Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 272047
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
447 PM EDT MON JUN 27 2016

.SYNOPSIS...
A cold front from the eastern Great Lakes through the Ohio Valley
will cross eastern sections of Pennsylvania and Maryland Tuesday
afternoon where low pressure will form.  The front and area of low
pressure will drift east, off the mid Atlantic coast Wednesday
morning. Weak high pressure follows Thursday. Another cold front
will move through the region Friday night or Saturday and then stall
to our south later in the weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Showers are moving across eastern Pennsylvania late this afternoon
and will progress eastward through this evening. These showers are
associated with a weak surface trough and short wave/vorticity
impulse aloft. There is not much instability, so lightning activity
has been minimal, and should continue into this evening. We will
still keep a slight chance of thunderstorms in the forecast however.

The weak trough will stall our near the area overnight, and another
stronger short wave/vorticity impulse is expected to approach the
area toward daybreak Tuesday. This may help enhance increase showers
potential across the southern areas overnight into daybreak. PW
values increase overnight, so if showers or thunderstorms do
develop, they could produce some moderate to heavy rainfall.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
Showers could be ongoing at the start of the day Tuesday across the
eastern portions of the area as the initial short wave/vorticity
impulse moves across the area. By the late morning into early
afternoon, the first round of showers may begin to move out and we
could get a brief break in shower/thunderstorm activity. However,
showers and thunderstorms are expected to develop to our west during
the day as the cold front approaches from the west. There is a
moderate amount of instability and shear to our west, so
thunderstorms could become strong during the day. The instability
weakens some as does the shear moving into our area, so the greatest
threat for severe weather may be north and west of our area.
However, there will still be the possibility for gusty winds and
small hail across our northern areas, so we`ve included this in the
forecast. PW values drop some during the day, but should still be
near 1.5 inches, so there could still be the possibility for some
moderate to heavy rainfall with some showers/thunderstorms.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
500 MB: A -1SD short wave nearing Buffalo NY Tuesday Night weakens
eastward Wednesday. A developing -2SD short wave trough moves
across Lake Huron Friday night.

Temperatures: The month of June through the first 26 days has
averaged 1 to 2 degrees above normal at PHL, RDG, ABE, TTN, within
.5 of normal at GED ACY and ILG and surprisingly -1F at MPO.
the final monthly departures should be within 3 tenths of degrees
of those listed above.

Calendar day averages over this coming long term period of Wednesday-
Sunday should average near normal, some days a bit above, others a
bit below.

Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/27
GFS/NAM MOS guidance Tuesday night - Wednesday night, thereafter the
12z/27 GFS MEX MOS for Thursday and WPC Guidance Thursday night-next
Monday. Max temperature guidance was on some days modified warmer
by the previous 330 am PHI forecast as well as the warmer 12z/27
ECMWF 18z 2m forecast temperatures. Nighttime lows were lowered
below guidance Wednesday morning and Friday morning across e PA
and nw NJ, where the radiating countryside should get down close
to the 12z/27GFS forecast 09z 2m temps.

Rainfall: not a bright outlook for alot of needed rainfall...it certainly
doesn`t look as if above normal rainfall can transpire in this
pattern. To me it looks like too strong a cyclonic flow at mid
levels.

The dailies...

Tuesday night...Any showers and scattered thunderstorms during the
evening, will tend to die out late at night. At most a marginal risk
of svr with 1000J of MLCape to start Delmarva area and 0-6KM bulk
shear increasing late evening but appears to arrive too late for
much impact in our CWA. Seems more like an SPS/MWS evening...marginal.
PWAT decreasing from 1.5". Confidence: average.

Wednesday...Tending to dry out and looking like a very nice
summers afternoon after morning skycover clears. PWAT around 1
inch. Cooling afternoon sea breeze possible along the immediate
coast. Seasonable temps. Confidence: above average.

Thursday...Dry and nice with cooling coastal seabreezes. Small
chance of a shower or thunderstorm along the coasts Thursday night
in response to the western edge of an instability burst developing
northeastward near the mid Atlantic coast. PWAT overall near 0.85
inches. Seasonable temps. Confidence: above average.

Friday...much less confidence on the days outcome both temps and
rainfall. Chance of a shower. Very warm...a bit above normal in
some areas of the interior. Confidence: below average

Saturday...Hot. Could be strong thunderstorms on the Delmarva late
day or Saturday night where pretty good instability and significant
0-6km bulk shear (40 kt) are modeled though MLCAPE is so far, is
modeled relatively low. Temps could reach the lower 90s in the
I-95 corridor. Confidence: average.

Sunday...Could have a lingering shower or thunderstorm threat in
association with the se Canada trough. Confidence: below average.

Monday (July 4)...For now it looks like a good day for outdoor
activity. Warm. Confidence: average or above average.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR conditions continue across the area late this afternoon/early
this evening across the TAF sites. An area of showers is moving into
our western areas, and will continue eastward through this evening.
It is possible that some showers may be heavy enough to lower
visibilities to 5-6 miles, so we will continue our TEMPO group with
the potential. This line of showers will move eastward and dissipate
through the evening, then we could be mostly dry for a good portion
of the overnight. More shower activity could develop and move into
the area around daybreak from the south and spread northward through
the morning. Additional showers and possible thunderstorms are
expected late in the day Tuesday as a cold front approaches from the
west.

Ceilings and visibilities are expected to begin to lower to MVFR
then IFR late this evening and overnight as moisture gets trapped
underneath a low level inversion. This will likely continue through
the day tomorrow ahead of the approaching cold front, although the
IFR may lift to MVFR during the day.

South-southwest winds continue for most inland areas, while closer
to the coast winds are more south-southeast. Sustained winds are
around 10 knots, with some gusts 15-20 knots. The winds will lighten
some after sunset, and become south-southeast everywhere 5-10 knots.

OUTLOOK...

Confidence for the periods discussed below is average or above
average,

Tuesday night...scattered leftover showers and isolated thunderstorms
should diminish and end. Patchy IFR stratus/fog should develop late.
Light winds.

Wednesday...becoming VFR after any early morning IFR stratus/fog
rapidly clears. Light west wind except possible afternoon sea
breezes coasts.

Thursday...VFR. Light west wind with coastal afternoon sea breezes.
Patchy IFR stratus/fog may develop late.

Friday...VFR. Chance for a shower. (least confidence of all the
days listed in this long term section)

Saturday...VFR. Chance of late day-or night time thunderstorms
Delmarva. Right now the northern fringe is in our area and some of
those storms could be strong.

&&

.MARINE...
Winds on the waters will continue to gust in the low 20s for this
afternoon into the early evening. A few gusts around 25 knots may
occur across the far northern waters off the coast of Monmouth, but
we believe they will be infrequent and brief enough to preclude the
need for a Small Craft Advisory. Winds will diminish some overnight,
but should increase in gusts again Tuesday. Wind direction will
continue to be from the south to southeast tonight into Tuesday.

A few isolated thunderstorms are also possible tonight into Tuesday.

There is a moderate risk of rip currents today, and this may
continue into Tuesday.

OUTLOOK...
Tuesday night through Saturday... Winds and seas expected to remain
below SCA criteria. A chance for showers and scattered thunderstorms
with a slow-moving cold front Tuesday night and then again
Saturday. Small chance of a shower Thursday night or Friday.

RIP CURRENTS...low to possibly moderate at times this week, in part
dependent on the amount of onshore wind. In other words, not much
change from the somewhat active month of June. AWARENESS: weak swimmers
for their own safety should swim only in the presence of lifeguards.
It is not worth being a rip current victim by swimming near
jetties, or after the lifeguards go home, or with untrained weak
swimming bystanders who wont be capable of saving a distressed
swimmer, except to call 911, which then could be too late.

&&

.CLIMATE...
Presuming less than one half of rain falls between now and the end
of June,  Allentown could end up top 10 driest June on record with
the period of record back to 1922. Currently, as of 440 PM (0.08
since 4P), Allentown`s 1.45" ranks #8 driest.

Elsewhere, with no additional rainfall, Atlantic City (1.32")
would rank 15th driest and Philadelphia (1.24") 14th driest.

For the month so far, deficits were generally 1.5 to 2.5 inches except
nil at KILG and near 1.5" KGED and KACY. That is generally 25 to
50 percent of normal (except near normal parts of DE).

Until we get any tropical rains, or the trough sharpens in the Ohio
Valley, the northeast states trough pattern is unfavorable for
persistent high humidity and associated widespread substantial
thunderstorm generated rainfall. Operational and ensembles so far
for at least the next 7 days, tend to keep paths of heavier rains
to the south and north of our forecast area. In other words no
significant change in we`ve been seeing the past month.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Drag
Near Term...Robertson
Short Term...Robertson
Long Term...Drag 447P
Aviation...Drag/Robertson 447P
Marine...Drag/Robertson
Climate...447P


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