Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
600 PM EST Friday Nov 28 2014
high pressure across the area tonight will move to the south and
east Saturday into Saturday night, before a warm front lifts north
of the area Saturday night into early Sunday. A cold front is
expected to sag down across the area Sunday night, before slowly
moving through the area Monday into Monday night. High pressure will
then briefly return to the northeast for Tuesday, followed by
another frontal system around Wednesday. High pressure is expected
to briefly affect the area again Thursday.
Near term /until 6 am Saturday morning/...
radiational cooling will develop this evening and it could mean temperatures
5 to 10 degrees colder than forecast over the snow covered region of
northwest New Jersey. Looks to ME like a solid overcast is not likely prior 06z there.
So the min temperatures at 630 PM will probably adjusted downward over the
snow covered region northwest I 78 tonight.
Flow backing slightly out of the west in the 850-700 mb layer late
tonight will be accompanied by a band of warm air advection and isentropic lift
that is expected to reach the western fringes of the County Warning Area late tonight.
Have added flurries out west toward ridge-Abe-mpo before sunrise.
Short term /6 am Saturday morning through 6 PM Saturday/...
high pressure will be centered along the eastern Seaboard Saturday
morning. The high will move offshore by the afternoon and return
flow will ensue. A warm air advection pattern will become established over the
middle-Atlantic region on Saturday as a result. Based on the 12z
NAM/GFS forecast soundings, there appears to be enough moisture
return in the middle levels and isentropic lift to see some snow
showers or flurries across eastern PA and New Jersey during the day.
Confined chance probability of precipitation to northeast PA and northwest New Jersey where the best
lift is forecast and flurries farther south and east.
Forecast maximum temperatures for Saturday are about 2-5f degrees warmer than
today, ranging from around freezing north of I-80 to the middle 40s in
coastal southern New Jersey and the Delaware-Maryland-Virginia.
Long term /Saturday night through Friday/...
by Saturday night, the high is expected to have pushed well
offshore, and a warm front is forecast to lift across the area.
There is not much vertical moisture aloft, although there is some
low-level moisture that should spread across the area. The question
is whether this just increases cloud cover, or if the low-level
moisture is enough to produce some patchy drizzle across the
northern areas as a weak short wave/vorticity impulse approaches
overnight. If any drizzle did develop, temperatures may be close
enough to freezing, even behind the warm front, that it could lead
to patchy freezing drizzle for the far northern zones. For now,
we will keep the weather dry and later shifts decide if there is
greater confidence to put this in the forecast.
On Sunday, the warm front should be well to our north, and we will
be in between the high to our east and an approaching cold front.
Another weak short wave/vorticity impulse slides across the area
during the day, while there remains some low-middle level moisture
across the area. There is some light quantitative precipitation forecast forecast, mainly north and
west of our area, but there will remain a slight chance of showers
A frontal boundary is expected to sag toward the area Sunday night,
then slowly move through the area into Monday into Monday night.
Most models indicate any precipitation associated with the boundary
will begin to dry out before reaching our area Sunday night into
early Monday, then possibly redeveloping across our southern areas
later Monday into Monday night. We will keep chance/slight chance
probability of precipitation across the area during this period.
The front should push to our south Tuesday as high pressure briefly
builds across the northeast. The European model (ecmwf) lingers some precipitation
across the southern areas during the day as the front gets caught up
to our south. We will keep the weather dry for most of the area for
now, except our southern zones.
There are now differences with the frontal system that is expected
to affect the area around next Wednesday. A warm front may lift
across the area Tuesday night as the high retreats northeastward.
The GFS keeps the cold front to our west until later in the week,
while the European model (ecmwf) pulls the front through Wednesday. We will stay
close to continuity and wpc, which lines up better with the European model (ecmwf).
This keeps chance probability of precipitation fro Tuesday night into Wednesday.
Staying close to wpc and ECMWF, high pressure is expected for
Thursday, which would keep the weather dry. If the GFS holds true
with the front lagging until later in the week, then we'd have a
better chance of precipitation Thursday into Thursday night.
Although for differences reason, both have a chance of precipitation
by Friday. The GFS remains due to lingering precipitation from the
front it's indicating, while the European model (ecmwf) shows another warm front
possibly lifting toward the area as high pressure lifts to our
northeast. So we will have chance probability of precipitation again during the day Friday.
Aviation /00z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...VFR clear with diminishing northwest wind becoming calm overnight
as hipres builds in then VFR ceilings developing at or above 7000 feet.
Saturday...predominantly VFR. There is a small chance of a snow
shower or flurry during the daytime, which may briefly reduce
visibilities to MVFR. The forecast likelihood of the happening is too
low to include in tafs, although Abe/ridge may have a slightly
better chance. A light southerly return flow around 5 knots develops
in the morning, increasing to around 10 knots during the afternoon.
Saturday night-Sunday night...mostly VFR. Southwest wind gusts
Monday-Monday night...chance of rain or snow showers. Generally VFR unless
precipitation occurs. Gusty northwest winds around 20 knots possible.
Tuesday night-Wednesday...MVFR conditions possible with a chance
of showers. Gusty southwest winds 15-20 knots.
will issue Small Craft Advisory cancel stmt at 602p but no reissuance of late Saturday
Small Craft Advisory at this time. Still currently marginal Small Craft Advisory conds some of the outer waters
at 5 PM EDT.
Northwest winds are expected to weaken to below Small Craft Advisory this evening and become
light late tonight into Saturday morning as high pressure moves over
the waters. Southerly winds are forecast to strengthen Saturday
afternoon once the high moves offshore. Winds may approach Small Craft Advisory
criteria in our coastal waters off the Delaware and southern New Jersey coast by
the late afternoon. Will hold off on issuing any Small Craft Advisory headline until
the current Small Craft Advisory expires.
Saturday night-Sunday night...Small Craft Advisory conditions
possible as high pressure pushes to our south and cold front
approaches late on Sunday night.
Monday-Monday night...Small Craft Advisory conditions remain
possible behind the cold front that moves across the area,
especially late in the day and overnight.
Tuesday...conditions expected to drop below Small Craft Advisory
conditions during the day as high pressure affects the waters.
Tuesday night-Wednesday...sub-Small Craft Advisory conditions expected.
with Thanksgiving upon US and meteorological winter knocking on
our door, its our annual look to see how past Winters have fared
based on preceding fall patterns and trends.
Our foray last fall about the winter of 2013-14 was an
unmitigated bust as the negative eastern Pacific oscillation
pattern (epo) took hold in November and never let go the entire
winter. While the colder November trended down our winter
temperature analogs to about normal, it was nowhere near enough.
It was also only the sixth time (out of forty six occurrences)
that a bottom third winter followed a warm October.
Once again we are heading into this winter with a rarer
combination of a warm October and colder November just like the
two previous autumns.
In terms of enso, the latest consensus of all dynamical and
statistical models for the winter season is for a weak El Nino to
occur. Of late the El Nino has looked healthier as a Kelvin wave
and a currently robust mjo cycle have/will help boost sea surface
temperature anomalies (ssta). As CPC has stated, there is still a
ssta and atmospheric response disconnect that exists. The latest
global wind oscillation readings, our atmosphere is still in an
enso neutral state even if water eastern tropical Pacific
temperature anomalies have become warmer.
Weak el ninos since 1950 in Philadelphia have had an average
temperature of 33.2 degrees and average snowfall of 21.8 inches.
Weak el ninos, like most non-uber el ninos, favor having more
major snow storms than the climatological average. In the ten weak
el ninos since 1950, Philadelphia has had eight snowfall events of
six inches or more, four of which were ten inches or more. The
most common month for major snows during weak el ninos is January,
but they have occurred in every month from November through March.
Looking at the middle and high latitudes, once again snow
coverage in eurasia was off to the races in September and October,
even faster than autumn of 2013. October 2014 only trailed October
1976 for total snow coverage. In the satellite era when both
September and October have had above average snow coverage, 64
percent of the ensuing Philadelphia Winters have been snowier than
the current average and had a 50/50 split with temperatures being
either above or below normal. While 64 percent may not sound
definitive, snowfall is not a normal distribution because seasons
like 2013-14 skew upward the statistical average. Since 1967 (the
start of the satellite era and our look at the Dr. Judah cohen
study) only 1 in 3 Winters has had above average snowfall. The
statistical median for snowfall in Philadelphia since 1967 is
about 18 inches.
Beyond Siberia, the Arctic oscillation averaged negative during
the month of October. When it has, 70 percent of ensuing Winters
has averaged negative. Thank-you meteorologist Matt lanza for this
information. Another phenomenon that favors a negative Arctic
oscillation for this upcoming winter is that we are in the
easterly phase of the quasi-biannual oscillation stratospheric
winds over the tropics. When we are in this phase, historically we
have had more sudden stratospheric warming events which often
splits and displaces everybody's favorite polar vortex from near
the North Pole. There is no guarantee the western hemisphere would
be the so called beneficiary of this Arctic displacement, but a
higher chance exists this winter vs no chance at all.
The Arctic oscillation's cousin, the North Atlantic oscillation
(nao), we have seen been the driver (winter of 2010-11) or the
cricket chirping (last winter) recently. Unfortunately this
important teleconnection index is tough to outlook more than weeks
in advance. While the Arctic oscillation and North Atlantic
oscillation normally work in tandem, its not always the case.
Since 1950, 60 percent of all Winters have averaged a negative
Arctic oscillation, but only 42 percent of all Winters have
averaged a negative North Atlantic oscillation. The late Jack
ordille pointed US to a research paper using Newfoundland region
Spring-Summer sea surface temperature anomalies as a predictor of
the nao for the ensuing winter. It has worked well the last couple
of Winters (here comes the jinx) and it favors a negative nao for
this upcoming winter.
This brings US to our last (but not least) oscillation index, the
Pacific decadal oscillation (pdo). Currently the oscillation is in
textbook positive position. So much so, that when its been this
positive during the month of October, it has never averaged
negative (here comes another announcer's jinx: 15 of 15 times
since 1900) during the upcoming winter. Eleven of those Winters
have averaged colder than the current average (and averaged around
20 inches of snow) in Philadelphia. Historically about 2/3rds of
all Winters since 1900 have averaged colder than normal in
Philadelphia when the pdo has averaged positive. In fact, the
greatest Point of failure when warm octobers have not been
followed by warmer Winters has been when the pdo has been strongly
positive in the autumn.
Locally, of the 46 warmest Winters in Philadelphia on record,
half of them have occurred after a warm October. Given the state
of the pdo, we don't have a warm feeling about that this winter.
This November will end again close to the cusp between the
unseasonably cold and normal terciles. Regardless this is a rarer
occurrence and a contradiction in the study first done in which
the strongest correlator for a warm winter is a warm October while
the strongest correlator for a cold winter is a cold November. In
2012 October won, last year November won. Unlike the last two
Winters, we are expecting a weak El Nino and not enso neutral
negative. While the Pacific favors cold again, the type of cold
looks different as positive sea surface temperature anomalies are
farther east than they were last autumn.
So here are our analogs for the upcoming winter. They are based
on warmer than current normal octobers and colder than current
normal novembers. The analogs are a combination of moderate, weak
and enso positive Winters. Seven of these also had positive pdo(s)
during the winter, the one exception (1953-4) we kept because it
was a weak El Nino and it also was a snowy November. As always
past performance may not be an indicator of future trends....and
now to the great eight:
Season Dec Jan Feb winter seasonal winter
average average average average snowfall precipitation
1905-06 39.2 39.4 33.6 37.4 20.5 8.61
1914-15 33.3 36.6 38.6 36.2 32.5 19.64
1939-40 38.1 25.3 34.8 32.7 22.3 7.77
1941-42 38.3 30.5 30.8 33.2 10.3 9.24
1951-52 38.7 37.3 38.2 38.1 16.2 12.21
1953-54 39.4 31.7 41.7 37.6 22.6 7.58
1986-87 37.9 31.9 32.5 34.1 25.7 11.64
2002-03 35.4 28.6 29.9 31.3 46.3 11.02
Average 37.5 32.7 35.0 35.1 24.6 11.59
1981-2010 normal 37.5 33.0 35.7 35.4 22.4 9.24
The official CPC outlook for the winter is for equal chances of
it being either warmer or colder than normal and a greater chance
of it being wetter than normal.
We hope everyone had a great Thanksgiving and we hope you will
have a Happy upcoming Holiday season. May this winter be beyond
your wildest expectations.
the Dix radar outage is expected to continue until the technicians
are able to replace the bad hardware on Saturday.
Marine...Small Craft Advisory until 6 PM EST this evening for anz430-
near term...drag/Klein 559