Scientific Forecaster Discussion
fxus61 kphi 201640
Area forecast discussion
National Weather Service Mount Holly New Jersey
1240 PM EDT sun Oct 20 2019
low pressure will track to our south and east later today into this
evening, then move out to sea tonight. High pressure builds into
our region monday; then a cold front moves through late Tuesday.
High pressure returns for Wednesday and thursday; then the next
cold front moves through later Friday with high pressure building
across the Great Lakes Saturday.
Near term /until 6 PM this evening/...
12:30 update: continued with higher pops as measurable rain
already overspread much of the region. Models are verifying too
dry with the lighter precipitation early this morning, which
brings considerable doubt to the hi- res solutions of the hrrr
and WRF- arw/nmm in the next 3-6 hours. The simulations
indicating higher quantitative precipitation forecast in the southern portions of the County Warning Area are
Worth considering, as models are trending farther north with the
precipitation shield in general. Raised pops in the northern
County Warning Area this afternoon and held onto pops longer in the North/East
County Warning Area this evening. Subsequent updates will likely require
refinements to quantitative precipitation forecast should the "farther north" trend continue.
With temps dropping down to the surface dewpoint, some patchy
fog has formed. Will add patchy fog to the forecast for a few
hours this morning, and then the fog should dissipate after
The remnant low of tropical storm Nestor lies over central
Georgia and will lift to the northeast towards the North
Carolina coast by this afternoon, and then will be south of
Delaware by this evening.
Although some light rain moves into the southern portions of
the forecast area this morning, the bulk of the rain will hold
off on moving into southern portions of Delmarva until the early
Href ensemble Max quantitative precipitation forecast indicating 3-4 inches across portions of
Delmarva and southern New Jersey, but this is high compared to
most of the guidance. NAM is closest at generally 2-3 inches,
and the GFS has 1-2 inches. Will generally go on the
conservative side of the quantitative precipitation forecast blending the nbm with wpc for a
total of 1-1.5 inches this afternoon and evening in Delmarva and
the coastal plains of southern New Jersey. For areas north and
west, expecting 1/4-1/2 inch quantitative precipitation forecast.
Periods of moderate to locally heavy rain will fall in those
far southeast areas in the late afternoon, but not expecting
widespread heavy rain.
East to northeast winds over southeast New Jersey and Delaware
will increase to 15-20 mph with gusts up to 30 mph due to the
Short term /6 PM this evening through 6 am Monday/...
the remnant low of Nestor moves out to sea tonight. Precip tapers off
fairly quickly from northwest to southeast, and rain ends by
midnight or so over southeast New Jersey. Weak high pressure builds
in from the north. Winds shift to the north behind the departing
low, but winds will be light. Since it will take some time for the
region to dry out, will add patchy fog to the forecast.
Lows tonight will be in the 40s.
Long term /Monday through Sunday/...
summary...a cold front moves through later Tuesday, followed by
another cold front later Friday with the potential for a surface low
developing along it.
Synoptic overview...an amplified but progressive flow aloft as
a deep trough across the plains and Midwest Monday shifts
eastward through Tuesday but lifts more into Canada and the
northeast. The flow turns briefly more zonal during the midweek
time frame before another trough amplifies from the Midwest
through the plains late Wednesday and Thursday. This feature
then shifts eastward through Saturday, however the southern
portion of the trough may close off across the southern states
and this introduces more uncertainty.
For Monday...our region is between systems with low pressure to our
east continuing to move out to sea while a large storm system is
carved out across the plains and Midwest. Meanwhile, a sliver of
surface high pressure extends southward across our area. Any
lingering breeze mostly along the coast is expected to diminish
through the day as the pressure gradient collapses due to high
pressure building in. Early clouds give way to increasing sunshine
for most areas which will result in a milder afternoon, although an
onshore wind will keep it a little cooler along the coast. There
will be some increase in warm air advection aloft Monday night ahead
of a strong Midwest storm system, and while a few sprinkles or light
showers are possible late Monday night, opted to keep it dry at this
point with the main forcing still well to our west.
For Tuesday...a strong area of low pressure is forecast to track
across the western Great Lakes and into adjacent Canada during this
time frame. The associated upper-level trough may take on some
negative tilt as it arrives across the northeast later Tuesday
night. An associated cold front is expected to move across our
region later Tuesday with the potential for a weak surface low to
develop near the triple point as it crosses our region. This may
tend to enhance the showers for a time. Given the uncertainty
regarding available instability ahead of and along the cold front,
held off including a thunder mention at this time. The front is
forecast to be progressive and therefore showers end Tuesday night,
although there may be a little bit of a wind surge in its wake with
some initial cold air advection and tightened pressure gradient.
For Wednesday and Thursday...high pressure across the southern
states Wednesday is forecast to build across our region Wednesday
night into Thursday before gradually shifting offshore. Given this
and the flow aloft turning more zonal, dry conditions are
anticipated. The afternoon temperatures Thursday may near 70 degrees
in some places as some return flow and warm air advection gets
For Friday and Saturday...a complex setup may occur as the next
upper-level trough amplifies eastward from the Midwest and plains.
This feature may split with a closed low developing across the
southern states while the northern branch trough slides eastward
across the Great Lakes and the northeast. The northern trough will
drive a cold front across our area later Friday, however it may slow
as it reaches the coast. The southern states energy looks to develop
a surface low along the tailend of the cold front and this system
may make a run at our region later Saturday into Sunday. Given much
more uncertainty regarding the timing and the overall synoptic
evolution, blended in the 00z wpc guidance with continuity and kept
any pops no higher than the chance range.
Aviation /18z Sunday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...cigs to continue to lower to MVFR. Rain has moved into
the region and will persist through the balance of the day with
MVFR vsbys at krdg/kabe, IFR conditions at kttn/kpne/kphl/kilg,
and IFR/LIFR conditions at kmiv/kacy. Rain may be heavy at
times at kmiv/kacy, especially late. Winds east-NE at 5-10 kt, and
to 15-20 kt with gusts up to 25 kt at kmiv/kacy this afternoon.
Tonight...MVFR/IFR early, then conditions improve to VFR after
midnight. Patchy fog develops thereafter, possibly resulting in MVFR
or even IFR conditions late. Light north winds.
Monday...VFR, then MVFR ceilings may develop overnight. Northeast to
east winds around 10 knots, becoming southeasterly 5 knots or less
at night. Low confidence regarding low cloud development at night.
Tuesday...MVFR/IFR conditions spread across the region through the
day with showers becoming more numerous in the afternoon into the
evening, then conditions should quickly improve to VFR during the
night. East to southeast winds around 10 knots, shifting to westerly
at night. Moderate to high confidence on conditions below VFR, but
low confidence on the timing of flight category changes.
Wednesday and Thursday...VFR. Westerly winds of 10-15 knots,
becoming light and variable Wednesday night then southwesterly
around 5 knots Thursday. Moderate confidence.
the remnant low of Nestor moves into the Carolina coast this
afternoon, and then out to sea tonight.
Northeast winds increase this afternoon, and Small Craft Advisory conditions will
develop on New Jersey and Delaware Bay waters, and gales will
develop on Delaware ocean waters. As the low approaches this
evening, gales will then spread to the north over most of New Jersey
ocean waters and should continue into most of tonight.
Monday...Small Craft Advisory conditions on the Atlantic coastal
waters as northeasterly winds gradually diminish however seas remain
elevated. The Small Craft Advisory for the northern New Jersey
Atlantic coastal waters has been extended through 22z/6pm Monday
(south of here an advisory will be needed followed the gale warning).
Tuesday...the winds and seas mainly below Small Craft Advisory
criteria, however southerly winds become westerly toward daybreak
Wednesday and may gust to around 25 knots.
Wednesday...Small Craft Advisory conditions possible especially in
the morning with westerly wind gusts to 25 knots.
Thursday...the conditions are anticipated to be below Small Craft
Marine...Small Craft Advisory until 6 PM EDT this evening for anz452-
Gale Warning from 6 PM this evening to 6 am EDT Monday for
Small Craft Advisory until 6 PM EDT Monday for anz450-451.
Gale Warning until 6 am EDT Monday for anz454-455.
Small Craft Advisory until 6 am EDT Monday for anz430-431.