Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 210152
Area Forecast Discussion
National Weather Service Mount Holly NJ
952 PM EDT Thu Oct 20 2016
A warm front Will move north across our area through 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/...
The warm front appeared to extend across southeastern
Pennsylvania and southern New Jersey this evening with mainly east
winds to its north and southeast winds to its south. Also, stratus
has become established to the north of the boundary.
We are fairly confident that the low clouds will hold through the
night across much of northern and central New Jersey and into the
Poconos, the Lehigh Valley, upper Bucks County and Berks County.
Our thinking is that the inflow of low level moisture on the
southeasterly flow will cause the low clouds to expand southward.
However, our confidence in the amount of low clouds over the
Philadelphia metropolitan area, southern New Jersey and the upper
Delmarva is not particularly high. Where low clouds exist there
is the potential for areas of drizzle and fog, as well.
The moderate to heavy showers over parts of western and central
Pennsylvania into western New York this evening should remain to
our west and northwest. However, scattered showers did begin to
develop over our northwestern counties this evening and that may
continue to be the case overnight in the upslope flow.
Temperatures should drop only into the upper 50s and lower 60s
which is near the normal maximum readings for this time of the
.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
.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
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 /02Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
IFR conditions are expected through the night and into Friday
morning at KABE and KTTN. MVFR ceilings are forecast to lower to
IFR at KRDG. We expect the low clouds to expand southward during
the night and they should impact KPNE, KPHL and KILG. While we are
anticipating that low clouds may reach KMIV and KACY, our overall
forecast confidence for those two locations is rather low.
The low clouds and fog should be slow to lift and dissipate on
Friday morning due to the lowering autumn sun angle. We expect
conditions to improve into the VFR category for the afternoon even
with the increasing potential for showers.
The wind direction will favor the southeast overnight and on
Friday morning, and the southwest on Friday afternoon. Speeds
should be mostly in the 6 to 12 knot range.
A strong cold front is forecast to arrive late in the day
bringing a shift to a northwesterly wind.
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
The following sites set new record daily high temperatures today
New RecordOld Record
Philadelphia, PA 81 80 (1916/1938)
Georgetown, DE 84 83 (1953)
MARINE...Gale Watch from Friday evening through late Saturday night for