Area forecast discussion 
National Weather Service Mount Holly New Jersey 
410 am EDT Tuesday may 21 2013 


Synopsis... 
high pressure will remain anchored just off the southeastern United 
States coast through Thursday. Low pressure will approach from the 
west, passing to our north, and will drag a cold front through the 
region late Thursday into Friday. High pressure will then build in 
from the west for the weekend before moving offshore later Sunday. 


&& 


Near term /until 6 PM this evening/... 
high pressure will remain across the southern Atlantic today, which 
will keep our area under a return flow. This will keep a flow of 
warm, moist air across the area. Patchy low clouds and fog early 
this morning will burn off my middle-morning, and eventually lead to a 
partly to mostly cloudy day. A frontal boundary will try to sink 
toward our area from the north today, but is not expected to reach 
this far southward. Model guidance indicate a short wave moving to 
our north along this boundary during the day, and another short wave 
is expected to skirt just to our south. Any organized precipitation 
would likely be focused near these areas. However, with a warm and 
moist airmass across the area, there will be some instability 
through the day. This could lead to some isolated to scattered 
showers/thunderstorms across the area, mainly late in the day. 


Mav/met MOS guidance gave some different numbers for highs today 
with the met several degrees warmer than the mav. Taking a look at 
925 mb temperatures, we decided to take a blend of the MOS numbers, 
which would give middle-upper 80s from much of the area, with low-middle 
80s for our eastern and southern areas. Areas right along the coast 
may not reach 80 degrees however. 


&& 


Short term /6 PM this evening through 6 am Wednesday/... 
the synoptic situation overnight does not change much from the 
daytime. A stronger short wave/vorticity maximum aloft is forecast to 
approach the area overnight, at the same time a weak surface trough 
may move across the area. There could still be some instability 
overnight, which could lead to the chance for isolated to scattered 
showers/thunderstorms across the area. We left fog out of the 
forecast overnight as there may be enough mixing to prevent much of 
the denser fog from developing. A blend of the mav/met MOS was taken 
for overnight lows. 


&& 


Long term /Wednesday through Monday/... 
high pressure dominates our weather over the next several days as it 
sets up shop over the southwestern Atlantic. With the high to our 
southeast, we will see a southwesterly flow continue across the 
region. This southwest flow will advect warm and moist air to our 
area and we will remain above normal for temperatures through at 
least middle week. With all that moist, warm air, we will also start to 
destabilize. This will allow for scattered showers and thunderstorms 
to develop through the week, mainly in the afternoon after 
sufficient daytime heating has occurred and convective temperatures 
have been reached. 


A low pressure system will approach from the west on Thursday, with 
the center passing off to our north. The attached cold front is 
forecast to move through our area Thursday into Friday, most likely 
later in the day Thursday into early Friday. The latest model 
guidance has slowed down the frontal passage and with little support 
overall, we have opted to keep the forecast largely the same and 
lean a bit more on the progressive side. 


The front pushes through and offshore by Friday morning. High 
pressure will build in behind the front, bringing in some cooler and 
drier air for the Holiday weekend. The models hint at a 
shortwave moving through the middle levels late Saturday or Sunday with 
a light shower possible. The air looks like it might be too dry for 
anything to make it to the surface and we have kept the Holiday 
weekend pop free. 


&& 


Aviation /08z Tuesday through Saturday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


MVFR/IFR ceilings/visibilities are now developing across the taf sites. The low 
clouds/fog will burn off through the middle morning hours, and 
conditions will eventually become VFR. There is a chance for some 
isolated/scattered showers/thunderstorms this afternoon, but 
confidence in them hitting a particular taf site is low, so they 
were left out of the forecast for the time being. 


Another round of low clouds/fog is possible again Tuesday night. 
However, there is also the possibility for isolated to scattered 
showers/thunderstorms overnight as well. Confidence in the showers 
occurring is still low, so they were left out for now. Also, with 
the potential for some mixing to occur, so we did not hit the low 
conditions hard just yet...we'll see how later guidance handles the 
overnight period. 


Outlook... 
Wednesday through Thursday night...mainly VFR. MVFR, possibly IFR, 
conditions possible during the early morning hours. Also, scattered 
showers and thunderstorms, mainly during the afternoon and evening, 
may reduce ceilings and visibilities at times. 


Friday...mainly VFR with a chance of showers. 


Saturday...VFR conditions expected. 


&& 


Marine... 
winds and seas are forecast to remain below advisory levels through 
today into tonight. However, winds could periodically gust around 20 
knots, especially later today into tonight. Also, seas will remain 
near 4 feet through the period, and may get close to 5 feet 
overnight. Confidence in conditions getting close to advisory levels 
is not high enough to issue an advisory. 


Outlook... 
high pressure anchored off the southeastern United States coast will 
bring a prolonged south to southwest flow for Wednesday through 
Thursday. As this flow strengthens, winds and seas will gradually 
increase. Seas will start to rise to near 5 feet by Wednesday 
afternoon with winds starting to gust in advance of an approaching 
cold front. A Small Craft Advisory may be needed for late Wednesday 
and Thursday on the ocean front. 


The cold front will cross the area waters late Thursday into Friday. 
Both winds and seas will start to subside and should fall below 
Small Craft Advisory criteria. Winds and seas should remain below 
criteria through the Holiday weekend as high pressure builds across 
the region. 


With such a warm, moist airmass in place through Thursday, there 
will remain a chance for some patchy dense fog to form over the area 
waters. 


&& 


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


&& 


$$ 
Synopsis...meola 
near term...Robertson 
short term...Robertson 
long term...meola 
aviation...Robertson/meola 
marine...Robertson/meola