Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
427 am EDT Monday may 4 2015
high pressure will move farther offshore today. A cold front moves
across the area Tuesday afternoon and night. The cold front is
forecast to stall south of the area through the end of the week with
high pressure nosing its way southward across the area through
Friday. The high builds offshore over the weekend, with return flow
developing across the area.
Near term /until 6 PM this evening/...
red flag warning in effect this afternoon for our Pennsylvania and
New Jersey zones...excluding the immediate coastal areas.
Surface ridging offshore will continue to usher in a warmer airmass
under its strengthening southerly flow in the low-levels. The main
concern today is a significant threat for fire spread. The region
has been very dry the past several weeks and the fire fuels have had
more than ample time to dry out...acting like kindling. We should be
able to mix upwards of 825 to 700 mb this afternoon where at least
25 knots of boundary layer winds resides...north of the Delaware-Maryland-Virginia
zones. The Delaware-Maryland-Virginia zones will see much less wind this afternoon
where the pressure gradient is bit weaker. Frequent gusts into the
low-20 knots range is expected allowing dewpoints to dry out...lower
than what guidance is showing, even under a southerly flow. Relative
humidity values should drop close to 20 percent during the peak
heating hours this afternoon helping to prime conditions for rapid
fire spread, should a fire occur.
Temperatures today will be the warmest of the year, thus far, as we
top out close to the middle-80s in a lot of places under sunny skies.
It is possible that a seabreeze may push inland a bit later this
afternoon, even though the synoptic flow is rather strong but not as
an opposing flow...west or northwest is opposing.
Short term /6 PM this evening through 6 am Tuesday/...
Still under the influence of subsidence with the ridging offshore,
but aloft an increase in moisture is expected...ahead of an
approaching cold front. As the front slides towards the region it is
expected to slow some as the flow aloft becomes more parallel
oriented to its convergence zone. We have slowed the chance probability of precipitation
back by a few hours as we expect most of the night to remain
dry...only the extreme northern zones could see the showers late
With more warm air advection taking shape tonight and some boundary
layer mixing occurring, temperatures will not radiate much. Expect
overnight lows to be several degrees above normal in the middle to upper-
Long term /Tuesday through Sunday/...
a cold front is expected to move southward through northeast PA/
northwest New Jersey Tuesday afternoon and southeast PA/central and southern
New Jersey/northern Delaware-Maryland-Virginia Tuesday night. Moisture flux along and ahead of
the front with result in dewpoints increasing to near 60f and precipitable waters
approaching 1.5 inches. Expect scattered showers to be mainly
focused near the front during the day without much of a lifting
mechanism other than low-level convergence along the front (though
it is possible a differential heating boundary may initiate
convection farther southeast). The 00z NAM/GFS and 03z sref are in
good agreement, showing a modestly unstable environment ahead of the
cold front with mixed-layer cape values averaging around 500 j/kg.
This, along with several other convective parameters, support the
potential for isolated thunderstorms during the afternoon/evening
hours but the forecast environment is not particularly conducive for
severe storms. A gradual decrease in intensity of convection is
expected with the loss of daytime heating Tuesday evening. Showers
may continue into the night once deeper lift associated with an
approaching upper shortwave trough arrives. Favored the warmer
met guidance for tuesday's highs from the I-95 corridor and
points south, where less cloud cover and stronger daytime heating
should occur in the pre-frontal warm sector.
Model guidance several days ago showed a much slower progression of
the cold front with some even stalling it over the area. The latest
00z guidance shows the front pushing south of Delaware/eastern Maryland
Wednesday morning. Trended drier with wednesday's forecast due to
faster movement of the front and a quicker arrival of high pressure
that will be building in from upstate New York. Expect any lingering
showers to be mainly confined to the Delaware-Maryland-Virginia in the morning.
Easterly flow in between the high centered to our north and the
lingering frontal boundary to our south will produce a light northeasterly
winds. Trended lower with temperatures Wednesday by several degrees since
cool marine air will advect inland. Highs on Wednesday may only be
in the 60s toward the coast and low 70s farther inland.
Bermuda high pressure will extend back toward the northern middle-
Atlantic region late in the week and this weekend. A closed low is
forecast to develop along the southeast coast Thursday. The low is
not expected to move much through the weekend since it developed
underneath the large-scale ridge where there is minimal steering
flow. This will allow the forecast area to remain mainly dry through
the weekend. However, we could see weakly-forced convection pop
up across the higher terrain during the peak heating hours both
Saturday and Sunday. Above normal temperatures will persist with highs in
the middle 70s to low 80s each day.
Aviation /08z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...VFR. Light and variable winds to start the day becoming more
southerly by late morning. Gusts into the low to middle-20 knots range
expected starting middle-afternoon through sunset. Could see a
seabreeze push into Acy by late afternoon.
Tonight...VFR. Light southerly winds decrease to less than 10 knots
with the more sheltered terminals dropping to less than 6 knots.
Tuesday and Tuesday night...predominately VFR. Visibility/ceiling restrictions
possible during the afternoon and night from scattered showers and isolated
storms. Restrictions would be localized/temporary.
Wednesday...MVFR ceilings possible, especially in the morning with
onshore flow developing. Showers expected to push south of the
terminals in the morning.
Wednesday night through Friday...VFR and light winds with high
pressure in control.
today - tonight...sub-sca conditions expected. Strengthening
southerly flow today and tonight will help to push seas close to 4
feet on the ocean front today with 20 knots of wind expected.
Tuesday and Tuesday night...southwesterly winds increase to 15-20 knots ahead
of a cold front. Isolated thunderstorms developing on land may move over
the waters Tuesday during the late afternoon and evening.
Wednesday through Friday...winds and seas below Small Craft Advisory criteria.
very dry fine fuels, increasing winds and gusts, combined with
lowering dewpoint this afternoon will prime the region for a high
risk in the spread of firs this afternoon. While the concern may
exist across the entire region, the winds are forecast to be
stronger across New Jersey and Pennsylvania today so we have
upgraded those states to a red flag warning.
Across the Delaware-Maryland-Virginia it does not look like we will reach the
sustained 20 miles per hour winds needed for red flag, but again this does not
mean that conditions are not already elevated. We will coordinate
with our Delaware and Maryland state partners later this morning.
PA...red flag warning from 1 PM this afternoon to 8 PM EDT this
evening for paz054-055-060>062-070-071-101>106.
New Jersey...red flag warning from 1 PM this afternoon to 8 PM EDT this
evening for njz001-007>010-012-013-015>023-027.