Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Mount Holly New Jersey
1208 PM EDT Friday may 29 2015

Synopsis...
high pressure builds off the North Atlantic coast today into
Saturday. A cold front is forecast to move slowly southeast across
the area late Saturday night through Sunday, then stall across our
southern areas or just south of the area Monday into Tuesday. High
pressure will build to our north early next week, before trying to
nose its way into our area Wednesday into Thursday.

&&

Near term /until 6 PM this evening/...
930 am estf: a very nice day in progress most of the forecast
area with remaining humidity, clouds, ml cape and potential for
heavy showers isolated thunderstorms confined mainly to the Delaware-Maryland-Virginia.
Dewpoints about 15f lower in portions of eastern PA and New Jersey
compared to this time ydy.

As of 9 am this morning, the 12z hrrr forecast redevelopment of heavy
convection between 17z and 19z focused on Queen Annes, Caroline
and Talbot counties in Maryland possibly with its rainfall canopy leaking
north and eastward into Kent counties of Maryland and Delaware as well as
western Sussex County Delaware. The 12z NAM suggests similar but is
developing middle afternoon. Confidence: below average for this
redevelopment but have boosted probability of precipitation to around 40 percent there and
lowered probability of precipitation in east PA, S NJ, coastal Delaware where its very difficult
to see any rain late today.

Did raise temperatures 1-2 degrees from the current forecast away from the
coast.

Otrw, little change to the previous forecast.

Fwiw, the 12z/28 NAM was terrible in its relative humidity tsection depiction
for this past night.

&&

Short term /6 PM this evening through 6 am Saturday/...
the next cold front continues progress east over the Great Lakes
region, but still looks to stay far enough west of our region to
have limited impact tonight. With the persistent southeasterly low
level flow, could see fog along the coastal waters. However, this
will be dependent on how much moist air advection will occur in the
later half of the day, as dew points will likely start the day in
the 50s.

&&

Long term /Saturday through Thursday/...
the surface high and ridge aloft will get pushed eastward
Saturday ahead of an approaching cold front, with southwest flow
both at the surface and aloft developing. This will allow for a
couple of short wave/vorticity impulses to move across the area
late Saturday while daytime instability develops as well. An
increase in shower/thunderstorm activity is possible, especially
for the western portions of the area.

The cold front is forecast to move into the area Saturday night
and slowly move across the area into Sunday. The GFS and European model (ecmwf)
have pretty good agreement with the timing of the precipitation.
Both agree that Sunday looks to be the period with highest
probability for precipitation as the front moves across and south
of the area. Precipitable water values increase to near 2 inches, so there could
be a period of heavy rainfall with any showers that develop during
the time period. There remains instability forecast ahead of the
front, so we will keep thunderstorms in the forecast, but once the
front passes, thunderstorm potential decreases.

High pressure returns to our northeast early next week as the
frontal boundary pushes south and likely stalls just south of our
area. With the high to our northeast, this will keep easterly flow
across the area. Southwest-westerly flow aloft will remain across
the area as well. Several short wave/vorticity impulses will
likely move across the area early next week, which could help
create precipitation across the area. It is looking like we could
have a period with good soaking rains, just hopefully it does not
come too quickly. With the easterly flow across the area, the
atmosphere should be stable, so we keep thunderstorms out of the
forecast Monday and Tuesday due to lack of instability.

The high pressure across the northeast should build south across
the area Wednesday into Thursday, starting another dry period.

&&

Aviation /16z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and

Today...VFR with scattered clouds at or above 5000 feet. Light NE-east wind becoming
southeast to S this afternoon.

Tonight...VFR to start. Light south wind. There is a small possibility
of fog and low stratus developing after 03z tonight across much of
the region as depicted in time height displays of both the GFS and
NAM. However, models appear to be underestimating the amount of
dry air advection currently, so despite easterly/southeasterly
winds for much of the period, conditions below VFR seem unlikely
for kphl, kabe, krdg, kttn, and kpne. At kilg, kmiv, and kacy
where the marine layer is more likely to advect in, low stratus
(around 2000 to 3000 feet agl) is possible.



Outlook...

Saturday...lower conditions possible early, then becoming VFR
during the day. Scattered showers and thunderstorms possible which
may locally reduce cigs/vsbys. Gusty south-southwest winds around
20 knots.

Saturday night-Tuesday...an extended period of MVFR/IFR
conditions possible. A chance of rain each day. Best potential for
thunderstorms is Sunday as a cold front moves through the area.
Wind become northeast behind the front and continue through
Tuesday. Winds could gust to 20 knots at times Sunday night
through Tuesday.

&&

Marine...
winds and seas will remain below small craft criteria today and
tonight.

Outlook...

Saturday-Tuesday...seas may return to 5 feet or greater late on
Saturday ahead ahead of an approaching cold front. Seas may remain
elevated into Tuesday, and winds may increase to 25 knots Monday
into Tuesday.

&&

Rip currents...
new weblink, works best on firefox. Displays the forecast graphic et cetera.

Www.Weather.Gov/phi/surfrip4

Upgraded the rip current risk along the central New Jersey coast per
observed concern and some data indicating potential for moderate.

Otherwise, low risk continues this afternoon Delaware coast and the
far northern and far southern New Jersey coasts where onshore winds are
lighter though a little concerned about a 1 foot 12 second east-southeast
swell showing up that could elevate the risk slightly there too.

Chilly to swim most of central and nnj beaches despite above normal
temperatures on the land with water temperatures there looking to be in the upper
40s to lower 50s. Further S near lbi...water temperatures maybe 55 to 60,
snj S of kacy 60-65 and then along the Delaware Atlantic coast upper 50s to
middle 60s depending on location.

The outlook for Saturday is low enhanced...with a stronger southerly
wind gusting to 20 miles per hour during the afternoon. Might be a close call
for a moderate risk depending on the swell size. For now keeping
it low risk but not locked into low.

&&

Climate...
may 2015...a top 5 warmest on record for large portions of our area.

All overnight and forecast information checked through 830 am
today - Friday may 29.

Conservative values listed below from our 5 am sft and cooling the
near midnight Sunday night may 31 low temperature due to northerly flow cold air advection Sunday
evening.

Allentown will probably average very close to 65.9 or 6 degrees
above normal. Por back to 1922. At least 5th warmest on record.
1991 67.2
2012 66.1
1944 66.0
2004 65.9



Philadelphia will probably average close to 69.7 degrees or 5.8
degrees above normal. Second warmest on record.

1991 70.8

Number 3 would be 69.2 in 2004.



Atlantic City may 2015 65.9 or 66.0 or 4.8 to 4.9 above normal
and probable #2 or #3 por back to 1874

2004 66.9
1991 66.0
2015



Wilmington Delaware solid por back to 1916 locked into #4 warmest
1896 70.1
1991 69.1
2004 68.2
2015 around 68.0

No available monthly historical data for kmpo kged kttn and krdg.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...none.

&&

$$
Synopsis...Robertson
near term...drag/Johnson
short term...Johnson
long term...Robertson
aviation...drag/Johnson/Robertson
marine...drag/Johnson/Robertson
rip currents...1207p
climate...

National Weather Service Glossary of Abbreviations