Area Forecast Discussion
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FXUS61 KPHI 292331
Area Forecast Discussion
National Weather Service Mount Holly NJ
731 PM EDT SUN MAY 29 2016
Tropical moisture will continue to track northward across our area
tonight through Monday. A cold front will then cross the area
Tuesday followed by high pressure for the middle of the week. A cold
front, attached to low pressure moving across eastern Canada, will
slide across the Mid Atlantic region early next weekend.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
An upper air analysis showed a ridge axis over the area and it
extends into Southeastern Canada. An upper-level jet was positioned
from Southeastern Canada to the Lower Ohio Valley. Meanwhile at the
surface, a cold front was draped from the Great Lakes to the
Tennessee Valley. A plume of tropical moisture continues to surge
northward, which is tied to Tropical Depression Bonnie that is
located near coastal South Carolina.
The forecast challenge is the extent of showers and the intensity.
The ongoing showers lifting northward from the Delmarva,
southwestern New Jersey into southeastern Pennsylvania appear to be
tied to the leading edge of the deeper moisture surge. This moisture
surge initially was feeding off of a pocket of instability across
the Delmarva however this decreased northward due earlier to lower
surface dew points. The dew points are on the rise though from south
to north as this initial moisture surge arrives. The PW values are
forecast to rise to about 2 inches through the night and the
forecast soundings show deep moisture along with high freezing
levels. This would indicate that showers and especially stronger
embedded cells can be efficient rainfall producers due to warm rain
processes. This however may temper the thunder chance.
The model guidance overall shows our area becoming better positioned
into the right entrance region of a 250 MB jet overnight. This is
when better forcing should then arrive and a band of heavy showers
could nearly train across some areas. The idea of locally heavy rain
remains, although the guidance has been battling where this actually
occurs. Given the south to southeast inflow, near and west of I-95
may end up being the areas that get the heaviest rain through the
night before it starts to shift eastward. There remains some meager
instability in the forecast soundings therefore some thunder can
occur, however we did tone down the mention given the rather moist
The temperature and dew point grids were adjusted using the latest
obs, then the lamp/lav guidance was blended in. Significant
adjustments were needed earlier to capture the much lower dew points
across portions of the central to northern areas and increasing
values across the south. The pops were adjusted based on radar
trends and then with some assistance by the HRRR model.
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
With the slower timing, it now appears that there will be more
precip on Monday, than earlier fcst. Periods of rain now look to
continue for a good portion of the day, especially for srn and ern
areas. Nrn and wrn areas cud see precip end durg the aftn, with srn
and ern sections most likely holding onto rain thru at least sunset.
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
The remaining showers from the back edge of the system affecting the
area during the short term will be moving offshore Monday evening.
Pops will then decrease below slight chc by dawn Tuesday. Except for
some fog overnight...fair weather is expected. Low temperatures will
be in the low to mid 60s.
High pressure will build in from the north Tuesday and remain into
Wednesday night. Dry weather is expected much of the time with
above normal temperatures in most areas. Highs both days will be in
the low/mid 80s in most areas with some 70s for highs along the
shore and the higher elevations well to the north. A few scattered
showers may creep into the Delmarva areas later Wed as the edge of
moisture associated with what will be left of Tropical Depression
Bonnie will be moving south/east of the area. The pops across srn
Delaware at these times will only be 20-25 pct at most.
The tropical moisture and an advancing h5 trough will be setting up
across our area towards the end of next week. This will bring some
unsettled conditions with typical late spring/early summer
showers/tstms to the area. Pops will be mostly in the chc range for
now with details yet to be specific with regards to timing and
locations. Temperatures during this period will be close to normal.
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Tonight...VFR ceilings lowering to MVFR through 06z from south to
north, then lowering to IFR overall. This timing will especially be
determined on the extent of the showers and intensity. The
visibility will lower to MVFR and IFR at times especially during
heavier showers. Some thunder should occur through the night,
however the areal coverage looks low and therefore it was not
included in the TAFs. Southerly winds less than 10 knots, becoming
light and variable at some terminals.
Monday...MVFR/IFR conditions in the morning along with times of
heavy showers and some thunder, then the main area of showers shift
toward the coast in the afternoon. The lower conditions last the
longest at KACY to KMIV, with possible improvement in the afternoon
to VFR at KABE and KRDG. South to southwest winds mostly in the 5-10
Monday night...Showers end from w to E, VFR conditions return.
Patchy fog possible late however.
Tue-Wed night...Mostly VFR. Few showers psbl far South Wed.
Thu- Fri...Mostly vfr but lower conditions psbl in sct
Wind may gust in the 15 to 20 kt range overnight before decreasing
to around 10 kts Monday aftn. Seas are expected to increase and
could reach nr 5 ft on the srn waters. Due to confidence being
lower than average, wind below criteria and ww possibly being
overdone, will not issue sca attm.
There is some lcl dense fog in the nr shore waters. If the rain
does not improve the visibilities then a dense fog advisory for a
portion of the marine area may be needed.
Sub-sca conditions expected most of the period. Seas on the ocean may
reach close to 5 ft Thu night...but low confid in this attm. Sct
tstms with higher winds/seas possible Fri.
Locally heavy rain is expected through the night and Monday which
may result in localized flooding. This is due to an influx of
tropical moisture from Tropical Depression Bonnie, which increases
the PWATs to near 2 inches. Depending on where the heavier showers
and some t-storms set up, isolated locations may possibly see 3
inches of rain. While the threat of localized flooding is there, the
areal extent is more uncertain and therefore we held off on a flash
flood watch at this time.
Daily record rainfalls that have a chance of exceedance, if heavy
showers can persist for 1 to 2 hours. Note, splitting amounts
between two days lowers the chance of a single day record event
There is a good chance several long term climate sites will increase
to a top 10 ranking for the month of May in our CWA. PHL ACY AND ILG
only need an inch of rain these last 3 days of the month to rank
as a top 10 wettest month of May.
ACY 3.07 1984 por 1874
PHL 1.74 1908 por 1872
ILG 1.10 1983 por 1894
ABE 1.68 1968 por 1922
TTN 1.62 1912 por 1865
GED 2.04 1984 por 1948
RDG 2.92 1904 por 1869 (highly unlikely to approach a record
MPO 1.86 1990 POR 1901