Scientific Forecaster Discussion
fxus61 kphi 291427
Area forecast discussion
National Weather Service Mount Holly New Jersey
1027 am EDT Mon may 29 2017
low pressure located off the middle Atlantic coast early this
morning will move farther out to sea today. Another weak low is
expected to follow along a trailing frontal boundary and it
should pass off the middle Atlantic coast on Tuesday night. A
cold front is forecast to approach from the northwest on
Wednesday and it should pass through our region on Wednesday
night. Another cold front is anticipated to arrive on Friday
night or Saturday.
Near term /until 6 PM this evening/...
an area of low pressure located offshore of the mid-Atlantic
this morning will continue to move eastward and away from the
area through today. The associated stationary boundary to our
south is forecast to remain to our south, while an approaching
occluded front will likely wash out and dissipate as it
approaches the area from the west this afternoon. High pressure
across the Canadian Maritimes will nose its way down the eastern
Seaboard and keep a cool and moist easterly flow across the
Showers and a few thunderstorms across NE Pennsylvania and the
northern half of New Jersey are continuing to move northeast and
will be out of the area around noon. A few showers have recently
developed across Chester County PA. Overall, the mechanisms for
precipitation are diminishing, but the low level moisture will
remain in many areas with the lowest flow still from the east. We
will likely see some breaks develop in the lo clouds, especially
across southeast PA and Delmarva. It's difficult to get too optimistic
with regards to how much sun will develop across New Jersey or NE PA.
Where clouds remain through the day, temperatures will likely
have a hard time rising, but if/where any breaks of sun occur
across the southern areas, temperatures will rise more. We used
a blend of available MOS and mosguide for daytime highs.
Short term /6 PM this evening through 6 am Tuesday/...
the aforementioned occluded front is expected to have
dissipated by this evening, while high pressure from eastern
Canada continues nosing down the eastern Seaboard. With an
easterly flow continuing across the area, this will keep cool
and moist conditions across the area through the night. It is
possible some isolated showers may develop overnight, but patchy
areas of fog and drizzle may also occur. Uncertain as how dense
fog will get because not much of the guidance gets visibilities
below 1-2 miles. So we will keep patchy fog and drizzle in the
forecast for now, but we are not expecting widespread dense fog
at this time.
Long term /Tuesday through Sunday/...
a mid level low is forecast to meander over upper Ontario and
vicinity during the mid week period before shifting eastward
over Quebec and eventually Atlantic Canada during the weekend.
An initial mid level trough axis is expected to pass over our
region around Wednesday night with a secondary axis anticipated
around Saturday night. The pattern should be rather unsettled
with the best chance for dry weather extending from Wednesday
night into early Friday.
We are expecting Tuesday to begin with a low overcast in much
of eastern Pennsylvania, New Jersey and the upper Delmarva. Some
fog is anticipated at that time, as well. A southeasterly
surface flow on Tuesday should keep the clouds from lifting and
breaking quickly. As a result, we are forecasting a mostly
cloudy day along with a chance of showers and perhaps some
thunder. High temperatures should be in the 60s up north and
right along the coast. Maximum readings are expected to be in
the lower 70s from the Philadelphia metropolitan area southward.
The most likely area for a substantial break in the cloud cover
is southern Delaware and the adjacent counties of northeastern
Maryland. There the highs could reach the upper 70s.
A weak surface low is forecast to pass off the middle Atlantic
coast on Tuesday night with partial clearing possible in its
wake for Wednesday. However, a cold front approaching from the
northwest along with some marginal instability may result in the
development of showers and thunderstorms mainly during the
afternoon and evening hours. The best chance for precipitation
at that time will be in eastern Pennsylvania and northern New
The cold front is expected to pass through our region on
Wednesday night followed by dry weather and seasonable
temperatures for Thursday and Thursday night.
Another cold front is anticipated to approach from the
northwest on Friday and it should pass slowly through our region
on Friday night and Saturday. We will mention another chance
for showers and thunderstorms in advance of the front.
The southward progress of the front over the weekend is a low
confidence forecast. The models differ on how progressive the
boundary will be. As a result, we will keep a chance or slight
chance of showers into Sunday.
Aviation /15z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
An easterly flow will continue through today across the area as
low pressure moves out to sea, and high pressure noses down the
eastern Seaboard across the area. This will keep plenty of
moisture low level moisture across the area through today.
IFR/MVFR conditions are expected to continue through much of
the day. However, there is a chance for some improvement this
afternoon into this evening. Even if this improvement does
occur, clouds are expected to fill back in overnight with low
clouds and fog developing again, leading to IFR conditions
overnight. There is also the possibility for patchy drizzle to
develop overnight as well.
Tuesday...IFR conditions in the morning improving to MVFR and
VFR during the course of the day. A chance of showers and
Tuesday night and Wednesday morning...conditions may lower back
to MVFR and IFR for a time.
Wednesday afternoon and evening...mainly VFR with a chance of
showers and thunderstorms.
Wednesday night through Friday morning...mainly VFR.
Friday afternoon...mainly VFR with a chance of showers and
a Small Craft Advisory flag has been issued for the Delaware and
southern New Jersey coastal waters for today. Seas at buoy 44009
have increased to around 5 ft and the sea seen via webcam near
Acy looks quite choppy. We will keep the flag for the daytime
hours, although this may be longer than necessary.
Small Craft Advisory continues across the northern half of the
Atlantic coastal waters as seas are being observed around 5
feet and winds will remain gusty to around 25 knots. We have
extended the flag for the remainder of the day.
Tuesday through Wednesday...wind speeds and wave heights are
forecast to remain below the Small Craft Advisory criteria.
However, some fog is possible on the waters.
Wednesday night through Friday...no marine headlines are
the potential for the development of dangerous rip currents is
low for today.
tidal departures of around 1 foot are expected again tonight for
coastal areas of New Jersey and Delaware and areas along
Delaware Bay. These tidal departures would lead to another
round of minor coastal flooding for tonight's high tide.
Therefore we've issued a coastal flood advisory for tonight.
New Jersey...coastal flood advisory from 10 PM this evening to 4 am EDT
Tuesday for njz012>014-020>027.
Delaware...coastal flood advisory from 10 PM this evening to 4 am EDT
Tuesday for dez002>004.
Marine...Small Craft Advisory until 6 PM EDT this evening for