Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 090908
Area Forecast Discussion
National Weather Service Mount Holly NJ
408 AM EST Fri Dec 9 2016
An area of low pressure will continue to slowly drift to the south
of Greenland through the weekend. With high pressure to our west, a
strong west to northwest flow will remain through Saturday . High
pressure briefly affects the area Saturday night, then moves
offshore Sunday. A warm front is expected to lift across the area
Sunday night into Monday, before an area of low pressure is forecast
to move north of the area Monday. This system will then pull a cold
front across the area Monday. Another frontal boundary is expected
to move across the area Tuesday night or Wednesday, and a coastal
low may develop along this frontal boundary Wednesday. A strong west
to northwest flow is expected to develop by the end of the week as
high pressure tries to build in from the west.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Another day of strong northwesterly flow resulting in breezy
conditions and below normal temperatures. Highs (mostly 30s to near
40 across the region) will be around 5 degrees lower than yesterday,
which will be 5 to 10 degrees lower than normal. Higher elevations in
the Southern Poconos may not get out of the 20s.
Snow showers, a result of the strong northwesterly flow/cold air
advection/lake effect, could propagate as far se as the southern
Poconos. However, a dry boundary layer has thus far kept any precip
from reaching the ground in our area, and by this afternoon low
level flow should become weaker, so the window of opportunity is
closing. If any snow showers do make it to our region by mid day,
snow accumulations should be near or below one half inch (note: the
storm total snow graphic is now for the Sunday night event since
that looks to be a potentially bigger impact event).
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
Surface high over the Ohio Valley tries to build west. As a result,
the pressure gradient relaxes resulting in the winds dropping off.
However, this doesn`t mean that we will have a milder night
temperature wise. If anything, we should be a bit colder tonight
(generally in the 20s, teens in the Poconos and NW NJ).
.LONG TERM /SATURDAY THROUGH THURSDAY/...
On Saturday, there will be fairly steep lapse rates combined with
some enhanced moisture across the far northern tier of the area.
With the west-northwest flow remaining across the area, there could
continue to be isolated lake snow showers/flurries developing which
could make their way across our area. We will keep
flurries/sprinkles for the middle part of the area as well as the
short wave passes just to our north.
High pressure briefly affects the area Saturday night, providing dry
conditions. Saturday will remain cold and windy, although winds are
not expected to be as high as Friday.
The high builds offshore Sunday ahead of the next storm system. As
this happens, it is possible that some showers could develop during
the day across the area as a short wave passes just to our north and
spreads an area of moisture across the area north of the advancing
warm front to our south. If any precipitation develops during the
day, temperatures should be cold enough for the northern half of the
area to see snow, or at least a rain/snow mix.
However, the best chance of precipitation looks to be Sunday night
into Monday. A warm front is forecast to lift across the area late
Sunday night and into Monday as an area of low pressure is forecast
to move north of the area Monday. Conditions are expected to be cold
enough overnight across the northern half of the area for snow to
fall for a period of time. However, as the warm front lifts
northward into the area, temperatures are expected to begin warming.
This should help precipitation begin to transition into a wintry mix
for the northern half of the area. It is possible that a period of
sleet and freezing rain could occur across the northern areas as a
chance over to rain occurs from south to north.
The most likely area to recieve accumulating snowfall is expected to
be the northern third of the area, although the middle third could
get some light snow before changing over to rain. This change over
would limit any accumulations. The southern third is expected to
stay rain through the event.
As the low continues to lift northward during the day, a cold front
is expected to move across the area late in the day and overnight.
Precipitation chances should diminish behind the cold front later in
the day and overnight. Any precipitation overnight should change to
snow for the northern half while the southern half would stay rain.
High pressure may briefly affect the area Tuesday, but will quickly
build offshore. Then a cold front is expected Tuesday night into
Wednesday, which could bring another round of precipitation. The GFS
and ECMWF have different timing with the front, as well as with a
possible coastal low that could develop and move along this
boundary. The GFS is slower, moving the front through Wednesday and
the coastal low up the coast late on Wednesday. The ECMWF moves the
front through Tuesday night, and moves the coastal low farther
offshore and then out to sea. We will keep a chance of precipitation
Tuesday night into Wednesday with the frontal passage and possible
effects of the coastal low if it gets close enough. Even if the low
remains offshore, we should get some precipitation from the front.
Strong west to northwest flow is expected again by Thursday as high
pressure tries to build in from the west. This is expected to usher
in very chilly air along with the breezy conditions. There could
again be a chance for isolated snow showers/flurries across much of
the area Thursday.
.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
VFR conditions are expected through the TAF period. Isolated
rain/snow showers may approach KABE and KRDG between 15 and 21Z, but
few visibility restrictions are expected and confidence that either
TAF site will be affected is low. Otherwise, few to bkn mid level
clouds (4000 to 6000 ft AGL) will be possible through the TAF period.
Breezy west northwesterly winds continue through the day today, with
winds dropping off beginning around 21Z.
Saturday-Saturday night...Generally VFR. Isolated showers or
flurries/sprinkles are possible across the northern half of the area
during the day which may temporarily lower conditions. Gusty west to
northwest winds 15-20 knots during the day.
Sunday...VFR early, lowering to MVFR by the afternoon. Rain or snow
possible late in the day.
Sunday night-Monday...MVFR early, then IFR overnight into Monday.
Rain or snow becoming likely. Accumulating snow possible for the
northern third of the area, with a chance of freezing rain around
daybreak. Rain/snow mix for central third of the area. Rain across
the southern third. All precipitation likely to become all rain
Monday. Winds could become gusty during the day Monday 20 to 25
Monday night...Improving conditions overnight to VFR.
Tuesday...VFR expected with west to northwest gusts around 15 to 20
Earlier gale gusts at the mouth of the Delaware Bay have diminished.
So have changed that gale warning to a small craft advisory as gusts
near or above 25 kt will be possible through the day time hours
today, and through the evening hours on the coastal waters. The
strongest winds are expected on the coastal waters adjacent to
northern and central NJ. We have already seen a few gusts right at
gale force, so have converted part of the gale watch to a gale
warning. Winds and seas should begin to diminish this evening, but
may not drop below SCA until very late tonight.
Saturday-Sunday...Conditions expected to remain below Small Craft
Advisory levels, although winds could gust around 20 knots at times.
Sunday night...Small Craft Advisory levels possible overnight.
Monday-Monday night...Small Craft Advisory conditions likely,
possibly reaching gale force for a period of time.
Tuesday...Small Craft Advisory conditions remain possible.
MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ452>455.
Gale Warning until 6 PM EST this evening for ANZ450-451.
Small Craft Advisory until 10 PM EST this evening for ANZ430-