Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
403 am EDT Tuesday Oct 13 2015
a cold front will cross the region this afternoon and evening with a
secondary front moving through on Wednesday. High pressure will
build across the southeastern United States through Thursday.
Another cold front will cross the region on Friday with a secondary
front moving through on Saturday. A large area of high pressure will
build across the Ohio Valley and into the middle Atlantic through
early next week.
Near term /until 6 PM this evening/...
early morning surface analysis showed a 987 mb low pressure over
James Bay. The cold front extends southward from the low into
Midwest and middle south regions of the US. There was another area of
low pressure off the middle-Atlantic coast, albeit much weaker than the
upstream one. The cold front is expected to move through our western
zones of eastern PA during the middle and late afternoon.
Isolated showers associated with the western edge of lift from the
system off the coast will continue early this morning for locations
along and east garden state Parkway.
The latest mosaic radar loop showed a solid band of precipitation ahead of
front positioned along the appalachian spine. The coverage of the
showers though have been decreasing throughout the night as it moves
eastward. Recent trends in the model guidance has been to slow down
the eastward progress of the pre-frontal showers and further
decrease the coverage of showers as it moves through our area. This
makes sense given the dissipating lift associated with a weakening
upper-level jet streak to our west. Based on these models and
confirmation by recent radar trends, delayed the arrival of precipitation
by several hours and lowered probability of precipitation compared to previous forecast.
Probability of precipitation initially increase to 50-60 percent in our western most zones
in PA middle morning. Probability of precipitation were capped at 20 percent for the I-95
corridor eastward as confidence in showers making it this far east
Despite the cloud cover increasing this morning and persisting into
the afternoon, maximum temperatures ahead of the cold front should once again
reach the low to middle 70s across most of the area except the higher
elevations of NE PA/northwest New Jersey.
Short term /6 PM this evening through 6 am Wednesday/...
the cold front is expected to continue its progress eastward through
the Delaware valley early this evening before moving off the coast
The plume of moisture ahead of the front should be shifting offshore
by the evening. This should limit the coverage of showers with the
front itself to isolated. Expect skies to clear out behind the front
as winds become W-nwly. However, cold air advection stratocu should reach the
Did not want to go too low on min temperatures tonight as the winds should
keep the boundary layer mixed, except maybe in the most sheltered
valleys. Lows range from the middle 40s in NE PA/northwest New Jersey to the middle 50s
in the cities and along the coast.
Long term /Wednesday through Monday/...
a secondary cold front will move into the area Wednesday
afternoon/evening and we should see skies clouding up through the
day. The moisture profile looks limited and the front appears to
weaken as it makes its way into our area. Not expecting much more
than sprinkles across the northern areas although some light showers
may develop as moisture becomes trapped beneath the inversion.
Expect the majority of the region to remain mostly dry.
Clouds should start to clear out behind the front, especially across
the southern areas, as high pressure builds across the southeastern
states. The high remains to the south of the area but we will see
influence from it as it pushes eastward and noses up towards our
The high gets pushed further south as a cold front approaches the
region for Friday. The cold front arrives Friday morning and should
move through fairly quickly, exiting offshore by late afternoon.
While moisture appears to be limited, once again, there looks to be
enough to allow for showers to develop. We have brought the start of
showers into Thursday night with all showers looking to end by
Models are indicating that a reinforcing secondary cold front will
pass through the region on Saturday. Another moisture starved
boundary but some sprinkles or flurries, that's right flurries, may
make it to our northern areas on the strong northwesterly flow. The
strong northwesterly flow will usher in a much colder airmass and we
will see temperatures below normal for the weekend and into early
next week. Expect the airmass to modify as high pressure pushes
across the Ohio Valley and into the Middle Atlantic States.
Coldest nights look to be Saturday night and Sunday night, where
temperatures will have a good shot to drop into the upper 20s to
lower 30s across a good portion of the forecast area. With such cold
temperatures comes the threat of frost and/or freeze conditions.
While a freeze across the northern areas has some really good
potential, a frost is not as quite clear cut in areas where
temperatures remain above freezing. Winds may become light at night,
but it doesn't look like we really lose that gradient flow so it may
be difficult for frost to form on these nights. Monday night will
also be cold, but not quite as cold as over the weekend.
Aviation /08z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy, and surrounding areas.
VFR through at least 09z. There is a potential for low clouds and, to a
lesser extent, fog developing around sunrise. Model guidance
continues to differ in the extent of the low clouds but the best
chance for IFR conditions early this morning would be out toward
rdg/Abe. After several hours of daytime mixing, expect MVFR ceilings to
develop across the area ahead of a cold front. Rain showers with the front
are expected to diminish in coverage and intensity as they move
eastward during the day. Limited the impacted on visibilities from any rain showers
at ridge and Abe. Farther east, a mention of rain showers in the tafs was
confined to a prob30 group.
Skies will clear behind the front from west to east this evening.
S-SW winds increase to around 10 knots this afternoon before becoming west-northwesterly
behind the front tonight.
Wednesday...mainly VFR conditions expected. Some MVFR ceilings
possible, especially north and west of kphl. West winds 10 to 15
knots with gusts up to 20 knots possible.
Thursday...mainly VFR conditions expects. West winds around 10
Friday...mainly VFR conditions expected. MVFR conditions possible in
showers as a cold front moves through the region. West to southwest
winds 10 to 15 knots.
Friday night and Saturday...mainly VFR conditions expected. West to
northwest winds 10 to 15 knots with gusts 20 knots or
Small Craft Advisory was issued for today that includes most of our coastal Atlantic
waters except for the northern most zone, anz450. S-southwesterly winds by
middle morning are expected to reach 15-20 knots with gusts as high as 25 knots.
Seas will respond by increasing to 4-5 feet this afternoon.
Winds become west-northwesterly late this evening behind a cold front but they
are expected to diminish at the same time the low-level lapse rates
steepen. Seas will gradually subside.
Wednesday through Thursday night...winds will strengthen in the
westerly flow and gusts may near 25 knots by Wednesday evening. The
flow should start to weaken with gusts remaining below 25 knots
through Thursday night.
Friday through Saturday...southwest winds increase ahead of a front
on Friday. Winds become westerly by late in the day behind the cold
front and continue into the weekend. The overall gradient with this
system is stronger than the midweek one and there is a higher chance
of Small Craft Advisory conditions being reached on all of the
waters, especially by Saturday.
Marine...Small Craft Advisory from 8 am this morning to 8 PM EDT this
evening for anz451>455.