Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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769
FXUS61 KPHI 290820
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
420 AM EDT Thu Jun 29 2017

.SYNOPSIS...
High pressure will become anchored off the East Coast through
Saturday, before moving farther out to sea into early next week. A
weak cold front will settle into our region late Sunday, however it
will then stall in our area next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Early this morning...broken deck near 15000 feet will somewhat
limit radiational cooling. Light southwest wind.

Today...Mostly sunny with cu/sc forming 9am to Noon and then
dissipating late in the day with patchy cirrus above. a gusty
southwest wind to 25 mph this afternoon. Dewpoints 10 to 15F
warmer than ydy. Max temp this afternoon 1 to 5f warmer than
normal.

Fcst basis was generally a 50 50 blend of the 00z/29 GFS/NAM
MOS except the GFS MOS temps look too cool today so used a combo
of ydys max temp (continuity) with the warmer 00z/29 METMOS.

Of interest this NAMMOS shows better cooling along the coasts
late this afternoon as an increasingly gusty south wind cools
the beaches and increases the risk for the formation of
dangerous rip currents, especially heading toward the 7PM low
tide (which occurs after beach patrols go home) - a more risky
time to be in the water without the immediately swift and sure
rescue opportunity provided by on-duty lifeguards.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
Fair (there may be a deck of sct-bkn clouds near 7000 ft,
especially late). Warm air advection with a stirring southwest
wind with scattered gusts 15-20 mph.

No NSSL WRF or HRRRX for 2 days but the 00z/29 NCAR ens have a
fair amt of measurable I-80 north tonight. That plus the 00z/29 EC
elevated instability is quite robust with SWI near -3 and TT51
toward dawn in the Poconos. Think the GFS is going be more
accurate than the qpf dry 00z/29 NAM/EC.

Otherwise, the forecast basis was a 50 50 blend of the 00z/29
GFS/NAM MOS.  Low temps tonight 5 to 11 degrees above normal.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Summary...Heat and humidity for awhile, although the humidity may
lower for a time next week. Times of some convection, with Saturday
afternoon and night looking to currently have the greatest chance.
The details though will depend on the timing and location of short
waves, and a weak cold front that ends up stalling across our region
next week.

Synoptic Overview...A strong short wave carves out a trough in the
Midwest and Great Lakes Friday and Saturday then gradually shifts
eastward later in the weekend and next week. There may be several
stronger short waves within this trough, which will impact the
sharpness and timing eastward. At the surface, high pressure remains
anchored offshore which will result in a very warm to hot and humid
southwest flow for awhile. The main feature is a weak cold front
that will settle into our area late Sunday, however it looks to then
stall in our vicinity next week. The presence of the incoming front
and trough nearby will result in some convection. We used a
model/continuity blend for Friday through Saturday night, then
blended in the 00z WPC Guidance thereafter. Some adjustments were
then made following additional collaboration with our neighboring
offices.

For Friday...High pressure anchored offshore will maintain a
southwesterly surface flow across our area. The low-level moisture
increases with dew points into the 60s. As the low-level warm air
advection continues in addition to perhaps some subsidence on the
northwest side of offshore high pressure, daytime highs will peak
around 90 degrees for several areas. This combined with higher dew
points will result in heat indices into the mid 90s during peak
heating. There will be a southwesterly breeze, and as mixing deepens
the dew points may locally lower some during peak heating which in
this case would keep the heat indices a bit lower. The dew points
however are expected to increase at night as mixing lessens and
additional moisture advection occurs from the southwest. There does
not appear to be a whole lot of forcing to initiate convection, with
perhaps some early near the Poconos within warm air advection. A few
storms may then develop mostly in the afternoon due to terrain
induced circulations/convergence. Therefore, we scaled back the
slight chance to low chance PoPs and confined them to the far
northwestern areas especially for the afternoon into the early
evening.

For Saturday and Sunday...Low pressure is forecast to track to the
north of our area into Sunday. This will pull a cold front slowly
eastward, and it is currently forecast to arrive into our area late
Sunday. The synoptic setup would suggest though that a lee-side
trough will be in place. The main upper-level trough is forecast to
hang back over the Great Lakes for Saturday, then more eastward
progress occurs Sunday. The bulk of the convection Saturday may
reside just to our west closer to the frontal zone, however some
convection is anticipated tied to the lee-side trough as buoyancy
and instability should be sufficient to allow for at least scattered
convection to develop. Much of the guidance has turned cooler for
Saturday, which is primarily due to more cloud cover and a quicker
development of convection. The cloud cover initially may be overdone
in the guidance, however the airmass will be very warm and humid.
Given the uncertainty, did not change the temperatures much. The
current forecast has the heat indices peaking into the mid to
perhaps upper 90s in the afternoon Saturday. It is still possible a
heat advisory may be needed, mainly for the urban corridor from
Wilmington to Philadelphia/Camden to Trenton. There is still some
potential that upstream organized convection moves across our area
Saturday night. Given less certainty with the overall coverage, held
PoPs no higher than the chance range.

The weak cold front slowly arrives later Sunday, however a lee-side
trough in place may still serve focus for some convection. There
could be a lull however between short waves, therefore only went
with low chance PoPs during the daytime then trended dry at night.

For Monday and Tuesday...As an upper-level trough remains in place
across the Northeast to the northern Mid Atlantic, Monday may end up
dry despite a weak frontal zone stalling in our region. There does
not appear to be much in the way of forcing. A weak surface low may
track along this boundary though and induce some convection during
Tuesday. This potential could be modulated by upstream convection.
Overall a very warm to hot airmass should remain in place, although
the dew points should lower some especially for about the northern
half of the forecast area.

For Wednesday...The influence of a west to east frontal zone should
eventually shift southward. This should allow a bit more cooling to
work in from the northwest, however there still looks to be the
chance for some convection. This may be more south than north where
deeper moisture resides, however this will depend on the position of
the front and timing of short wave energy.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through today...VFR sct-bkn aoa 15000 ft through 12z, then a
sct deck of 7000 ft develops late this morning with 3000-4000 ft
sct developing in NJ this afternoon where a little more low lvl
moisture is modeled. Southwest wind becomes gusty 20-25 kt this
afternoon.

Tonight...VFR sct to possibly bkn clouds near 6000 or 7000 ft.
South to southwest wind with scattered gusts to 15 kt.

We noted guidance hinting at LLWS late tonight but its not in
the fcst attm.

OUTLOOK...
Friday and Saturday...An isolated thunderstorm possible Friday
mainly near and north and west of KABE and KRDG. Some showers and
thunderstorms should then increase Saturday from west to east.
Significant but brief reduced conditions, especially visibility,
will occur during any heavier showers/storms. Southwest winds
increase each day to 10-15 knots, with local gusts up to 20 knots
possible.

Sunday...Mostly VFR, however scattered showers and thunderstorms are
possible. West-southwest winds 5-10 knots.

Monday...VFR overall. West-northwest winds less than 10 knots.

&&

.MARINE...
SCA headlines posted.

Winds and seas will begin to build mid day. Small craft advisory
conditions are expected to develop by mid afternoon along the
Atlantic coastal waters. 30 kt gusts should develop north of
Little Egg inlet this afternoon (ACY).

On the Delaware Bay, expanded the SCA to the upper Bay and ended
it later on DE Bay.

OUTLOOK...
Friday...A Small Craft Advisory may be needed during the day,
especially for the ocean zones. However, held off for now as there
is some uncertainty in how much mixing occurs outside of right along
the coast. For now, capped the wind gusts at 25 knots. This will
also have an impact on the seas. Any increase in the winds should be
diminishing at night.

Saturday and Sunday...Other than some increase in the winds
Saturday afternoon, the conditions are anticipated to be below
Small Craft Advisory criteria. Some showers and thunderstorms
are expected at times.

Monday...Sub-advisory conditions are anticipated with weaker winds.

RIP CURRENTS...
We start low this morning and remain low on DE this afternoon
but will forecast a Moderate risk for the formation of
dangerous rip currents on the NJ coast as southerly winds
increase with gusts to 25 or 30 mph.


Low risk does not mean NO risk and it is always advised for
ultimate safety, swim in the presence of the lifeguards. They
have the flotation devices that can more easily save a life.

Where the surf zone waters are steeper, there may be fewer rip
currents, but there, the danger of wave related injury increases.

An ongoing DE 6+ year study shows the bulk of the injuries (45%)
occur in 10-20 year old age bracket with also another 40 pct of
the injuries to 40-60 year old age group. The 10-20 year old
surf zone injuries are associated with body boarding and body
surfing, while the 40-60 year old waders are knocked down by
wave action, especially with back turned to the ocean.

Males are statistically far more likely to be injured or lose
their life in the surf zone but as June 15 reminds us...ANYONE
is vulnerable.

&&

.CLIMATE...
Updated as of 418 AM Thursday.

Monthly avg temp for June

PHL projecting 74.5 or 1.2 degrees above the average of 73.3

ABE projecting 70.7 or 1.6 degrees above the average of 69.1

Seven of our eight long term climate sites will average above
normal probably from about 8 tenths of a degree for TTN/ILG to
as much as 2 degrees for GED.

Mount Pocono is our only below normal average and projecting
1-1.5 below).

These projections were based on our 330 am Thursday forecast.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 6 AM EDT
     Friday for ANZ431-450>455.
     Small Craft Advisory from 2 PM this afternoon to midnight EDT
     tonight for ANZ430.

&&

$$
Synopsis...Gorse
Near Term...Drag
Short Term...Drag 418
Long Term...Gorse
Aviation...Drag/Gorse 418
Marine...Drag/Gorse
Climate...418



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