Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KPHI 240100
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
800 PM EST Mon Jan 23 2017

.SYNOPSIS...
Strong low pressure near the Virginia Capes early this evening
will drift northeast toward Long Island through Tuesday
morning, before passing east of Cape Cod Tuesday evening. Weak
high pressure crosses our region on Wednesday. A cold front
passes southeastward off the mid Atlantic coast Thursday and
with another cold frontal passage possible again Sunday or next
Monday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
745 PM Update...The remaining Wind Advisory was cancelled. The
High Wind Warning for the coastal counties has been downgraded
to a Wind Advisory (through Midnight) as the tightest pressure
gradient and associated intense easterly low-level jet continues
to work northward.

A very dynamic storm centered to our south, with ample lift to
its north due to an intense easterly low-level jet along with
robust warm air advection in about the 800-850 MB level. This
is occurring as cooler air and some lower dew points have
advected southwestward from points to our north. This has
lowered the wet bulbing across the far northwest zones, with
freezing rain and sleet occurring especially above 1000 feet in
elevation. Some reports indicate rather icy road conditions in
the higher elevations of Monroe and Carbon counties in
Pennsylvania. A distinct dry slot has worked northward as is now
across about the southern half of our area. This should start
to pivot some as the closed low to our south makes the turn more
northeastward and the surface low off the coast strengthens
some. It appears that the chance of additional rainfall
particularly across our southern zones has decreased quite a bit
now (some drizzle looks to be occurring though currently). Some
adjustments to the Pops will be made to account for this.

Otherwise, most of the precipitation will fall as rain with
some sleet mixing in just north and west of I-95. The exception
to this will be Carbon and Monroe, Pennsylvania and Sussex, New
Jersey. Portions of these counties, especially higher elevations
are expected to be below freezing through tonight. So a wintry
mix is expected across portions of these counties, especially
the higher elevations. The question becomes how much of each
P-Type falls across the area. Forecast thermal profiles vary
through the night and we could give a period of each, freezing
rain, sleet, and some snow. We are expecting 2-5 inches of
snow/sleet combination as well as up to one to two tenths of an
inch of freezing rain. So we have kept the Winter Weather
Advisory in place and as is for now. It is possible that more
sleet could fall, which would make the snow and ice amounts less
than forecast.

Generally 1 to 2 inches of storm total QPF are forecast for much of
the area, with portions of the Delmarva and southern New Jersey
seeing the least, while portions of northeast New Jersey seeing the
most. We continue with the Flood Watch for northeastern New Jersey
which has 1.5 to 2 inches QPF, and isolated higher amounts possible.

Winds are expected to diminish some through the night, but will
remain gusty at times, between 25-35 mph.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The coastal low will slowly drift to the east northeast during the
day Tuesday. As the low moves away from the area, we could get some
wrap around moisture across the area which could keep some light
precipitation through the day. Current forecast temperatures
would keep everything rain for most areas, except where the
Winter Weather Advisory is in effect. If temperatures do not
rise much during the day, it is possible that some areas could
see snow or sleet mix in at times with any rainfall that occurs.
For the areas under the Winter Weather Advisory, they have the
better chance of seeing a winter mix into the day. For now, we
will keep the end time of noon time, but this may need to be
extended in time in the future.

Winds will become northwesterly as the low moves to farther to our
east and will remain gusty through the day with gusts around 20-25
mph expected.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
500 MB: Weak ridging follows the departure of our coastal storm
Tuesday night and Wednesday, followed by a series of short
waves that carves out a positive tilt trough in the eastern USA.

Temperatures: around 10 degree above normal Wednesday, 10 to 15
above normal Thursday, 5 to 10 above normal Friday, cooling to
near normal Sunday and Monday.

Forecast basis: Unless otherwise noted, a 50 50 blend of the
12z/23 GFS/NAM MOS guidance Tuesday night-Wednesday night,
thereafter the 12z/23 GFS MEXMOS Thursday and Thursday night,
and then the 15z/23 WPC guidance Friday-Monday, at times blended
with the 12z/23 GFS MEXMOS guidance or the long term temps were
adjusted because of the 12z/23 ECMWF 18z 2m temperatures.

The dailies...

Tuesday night and Wednesday: a little leftover mixed
precipitation is possible but it should not last long, if there
is any. Conditions dry out Tuesday night as high pressure builds
into the region and moves offshore during the day Wednesday.
Gusty northwest winds to 20 or 25 mph Tuesday night and
Wednesday morning become west or southwest Wednesday afternoon
and diminish a bit.

Wednesday night and Thursday...warm air advection ahead of cold
front. Maybe a few showers. Lots of uncertainty regarding
whether it will rain. Blended the MEX POPS with the previously
drier forecast.

Later Thursday into the weekend...gradual cool down with
generally dry weather expected. Breezy at times.

Next Monday...by then another cold front has either passed or
is passing and the GFS is the first of our usual reviewed global
models to suggest low pressure forming on the front over the
mid Atlantic states. To say the least, uncertainty and so we
stayed with the dry WPC fcst.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

MVFR/IFR ceilings tonight. As areas of rain and drizzle occurs
VSBYS will lower especially during any heavier rain. There will
be a break in the rain for awhile from about PHL on south and
east. Some sleet or snow may mix in at ABE and RDG later this
evening and overnight. Conditions are expected to return to
MVFR during the day Tuesday.

Northeast winds 15-25 knots with gusts 30-40 knots (strongest
gusts mainly in the MIV and ACY areas), will diminish some
during the remainder of this evening and overnight. The winds
will turn north and then northwest later tonight and Tuesday,
with speeds in the 10-20 knot range Tuesday with some gusts.

OUTLOOK...
Tuesday night and Wednesday...VFR. NW winds 10-15 KT with gusts
to 20 kt with winds backing to west in the afternoon.

Late Wednesday night or Thursday...Isolated showers, possibly
briefly lowering conditions to sub-VFR.

Friday and Saturday...VFR. West winds 10-20 KT with gusts 25 to
30 kt.

&&

.MARINE...
An intense easterly low-level jet continues to move northward
along with the tightest pressure gradient. This is allowing the
winds to diminish some across much of the area. As a result,
the remaining Storm Warning has been lowered to a Gale Warning.
This ends from south to north later tonight and early Tuesday
morning. Small Craft Advisory level winds are then expected on
Tuesday. Seas are in the 10-20 foot range (mainly 3-7 feet on
Delaware Bay), however these will slowly subside late tonight
and during Tuesday.

OUTLOOK...
Tuesday night...northwest SCA, possible low end leftover gale
early in the evening.

Wednesday...Sub-SCA conditions expected.

Thursday through Friday...West wind gusts 25-30 KT possible.

Saturday...West wind gusts 20-25 knots possible.

&&

.HYDROLOGY...
Flood Watch is in effect for this evening and tonight for
central and NE NJ, where the flooding risk is highest (heaviest
rainfall and most prone to flooding issues in urban locales).
Impacts will be due to excessive rainfall, as between 1.5 and
2.0 inches of rain with locally higher amounts are expected from
late this afternoon through tonight.

No main stem river flooding is anticipated. However, minor
flooding is possible along small streams and creeks and in areas
of poor drainage.

The entire region has some positive things working in its
favor...precipitation has been below normal the last 30 days,
there`s really no consequential snow cover to speak of, there`s
no ice on area waterways, streamflows are either running at or
below normal as is soil moisture, and last but not least, the
ground isn`t frozen. We think all the above will help mitigate
the flood threat especially for our counties outside the Flood
Watch.

&&

.TIDES/COASTAL FLOODING...
A Coastal Flood Warning is in effect through Tuesday morning
along the NJ and DE coasts and along Delaware Bay. Storm surge
values of 3 to 4 feet are occurring. Fortunately, the
astronomical tides are low and it should limit our region to
widespread minor flooding with some areas of moderate flooding
around the times of high tide late today and again on Tuesday
morning.

Strong wave action and the resulting beach erosion will likely
compound the effects of the surge. Waves breaking along the
shore may build to 6 to 10 feet. The expected surge along with
the wave action and the forecast rainfall will likely result in
additional and more widespread minor flooding around the high
tide into this evening.

We will keep the Coastal Flood Warning going for the tidal
Delaware River and far upper Delaware Bay between New Castle
County and Salem County for this evening`s high tide. The surge
should lessen considerably there for Tuesday morning`s high tide
based on the latest guidance.

Based on the forecast guidance and the expected pattern we are
not anticipating any coastal flooding on the upper eastern shore
of Maryland. Also, the potential for anything more than spotty
minor tidal flooding appears low for the tidal Delaware River
above the Commodore Barry Bridge.

The onshore flow is expected to begin backing toward the north
tonight and to the northwest on Tuesday, lessing the threat for
additional coastal flooding beyond Tuesday morning.

&&

.CLIMATE...
Rechecking monthly normal. The January departure at
Philadelphia, when all is said and done, should end up 5 degrees
above normal or 10th to 17th warmest January in the period of
record.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 11 AM EST Tuesday for PAZ054-055.
NJ...Flood Watch until 5 AM EST Tuesday for NJZ008-010-012>015-020-
     026.
     Coastal Flood Warning until 11 AM EST Tuesday for NJZ012>014-
     020>027.
     Wind Advisory until midnight EST tonight for NJZ013-014-020-
     022>027.
     Coastal Flood Warning until 11 PM EST this evening for NJZ016.
     Winter Weather Advisory until 11 AM EST Tuesday for NJZ001.
DE...Coastal Flood Warning until 11 AM EST Tuesday for DEZ002>004.
     Wind Advisory until midnight EST tonight for DEZ004.
     Coastal Flood Warning until 11 PM EST this evening for DEZ001.
MD...None.
MARINE...Gale Warning until 6 AM EST Tuesday for ANZ450>453.
     Gale Warning until 1 AM EST Tuesday for ANZ430-431-454-455.

&&

$$
Synopsis...Drag
Near Term...Gorse/Robertson
Short Term...Robertson
Long Term...Drag
Aviation...Drag/Gorse/Robertson
Marine...Drag/Gorse/Robertson
Hydrology...
Tides/Coastal Flooding...
Climate...


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.