuesday 
morning commute across our northwest zones. System moves off towards 
the northeast on Tuesday, with rain still ongoing, but we are 
gearing up for the bigger event on Christmas evening. 


Wednesday...still watching a large low pressure form to our west and 
track into the Great Lakes region on Wednesday. This would keep our 
region under a warming thermal profile with a lot of moisture to 
work with...an all liquid event is expected at this point. Guidance 
continues to show a weaker secondary development along a triple 
point over our region during the day. This would help to intensify 
rainfall amounts and enhance the low-level pressure gradient. Heavy 
rain with strong winds are expected so it is entirely possible we 
are looking at another multiple headline event. Coastal flooding 
could also become an issue with the stronger onshore winds during 
wednesday's high tide. Have gone with categorical probability of precipitation for thais 
timeframe. We will continue to have wording in the severe weather potential statement for this 
event. Looks like Rudolph and the other reindeer will have their 
work cut out for them this Christmas evening. 


&& 


Aviation /09z Friday through Tuesday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


Mostly VFR conditions are expected through the taf period. There 
should be persistent clouds between 3000 and 5000 feet above ground level for much of 
the day, so could see localized MVFR ceilings right at 3000 ft, but 
mostly ceilings should be between 3500 and 4000 feet. Northwesterly 
winds may gust at times to 20kt through early this afternoon, but by 
tonight should be less than 10kt. 


Outlook... 
Saturday - Sunday...VFR. North-northeast winds expected. Ceilings could be 
lowering throughout the day 


Monday - Tuesday...sub-VFR expected with scattered rain/snow 
showers, becoming all rain by Tuesday. 


&& 


Marine... 
winds and seas should stay below Small Craft Advisory criteria. However, gusts near 
or just above 20kt will be possible through this evening. 


Outlook... 
Saturday - Sunday...sub-sca expected for the most part. Seas remain 
around 3 to 4 feet. Confidence: average to slightly below average. 


Monday - Tuesday...Small Craft Advisory conditions should present themselves later on Monday 
under a strengthening easterly flow and building seas. Confidence: 
average. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...none. 


&& 


$$ 
Synopsis...gigi 
near term...Johnson 
short term...Johnson 
long term...Heavener 
aviation...Heavener/Johnson 
marine...Heavener/Johnson 












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