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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 150601
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
201 AM EDT Sun Oct 15 2017

.SYNOPSIS...
-- Changed Discussion --
High pressure is centered well east of the Mid-Atlantic coast
overnight, however it extends to over our region. A strong cold
front crosses our region Sunday night, then high pressure
builds just to our south by Tuesday. High pressure will remain
nearly stationary for the rest of the week and into next
weekend.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
The disturbance off the coast will continue to dissipate tonight
while weak high pressure builds towards our area. Overall, there is
not enough mixing or dry air to scour out the low clouds over our
area. It`s expected that drizzle and fog will return to many
areas overnight. We have continued with the fcst much as it was
before. Low tonight will drop only into the upper 50s across the
north and low/mid 60s over Philadelphia/srn NJ and Delmarva.
Winds will be light and variable overnight.

Updated the forecast to better reflect the current temperatures
and trends.

&&

.SHORT TERM /SUNDAY/...
-- Changed Discussion --
High pressure will move across the area while a strong cold
front approaches from the west. The pressure gradient improves
through the day, resulting in increasing SW winds through the
day. The mixing will scour out the low clouds during the morning
and sunny skies should occur by late morning and last into the
afternoon. Temperatures will soar to much above normal readings.
Highs should top out in the upper 70s north and low 80s south
and central areas.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
-- Changed Discussion --
Hazards: Frost advisory likely portions of northeast PA and nw
NJ north of I-78 early Tuesday. First period issuance at this
time and just too far in advance for a seasonably normal and
somewhat marginal expected occurrence due to late developing
decoupling.

Summary...Breezy and mild Sunday night with Mondays max temps
possibly at 1 am Monday at which time a strong cold front moves
through with brief but significant cooling early next week, then
steadily warmer mid week into next weekend as high pressure parks
nearly overhead.

500MB:  A -1sd trough crossing the Great Lakes Sunday night reaches
New England Monday.  Another trough passes by, further north across
Quebec Tuesday, then very strong ridging (several standard deviations
above normal) develops across the Great Lakes and northeast USA later
in the week into next weekend.

Temperatures...

October has averaged 8 to 10 degrees above normal for the first 13
days of the month, excluding the ACY Marina where departures from
normal are less due to the tempering influence of the nearby
ocean (both warm and cold). Calendar day averages Monday should
be 2 to 5 degrees above normal with the min occurring at 1259
AM Tuesday, then Tuesdays calendar day average should be a
degree or two below normal, warming Wednesday to nearly 5
degrees above normal, and eventually to daily averages 10
degrees or more above normal Friday and Saturday. The daily
diurnals will be larger than usual due to the dry airmass in
place and light wind fields, nighttime lows probably a little
colder than statistically modeled.

Forecast basis...unless otherwise noted a 50 50 blend of the 12z/14
GFS/NAM MOS Sunday-Monday night, the 12z/14 GFS MEXMOS Tuesday and
thereafter the D4-8 WPC 15z/14 12 hourly max/min T and POP, and the 6
hourly td, wind and sky.

The dailies...

Sunday night...no change from the early morning thinking and here is
that portion of the discussion.

An upper-level trough moving across the Great Lakes and Ohio Valley
will drive surface low pressure well to our north Sunday night. This
will sweep a strong cold front across our area during Sunday night,
with a sharp wind shift to the northwest with its passage. The
guidance shows that the bulk of the large scale forcing shifts to
our north, however enough convergence with the cold front along with
some instability should allow for a band of showers to arrive into
our western zones. The question is how much does this weaken with an
eastern extent. The organization of the showers should be on the
decline with an eastern extent given the timing and little
instability in place. As a result, no thunder and continued
with the highest PoPs (likely) from near the I-95 corridor
westward, tapering to chance (scattered) farther south and
east. Much of the model guidance hints that the showers occur
behind the cold front/wind shift, and this characteristic could
allow some more organized showers to continue farther east.
There should also be a period gusty northwest winds 20-30 mph
toward dawn Monday.

For Monday...Partly to mostly sunny, breezy and much cooler behind
the cold front (afternoon temps around 20 degrees cooler than
the day before) with a gusty northwest wind to 25 mph. The
calendar day max temp is expected to occur near 1 am Monday, and
be on the order of 5 degrees warmer than the Monday afternoon
high temperature. One note for Monday afternoon...Right now our
Min RH is forecast above 30%, BUT if our forecast ends up drying
RH`s out below 30%, and if minuscule less than .05 inch amounts
of showers occur 12 hours previous, then our partners may wish
us to post an SPS for an elevated FWX concern. No action needed
at this time since its a marginal risk, benefiting from review
of future model guidance and partner input.


Monday night... A frost advisory will likely be needed and some
places may see freezing temps of 30-32F. This falls sort of in
the normal range of first freeze, ultimately depending on what
actually occurs. Gusty north to northwest winds early to around
20 mph decrease - decouple inland late at night but gusty north
to northwest winds may continue along the immediate couple of
miles of the coast all night.

Tuesday...Sunny and seasonably cool.  Northwest wind backs to
west or southwest. The coolest day of the week.

Wednesday through Saturday...Looks fantastic for mid October. As
a gradually building ridge approaches from the west with rising
heights, surface high pressure is forecast to be nearly
stationary right over our area through Saturday. This will
translate to slow moderation in the temperature department
during this timeframe. Larger than normal diurnals are expected.
Since this looks to be primarily a west or northwest pressure
gradient wind flow pattern, very little late night fog is
anticipated...just a bit too dry.

This pattern could hold Sunday into Monday before troughing just to
our west complicates the weather forecast beginning the 22nd or 23rd.
-- End Changed Discussion --

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Through today...MVFR/IFR to locally LIFR ceilings early this
morning are expected to improve by late morning, then to mostly
VFR this afternoon. MVFR to IFR visibility due to fog and even
local drizzle is expected to improve by mid morning. The timing
of the improvements is of lower confidence. Light winds,
becoming southwest and increasing to 10-15 knots with local
gusts to about 20 knots. While confidence is high regarding the
increase in winds, especially this afternoon, there is lower
confidence regarding the extent of the gusts.

Tonight...VFR overall, although some showers move through later
this evening and overnight (local MVFR possible) as a strong
cold front arrives. Southwest winds around 10 knots, however
gusts up to 25 knots are possible at times especially with a
wind shift to the northwest behind a cold front.

OUTLOOK...
Monday...VFR. Northwest winds 10-15 knots with gusts 20-25
knots diminishing toward midnight Monday night.

Tuesday...VFR. light northwest wind to start becomes west southwest
during the afternoon then northwest at night. Gusts under 20 kt.

Wednesday...VFR. Light northwesterly winds becoming variable at
night.

Thursday...VFR.  Light wind.
-- End Changed Discussion --

&&

.MARINE...
We have cancelled the SCA for the northern NJ coastal zones as
sea at buoy 44065 have been below 5 feet for several hours. We
will continue with the SCA for the remaining coastal zones of NJ
and DE through Sunday morning.

Mostly cloudy conditions with patchy fog and drizzle expected
tonight and Sunday morning. More SCA conditions expected later
Sunday as winds and seas increase ahead of the approaching cold
front. After some morning fog and drizzle, fair weather is
expected Sunday.

Winds and seas are expected to increase through Sunday afternoon
and the SCA may need to be extended.

OUTLOOK...
Sunday night...SCA possible ahead of and certainly behind the cold
front with gusts to near 30 kt by dawn Monday, induced by surface
pressure rises and cold air advection.

Monday...Conditions will be close to Small Craft Advisory criteria
through Monday night...possibly strongest winds around 25 kt at
sunrise and sundown.

Tuesday...Winds and seas diminish and no marine hazard anticipated
after daybreak. Light north becoming west during the day then
northwest late at night.

Wednesday...The conditions are anticipated to be below Small Craft
Advisory criteria with a northwest wind becoming light and variable
at night.

Thursday...No marine hazards. Light wind.

&&

.CLIMATE...
Much warmer air arrives for Sunday. Some places could be close to
record high temperatures. Below are the October 15th record high
temperatures for the official climate locations that are currently
forecast to be within 3 degrees of their record.

Allentown, PA     82 in 1947
Reading, PA       83 in 1989
Trenton, NJ       84 in 1975
Georgetown, DE    84 in 1975

October projected positive departures continue to indicate a top
10 warmest October is likely to occur in our forecast area, in
some places possibly top three.

On October 9th we projected the PHL October avg temp to be 62.2 or
4.7 degrees above normal...or 7th warmest on record.

Today`s projections using this mornings 330 am D1-7 max/min temps,
the 00z/14 FTPRHA GFS model 2meter max/min temps for D8-11 and
then daily normal temps the 25-31st yields an avg of 62.7 degrees
or 5 degrees above normal and a rank of #3 warmest on record
(official records back to 1874). Confidence is very high that
the month of October will be a top 15 warmest in PHL and other
climate sites in our forecast area,, above average for top 10,
and possibly vying for the warmest ever October. In PHL that
warmest ever October was a 64.5 degree avg in 2007, followed by
63.5 in 1971 and then 62.7 in 1947.

NAEFS odds somewhat favor an ultimately warmer average than that
which is projected above, as the NAEFS has us in its coolest period
with regard to normal, this coming week of the 16th-20th. The
NAEFS probabilities warm us, relative to normal, the last 10
days of the month. The caution here... the GEFS is trending to
several stronger and stronger cold troughs trying to dig down
into the Ohio Valley late in the month so the NAEFS is not
necessarily a lock yet on anything warmer than what we`ve
projected today.


For Allentown PA...using the same process as for Philadelphia,
Allentown projects the 2nd warmest October on record (back to 1922).
The warmest was 60.8 degrees in 2007,  followed by possibly 2017 at
59.7, October 1984 was the next cooler October, averaging 59.5
degrees.

IF...IF these positive departures are equal or greater than
what is projected above... then for both PHL and ABE this would
make it the 4th month this year with a monthly positive departure
of 5 degrees or greater (J,F,A,O) with no month this year
having any average negative departure greater than 2 degrees. In
fact only 3 months of the first 10 will have averaged cooler
than normal...March, May and August.


These average temperature projections will change, but I dont
think by more than a degree or two.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
     ANZ452>455.
-- End Changed Discussion --

&&

$$
Synopsis...Drag
Near Term...Meola/O`Hara
Short Term...O`Hara
Long Term...Drag
Aviation...Drag/Gorse
Marine...Drag/Meola/O`Hara
Climate...