Scientific Forecaster Discussion
fxus61 kphi 281024
Area forecast discussion
National Weather Service Mount Holly New Jersey
624 am EDT sun may 28 2017
a weak area of high pressure will shift east of the New England
coast this morning, keeping a warm front to our south and west
today into tonight. A stronger low pressure system will move
into southeastern Canada Monday, bringing a cold front through
our area. A couple of cold fronts will then move through our
region through about midweek, before high pressure builds toward
our area Thursday and Friday. A weak cold front however may
settle across our area Friday night and Saturday.
Near term /until 6 PM this evening/...
high pressure located off the New England coast early this
morning will progress northeastward today. Meanwhile, a frontal
boundary will extend from the Ohio River valley and the Great
Lakes southeastward to the waters off Virginia and North
The sky was mostly cloudy over the Poconos and far northern New
Jersey, and over northeastern Maryland, Delaware and southern
New Jersey around 6:00 am. The sky was partly cloudy over areas
between the two with some patchy stratus and fog in that area.
The low clouds and fog should dissipate by mid morning.
An onshore flow is expected to develop for today. Additional
clouds will overspread our region from the west. It appears as
though the daylight hours will be mainly rain-free with
conditions remaining fairly stable. We may see some showers
begin to spread into eastern Pennsylvania and the upper Delmarva
from the west early this evening.
High temperatures are expected to range from the upper 60s to
the middle 70s. Readings should get no higher than the middle
60s right along the coast due to the onshore flow.
Short term /6 PM this evening through 6 am Monday/...
a mid level trough over the central part of the country early
this morning will work its way eastward. Showers and
thunderstorms will develop ahead of the feature and they should
move into our region from the west tonight. As a result, we will
carry categorical or likely probabilities of precipitation for
much of our forecast area. Generally, rainfall amounts should
favor the quarter to half inch range.
The continued onshore flow and the precipitation are
anticipated to result in the development of low clouds over much
of our region for tonight.
Low temperatures should favor the upper 50s and lower 60s.
Long term /Monday through Saturday/...
summary...remaining shower/thunder chances through the first
half of this upcoming week. Temperatures overall on the
Synoptic setup...a closed low initially centered near the upper
Great Lakes will slowly shift eastward through much of this
upcoming week. While the core of this feature is forecast to
remain well to our northwest and north, spokes of energy will
rotate around the parent closed low. A potentially stronger
short wave is forecast to shift eastward Wednesday, which is
tied to a cold front. This short wave may sharpen the southern
extent of the long wave trough some, potentially enhancing a
ribbon of lift. As we go toward the end of the week and to start
next weekend, the closed low shifts closer to the Canadian
Maritimes and perhaps weakens some. Additional short waves on
the western and southern side may amplify the trough across the
northeast Friday into Saturday before the entire system shifts
more eastward. This all results in a few episodes of possible
showers/thunder, although exact timing and coverage is less
certain. We used a model/continuity blend for Monday through
Tuesday night, then blended in the 00z wpc guidance thereafter.
Some adjustments were then made following additional
collaboration with our neighboring offices.
For Monday and Tuesday...the center of a closed low is forecast
to move to a position between the Great Lakes and James Bay
Canada. A stronger short wave is forecast to be lifting across
the northeast Monday, with a narrow trough axis possibly taking
on some negative tilt. This will produce a ribbon of enhanced
forcing, resulting in a band of showers and perhaps thunder.
This looks to quickly lift to our north and east during the
morning. A weakening cold front then moves through during
Monday, however there may not be much in the way of forcing once
the earlier morning band of showers clears the area. The
forecast soundings overall indicate the column dries out in the
afternoon especially for the central and southern areas. As a
result, pops were lowered faster but still kept in some low pops
in through the day. Another cold front or surface trough
arrives during Tuesday, and with short wave energy accompanying
it a band or two of showers will be possible. There could be
just enough instability to allow for some thunder Tuesday
afternoon. Daytime temperatures are expected to be mild/warm,
however the far north and northeast areas on Monday may be
cooler depending on the amount of clearing.
For Wednesday and Thursday...as the center of the closed low
slowly shifts across southeastern Canada, a stronger embedded
short wave allows for the southern part of the long wave trough
to amplify across the northeast Wednesday. This should be
reflected by another cold front at the surface. While some
instability is forecast to develop during Wednesday, soundings
generally show it being meager with any convection being low-
topped. If the boundary layer warms more, low-level lapse rates
would steepen and result in a bit more instability. Therefore, a
thunder mention was expanded south and eastward some in the
afternoon. The challenge is how much coverage occurs with
showers/thunder Wednesday. Some guidance suggest coverage could
be fairly widespread in the afternoon. For now, kept mostly
chance pops with the idea there will be at least scattered
activity around. The flow aloft may start to turn more zonal
Thursday allowing for a dry day, however more short wave energy
diving into the base of the closed low looks to start another
For Friday and Saturday...the details of the forecast during
this time frame mostly depend on the speed of the closed low to
our north. While it will gradually shift eastward and probably
eventually weaken, some guidance shows more amplification as
strong short wave energy slides across the southern portion of
the trough. This sends another cold front our way, which may be
mostly just to our north. The evolution of the energy and
therefore chances for convection is less certain. The entire
system eventually shifts closer to the Canadian Maritimes with
less influence on our region. As of now, kept slight chance pops
for Friday and dry on Saturday.
Aviation /12z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Variable conditions are expected through 1300z. Ceiling and
visibility values should favor VFR. However, there will be areas
of MVFR and IFR.
VFR conditions are anticipated from about 1300z until 0000z
although there should be a fair amount of cloud cover for much
of the day.
Ceilings are expected to lower into the IFR range for tonight
with the arrival of showers and scattered thunderstorms from the
west, along with an onshore wind flow. The timing and coverage
of thunderstorms for tonight remains a bit uncertain so we have
mentioned only showers in the taf at this time.
A light and variable wind early this morning should settle into
the southeast today at 5 to 10 knots. The wind direction is
forecast to back toward the east tonight.
Monday...MVFR/IFR conditions with some showers and
thunderstorms mainly in the morning, then improving in the
afternoon and at night as a cold front moves through. Some fog
or low clouds are possible late at night.
Tuesday and Wednesday...some possible fog or low clouds to
start Tuesday, otherwise generally VFR through Wednesday. Some
showers and thunderstorms possible mainly each afternoon and
evening, however timing and coverage is less certain.
Thursday...VFR is anticipated with dry conditions.
as high pressure moves away to our northeast today, a southeast
to east wind is forecast to increase to 10 to 15 knots. Wind
speeds may rise into the 15 to 20 knot range for tonight,
especially on the waters off New Jersey.
Wave heights of 2 to 3 feet on our ocean waters today should
build to 3 to 4 feet tonight. It appears as though they may
reach 5 feet on our coastal waters from north of Ocean City New Jersey
to Sandy Hook. We have placed those areas under a Small Craft
Advisory beginning at midnight.
waves off the coast are forecast to be in the 2 to 3 foot range
for today. An southeast to east wind is expected around 10
knots or so. It appears as though the risk for the development
of dangerous rip current will be low for much of the day.
However, it may begin to approach moderate toward evening as
wind speeds increase gradually.
The outlook for Monday is a low risk for the development of
dangerous rip currents, as winds should become about 10 knots or
less mainly from the southeast and south and waves lower some.
Monday through Thursday...east to southeast winds are forecast
to be strongest (gusts near 25 knots) Monday morning across the
northern ocean zones before diminishing. This should maintain
seas to about 5 feet at least in the morning before subsiding.
Therefore, a Small Craft Advisory has been issued for our three
northern ocean zones through 16z Monday. Otherwise, generally
sub-advisory conditions are expected through Thursday.
Some showers and thunderstorms are expected, mainly Monday
morning and again Tuesday and Wednesday afternoons.
the development of an onshore flow for today into tonight and
the continued high astronomical tides should result in another
round of minor coastal flooding tonight. As a result, we will
issue another coastal flood advisory for tonight's high tide. It
will cover the coastal counties of New Jersey and Delaware, as
well as the counties along Delaware Bay and the lower Delaware
River up to the area just below the Commodore Barry bridge.
Based on the guidance and on the fact that the astronomical
tides are decreasing as we move away from the new moon,
tonight's coastal flood advisory should be the last one for a
New Jersey...coastal flood advisory from 9 PM this evening to 3 am EDT
Monday for njz012>014-020>027.
Coastal flood advisory from midnight tonight to 4 am EDT
Monday for njz016.
Delaware...coastal flood advisory from 9 PM this evening to 3 am EDT
Monday for dez002>004.
Coastal flood advisory from midnight tonight to 4 am EDT
Monday for dez001.
Marine...Small Craft Advisory from midnight tonight to noon EDT Monday