Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
353 PM EDT Tuesday Jul 22 2014
high pressure will continue to move eastward tonight allowing for a
better return flow tomorrow ahead of a potent cold front. The front
should move through later on Wednesday into Thursday morning. High
pressure will fill in behind the departing front through the first
half of the weekend before a complex system approaches Sunday
spilling into the new work week.
Near term /until 6 am Wednesday morning/...
conditions remained fairly stable over the coastal plain this
afternoon even with the development of some cumulus. It was
marginally unstable over eastern Pennsylvania and northern New
Jersey. There were isolated light rain showers in Lancaster County
and vicinity at middle afternoon. We will mention the possibility of
isolated showers from Berks County and Chester County up into
northern New Jersey until about 6 or 7 o'clock.
The cumulus will likely be on the decrease this evening with the
loss of daytime heating. However, the southerly surface flow will
continue to draw low level moisture into our region. As a result,
there may be patchy low clouds, fog and haze toward morning.
Minimum temperatures should range from the middle 60s to the lower
Short term /6 am Wednesday morning through 6 PM Wednesday/...
the guidance has been fairly consistent during the past several days
regarding the forecast for Wednesday. Temperatures at the 850 hpa
level are forecast to rise around 18c or 19c, so maximum
temperatures mainly in the lower 90s continue to seem reasonable.
Dew point readings should be right around 70 resulting in maximum
heat index values in the middle and upper 90s. The wind is
anticipated to favor the south on the coastal plain and the
southwest inland at speeds around 10 miles per hour.
Instability will be on the increase through the morning and early
afternoon with mixed layer cape values expected to rise around 2500
j/kg in areas along and to the northwest of the Interstate 95
corridor. A bit of a middle level cap may prevent much activity from
developing during the early to middle afternoon. However, a line of
thunderstorms should develop ahead of a cold front approaching from
the northwest. The convection will likely move into our northwestern
counties by late afternoon and it should reach the Interstate 95
corridor during the early evening. The Storm Prediction Center
continues to suggest that the greatest threat of severe weather
ahead of the front will be up in New England. However, a few strong
storms and isolated severe weather remain possible in our area.
Long term /Wednesday night through Tuesday/...
cold front should be at our doorstep at the start of the longterm
period though as the case during the Summer, it will not a quick passage.
Upper level support with the right entrance region of the jet
overhead and deeper troughing nudging in from the west combined with
precipitable waters nearing 2 inches, again, could produce heavy rain with any of
the storms. Shear values will be rather robust, around 25
knots...better the further north you go, so organized convection
seems plausible and the storms will be moving. With the deepening
trough expected overhead on Thursday, the front should be slow to
clear the region so we keep chance to likely probability of precipitation in across the
southern zones through most of the afternoon...could be long in The
The base of the trough begins to flatten out by Friday, though not
entirely becoming zonal. This yields slightly below normal
temperatures and decreased chances for convection given a drier
airmass in place. Still a bit uncertain about the Saturday evening
timeframe as some of the operational guidance swings a piece energy
through the base of the trough which could touch off a couple
stray/isolated showers...better east than west with better moisture
pooling and seabreeze interaction.
Ridging builds into the west sending stronger shortwaves of energy
into the trough overhead allowing for another bout of deeper
troughing. Expect unsettled weather through the remainder of the
longterm as a series of embedded waves pushes through aloft touching
off showers and thunderstorms.
Aviation /19z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Scattered to broken clouds with bases generally in the 4000 to 5000
foot range are anticipated for the balance of the afternoon.
Isolated rain showers are possible around krdg and kabe. The cloud
cover is forecast to decrease during the evening hours with the loss
of daytime heating.
VFR conditions are anticipated for early tonight. Increasing low
level moisture in the southerly flow may result in the development
of some low clouds, haze and fog for late tonight into early
VFR conditions are expected from middle morning on Wednesday into the
middle afternoon hours. However, thunderstorms out ahead of a cold
front approaching from the northwest should impact our region during
the late afternoon and evening hours.
A southerly wind around 5 to 10 knots today should diminish to 6
knots or less for tonight. A southwest to south wind around 10 knots
is anticipated for Wednesday.
Wednesday night and Thursday...MVFR and IFR conditions at times in
showers and thunderstorms. Patchy fog Thursday morning.
Thursday night through Saturday...mainly VFR.
Sunday...sub-VFR possible in scattered showers and thunderstorms.
high pressure off the coast and a cold front approaching from the
northwest should maintain a southerly flow over the coastal waters
of New Jersey and Delaware for tonight and Wednesday. Wind speeds
will favor the 5 to 15 knot range.
Wave heights on our ocean waters should be 2 to 4 feet. Waves on
Delaware Bay are expected to be 2 feet or less.
There is a chance of thunderstorms late on Wednesday.
Thursday through Sunday...high pressure overhead will keep seas and
winds below Small Craft Advisory criteria.