Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
629 PM EST Monday Nov 30 2015
low pressure and a warm front will approach from the south tonight
and Tuesday. That low passes south of Cape Cod Tuesday night as yet
another low forms over the Middle Atlantic States early Wednesday.
That second low Ushers a cold front off the coast Wednesday night
while the low intensifies toward the Maritimes Thursday.
Strengthening Southern Plains high pressure follows to the Middle
Atlantic States Friday into next weekend.
Near term /until 6 am Tuesday morning/...
a strong closed low is located across the Central Plains this
evening, with an associated surface low near western Iowa. Farther
to the east, a bit of ridging is from the eastern Great Lakes
southeastward. A weak surface low is near the southern Appalachians.
The water vapor imagery shows the closed low well, however it also
shows the subtropical jet that is active which extends through the
middle Atlantic area. There continues to be some warm air advection at 850 mb across
the middle Atlantic in advance of a surface warm front. This is
occurring up and over a wedge of surface high pressure that will
gradually weaken overnight. Meanwhile, surface low pressure is
forecast to develop off the Delaware-Maryland-Virginia coast overnight. As a result,
some isentropic lift is maintaining some showers across mainly the
southern half of the area thus far.
As we go through the overnight, isentropic lift should strengthen
some with the warm air advection aloft as an incoming short wave arrives. It
appears that most of the quantitative precipitation forecast is on the light side and given a cooler
easterly low-level flow there could be some drizzle as well. It
appears that any patchy light freezing rain/drizzle across portions
of northeastern Pennsylvania and far northwestern New Jersey is on
the low side, however we are noting a few spots down to 32 degrees
as of 23z in Sussex County New Jersey. The clouds though continue to
thicken and with the light east to southeast low-level flow the dew
points are expected to gradually increase through the night. In
addition, the bulk of the precipitation should arrive as
temperatures are above freezing. As a result, we are not
anticipating much if any freezing precipitation however we will
continue to monitor /a mention remains in the hazardous weather
The hourly grids were adjusted based on the latest observations,
then lamp/lav guidance was used to help assist. This included
showing a gradual rise in temperatures overnight. We adjusted the
probability of precipitation based on radar trends and also some high resolution short term
guidance. The initial activity is mainly showery, however to keep
the forecast more simple we maintained the rain mention.
Short term /6 am Tuesday morning through 6 PM Tuesday/...
rainfall should be affecting everyone by daybreak Tuesday as ample
moisture/lift spreads across the area. During the day, an area of
low pressure will be lifting northward along the coast, while a warm
front lifts across the area as well. Also, a stronger short
wave/vorticity impulse is expected to lift across the area, so this
could lead to a period of more moderate rainfall during the morning
into the early afternoon. Rainfall should decrease some during the
late afternoon as the short wave passes and the warm front lifts
through the area, but there will still be some light rain
Long term /Tuesday night through Monday/...
500 mb: a vertically-stacked low over the upper Midwest Tuesday
evening is forecast to weaken and eventually become an open wave as
it progresses eastward across the northeast states Wednesday night
and Thursday. A Canadian rockies short wave on Thursday may shift
down into the northeast states by next weekend though there is
considerable model disagreement. The disagreement is with regard
to timing the arrival of ridging - warming aloft which should reach
the East Coast by Sunday. However, it may arrive sooner and minimize
the impact of The Rockies short wave on our weather next weekend.
Temperatures: the November summary is in the climate section of
the afd, including kabe snow and precipitation. Calendar day averages
for December will be mild. The lack of early season snow cover to
the northwest side of our area is a contributor to the milder than
normal weather. Averages will be ten to 15 degrees above normal
Wednesday December 2, still 5 to 10 degrees above normal on Thursday
then cooling to a couple of degrees above normal next Friday and
Saturday. It warms again to more than 5 degrees above normal next
Sunday and Monday. Low temperatures Wednesday morning should be 15
degrees or more above normal.
Forecast basis: unless otherwise noted, a 50 50 blend 12z/30 GFS/NAM
MOS guidance Tuesday night-Wednesday night, thereafter the 12z/30
GFS mex MOS Thursday and Thursday night, then the 18z/30 superblend
inclusive of multi model 12z/30 model and MOS guidance, 14 day
bias corrected guidance, 1521z/30 wpc guidance and our prior
0930z/30 Monday forecast.
Tuesday night-Wednesday...could be quite foggy in some parts of
our area. Consider the time of season - long nights and weak
boundary layer winds in the moist baggy area of the pressure
gradient. Periods of mostly rain and drizzle anticipated. Small
diurnal variation due to cloud cover.
If there is a warm frontal passage at the surface...suspect it will be limited
to the coastal region.
Called it rain Tuesday night but it might be light rain or drizzle.
The rain Wednesday should be a little heavier due to the convergence
of the newly developing surface low overhead which is a response
to the approaching weakening Midwest short wave. The wording
optimizes the use of the 18z/30 wpc quantitative precipitation forecast. Fog may continue to be a
problem Wednesday and it will be mentioned in the severe weather potential statement. For now,
thickest fog should be in the highest terrain (poconos and northwest nj)
as well as Delaware/S New Jersey closer to the warmer dew points.
Wednesday night...after evening leftover showers/mist and fog,
clearing develops late with increasing northwest winds gusting 20
miles per hour.
Thursday...partly sunny and breezy. West to northwest gusts 30
miles per hour.
Friday...partly to mostly sunny. West winds may be gusty 20 to 25
miles per hour during the midday/afternoon, before shifting to northwest at
Saturday...sunny and nice! North winds.
Sunday and Monday...partly to mostly sunny and nice. (Cirrus).
This forecast may be too conservative on maximum temperatures. There is a
smattering of guidance that offers an option for more moisture but
at this time, we are forecasting the dry and nice scenario.
Aviation /00z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...VFR ceilings will lower to the 1500-2500 foot range from
south to north by late this evening, then some IFR ceilings should
develop after 04-06z. Periods of rain and drizzle from south to
north will lower the visibility mostly into the MVFR range,
especially after midnight. Northeasterly winds mainly 10 knots or
Tuesday...IFR to LIFR ceilings are expected, with MVFR to IFR
visibilities at times as periods of rain continue. Easterly winds
mostly near 10 knots, however some gusts up to 20 knots are expected
Tuesday night...conditions should lower to widespread IFR or LIFR
in fog, drizzle and/or rain. Light wind. Confidence: above
Wednesday and Wednesday evening...IFR or LIFR may persist all day in
fog/stratus and periods of showers or drizzle, except it may
improve to MVFR conds vicinity kmiv and kacy? Light wind tending
most likely to be southerly at kmiv and kacy. Confidence: average.
Wednesday night...MVFR or even IFR may linger early in the night.
Conditions eventually improve to VFR from west to east. West-northwest winds
increase throughout the night, becoming 10-15 knots. A few gusts in
the 20-25 knots range possible. Confidence: average.
Thursday...VFR. Northwest wind 10-15 knots with gusts 25 knots to 30
knots. Winds subside late in the day and at night. Confidence:
Friday...VFR. West winds gusty 20 to near 25 knots Friday midday-
afternoon. Winds shift to northwest Friday night. Confidence:
Saturday...VFR. North winds. Confidence: average.
the Small Craft Advisory continues through Tuesday for the Atlantic
coastal waters as seas will remain elevated due to the persistent
northeast to east fetch. Winds could also gust around 25 knots
tonight, as well as 30 knots on Tuesday. Wind may approach gale
force as an area of low pressure lifts toward the southern waters
early in the day, but we believe that gusts should remain below at
A Small Craft Advisory has been issued for the lower Delaware Bay as
winds have begun gusting around 25 knots. We'vr ran in through the
night as the gradient could remain into the night, but begin to
Small Craft Advisory extended through Tuesday night on the Atlantic waters.
Tuesday night and Wednesday...sca, eventually for hazardous seas
into Wednesday morning for the Atlantic waters, since east to
south winds will be relatively light. Fog may become a substantial
marine navigation hazard all waters. Confidence:above average.
Wednesday night and Thursday...Small Craft Advisory expected westerly winds increase to 15-
20 knots Wednesday evening and become northwesterly late. Gusts up to 30 knots are
probable in the southern Delaware Bay and coastal Atlantic waters. Scattered
marginal gale force gusts to 35 knots possible Thursday morning.
Confidence: above average.
Friday...west winds may be gusty to near 25 knots in the afternoon.
Saturday...no Small Craft Advisory expected. Diminishing wind as the high approaches.
November will be a top 10 warmest month for virtually all of our
This preliminary final evaluation prior to tomorrow mornings final
numbers, includes this mornings low temperature and the projected
Looking at the 430 PM maximum/mins so far for today...the rankings
will remain the same as noted below.
Phl #2 at 53.2 plus 5.6 normal 47.6 por 1874
Ilg #6 at 50.9 plus 4.3 normal 46.6 por 1917
Ilg has missing monthly data between the late 1890s and 1917 so
we know the database is useful back through 1917.
Abe #3 at 48.0 plus 5.3 normal 42.7 por 1922
Allentown also will have had a trace of snow for the month which is
below the monthly normal of 0.7 inches. A trace in November is not
unusual...having occurred in 2009 and 2013, both of which ended up
big Winters with around 59.8 and 68.1 inches of snow respectively
including big february's of 3 foot monthly snowfall.
Of interest also is the that Allentown is probably going to have the
6th driest November on record dating back to 1922 when records began
at this representative location. The final value will be determined
at midnight tonight, dependent on any rainfall prior to midnight.
As of now the driest november's for Allentown are
2012 and 1946 both 1.00
Acy 8 at 51.1 plus 4.3 normal 46.8 por 1874
Marine...Small Craft Advisory until 5 am EST Wednesday for anz450>455.
Small Craft Advisory until 6 am EST Tuesday for anz431.