Area Forecast Discussion
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FXUS61 KPHI 301628
Area Forecast Discussion
National Weather Service Mount Holly NJ
1228 PM EDT Thu Mar 30 2017
High pressure will move offshore today. Low pressure moving
through the Ohio Valley on Friday will redevelop near the New
Jersey coast Friday night and move offshore on Saturday.
Canadian high pressure will move into the area for Sunday and
Monday. Low pressure over the Ohio Valley on Tuesday will move
through the middle Atlantic Tuesday night and offshore on
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Dry weather continues today as high pressure slides through the
region. Mid and high clouds will increase and thicken into this
afternoon as clouds associated with low pressure over the
Midwest stream into the Northeast and Mid-Atlantic.
Temps on track to top off in the 40s in the Poconos and in the
low to mid 50s elsewhere. Light NE winds will become SE through
the afternoon as the high moves offshore.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
Low pressure will continue its track eastward tonight along a
warm front positioned over the Midwest. The nose of a southerly
low-level jet ahead of this system will be positioned over the
Mid Atlantic tonight. Forcing for ascent over the region will
predominately be provided by isentropic lift as warm, moist air
overruns the low- level baroclinic zone situated over the Ohio
Valley-Delmarva. PoPs increase from NW to SE this eve. Did not
ramp up PoPs quite as fast as I would normally like to in this
close to the event due to some notable timing differences with
respect to onset of precip this eve. Did have enough confidence
to increase to PoPs to likely for southern Poconos this evening
and then eventually the remainder of the CWA overnight. QPF
amounts will generally be light tonight (under one-quarter inch)
with the deeper/stronger lift still upstream of the region.
Despite the center of the high retreating to our northeast, CAD
wedge will be reinforced in-situ owing to the effect of
evaporative cooling when precip initially falls into an
relatively dry boundary layer. Temperatures were populated using
a blend with much of the weighting from the NAM 12km/NAM 3km
nest as this model has shown to handle complex thermal profiles
in CAD setups like this. Freezing rain is likely overnight
tonight in the mountains of Carbon and Monroe Counties in PA and
Sussex County, NJ as temperatures fall into the lower 30s. Held
off on issuing a late second period Freezing Rain Advisory
since areal coverage looks to be limited to the highest
elevations (approximately above 1300 ft). However, places like
Mount Pocono and High Point may see a few hundredths of an inch
of ice accretion late tonight, especially on elevated surfaces
such as trees and wires.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
The primary players during the long term continue to be two southern
stream systems that are expected to impact our region in the Friday-
Saturday and Monday-Tuesday time frames.
The first system will produce a wide swath of rainfall across the
region, with localized amounts in excess of 1.5 inches, especially
across the I-95 corridor. While urban and poor drainage flooding are
possible, and have been mentioned in the HWO, we do not expect major
impacts on rivers and streams.
Freezing rain looks to persist into at least the morning on
Friday along the higher elevations of Carbon, Monroe and Sussex
(NJ) counties. Currently, our weather grids indicate a change
over to just plain rain with temperatures rising above freezing
in these high elevations by the afternoon. However, some of the
colder model solutions indicate the potential for freezing rain
to persist into Friday afternoon and perhaps Friday night. The
latest storm total ice graphic was populating running the FRAM
off our forecast database and represented an increase in the
icing amounts ranging from a few hundredths of an inch in these
counties at around 1000 ft in elevation to almost a quarter inch
at above 1800 ft in elevation (isolated areas in Monroe
County). These amounts may need to be increased if trends toward
a prolonged icing event (i.e., freezing rain persisting into
Friday afternoon/night) continue.
Looking ahead to early next week, the next system is expected to
bring more precip to our region, especially Monday night into
Tuesday. This setup continues to look warmer compared to the
previous system, given the absence of high latitude blocking,
and would favor predominantly rain.
Temperature-wise, daily means are expected to average near normal
Friday thru Sunday, then around 5 to 10 plus degrees above normal
Monday thru Thursday.
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
VFR. BKN-OVC CIGs will lower to 5000 ft by 00Z Friday. Winds
will generally turn to the SE at 5-7 KT through this afternoon.
CIGs lower from W to E tonight as precip arrives. Held off MVFR
CIGS/VSBYs until closer to midnight EDT for ABE/RDG and until
07-09Z farther east toward I-95 terminals. However, there is a
low chance that MVFR begins 2-4 hours earlier than that if
precip moves in faster than currently forecast. PROB30 group
covers this potential. SE winds 6-12 kt are expected tonight.
MVFR possible in low clouds Friday and Friday night, then again
Monday night into Tuesday. Otherwise, predominantly VFR. Southeast
winds may gust 20 to 25 knots on Friday, and northwest winds may
gust around 20 knots on Saturday.
Winds and seas below SCA today and tonight. NE winds 5-15 kt this
morning will become SEly this afternoon and tonight. These SE winds
will initially be light this afternoon but increase to 15-20 kt by
We have issued a Gale Watch from 18Z Friday to 09Z Saturday for the
northern NJ coastal waters (ANZ450-451) for southeasterly wind
gusts up to 35 knots during this time frame.
Outside of the Gale Watch, a Small Craft Advisory is in effect
for Friday and Friday night for the southern New Jersey and
Delaware coastal waters. Hoisted a SCA for northern DE Bay in
addition to lower DE Bay, but for Friday afternoon/early
A Small Craft Advisory may be needed on Saturday for northwest wind
gust of 25 to 30 knots and seas of 5-8 FT, especially across the NJ
Another SCA may be needed Monday night into Tuesday, as
southeasterly winds and seas increase.
Though astronomical tides will be gradually diminishing through the
week now that we are past the new moon, the threat of minor tidal
flooding along the NJ and DE Atlantic coasts increases by
Friday. Tidal anomalies are currently around 0.5 feet above
astronomical this morning. We expect this to continue today.
Beginning tonight, a low pressure system will bring a prolonged
period of onshore flow, further increasing the surge.
Forecast tidal levels from the ETSS have trended slightly
upward for tonight, indicating Reedy Point, Lewes and Sandy
Hook could reach their minor coastal flood stage with the high
tide cycle late this evening. These ETSS forecasts would fall
just shy of threshold for Coastal Flood Advisory with spotty minor
coastal flooding tonight. OFS guidance for tonight is
significantly lower than ETSS. It seems the ETSS may be a bit
overdone since with the expected SE wind direction and lighter
wind speeds, we should not see a surge any higher than what we
currently have tonight.
The high tide of most concern is still Friday evening and
Friday night, particularly along the northern and central New
Jersey Shore. By this tide cycle, it will take a surge of 0.8 to
1.0 feet to reach minor flooding thresholds, which is likely.
However, not sure yet if we will have another 0.3 feet surge to
reach advisory thresholds. The exact magnitude of the surge will
be dependent on how quickly the onshore flow develops and how
strong it will be by Friday.
Given the fetch and duration of southeasterly flow, some of the
surge guidance is also raising water levels along the eastern
shore of Maryland, particularly for the Friday evening high
tide. At this time, none of the guidance reaches the minor
flooding threshold, but this will bear watching.
MARINE...Small Craft Advisory from 8 AM Friday to 5 AM EDT Saturday for
Gale Watch from Friday afternoon through late Friday night for
Small Craft Advisory from 2 PM to 8 PM EDT Friday for ANZ430.
Small Craft Advisory from 8 AM to 8 PM EDT Friday for ANZ431.