Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
632 am EDT sun Apr 19 2015
high pressure centered to our north this morning will gradually
shift off the New England coast late today and tonight. Low
pressure organizing in the Great Lakes region tonight will lift
into Canada Monday and Tuesday. An associated warm front will lift
into a portion of our region Monday, followed by a cold front
Monday night. As low pressure slowly moves eastward across New
England, a cold front will cross our region late Wednesday into
Thursday with another one late Thursday into Friday.
Near term /until 6 PM this evening/...
a middle level ridge extended from the waters off the southeast
coast to the Great Lakes early this morning. The ridge will
progress to the east and its axis is forecast to pass overhead
this afternoon. Meanwhile, surface high pressure will nose down
from Quebec for today. We are anticipating a mostly sunny day even
with a fair amount of cirrus overhead.
The wind is expected to settle into the east for today due to the
circulation around the high to our north and northeast. Wind
speeds are expected to increase to 10 to 15 miles per hour in much of our
The onshore flow will result in our highest temperatures being in
eastern Pennsylvania and northern New Jersey where readings should
get into the middle 60s this afternoon except in the elevated
terrain where highs should be around 60. Maximum temperatures are
anticipated to favor the lower 60s on the coastal plain with highs
only in the middle and upper 50s near the coast.
Some low clouds may begin to drift off the ocean and over parts
of our coastal counties toward evening.
Short term /6 PM this evening through 6 am Monday/...
middle level clouds will approach from the west and southwest this
evening. Meanwhile, low clouds will move inland off the ocean as
the easterly surface flow continues through the night. Wind speeds
are forecast to favor the 10 to 20 miles per hour range with the strongest
winds on the coastal plain.
Rain will begin to arrive from the southwest toward midnight. The
leading edge of the rain is forecast to reach a line from the
Poconos to Philadelphia to Cape May around 200 am with the
precipitation expected to overspread the remainder of New Jersey
by about 400 am.
The model guidance is indicating a southeasterly low level jet of
50 knots or greater over our region late tonight. The low level
jet will draw moisture off the ocean. The enhanced lift will
likely increase rainfall rates at that time. Precipitable water
values are forecast to increase to about 1.5 inches.
We are expecting rainfall amounts of a third to three quarters of
an inch by daybreak on Monday with locally higher amounts, close
to an inch possible. We should be able to handle those totals
based on the relatively dry antecedent conditions. However,
ponding of water on roadways and in areas of poor drainage is
Long term /Monday through Saturday/...
the synoptic setup is comprised of an amplifying upper-level
trough from the Midwest to the lower Mississippi Valley Monday,
which then closes off and strengthens across the Great Lakes
region through Tuesday. This feature may elongate into New England
Wednesday as short waves rotate around it, however it should then
become centered over New England Friday and Saturday. The most
notable precipitation event during this time frame is on Monday as
the pattern changes into a highly amplified one. Given the surge
in moisture, the rain could be heavy at times Monday morning. The
pattern thereafter results in cyclonic flow across the east along
with cooler temperatures as a couple of cold fronts move through.
We used a model blend for Monday into Wednesday, then blended in
the 00z wpc guidance. Some adjustments were then made following
additional collaboration with our neighboring offices.
For Monday and Tuesday...a deepening and increasingly closing off
low results in surface low pressure in the Great Lakes region to
start which then lifts into Canada. A robust low-level jet during
Monday morning combined with warm air advection, deep moisture, large scale
ascent and strong frontogenetic forcing results in an area of rain
lifting northeastward. There could be a little elevated
instability within this, however we are not anticipating thunder
at this time. The precipitable water values of about 1.5 inches will result in some
heavier rain. Other than some typical ponding of water on the
roadways and poor drainage flooding during heavier rain, no other
flooding is anticipated at this time.
The warm sector may not be clean and may not clear our entire County Warning Area
but it should get into at least the southern half of the County Warning Area. This
will have an impact on high temperatures Monday. It appears an
area of middle level drying overspreads the region as the strong lift
and low-level jet clears our County Warning Area by about the early afternoon.
This may result in a lull, then incoming lift with the
cold/occluding front along with cooling aloft should trigger
additional showers. It is at this time when some thunderstorms may
also occur. There may be two target areas during Monday afternoon
and evening, one being across the western zones /incoming short
wave and front/ and the other across the Delaware-Maryland-Virginia /short wave and
pre- frontal trough/. The southern areas may have better
instability as the warm sector should arrive sooner. If we can
destabilize enough, shear profiles suggest some line segments or
multicell/clusters moving across portions of the area. Depending
on the organization of the convection, locally strong wind gusts
and some hail cannot be ruled out. The thunder mention was
expanded north a bit more in the afternoon and early evening. The
aforementioned Monday morning robust low-level jet should allow
for gusty onshore surface winds, with the strongest gusts closer
to the coast and the higher elevations.
A weak low looks to develop near the triple point, and this along
with the cold/occluding front should be exiting to our east late
Monday night into Tuesday morning with any showers ending. A
closed low over the Great Lakes though will provide cyclonic flow
into the area, and with some short wave energy nearby a few
showers in the afternoon cannot be ruled out mainly across the
For Wednesday through Saturday...a closed low centered near the
Great Lakes Wednesday should shift to New England Friday and
Saturday. There looks to be several short waves embedded in the
cyclonic flow and these will rotate through our area, pulling a
cold front through late Wednesday into Thursday. Some showers will
be possible, especially across the northern and western areas.
Another cold front should push through late Thursday into Friday,
with additional cooling behind it. The closed low looks to be
closest to our area late Friday into Saturday, and the cyclonic
flow will result in even cooler temperatures. There could be some
frost in parts of the area Friday and Saturday mornings, however
this will be dependent on cloud cover and winds. The details are
of lower confidence during this time frame as it will depend on
the timing of the closed low as well as the embedded short waves.
We mainly blended in the 00z wpc guidance with continuity during
this time frame.
Aviation /10z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy, and surrounding areas.
VFR conditions are expected for today with high clouds overhead.
The wind will favor the east through the day at speeds around 8 to
Low clouds are forecast to move into our region from the ocean
this evening, lowering conditions into the IFR category. Rain will
overspread our taf sites from the southwest after midnight
resulting in a further deterioration of conditions. The surface
wind will remain from the east around 10 to 15 knots with gusts
around 20 knots, especially from kphl east and southward.
A 50 plus knot low level southeasterly jet is forecast to be
located over our region late tonight. As a result, we will mention
the potential for low level wind shear.
Monday...MVFR/IFR with rain in the morning, then some showers
with potentially improvement to VFR from south to north in the
afternoon and evening. A few thunderstorms are possible in the
afternoon and evening. Low-level wind shear should occur in the
morning as a low- level jet moves through with a warm front.
Southeast surface winds 10 to 15 knots and gusty early in the
morning especially closer to the coast, then turning southerly
5-10 knots in the afternoon and evening.
Tuesday...VFR overall. Some showers are still possible mainly
near and north/west of kabe and krdg. Westerly winds 10-15 knots,
diminishing at night.
Wednesday and Thursday...mainly VFR. Some showers are possible,
especially from kttn to kphl metropolitan and kilg to the north and west
during each afternoon and evening. West-southwest winds mainly
near 10 knots.
high pressure located over Quebec this morning will slide to the
east. A warm front is forecast to approach our region from the
southwest tonight. The surface flow will favor the east through
We will begin a Small Craft Advisory for our ocean waters from
Little Egg Inlet, New Jersey southward to Fenwick Island, Delaware
and for the lower part of Delaware Bay at noon today. The easterly
flow should cause wave heights on the above mentioned ocean waters
to build to 5 feet this afternoon and wind gusts in the advisory
area will approach 25 knots at that time. The Small Craft Advisory
conditions are anticipated to expand across our ocean waters north
of Little Egg Inlet and to the waters of upper Delaware Bay this
evening. As a result, a Small Craft Advisory will begin for those
areas at 600 PM.
Monday and Tuesday...a potent low-level jet will move through
Monday morning. The forecast soundings continue to show a strong
low-level inversion in place and therefore more stability.
However, rather strong winds are forecast to be not to far above
the surface. The GFS does appear to be stronger, and this would
introduce a period of gales especially across the far northern
waters as there is a longer period of easterly inflow. This could
be overdone and since our confidence is low on the magnitude and
duration, we held off on a gale watch and maintained a strong
Small Craft Advisory. The winds should settle during the course of
Monday and turn more southerly as the low-level jet exits, then
turn westerly Tuesday.
Seas will build to the 5-9 foot range on the ocean and then
gradually subside Monday night and Tuesday. The Small Craft
Advisory on the Bay ends at 14z Monday, and on the ocean we
extended it to 10z Tuesday for elevated seas. It may need to be
extended more depending on how the seas behave /we did go a foot
below wave watch as the GFS may be to strong with the surface
Wednesday and Thursday...the conditions should be below Small
Craft Advisory criteria. Some increase in the winds should occur
out of the southwest Wednesday, then shift to the west for
relative humidity values are forecast to lower into the 20s
during the late morning and afternoon in much of eastern
Pennsylvania and New Jersey. Minimum relative humidity values
should be in the 30s in much of Delaware and northeastern
Maryland. Fine fuels will continue to dry today.
It appears as though maximum wind gusts will be in the 15 to 20
miles per hour range in much of our region today.
Conditions are anticipated to remain just below the red flag
warning criteria in eastern Pennsylvania and New Jersey. We will
keep an eye on the situation as the morning progresses. Meanwhile,
the forecast relative humidity values will limit the concern for
wildfire spread in Delaware and in northeastern Maryland.
a moderate easterly surface flow is expected for today and
tonight. The latest guidance is bringing tide levels close to the
minor flooding threshold in New Jersey and Delaware for this
evening's high tide. We are concerned that the guidance is a bit
low considering the long easterly fetch that is developing. We
will continue to monitor the situation for a possible coastal
A warm front is forecast to lift through our region on Monday
causing the wind to shift to the south. However, the easterly wind
may persist through much of the day along the northern part of the
New Jersey coast. There is the continuing potential for minor
tidal flooding on Monday morning, especially from Atlantic City
northward to Sandy Hook.
Marine...Small Craft Advisory from noon today to 6 am EDT Tuesday for
Small Craft Advisory from 6 PM this evening to 6 am EDT
Tuesday for anz450-451.
Small Craft Advisory from 6 PM this evening to 10 am EDT
Monday for anz430.
Small Craft Advisory from noon today to 10 am EDT Monday for