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Area Forecast Discussion (AFD)

Issued by Philadelphia/Mt Holly (PHI)

FXUS61 KPHI 160117

Area Forecast Discussion
National Weather Service Mount Holly NJ
917 PM EDT Sun Sep 15 2019

A cold front will stall south of our area through today while
high pressure weakens to our west. A weak area of low pressure
slides near our region on Monday. High pressure builds across 
the Northeast Tuesday into Wednesday, then shifts southward 
across the Mid-Atlantic region Thursday. The high is forecast to
shift to our south Friday, then offshore next weekend.


Latest Northeast radar showing some streamers moving in from the
north and west. Not much precip associated with it, but will go
ahead and mention some scattered sprinkles, mainly across
northern and western zones, for a few hours through this

Otherwise, some higher level clouds will arrive through the 
night from the west within the gradually sharpening upper-level 
flow. There are some hints in the guidance, mainly the NAM, 
that some low clouds may try to develop offshore and move into 
the coast overnight. This is of low confidence. Low temperatures
are mostly a blend of the statistical guidance and continuity.


An upper-level trough remains in place across eastern Canada 
and the Northeast Monday. This will favor northwesterly flow 
aloft and embedded within this flow is a weak disturbance with a
weak surface low reflection. This may be the remnant energy 
associated with an MCS yesterday in the Midwest (ongoing cloud 
debris moving into the Ohio Valley). Some increase in the clouds
are expected, with this the most prevalent across the northern 
portions of the area. 

The majority of the guidance shows some shower potential with 
the rather weak surface low as it tracks east-southeast from the
upper Ohio Valley to start the day to near Delmarva by late 
afternoon. This weak system should track along the weak stalled 
surface front in the vicinity. The combination of all of these 
weak systems along with our northern areas being near the right 
entrance region of a mid level jet by late afternoon, should 
result in some shower activity. The main focus for this is 
across the west and northern areas where slight chance to low 
chance PoPs are maintained for the afternoon. The 12z NAM shows 
a rapid development in convection from the Baltimore area to 
southeastern Pennsylvania after 21z, however this looks 

As for the high temperatures, opted for a model blend given some 
additional variability. Highs in the mid to upper 80's south of the 
lingering weak front. A sea breeze is expected once again.


Synoptic Overview:

An extended period of quiet weather looks likely over our area 
for the long term. At the mid-lvls a fairly amplified ridge will
reside upstream of the area for essentially the entire long-
term period (although at times oscillating in orientation and 
mean-position). At the surface the upstream ridge positioning 
will promote anticyclogenesis with the initial surface high 
centered north of the area. By the end of the workweek the high
will re-orient itself south of the area shifting the low-lvl 
flow from onshore to offshore with a corresponding increase in 
temperatures expected. 


Monday night through Tuesday: The only chance of any
precipitation through the extended will be in the overnight 
period Monday into Tuesday morning as a shortwave lifts 
northeast of the area and an associated weak front moves through
the area. Given the clipping nature of the upper level system 
capped PoPs at slight-chance with nothing significant expected.
The boundary will be largely south of the area by Tuesday 
afternoon with highs generally in the 70s areawide.

Wednesday/Thursday: Should be dry and mild with onshore flow 
prevailing. Highs will generally be near climo (low to mid 70s)
with lows in the low to mid 50s. Mostly sunny outside of some 
occasional stratus (most prevalent near the coast).

Friday/Saturday: The high will relocate south of the area
towards the late week-early weekend with the flow shifting more
westerly as a result. This will usher in a warming trend into 
the weekend with maxes increasing into the upper 70s/lower 80s 
on Friday, and then increasing further into the mid 80s on 
Saturday. Precipitation chances remain essentially nil. A 
mostly quiet long term period is expected, with only a small 
chance of precipitation at the beginning of the period..


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, 
KILG, KMIV, KACY and surrounding areas.

Tonight...VFR overall. There is some potential that low clouds 
develop overnight near the coast and reach ACY, however this is 
of low confidence. Light and variable to locally calm winds.

Monday...Some low clouds possible near the coast early, 
otherwise VFR with any ceilings mainly above 8000 feet. Some 
showers possible in the afternoon mainly near and north/west of 
ABE and RDG. Light and variable winds becoming west-northwest 
4-8 knots in the morning, then turning southwesterly before 
becoming northwest toward early evening.


Monday night...Generally VFR although some sub-VFR conditions
possible in showers/lower clouds. Winds north-northeast 5-10kts. 

Tuesday-Wednesday night...Mostly VFR during the day, with a 
chance of MVFR conditions overnight in stratus. East to 
northeast winds 5-10 knots 

Thursday-Thursday night...Generally VFR conditions expected with
east-southeast winds 5-10 kts.


Conditions will remain below Small Craft Advisory criteria 
through Monday. A stalled weak front in the vicinity will result
in light enough flow for sea/bay breeze influences and 
therefore wind shifts to more southerly. 


Monday night through Tuesday morning...Conditions are expected 
to remain below advisory levels with seas around 3-4 ft. and NE
winds increasing to around 15 kts by Tuesday morning.

Tuesday-Thursday...SCA conditions potentially developing as 
early as Tuesday but likely by Wednesday. Seas will increase to 
5-7 ft by late Wednesday with northeasterly wind gusts likely 
increasing to 25 kts or so as well.S


There is a low risk for the development of dangerous rip 
currents at New Jersey and Delaware beaches on Monday due to 
light southerly flow and waves of 2-3 feet in the surf zone.




Near Term...Gorse/MPS
Short Term...Gorse
Long Term...Carr