Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 202100
Area Forecast Discussion
National Weather Service Mount Holly NJ
500 PM EDT Thu Oct 20 2016
A warm front just south of our region will move north across our
area on Friday. Meanwhile, low pressure will strengthen across the
Ohio Valley and move north of the region into Friday. A strong front
associated with the low will cross the area Friday evening, while
the low remains over New England into the weekend. Gradually, high
pressure will build across our area into the middle of next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Warm front lifting north of I-78. South of the front, temps have
risen well into the mid and upper 70s, and even into the low 80s
across MD/DE. North of the front, temps are in the upper 60s to low
70s. As the front lifts to the north, those warmer temps should
continue to lift to the north, but there is not much daytime left
for temps to reach 80 across northern zones.
Abundant stratus just offshore has spread westward, and cloudy skies
in place for much of NJ. That warm front has scattered out some of
the clouds in southern and western NJ, but after sunset, expecting
those clouds to spread back to the west, and widespread low clouds
and fog will develop across the region. MOS guidance indicating the
potential for dense fog, and do think that some spots may have
visibilities less than 1/2 mile, but at this time, not confident
enough to issue a Dense Fog Advisory. Think best chances will be
along coastal NJ, as well as across the Lehigh Valley, as sfc
dewpoints continue to rise into the 60s, and air temps drop back
into the 60s. With a saturated airmass, will include areas of fog
and drizzle in the forecast, from mainly after midnight tonight.
Low pressure over the OH valley will track to the north and east
through western NY and PA, and the bulk of the rainfall should stay
well to the west. Some rain may spread out ahead of that low, and
will therefore carry low chance PoPs, mainly for northern zones,
tonight. Not expecting much, if any, actual rainfall aside from some
drizzle across central and southern areas.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
There are 2 areas of low pressure that will impact the region on
Friday. The first is the primary low over western NY/PA that will
track to the north and east, dragging a strong cold front with it.
Based on latest model QPF fields, not expecting much precip to
spread into the local CWA until the afternoon. Will carry likely
PoPs for NW zones early, but think the bulk of the showers will hold
off until late afternoon, possibly even Friday evening. There may
even be enough upper level energy to support some scattered
thunderstorms in the afternoon, so will mention that in the
The second wave of low pressure that could impact the region will
spin off of low pressure over the western Atlantic Ocean waters.
Looks like some rain will spread to the north along the Jersey
Shore. High chance to low end likely PoPs will cover this
With strong southerly flow ahead of the approaching cold front,
looks like there will be another day of unseasonably warm temps,
especially if enough sun can break through the clouds. Used a blend
of MOS guidance for highs in the mid to upper 70s for most areas.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Friday night and Saturday...500 hPa closed low traverses the
region during this time frame. A strong cold/occluded frontal
passage Friday night will lead to gusty northwest winds thru
Saturday. Given the strong cold air advection, in concert with
a tight pressure gradient, mixing to 850 hPa yields gusts close
to advisory criteria (46 mph) Saturday afternoon and evening,
especially in the coastal plain. Therefore, a wind advisory
may be needed in future forecast packages. There will be
considerable cloud cover on Saturday, especially north of
Delmarva. Given the strong PVA aloft and abundant low-level
moisture, expect scattered rain showers, especially over the
higher terrain (less downsloping).
Saturday night and Sunday...Northwest flow continues, albeit
lighter, with gusts 30 to 35 mph still possible into Sunday
afternoon. Otherwise, clear to partly cloudy and dry.
Sunday night thru Tuesday...A quick moving disturbance in the
northwest flow aloft will lead to an increase in cloudiness by
Sunday night. Cannot rule out a light shower over the higher
terrain, but the stronger dynamics and deeper moisture are not
in concert, in addition to the downsloping flow. During Tuesday,
another disturbance, very similar to the previous one, moves
just northeast of the region. Given the disjointed moisture
and dynamics, forecast was kept dry at this time.
Wednesday and Thursday...A storm system moving through the
Great Lakes sends a warm front toward the region Wednesday
with an increase in cloudiness. At this time, any appreciable
precip looks to hold off until Thursday.
.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Stratus and fog over the western Atlantic has spread into eastern NJ
with MVFR to IFR CIGs. Some of the clouds scattered out over SE PA
and SW NJ. Going into tonight, with a saturated airmass over the
area, expecting CIGs and VSBYs to lower to LIFR, with RDG/ABE and
possibly ACY having the potential to drop to VLIFR.
Conditions will gradually improve to VFR late Friday morning. Showers
and scattered thunderstorms approach in the afternoon.
Fri night...-SHRA likely with MVFR restrictions possible. Northwest
wind gusts to 25 knots possible late.
Sat through Sun...Predominantly VFR conditions anticipated.
Northwest wind gusts up to around 35 to 40 knots possible
Saturday, dropping of to around 25 to 30 knots Sunday.
Mon and Tuesday...Predominantly VFR conditions anticipated.
Sub-SCA conditions expected on the waters tonight through Friday.
There may be VSBY restrictions tonight over the waters due to fog
and low clouds. Those restrictions should lift Friday morning.
Fri night thru Sun...A Gale Watch remains in effect Fri night
thru Sunday morning, but may eventually need to be extended thru
Sunday. Strong gusts and rough seas are expected.
Sun night thru Tue...SCA conditions anticipated in a continued
Water levels remained a bit elevated along the coasts of New Jersey
and Delaware today and there was some isolated minor flooding around
the midday high tide.
The onshore flow is expected to weaken tonight and the flow should
veer toward the south on Friday. As we get further away in time
from the recent full moon astronomical tides will be a few tenths of
a foot lower on Friday than they were today. As a result, we are
not expecting any coastal flooding issues on Friday.
-- Changed Discussion --Preliminary update as of 4:45 PM...The following sites set new record
daily high temperatures today (Thursday, 10/20). The final climate
report will be issued at 5:30 PM.
New RecordOld Record
Philadelphia, PA 81 80 (1916/1938)
Georgetown, DE 84 83 (1953)
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MARINE...Gale Watch from Friday evening through late Saturday night for