Scientific Forecaster Discussion
fxus61 kphi 190731
Area forecast discussion
National Weather Service Mount Holly New Jersey
331 am EDT Sat Oct 19 2019
high pressure will build to our east later today and tonight. Low
pressure tracks from the eastern Carolinas later tonight to offshore
of the mid-Atlantic coast during Sunday, then it moves out to sea
into Monday. A cold front moves through our region late Tuesday,
followed by high pressure Wednesday and Thursday. The next cold
front should arrive later Friday.
Near term /until 6 PM this evening/...
frost advisories remain in effect for much of southeast Pennsylvania
and most of New Jersey and freeze warnings remain in effect for
Sussex County, New Jersey through this morning. Temperatures will
warm up fairly rapidly after sunrise.
High pressure centered over central Pennsylvania will pass over New
Jersey today, and then offshore by the end of the period. Abundant
sunshine on tap for the day. Return flow sets up this afternoon, and
temperatures warm up a bit compared to Friday. Highs top off in the
upper 50s in the southern Poconos, and otherwise in the low to mid
Short term /6 PM this evening through 6 am Sunday/...
high pressure continues to drift offshore tonight. Meanwhile,
tropical storm nester will be over the southeast U.S. This evening,
and will lift towards the Carolina coast during the overnight hours.
The significant impacts will remain well to the south of the
forecast area, but rain will begin to lift into southeast Maryland
and Delaware towards daybreak Sunday.
With increasing clouds and warm air advection, lows tonight will be warmer, in the
low to mid 50s for most of the region, and around 50 in Delmarva.
Long term /Sunday through Friday/...
summary...rain associated with current tropical storm Nestor moves
across much of our area Sunday before ending Sunday night. A cold
front moves through later Tuesday with another cold front arriving
Synoptic setup...amplified flow aloft with a trough ejecting
into the plains with another trough from the Great Lakes to the
mid- Atlantic Sunday, then ridging builds across the east into
early next week as a significant trough digs across the plains.
This trough shifts eastward through midweek before lifting into
Canada with some zonal flow in its wake across the northern
tier. Another trough amplifies into the northern plains late
Wednesday, which then shifts eastward through Friday.
For Sunday...low pressure (remnants of current tropical storm
nestor) is expected to move northeastward across the eastern
Carolinas, exiting off the coast near Cape Hatteras during Sunday.
The low is then forecast to move out to sea during early next week.
Despite the trough aloft weakening some as it slides across our
region Sunday, the track of the surface low and ascent to its north
and northwest side will result in a shield of rain. The highest
rainfall amounts are expected to be across southeastern New Jersey
and into southern Delaware. However, much of the guidance brings
measurable rain to much of region. Based on this and the latest quantitative precipitation forecast
forecast from wpc, increased the pops north and westward during the
day Sunday. There will be a period of gusty onshore winds mainly
along the coast Sunday into Sunday night, and while there is some
uncertainty with the magnitude some guidance suggests 40-ish mph
gusts. As of now though, we kept the winds well below advisory
criteria. The conditions should quickly improve during Sunday night
from west to east as the system moves far enough away and the flow
turns more from the north, allowing some drying to work in.
Temperatures were lowered Sunday across much of the area given
onshore flow along with clouds and rain.
For Monday...a sliver of surface high pressure extends southward
across our area. Any lingering breeze along the coast is expected to
subside as the pressure gradient collapses due to high pressure
building in. The return of some sunshine should result in milder
For Tuesday...a strong area of low pressure is expected to lift from
the upper Mississippi Valley and the western Great Lakes Monday and
into western Ontario during Tuesday. This feature is anticipated to
pull a cold front through our region late Tuesday. The amplification
of the parent upper-level trough should result in a slower arrival
of the cold front. We continue to mention a chance of showers ahead
of and with the front, however given uncertainty regarding available
instability held off in adding a thunder mention.
For Wednesday and Thursday...high pressure is forecast to build
across the southern states Wednesday, then across our region and off
the coast Thursday. This should have enough of an influence on our
weather and therefore we anticipate dry conditions.
For Friday...the next cold front arrives later during this time
frame, although timing is somewhat uncertain. Given the synoptic
setup that is forecast, there is the potential for a surface low to
develop along the front as it is crossing our area. If this were to
occur, the precipitation would be enhanced across our region. For
now and based on wpc guidance with the front arriving late, kept
some slight chance pops in the gridded forecast.
Aviation /08z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...VFR/skc. Light/vrb winds this morning, becoming SW less than
10 kt this afternoon. High confidence.
Tonight...VFR. SW winds less than 10 kt become light/vrb after 00z.
Sunday...MVFR/IFR conditions probable, especially for phl/pne, ilg,
ttn, miv and Acy, due to rain and low ceilings. Conditions should
improve to VFR during the night. East winds 5-15 knots becoming
northeast, then north at night. At miv and Acy, winds of 15-20 knots
with gusts up to 30 knots are possible especially in the afternoon
and evening. Moderate confidence regarding a period of MVFR or lower
conditions, but low confidence on the timing and also wind speeds.
Monday...VFR into the evening, then conditions may lower to MVFR or
IFR during the night with some possible showers especially at Abe
and ridge. Northeast to east winds 5-10 knots, becoming southeast at
night. High confidence during the day; low confidence at night.
Tuesday...MVFR/IFR conditions spread across the region through the
day with showers, then conditions should quickly improve to VFR
during the night. Moderate to high confidence on conditions below
VFR, but low confidence on the timing of flight category changes.
Southeast to south winds around 10 knots, shifting to northwesterly
Wednesday...mostly VFR. Westerly winds of 5-15 knots. Moderate
sub-Small Craft Advisory conditions on tap for today and tonight. Northwest
winds around 15 kt with gusts up to 20 kt, become around 10 kt this
morning, then become light and variable this afternoon. Winds
tonight become S-southeast around 10 kt. Seas 2 to 3 ft.
Sunday...east to northeast winds increase with Small Craft Advisory
conditions expected in the afternoon and at night. A period of gale
force wind gusts are possible later Sunday especially south of
Little Egg Inlet, New Jersey where a gale watch has been issued. Low
confidence regarding possible gale force gusts in the lower Delaware
Bay (around the Bay mouth). The seas build significantly especially
across the Atlantic coastal waters.
Monday...while wind gusts should drop below 25 knots, seas on our
ocean waters are forecast to remain elevated.
Tuesday...the conditions should be mostly below Small Craft Advisory
criteria during the day, however a wind shift to northwesterly
behind a cold front at night may result in a wind surge with gusts
to around 25 knots.
Wednesday...west or west-northwest wind gusts to around 25 knots
probable before diminishing at night.
PA...frost advisory until 9 am EDT this morning for paz060>062-
New Jersey...frost advisory until 9 am EDT this morning for njz007>010-012-
Freeze warning until 9 am EDT this morning for njz001.
Maryland...frost advisory until 9 am EDT this morning for mdz008.
Marine...gale watch from Sunday afternoon through Sunday evening for