Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
338 PM EDT Friday Sep 4 2015
a backdoor cold front will push south of the area today. High
pressure will build across the region from the north Saturday,
before moving offshore Sunday. However, it will continue to affect
the area through early next week. A cold front is expected to
approach the area from the west Wednesday, then slowly push move
through Thursday, before another front possibly impacts the area
Near term /through tonight/...
the boundary associated with a backdoor cold front was diffuse this
afternoon, but located somewhere near the Mason-Dixon line and lower
Delaware-Maryland-Virginia. Meanwhile, high pressure over southeastern Canada is
building southward into New England and toward the northern middle-
Convection has been weak and very isolated thus far across the
western half of the County Warning Area. However, there was a complex of storms that
had developed just north of the backdoor front along a subtle
differential heating boundary across southern New Jersey. This activity will
sink to the west-southwest across the northern Delaware-Maryland-Virginia before it
crosses the Delaware-Maryland-Virginia between 5 and 6 PM. Additional scattered
showers and isolated thunderstorms over eastern PA will also track
to the west-southwest late this afternoon. The Delaware River valley
and points eastward will dry out through the remainder of the
afternoon. Expect all of the activity in our western zones to move
out of the forecast area by around sunset.
Cooler and drier air will move into the forecast area tonight as
high pressure builds into the area. However, NAM/GFS/rap/hrrr model
soundings show a layer of moisture trapped at the top of the mixed
layer beneath the middle-level subsidence inversion. This would favor
marine stratocu to move inland tonight. The cloud cover and
northeast winds should keep temperatures up tonight. The Poconos and
northwest New Jersey may radiate better, where low clouds are less likely.
Short term /Saturday/...
surface high pressure will drift eastward into the Gulf of Maine on
Saturday but the high will still nose southwestward into the middle-
Atlantic region. Looking aloft, the center of anticyclone will build
over the northeast and northern Middle-Atlantic States.
Winds out of the northeast to east will persist into the day and be
breezy along the coast. Expect the stratocu at the start of the day
to gradually mix out in the morning as drier air around the
anticyclone advects southwestward into the area. This setup should
yield increasing sunshine during the afternoon.
The end of this late season heatwave is brought to you by the
onshore flow. Maximum temperatures in the low 80s will be common, with a few
middle 80s in the urban areas and 70s along the coast and in the
Long term /Saturday night through Friday/...
high pressure continues to build across the East Coast Saturday
night, before it moves offshore Sunday. The high will continue to
affect the area through Tuesday, which will provide mostly dry
weather across the area. Guidance is indicating there may be some
shower activity on the southern edge of the high pressure, but
this may remain mostly south of our area. If it were to affect ay
portion of the area, it would be across the far southern portions
of the Delaware-Maryland-Virginia.
The cold front that is expected next week continues to be slowed
down by the models. It is expected to approach the area late
Wednesday and move across the area Thursday. The GFS and European model (ecmwf) have
differences in how they handle the situation late next week. The GFS
pushes the front offshore, before bringing another front down from
the northwest as it moves an area of low pressure into the northeast
on Friday. The European model (ecmwf) stalls the front near the area while it
develops a couple of areas of low pressure along the boundary. In
either case, late next week looks like our next best chance for any
precpitation. With the uncertainty in the models late next week,
we've stayed closer to wpc, which generally used the ensemble
Aviation /19z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Expect mainly VFR conditions through sunset. There are isolated showers and
storms in eastern PA, which may briefly impact Abe and ridge through
about 21z and 22z, respectively. A more oraganized complex is moving
west and away from ilg so the I-95 corridor and southern New Jersey taf
sites should be precipitation free through the forecast period.
Model guidance shows a saturated layer developing in the low-levels
after 00z this evening as marine air draws inland. This will favor
development of low clouds with MVFR ceilings between 1500 and 2500 feet
tonight. It should be noted that lamp and GFS/nammos guidance do not
indicate any low clouds tonight.
Low clouds should mix out during the middle morning, except maybe near
the coast. Therefore, MVFR ceilings could persist into the afternoon at
Saturday night-Wednesday night...mostly VFR. Patchy fog/stratus
possible around daybreak each day. Chance of showers northern
a Small Craft Advisory is in effect for the ocean waters through
Saturday. A Small Craft Advisory is in effect for the lower Delaware
Bay through Saturday morning.
Increasing seas and increasing winds are expected through this
evening as high pressure builds down from the north. The pressure
gradient tightens up this afternoon and evening and we will see eas
to northeast winds will become gusty, between 25 and 30 knots into
tonight. Winds will diminish late tonight and into Saturday morning
before once again gusting during the daytime hours, gusts round 25
knots, before starting to diminish through the afternoon.
Seas will continue to build in the easterly flow and rise to 4 to 6
feet by tonight, remaining elevated through Saturday.
Winds on the lower Delaware Bay don't look quite as robust int he
easterly flow but the guidance shows that winds will gust around 25
knots for a period of time tonight. Winds look to subside a bit by
Saturday morning and we do not feel that the Small Craft Advisory
needs to be extended at this time. Confidence is not as high in the
Bay as it is on the ocean.
Saturday night...winds should diminish below Small Craft Advisory
levels by Saturday night. Seas may remain elevated into the early
half of the night, then subside through the night.
Sunday-Wednesday night...winds and seas expected to remain below
Small Craft Advisory levels through Wednesday night. Winds may
periodically gust near 20 knots through the period.
the threat for dangerous rip currents will be enhanced for today and
the upcoming Labor Day weekend.
A moderate risk for dangerous rip currents will continue this
afternoon and likely through the majority of the Holiday weekend.
A northeast to east wind is expected to continue along the New
Jersey and Delaware coasts through the weekend. Winds look to be
strongest on Saturday, which is when seas will also be at their
highest. The winds and waves along the coast should gradually
subside late Saturday into Sunday.
As of now, in-house guidance continues to suggest a solid moderate
/possibly nearing high/ for Saturday. The risk should lower some for
Sunday, possibly remaining moderate, and then lower more for Monday.
It is particularly important for safety awareness to share this
information with beachgoers and lifeguards, as the beach crowd is
anticipated to be larger than normal given it is Labor Day
Marine...Small Craft Advisory until 6 PM EDT Saturday for anz452>455.
Small Craft Advisory until 6 PM EDT Saturday for anz450-451.
Small Craft Advisory until 8 am EDT Saturday for anz431.