Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 240757
Area Forecast Discussion
National Weather Service Mount Holly NJ
357 AM EDT FRI JUN 24 2016
A stalled front will remain near the Delmarva today before pushing
southward tonight. High pressure will build into the region for
this weekend. As the high moves offshore Monday, a slow moving
cold front will approach from the northwest Tuesday, and move
through the region Wednesday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A cold front was located over the area (somewhere near the I-95
corridor) early this morning. The front was marked by surface winds
from the north or northeast and temps/dewpoints in the upper 50s to
lower 60s north of the boundary while southerly winds and
temps/dewpoints in the upper 60s to lower 70s resided to the south.
There were isolated showers present for much of the night near the
frontal boundary in southern NJ and the northern Delmarva. These
showers have been very light thus far. Interestingly, the HRRR has
been remarkably persistent/consistent over the past five or so runs
(ending with the 05Z run) that showers and thunderstorms form over
the Delmarva early this morning, resulting in a localized area of
heavy rainfall of 2+ inches (the 03Z HRRR showed a band of 5-8 of
rainfall in 4 hours but successive runs have since backed off from
these extreme amounts). Though it`s an extremely unlikely scenario
that is not supported by other model guidance, LAPS/SPC mesoanalysis
shows about 500-750 J/kg of MUCAPE and a local PWAT maximum near 1.7
inches over the northern Delmarva, which would be enough to support
low-topped heavy rain producers in this environment. PoPs early this
morning were raised to about 40 percent across these southern zones.
The front will eventually push south of the area later this morning
and afternoon as high pressure build in from the Great Lakes. With
breaks in the clouds today, temperatures could peak in the mid 80s
along and west of I-95. An easterly wind off the ocean will keep
temperatures cooler (70s) in the coastal plain today. We could see a
fair amount of stratocu develop in this maritime airmass during the
While most of the CWA should remain dry today, there are two areas
for potential shower development this afternoon. First, the
juxtaposition of lower-tropospheric convergence at the nose of weak
easterly jet to the north of a H9-H8 trough and upper-tropospheric
divergence in the right entrance region of a jet streak implies
forcing for ascent that is needed to maintain any convection across
the Delmarva today. Model forecast soundings support adding in a
slight chance for thunderstorms during peak heating. There is lesser
confidence for the development of upslope showers in our far western
zones in eastern PA but a mid-level shortwave trough could
potentially provide a brief period of deeper lift as it approaches
from the west this afternoon.
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
The center of the surface high retreats off the New England coast
tonight. However, the high will still control our weather pattern
with the ridge axis expected to extend southwestward from the high
in to the northern mid-Atlantic region. Surface winds will back from
easterly at the start of the period to northeasterly by early
morning as low pressure moves offshore.
There is a potential for marine stratus to advect inland tonight
owing to the onshore flow. These low clouds in addition to higher
convective debris clouds are anticipated to curb radiational
cooling, especially the closer you are to the coast. Forecast lows
are in the mid to upper 50s in northeast PA/ northwest NJ and low to
mid 60s elsewhere.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
The weekend will be dry with high pres over the region. The high
will slowly move ewd and offshore by Mon. As the high departs, low
pres in Ontario will move ewd. Its attendant cdfnt will approach
from the w, and cross the area on Tue. The GFS then keeps things
dry Wed into Thu. However, the ECMWF (with some support from the
CMC) wants to bring a second front through on WEd and another
shot of precip, before drying things out later Wed into Thu. For
right now, will carry low pops Tue wino erly Wed and no pops
Temps look to be nr nrml with comfortable humidity values thru the
.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Brief/local MVFR restrictions is possible early this morning at ILG,
MIV or ACY if a shower moves over the terminal. Coverage of showers
are too low to include in 06Z TAFs but will issue amendments if
necessary. Additionally, brief visibility restrictions are possible
farther north if patchy fog develops toward sunrise. Otherwise,
expect mainly VFR today. Winds are currently light and variable, but
will become northeasterly around 5-10 kt after sunrise. Winds veer
to easterly this afternoon with speeds of 10-15 kt.
There is a potential for low clouds to develop offshore and move
inland late this evening and overnight. This may yield MVFR or IFR
restrictions. Forecast confidence decreases farther away from the
coast. Therefore, limited IFR restrictions in the forecast to MIV
Sat and Sun...Predominantly VFR. Patchy ground fog may lead to
sub-VFR conditions late Saturday night and early Sunday morning,
mainly at ABE, MIV, and RDG. Moderate Confidence.
Mon and Mon night...VFR. High Confidence.
Tue...A cdfnt will move slowly acrs the region and be accompanied
by shra/tsra. VFR will prevail, then MVFR/IFR psbl with fropa.
Still some timing diffs with cfp. Moderate confidence.
Light onshore flow will develop this morning and increase to 10-15
kt with gusts to 20 kt this afternoon and tonight. Seas will
accordingly build to around 4 ft in our coastal Atlantic waters by
tonight. There is a potential for wave heights to approach 5 ft by
late tonight but confidence in this happening was too low to issue a
SCA at this time.
Sat...Latest guid indicates that we cud have sca conds with a e to
ne flow which cud linger into Sat night.
Sun thru Tue...No marine headlines anticipated.