Scientific Forecaster Discussion
fxus61 kphi 260148
Area forecast discussion
National Weather Service Mount Holly New Jersey
948 PM EDT Thu may 25 2017
an area of low pressure will move across the area tonight, then
move away to our northeast through Friday. A weak surface
trough is expected to cross the area during the day Friday. Weak
high pressure may briefly move across the area Friday night
into early Saturday. A weak low is forecast to move along a
developing stationary front to our south Saturday into Saturday
night. Another area of low pressure is forecast to weaken as it
moves into the eastern Great Lakes Sunday into Sunday night,
then an occluded frontal system is expected to affect the area
Sunday night into early Monday. A series of cold fronts are
forecast to move across the area Monday through Wednesday.
Near term /until 6 am Friday morning/...
focus of convection is a line from just south of reading, PA to
Mount Holly, NJ, to Atlantic City, New Jersey. This wave continues to
lift to the north and east. The first wave of convection that
impacted SW New Jersey and southeast PA has lifted into northern New Jersey and is
dissipating. Weak low pressure over southern New Jersey continues to
lift to the north and east, and strong 500 mb vort Max just lifting
into southeast PA and the Delmarva.
With loss of diurnal heating, sb cape values are dropping back
to around 250 j/kg, but MUCAPE values are still upwards of
around 500 j/kg, so there still is enough instability to keep
these storms going for a while.
Will follow with the timing trend of the latest hrrr, and have
the heaviest showers and storms north of the region by 06z, but
will then keep slight chance-chance pops for lingering showers
into daybreak Friday. Pwats generally 1-1.25", and there have
been some locally heavy downpours. Additional rain will be
light, as the bulk of the lift will be gone once the vort Max
lifts to the north and east.
With abundant low level moisture across the region, fog has
developed, so it was added to the forecast. With a drying
westerly wind developing behind the departing low, most of the
fog should dissipate prior to daybreak.
Lows generally in the 50s, maybe near or slightly above 60 near
the coast and in Delmarva.
Short term /6 am Friday morning through 6 PM Friday/...
the main upper low shifts into New England on Friday, with
westerly flow prevailing across the area during the day. Several
perturbations in the flow are likely to move through the area
during the day, especially in the morning. This should keep
skies partially to mostly cloudy most of the day, and may allow
for a sprinkle or light shower to occur, especially north of the
Mason-Dixon line. The 18z NAM has a few showers farther to the
south as a vort Max rotates southeastward through the mid-
Atlantic around midday, but there is not a lot of support from
higher-resolution guidance at the moment. As such, kept pops low
or non-mentionable for the most part south of the I-78/I-195
Main sensible weather impact tomorrow may be the winds, with
some stronger mixing likely to occur during the afternoon hours.
Winds above the boundary layer are not particularly strong
(20-30 kts), but gusts of 20-30 mph are likely by afternoon
across most of the area.
Forecast Max temperatures range from the mid 60s in the Poconos
to the mid 70s in the urban corridor to around 80 in southern
Long term /Friday night through Thursday/...
an unsettled weather pattern continues for much of the extended
forecast with several periods of rain possible.
Friday night through the early part of Saturday is expected to
be mostly dry as weak high pressure quickly moves across the
area. However, later in the day, a weak area of low pressure
will be approaching from the west but passing to our south along
a developing frontal boundary to our south. Also, a short
wave/vorticity impulse is expected to move across the area
during the day, so there will be a chance of an isolated shower
during the day Saturday.
On Saturday night, the frontal boundary is expected to remain
to our south, but should begin lifting northward toward the area
Sunday. It will likely not make its way into the area until
Sunday night. There will be a chance of showers overnight
Saturday into Sunday, but the best chance of showers is expected
to be Sunday night as the occluded front moves into the area.
A series of cold fronts are forecast to move across the area
Monday through Wednesday of next week as low pressure remain
nearly stationary across southern Canada just north of the Great
Lakes region.As any short wave/vorticity impulses slide across
the area, they could lead to additional showers or thunderstorms
early next week.
High pressure tries to build back into the area for Thursday, which
would provide a dry forecast.
Aviation /01z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Low confidence forecast for the taf period through 12z Friday.
Rain showers/thunderstorms and rain mixing up the atmosphere enough to scour out some of
the low cigs, resulting in brief MVFR/VFR conditions. Once the
rain taper off, winds should be light enough for fog/stratus to
redevelop into Friday morning.
Westerly winds pick up (5-10 kt) prior to daybreak, and that
should help scour out the fog/stratus during the early morning
Rain showers/thunderstorms and rain will lift to the north and east through the overnight,
and should be through northern New Jersey between 06-08z. A few
lingering showers possible thereafter.
VFR conditions develop Friday morning. Winds veer to the west-northwest
late Friday morning, and increase to 15-20 knots with gusts up to
Friday night...generally VFR.
Saturday...generally VFR. Showers moving into the area later in the
day, which could lead to lowering ceilings.
Saturday night-Sunday...MVFR ceilings possible. Chance of scattered
Sunday night...MVFR to IFR conditions possible with periods of low
clouds and rain.
Monday...generally improving to VFR during the morning. Scattered
showers and thunderstorms possible during the day.
Monday night-Tuesday...generally VFR. Chance of showers or
thunderstorms on Tuesday.
Small Craft Advisory continues, mainly for high seas, through
Friday afternoon. Seas at the buoys have increased to 5-6 feet.
Gusts to 25 knots will develop tonight, and then gusty west-northwest winds
could continue to gust to 25 knots on Friday.
Showers and thunderstorms likely on the waters tonight. Gusty
winds, small hail, and frequent cloud-to-ground lightning are
all threats from these storms. Locally strong winds/rough seas
are likely in vicinity of these storms.
Winds become westerly on Friday. A light shower or two may
occur, especially off the New Jersey coast.
With increasing westerly winds developing during the day Friday,
will keep a moderate risk for the development of dangerous rip
currents in the forecast.
Friday night-Tuesday...conditions expected to remain below advisory
levels, although winds may gust around 20 knots at times.
coastal flood advisory remains in effect through 1 am for
coastal counties of Delaware and New Jersey, as well as counties
along the Delaware and Raritan bays. The astronomical tides
with the new moon are particularly high with the evening high
tide cycle, and the persistent onshore flow has lead to a 1-2
foot tidal departure. It is possible that additional spotty
flooding may occur with the evening high tides Friday and
New Jersey...coastal flood advisory until 1 am EDT Friday for njz012>014-
Delaware...coastal flood advisory until 1 am EDT Friday for dez002>004.
Marine...Small Craft Advisory until 6 PM EDT Friday for anz450>455.