Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 231547
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1047 AM EST Mon Jan 23 2017

.SYNOPSIS...
Low pressure over the Southeast will drift northeastward to the
Mid-Atlantic by this afternoon. This low will then meander off
the New Jersey coastline Monday night before departing late
Tuesday. Weak high pressure builds across the region on
Wednesday. Low pressure passes north of the area Wednesday
night, and then a deep upper trough builds into the Eastern
United States for the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Strong low pressure continues to move northeast along the
central Appalachians this morning and will move offshore of the
Mid-Atlantic later this evening. Meanwhile, high pressure
remains to our north across eastern Canada. A tight pressure
gradient remains across the area today and will continue to lead
to increasing winds. Winds have already gusted 40-50 mph and
will continue to increase through this morning and into this
afternoon, especially from I-95 eastward. We have upgraded the
areas along the I-95 corridor south and eastward to a High Wind
Warning through late this afternoon. Areas north and west of
of I-95 remain in a Wind Advisory.

As several vorticity impulses move across the area in the
diffluent southerly flow aloft, periods of rain and drizzle will
continue into this afternoon. The heaviest precipitation is
expected to move in from south to north during the 18Z-06Z time
frame. Models are quite variable with QPF totals. Location of
maximum QPF will be highly dependent on exact placement of the
coastal front, frontogenetical forcing and the axis of
deformation to the northwest of the surface low, and exact
influence of the low- level jet developing just downstream of
the surface low. It still appears that coastal New Jersey should
see the best chance of highest precipitation. Current Flood
Watch looks OK for now.

This storm will also impact our northern most zones with winter
weather. Light snow has already been reported in some areas
across Sussex, New Jersey. Temperatures are below freezing
across portions of Sussex, New Jersey as well as Carbon and
Monroe, Pennsylvania. So any precipitation that falls in the
higher elevations of these counties will see a wintry mix of
snow, sleet, and freezing rain through today. Therefore the
Winter Weather Advisory continues for these counties.

Snow and snow/sleet mix looks to become heavy for a period
tonight. It`s very important to note that there are still subtle
thermal differences between model guidance, which leads to
quite a bit of uncertainty with regards to how ptypes transition
through the event. Therefore, forecast confidence in snow/ice
accumulations is definitely lower than what we would like to see
for this close out and with a winter headline in effect.
Nonetheless, it only takes a light glaze of ice to produce
hazardous travel...which is enough to warrant the headline.
Please see WSW for more details.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
The main band of precipitation is expected to be moving across
the area this evening as the deepest lift associated with the
strong system moves through. The highest QPF totals will likely
occur during this time, with storm totals (liquid equivalent)
1-3 inches area wide, much of this occurring in the
aforementioned 18Z-06Z period. As this steadier precipitation
moves through, precipitation in the higher elevations of Carbon,
Monroe, and Sussex County (NJ) will likely transition to sleet
and wet snow. Combined with the strong winds this evening, this
will make for treacherous travel in these areas. As most
precipitation is expected to be sleet, antecedent ice
accumulations and subsequent snow accumulations are currently
expected to remain below warning thresholds. However, much
uncertainty remains as to the exact evolution of precipitation
type with this storm -- i.e., this forecast is of below average
confidence.

Synoptically-driven low-level jet stream will slowly move
northeast away from the region during the evening hours. As this
does so, the strongest lift should depart the area after
midnight, and winds should begin to decrease. Nevertheless, the
proximity of the surface low will permit winds to continue
gusting up to 40 mph across much of the area, especially in New
Jersey and southeastern Pennsylvania. Light precipitation will
likely continue, especially with any wraparound on the northwest
side of the cyclone (indicated by virtually all operational
guidance, though there remain considerable discrepancies
regarding exact placement). As precipitation winds down in the
southern Poconos and adjacent Sussex County, NJ, precipitation
may transition to light freezing rain or drizzle as ice crystals
become more difficult to generate as the midlevels dry out.

Temperatures are expected to stay just above freezing from the
I-95 corridor southeastward to near freezing in the Lehigh
Valley to below freezing in the southern Poconos and adjacent
Sussex County.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
From Tuesday Night on:

Although surface low departs Tuesday morning, upper level low
will lag behind. With several strong shortwaves wrapping around
this low, can expect another shot of precip to impact the region
through Tuesday afternoon. precip should be rain for the bulk
of the area, but a wintry mix is possible for Carbon and Monroe
counties.

Conditions dry out Tuesday night as high pressure builds into
the region and moves offshore during the day Wednesday.

Temps will run a few degrees above normal on Tuesday, generally
in the upper 30s to mid 40s, while a return to above normal
temperatures expected on Wednesday with highs in the 40s and
50s.

Low pressure will organize over the Great Lakes as a deep upper
trough builds into the western U.S. This portends a pattern
change for the end of the week and weekend. Cold front pushes
through the region Wednesday night. For now, expecting dry
conditions. However, GFS is indicating an area of precip
developing offshore with the passage of the front. It is
possible that more organized precip can develop, but models
currently keep it offshore, so will go with a mainly dry
forecast with its passage.

Colder air then builds into the region for the end of the week
and weekend with a return to more normal temperatures. Highs
will fall into the 20s and 30s over the weekend.

&&

.AVIATION /16Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Conditions are generally MVFR this morning across the TAF sites,
but are expected to lower to IFR through this afternoon and
tonight. Low clouds, drizzle, and fog will continue this
morning before steadier rain moves in this afternoon and this
evening. There is a slight chance of some wintry precipitation
tonight at KABE/KRDG, but confidence was too low to include in
the TAFs at this time.

Strong east to northeast winds are expected through this
evening, with gusts 30-40 kts for ABE, RDG and 40-50 kts
possible for ACY, ILG, MIV, PHL, and PNE through today. Winds
will decrease some this evening and overnight, but remain gusty
25-35 kts.

A strong low- level jet will generate easterly low-level wind
shear this afternoon and evening across the entire area.

Precipitation will likely diminish from south to north by late
this evening or overnight, but with little recovery of
ceilings/visibilities expected. GUSTS UP TO 50 KT.

OUTLOOK...

Tuesday...Lingering IFR conditions with rain continuing through
the day. Sleet or snow may briefly mix in at ABE before ending.
Gradually improving to MVFR and then VFR from S to N late in
the day.

Tuesday night and Wednesday...VFR. NW winds 10-15 KT with gusts
to 20 kt.

Thursday...Isolated showers, possibly briefly lowering
conditions to sub-VFR.

Friday and Saturday...VFR. West winds 10-20 KT.

&&

.MARINE...
The Storm Warning remains in place for the Atlantic waters
adjacent to New Jersey and Delaware. We`ve upgraded the
Delaware Bay to a Storm Warning as winds are already gusting
40-45 knots, and are expected to increase to 50 knots.

The winds will diminish some this evening and overnight, but
will likely remain around gale force through the night for much
of the waters.

OUTLOOK...

Tuesday...Strong SCA conditions expected, with another round of
Gales possible on the ocean waters Tuesday afternoon.

Wednesday...Sub-SCA conditions expected.

Thursday through Friday...Wind gusts 25-30 KT possible.

&&

.HYDROLOGY...
Flood Watch is in effect for this afternoon 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 1-3 inches
of rain with locally higher amounts, possibly up to 4 inches,
is expected from late this afternoon through tonight.

River flooding should be limited unless basin-wide rainfall
averages climb above three inches. The most sensitive responding
rivers still appear to be the Millstone and the Rancocas.

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.

&&

.TIDES/COASTAL FLOODING...
A Coastal Flood Warning is in effect for this afternoon/evening
along the NJ coast from Atlantic County northward to Monmouth
County. The latest ETSS has trended higher with tidal forecasts
at both Atlantic City and Sandy Hook. Even though ETSS keeps
Sandy Hook below moderate, we think guidance is trying to play
catch up. The trend has been for the duration of very strong
onshore winds to extend later into the day and even into part of
tonight. The timing of the peak storm surge now looks to coincide
with the late afternoon/evening high tide to yield moderate
tidal flooding in the warned area.

A Coastal Flood Advisory remains in effect for the coastal
areas of Delaware and the remaining portion of the coastal areas
of New Jersey, Delaware Bay and the tidal Delaware River below
the Commodore Barry Bridge area. The advisory covers the high
tide cycles through this evening, but it will likely need to be
extended into the following high tide early Tuesday morning.
There is a concern that moderate coastal flooding develops with
this afternoon/evening`s high tide but did not have as much
support from the guidance as we did at Atlantic City and Sandy
Hook. We will continue to closely monitor the situation.

Increasing wave action and the resulting beach erosion will
likely compound the effects of the surge. Waves breaking along
the shore may build to 5 to 8 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 from late this afternoon and evening.

The onshore flow is expected to begin weakening from south to
north tonight as low pressure passes off the Middle Atlantic
coast and the tight pressure gradient ahead of the system lifts
into New England. However, lingering minor coastal flooding is
again possible for the high tide early on Tuesday morning being
that the flow is not expected to become fully offshore until
Tuesday afternoon.

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.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...High Wind Warning until 4 PM EST this afternoon for PAZ070-071-
     102-104-106.
     Wind Advisory until 4 PM EST this afternoon for PAZ060>062-101-
     103-105.
     Winter Weather Advisory until 11 AM EST Tuesday for PAZ054.
     Winter Weather Advisory until 11 AM EST Tuesday for PAZ055.
NJ...Flood Watch from 4 PM EST this afternoon through late tonight
     for NJZ008-010-012>015-020-026.
     Wind Advisory until 7 PM EST this evening for NJZ007>010.
     High Wind Warning until 4 PM EST this afternoon for NJZ015>019-
     021>025-027.
     Coastal Flood Advisory until 9 PM EST this evening for NJZ021-
     023-024.
     High Wind Warning until 9 PM EST this evening for NJZ012>014-
     020-026.
     Coastal Flood Warning from 2 PM this afternoon to 11 PM EST
     this evening for NJZ012>014-020-022-025>027.
     Coastal Flood Advisory until 2 PM EST this afternoon for
     NJZ012>014-020-022-025>027.
     Coastal Flood Advisory until 10 PM EST this evening for NJZ016.
     Winter Weather Advisory until 11 AM EST Tuesday for NJZ001.
DE...High Wind Warning until 4 PM EST this afternoon for DEZ001>004.
     Coastal Flood Advisory until 9 PM EST this evening for
     DEZ002>004.
     Coastal Flood Advisory until 10 PM EST this evening for DEZ001.
MD...High Wind Warning until 4 PM EST this afternoon for MDZ008-012-
     015-019-020.
MARINE...Storm Warning until midnight EST tonight for ANZ452-453.
     Storm Warning until 4 AM EST Tuesday for ANZ450-451.
     Storm Warning until 6 PM EST this evening for ANZ454-455.
     Gale Warning until 7 PM EST this evening for ANZ430-431.

&&

$$

Synopsis...CMS/MPS
Near Term...CMS/Klein/Robertson
Short Term...CMS/Klein
Long Term...Klein/MPS
Aviation...CMS/Robertson/MPS
Marine...CMS/Klein/Robertson/MPS
Hydrology...Klein
Tides/Coastal Flooding...Klein/Iovino


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