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Area Forecast Discussion
National Weather Service Mount Holly NJ
1218 AM EDT FRI JUL 29 2016

.SYNOPSIS...
Low pressure in the Virginias will organize and move along a warm
front through the Delmarva early Friday then off the New Jersey
coast by midday Friday. Weak high pressure follows across New York
and New England Saturday. Low pressure develops near the Delmarva
Sunday and moves out to sea Monday. Drier and less humid weather
is expected for much of next week as high pressure builds over the
region.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
FF potential continues fairly high and the watch continues.
Greatest concern is se PA, S NJ, ne MD, central and northern DE,
where it rained hard this afternoon, and/or where 3 hrly ffg is
under 3".

Svr wx threat may expand northward to near ILG-ACY axis as low
pres in northern VA cuts enewd through s NJ. Tor parameter
remarkably large toward 09z on the sref in snj.

We can benefit from all damage reports, as well as unusual
flooding reports and any rainfall over 2 inches.

PWAT increase to 2.3" by 09z philly area. If it thunders at that
time, short term rainfall could easily be excessive for urban
areas.

Normally heaviest rainfall occurs near the path of the sfc low,
near the most unstable air which tends to pool near the wind shift
between south-northeast sfc wind convergence zone. Am expecting
modeled qpf to be too far north.

So, another round of heavy rain looks to move in late tonight as
a wave of low pressure tracks northeastward along the stalled
front. Heavy rainfall with this second round may be more
widespread. Also, backed flow in the low levels ahead of the low
may provide a source of low- level helicity. Given very low LCL
heights, a weak tornado or two may occur toward early morning near
the front as long as instability remains near surface based.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 AM SATURDAY/...
Precipitable water values of 2.2 to 2.4 inches will overspread
our forecast area from the south for tonight. Conditions are
expected to remain unstable, especially across our southern
counties. Also, surface low pressure approaching from the west
will result in the development of a favorable low level wind
profile for organized convection tonight. The surface wind should
begin to favor the east to south quadrant late tonight, especially
on the coastal plain, while winds around 800 HPa will be from the
southwest.

The very high precipitable water values should result in heavy
rainfall in any organized convection. As a result, the Flash Flood
Watch remains in effect for southeastern Pennsylvania, central and
southern New Jersey, Delaware and northeastern Maryland.

The cloud cover and high humidity will keep temperatures from
falling below the 70s for tonight except in the Poconos and far
northern New Jersey.

&&

.LONG TERM /SATURDAY THROUGH FRIDAY/...
Highlights...

* Scattered showers/t-storms w/locally heavy rainfall this weekend
* Drier/less humid weather for much of the next work week

Details...

Friday night...

Dry weather expected Friday night with subsidence behind
departing shortwave. May see some patchy fog develop overnight
with wet ground and lingering low level moisture.

Saturday and Sunday...

A couple of additional shortwaves will move across our region
this weekend along with a frontal boundary in the vicinity. Timing
is uncertain this far out, but more scattered showers and
thunderstorms are expected at times this weekend. Pwats will still
be between 1.5 and 2 inches, so the threat will exist for locally
heavy rainfall. Clouds and the threat of precipitation should hold
high temps mainly in the 80s both days.

Monday through Thursday...

High pressure will build over the region, bringing us drier and
less humid weather. There still will at least be a low risk for a
few showers early in the work week, but either way dry weather
should dominate through Thursday. High temps will mainly be in the
80s.

&&

.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...vfr showers with probably periods of ifr conds and
gusty winds to 25 kt in sct tstms, otherwise sustained winds
under 10 kt will tend to become northeast toward morning.
Confidence is low for the timing of heaviest oncoming convection
at any particular TAF site, but high that storms will be in the
region through early Friday morning.

Friday...showers and thunderstorms end from west southwest to
east northeast. mvfr or ifr conds 12z-15z in showers/sct tstms
then improving to vfr cigs in the afternoon with a northeast
backing to north wind gust 20 kt.

Outlook... 
Sat through Sun...Shra/tsra will lower cigs/vsbys at times
Otherwise VFR expected. Moderate Confidence.

Mon...Mainly VFR. Moderate Confidence.

&&

.MARINE...
The svr tstm risk will probably increase early friday morning
along the De and S NJ coasts as low pressure crosses the area.

Winds turn northeast to north behind the low Friday morning then
more north to northwest late Friday afternoon.

Expect seas to respond by building to 2 ft in the morning and
possibly 3 to 4 ft during the afternoon in our coastal waters.

Outlook...Friday night through Tuesday...
There is a low risk for marginal small craft seas Friday night
but for now kept them just below 5 feet. Otherwise, winds/seas
should generally remain below small craft advisory thresholds
through the period. Biggest concern for mariners will be the risk
for thunderstorms this weekend. Drier weather should arrive early
next week.

RIP CURRENTS...We have forecast low risk Friday but if the wind
turns onshore with gusts 15-20 kt, we may need to increase the
risk to mdt for a portion of the NJ coast.

Outlooking: Still generally low risk for awhile, possibly low
enhanced. we do note some longer period swells anticipated by the
GFS around the 3rd/4th which may increase the rc risk. Also the
tropics have been quiet this July, but there are a couple of
disturbances in the eastern Atlantic that are being monitored.

&&

.CLIMATE...
GED: a record daily rainfall has occurred so far today.

PHL: heading for top 10 warmest July on record. July avg temp for
PHL will be about 80.9F, 8th warmest July in the period of record
since 1874.

ACY: already as of 850 pm this evening...is 7th wettest July on
record with its monthly record of 13.09 set in 1959. The por is
back to 1874. total for the month as of 850 PM: 8.34" with 1.17
today, so far.

daily record rainfall

      today    friday the 29th
acy 2.05 2012  2.21 - 1884

phl 8.02 2013  3.53 - 1980

ilg 2.34 1914  1.85 - 1913 

abe 3.00 1916  1.64 - 1979

ttn 2.35 2012  2.84 - 1961

ged 1.98 1994  1.07 - 1969

rdg 3.57 1969  2.51 - 1961

mpo 2.15 1969  4.59 - 1969

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flash Flood Watch until noon EDT today for PAZ054-055-060>062-
     070-071-101>106.
NJ...Flash Flood Watch until noon EDT today for NJZ001-007>010-
     012>027.
DE...Flash Flood Watch until noon EDT today for DEZ001>004.
MD...Flash Flood Watch until noon EDT today for MDZ008-012-015-019-
     020.
MARINE...None.

&&

$$

Synopsis...Drag/99
Near Term...Drag/Iovino/Klein
Short Term...Klein
Long Term...99
Aviation...Drag/99
Marine...Drag/99
Climate...

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