Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 182118
Area Forecast Discussion
National Weather Service Mount Holly NJ
418 PM EST Sat Feb 18 2017
Low pressure in southeast Canada will send a cold front southward
into and through our area Sunday or Sunday night. Canadian high
pressure will extend south into the mid Atlantic states Monday, then
move into the western Atlantic late Tuesday. A warm front passes
eastward through our area early Wednesday. A cold front may sag
southward into Pennsylvania and New Jersey Thursday night. It should
move north of our area Friday night as strong low pressure moves
from the Great Lakes into southeast Canada. Its trailing cold front
is expected to move off the east coast later Saturday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A spring-like afternoon in progress as low-level warm advection
has increased as a warm front continues to lift north of our
area. The 12z Sterling, VA raob showed +14C at the top of a
strong low-level inversion (about 1500 feet). Some cooler
temperatures are noted right along the coast though with a more
southerly wind component off the chilly ocean water. Through
tonight, our region is mostly between systems. One tracks well
to our north as the parent trough slides from Hudson Bay toward
the Canadian Maritimes. This will however push a weak cold front
into our area later tonight. The second system is a closed low
that will open up/weaken as it tracks eastward from the
Tennessee Valley to the southern Mid Atlantic overnight.
Is is mostly the southern system that is driving an increase in
mostly high level cloudiness across our area this afternoon and
especially tonight. There is a low-level jet around 40 knots
forecast to develop close to our northern zones for a time tonight
before shifting into coastal New England. This will aid in some
moisture advection, however forcing with the incoming cold front is
weak and moisture looks rather limited. As a result, perhaps some
sprinkles across mostly our southern zones overnight. Given the
expected cloud cover on the increase tonight in combination with a
southwesterly wind, will result in milder temperatures. Low
temperatures are mostly an even blend of MOS and continuity.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
Surface low pressure will move into the Canadian Maritimes Sunday,
with a weakening upper-level trough sliding offshore of the southern
Mid Atlantic region. A weak cold front associated with the northern
surface low will settle across our area but then tend to stall or
even wash out. There is a secondary cold front that is forecast to
stay to our north during the day Sunday, and colder air is found
behind it. The initial front has little change in temperature with
it with just some weak cold air advection forecast in the afternoon,
however the boundary layer remains warm. The low-level flow turns
more from the west and northwest during the day which will add a
downslope component for the coastal plain. As a result, another warm
afternoon is expected although the far north should be a bit cooler
given the weak cool air advection settling in. Some spots, mainly
from Philadelphia on south and east, may be very close to their
record high temperature for the date.
An area of mainly mid level clouds associated with the southern
system will exit to the east in the morning, with an increase in
sunshine expected. High temperatures are a MOS blend, however these
were boosted a bit especially for the coastal plain (I-95 south and
east) given a downsloping component to the flow. It should be warmer
at the coast given enough of an offshore flow.
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
-- Changed Discussion --500 MB: A southeastward moving strengthening short wave in Quebec
Sunday night moves past the Maritimes Tuesday while a strong
ridge in the Great Lakes slides east. A weak short wave cuts
eastward into the ridge across New England Wednesday. In the
wake of the short wave, a ridge dominates over the mid Atlantic
States Thursday into Saturday before a strong short wave moves
into the Great Lakes over the weekend.
Temperatures: As our forecast area proceeds to a top 5 warmest
February on record and a top 12 warmest winter in the period of
record dating back to the late 19th century, the coming week of
Monday through Saturday should average 10 to 15 degrees above
normal. The coolest day is expected to be Tuesday...only several
degrees above normal, but thereafter, some model guidance points
to a three day period of temperatures 15 to 20 degrees above
normal between Thursday and Saturday. BUT... there may be a a
wrinkle developing. Dependent on the strength of the short waves
exiting the western USA late this week and weekend, there is a
chance of a low level cooler-colder flow setting up near and
north of I-78 Friday onward.
Forecast basis: Unless otherwise noted, a 50 50 blend of the
12z/18 GFS/NAM MOS guidance Sunday night-Monday night, thereafter
the 12z/18 GFS MEXMOS Tuesday, and then the 15z/18 WPC guidance
Thursday - Saturday, except used the warmest avbl guidance for
Wed-Thu which was the 12z/GFS MEXMOS which am confident is onto
the warmth...and our forecast may be 5 degrees too cool Wed and
As an example of guidance...todays high temp at phl 67... warmer
by 3 degrees than ydys warmest guidance which was the highres
NMM and WRF and against this mornings 00z/18 guidance was
warmer than the warmest guidance which were the ADJUSTMET and
HIRESWRF. Modeled MOS southwest flow warmth seems to have a
The dailies including any possible significant insight...
Sunday night...Mostly clear. Small chc some strato cu toward dawn
Monday (NAM has a layer of high rh near 950MB). Northwest wind gust
15 mph. Confidence: above average.
Monday...After any low strato cu dissipate, mostly sunny with a
cooler north northwest flow gusting near 20 mph. Still above normal
temps. Confidence: above average.
Tuesday...WAA increasing high clouds limiting max temperature potential.
Chance showers may invade E PA late in the day in the leading
portion of the instability burst. Wind light southeast to
south. Confidence: average on max temps which have favored the
milder of the avbl guidance.
Tuesday night...Chance of light showers ahead of a warm front.
Low probability there could be a touch of freezing rain high
terrain north of I-80. This ice risk isnt in the HWO or zones
since confidence is below average and guidance favors min temps
during any rain, above freezing. Confidence: average or below
average on the occurrence of any rain.
Wednesday...Becoming Sunny and warmer. Forecast temps may end up
several degrees warmer than now predicted. West wind.
Confidence: above average except confidence on max temps
remaining this cool is below average.
Thursday...mixed clouds and sun and warm. Max temps may end up
5f warmer than now predicted. Southwest wind. Confidence: above
Friday...early morning stratus/fog along a cool front that has
settled into our area. maybe a shower north of the boundary or
maybe the boundary doesn`t make it down into our forecast area.
otherwise variable clouds. Confidence: below average on the
scenario. This ECMWF colder soln will need to be monitored for
future impact in our area. Confidence below average on the temps
and chance of any rain.
Friday night...a good chance of showers ahead of the cold front
moving east into our area or the ECMWF solution of a warm front
moving north from I-78. Shower timing and temperature uncertainty
as well as wind uncertainty, though probably turning southeast to
southwest, depending on latitude in our area.
Saturday...Maintained continuity despite the faster GFS solution.
EC and GGEM operationals are slower and at this time, did not
want to raise hopes for the GFS blustery dry westerly flow
on Saturday. Confidence below average.
-- End Changed Discussion --
.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
This Afternoon...VFR with some increasing high level clouds.
Southwesterly winds around 10 knots, with some local gusts up to
Tonight...VFR with thickening clouds, and a ceiling lowering into
mainly the 7000-10000 feet range. Southwest winds less than 10
knots, becoming westerly.
Sunday...VFR. A ceiling between about 7000-10000 feet to start,
which then thins out. West to northwest winds increasing to around
Sunday night...VFR northwest wind. MVFR sc may develop toward dawn.
Overall confidence: above average.
Monday...Possible MVFR sc early otherwise a VFR northwest to
north wind... gusty 15 to 20 kt. Confidence: above average.
Tuesday...VFR lowering high cigs develop during the day. chance
of showers late in the day vcnty KABE KRDG. southeast to south
wind. Confidence: above average.
Tuesday night...Conditions may briefly lower to MVFR overnight
into early Wednesday morning with a chance of showers and a
southwest wind. Confidence: average.
Wednesday...Becoming VFR and a west wind develops. Confidence:
Thursday...VFR. Southwest wind. Confidence: above average.
-- End Changed Discussion --
The conditions are expected to remain below Small Craft Advisory
criteria through Sunday. A southwesterly flow through tonight will
gust to around 20 knots at times, then turn west and northwest late
tonight and Sunday as a weakening cold front moves through.
Sunday night - Monday...Sub Small Craft Advisory conditions expected,
although northwest to north winds may approach advisory levels across
the northern New Jersey coastal waters overnight Sunday into Monday
morning. Confidence: average.
Monday night-Thursday...Sub Small Craft Advisory conditions expected
although winds may gust up to 20 knots at times. Confidence: above
-- Changed Discussion --Record max temps Sunday that may be approached (within 2f) or
-- End Changed Discussion --
Long Term...Drag 417