Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
327 am EDT Thursday Sep 3 2015
a backdoor cold front will slide southwestward across the area later
tonight and early Friday morning. High pressure will then build into
our region from the north Saturday and Sunday before shifting
offshore early next week. A weakening cold front is then forecast to
gradually arrive later Wednesday.
Near term /until 6 PM this evening/...
a surface trough was located over the coastal plain in our region
around 300 am. The boundary should pass off the coast this morning
before drifting back inland and over the coastal plain for this
A weak northwest to north surface flow on the west side of the
trough should prevent widespread low clouds and fog from developing
early this morning. We will simply mention some patchy fog on the
coastal plain in the vicinity of the trough until about 800 am.
We should remain precipitation-free for this morning. We will
mention a slight chance of a shower or thunderstorm for this
afternoon in much of our region. The guidance suggests the best
instability in our forecast area will extend from the Chesapeake Bay
region up into eastern Pennsylvania. However, the surface trough may
provide a trigger on the coastal plain. Regardless, the chance of
rain is rather low at any given spot.
The air mass remains quite warm. We continue to expect high
temperatures in the lower 90s at most locations. Maximum
temperatures should be in the 80s in the elevated terrain of the
Poconos and northwestern New Jersey, as well as in the communities
along the immediate coast.
Short term /6 PM this evening through 6 am Friday/...
the slight chance of a shower or thunderstorm will continue into
early tonight with some lingering instability and with the surface
trough. A cold front approaching from the north is anticipated to
drop through our region late tonight. The front is not expected to
enhance our chance for precipitation as conditions are forecast to
stabilize gradually during the night.
Minimum temperatures should be mainly in the upper 60s and lower 70s.
Long term /Friday through Wednesday/...
the synoptic setup is comprised of a ridge sliding eastward over our
area Friday and Saturday. This ridge is then forecast to flatten out
early next week as a short wave trough slides across the northern
tier of states. Overall, this pattern should favor warmth and
dryness although a brief break occurs Saturday into Sunday in the
wake of a backdoor cold front. The region needs rain, however it
looks like the chances are rather low given no organized systems moving
through. We used a model/continuity blend for Friday into Sunday,
with a 00z wpc guidance/continuity blend thereafter. Some
adjustments were then made after additional collaboration with our
For Friday...a backdoor cold front is forecast to be shifting west
and south of our area. Any convection should therefore be shifting
southwestward with time as surface high pressure starts to build
across New England. This will result in the low-level flow being
from the east or northeast, and with more of an ocean influence some
cooling of the airmass is anticipated. The drier air may win out and
therefore despite the onshore flow we should have some decrease in
the clouds especially across the northern areas. However if the
transition is delayed or is not clean like some guidance suggests,
then a period of low clouds may be possible before the drier air
presses farther south. If this were to occur, the southern and
western portions of the area should have the highest chance. Since the
prospects of showers and thunderstorms is on the lower side, we kept
the probability of precipitation at or below low chc, with the better chance looking like the
western zones to portions of the Delaware-Maryland-Virginia. There does appear to be a
window where breezy conditions develop especially closer to the
coast. The idea of more cloudiness/low cloud development was
incorporated into the sky grids in the afternoon and at night,
mainly for the southern portions of the County Warning Area.
For Saturday and Sunday...as the upper-level ridge crests across the
area, surface high pressure should ease eastward. This will allow
the onshore flow to weaken and eventually turn southerly. There
could be some residual cloudiness mainly across the far southern
zones to start Saturday depending on the dry air push, otherwise no
significant weather is anticipated at this time. We start to lose the cooler
onshore influence, and therefore the daytime temperatures are
anticipated to rebound Sunday afternoon for much of the area.
For Monday through Wednesday...a short wave trough moving near the
U.S.-Canadian border should flatten the ridge. This will also force
high pressure more offshore, and a weak cold front should be
gradually sliding eastward across the Great Lakes. The bulk of the
energy looks to track well to our north Tuesday, therefore the chances
for convection should mostly remain to our west. Some guidance
suggests the initial short wave trough lifting well into Canada as a
secondary short wave trough crosses the Midwest Wednesday. It is a
weak cold front with this feature that may end up moving through our
area later Wednesday. There is more uncertainty with the timing of
these features this far out. Given the lingering ridge to the south,
a slower eastward progression of the surface front may result. As
the flow is more southerly, a rather warm airmass looks to be in
place with some increase in the dew points.
Aviation /08z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
We will continue to carry MVFR visibility restrictions through about
1300z. There may be a period of IFR ceiling and visibility
restrictions at kmiv and kacy early this morning.
VFR conditions are anticipated from 1300z and into this evening at
our taf sites. Some visibility restrictions are again possible late
Isolated showers and thunderstorms may affect our region from this
afternoon into early tonight. However, the chance of any of our taf
sites being affected is low and we will not mention the potential in
the taf products.
The wind is forecast to favor the north and northwest for today at
less than 10 knots. However, a surface trough is expected to move
inland from the ocean and it should affect kacy this afternoon
bringing the wind around to east and southeast there.
A light and variable wind this evening should become northeast late
tonight as a cold front drops through our region from the north.
Wind speeds are forecast to remain less than 10 knots.
Friday...VFR overall. Some showers or thunderstorms are possible,
especially from near the kphl area on west and south. There is a
chance for a period of low cloud /MVFR/ development in the
afternoon and evening especially from about krdg to kphl to kacy
on southward, however this is of lower confidence at this time.
East- northeast winds increase to 10-15 knots, with some gustiness
in the afternoon and evening mainly closer to the coast.
Saturday through Monday...mostly VFR. East-northeast winds mainly 10-
15 knots Saturday, diminishing and becoming southeasterly Sunday
before turning south-southwest on Monday.
a surface trough is forecast to be over our coastal waters this
morning before it drifts inland this afternoon. A cold front is
expected to arrive from the north late tonight.
The wind is anticipated to be variable this morning before settling
into the southeast for this afternoon and early tonight. The wind is
expected to become east to northeast late tonight. Speeds should
remain at 10 knots or less.
Wave heights on our ocean waters are forecast to be around 2 feet
for today and tonight with waves on Delaware Bay being 2 feet or
Friday and Saturday...as a backdoor front moves through, the winds
will turn from the east and northeast and increase. It appears that
gusts to around 25 knots occur from north to south on the coastal
waters later Friday afternoon through Saturday morning before a
decrease begins. As a result, a Small Craft Advisory looks to be
needed. The onshore flow will also build the seas to around 5 feet
starting late Friday on the coastal Atlantic waters.
Sunday and Monday...the winds are anticipated to be below Small
Craft Advisory criteria as they shift from east-northeast to
southeast and south. The seas are currently anticipated to below
advisory criteria, however this will depend on how high they get on
the Atlantic coastal waters Friday and Saturday.