Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1148 am EDT Tuesday Jul 7 2015
a trough of low pressure located to our south today will merge
with a cold frontal boundary approaching the region tonight. This
frontal boundary will very slowly move through the region by
Friday, becoming nearly stationary. Several waves of low pressure
will also travel eastward along the boundary. A warm frontal
boundary will then lift northeastward through the region next
weekend giving way to another cold frontal boundary by the middle
of next week.
Near term /until 6 PM this evening/...
the sky varied from partly to mostly cloudy over our forecast
area late this morning. Scattered showers were developing in Berks
County, the Lehigh Valley, the Poconos and northwestern New
Jersey. Also, there were isolated rain showers in southern New
The isolated showers in southern New Jersey should dissipate
during the early afternoon. Most of the guidance, including the
hrrr, is focusing the best chance for showers and thunderstorms
for this afternoon from eastern Pennsylvania into northern and
central New Jersey. It appears as though northeastern Maryland,
Delaware and southern New Jersey will become rain-free.
A middle level short wave trough extended from western Pennsylvania
to central Virginia late this morning. The feature will progress
to the east and it should pass over our region from about middle
afternoon to early evening. The short wave trough will help to
trigger the development of additional showers and thunderstorms
across the northern part of our forecast area. Mixed level cape
values should rise to around 750 to 1000 j/kg during peak heating.
While precipitable water values are expected to drop from around
1.75 inches this morning to about 1.5 inches this afternoon,
locally heavy rainfall remains possible.
Temperatures ranged mainly from the upper 70s to the middle 80s
late this morning. Temperatures are forecast to rise near 90
degrees in much of our region during the afternoon. Readings
should get no higher than the lower and middle 80s in the elevated
terrain and along the immediate coast.
Short term /6 PM this evening through 6 am Wednesday/...
rainfree this evening and quite warm! Then a band of convection
ahead of the eastward moving cold front may arrive and cross NE PA and
northwest New Jersey near and after midnight with isolated embedded thunder. Precipitable water
in the early evening briefly dries to 1.4 inches but with the
convective band, increases to 1.85 inches by Wednesday morning.
Otherwise...I call it summertime fair-a typical warm Summer
Used the warmer of the available MOS guidance for tonight.
Light SW wind.
Long term /Wednesday through Monday/...
Wednesday and Wednesday night: a cold frontal boundary begins to
enter the picture Wednesday afternoon and evening giving US the
trigger missing today for a more widespread shower and
thunderstorm chance. With the higher chances of rain, high
temperatures may not reach the full potential due to the presence
of more clouds. Did knock down the highs but not as much as met/
mat European model (ecmwf) MOS do, given the majority of precipitation holds off
till after 18z. Plenty of window for warming ahead of the front.
Another result of the prospects for increased cloud cover is that
modeled instability has decreased to under 1000 j/kg of cape in
some parts of the region coupled with less in the way of modeled
steep lapse rates. Shear continues to look to be minimal as well
in the region. This points to any strong/severe storm to be
isolated. Heavy rain looks to be the primary concern with precipitable water
values near 2 inches. Storm motions look faster as well, so even
with the increased converge any occurrences of flash flooding may
not be widespread. This would lead to more typical poor drainage
flooding issues. A warm, muggy night is likely Wednesday night as
well with plenty of cloud cover to keep temperatures up.
Thursday through Friday night: the frontal boundary will likely
slowly sag to our south in this time frame with the potential for
a wave of low pressure late Thursday to buckle it back north for a
short period. This keeps a shower/storm chance going as well into
Friday. After the passage of the front, a cooler air mass will
advect into the region. Modeling does differ on how fast the front
comes through the region. The 00z 7/7 NAM and European model (ecmwf) are slower and
take a low pressure system into the eastern lakes/ north of our
region, bringing renewed warm and instability advection into the
region late Thursday (warm front) before sending the front back
south on Friday. These possibilities place a higher shear
environment in the region coupled with the increasing instability
late Thursday, more of a severe threat. The more progressive
solutions Aka the GFS and CMC weaken the low pressure to our
south. Our forecast raises probability of precipitation and sets up a quantitative precipitation forecast maximum area across
northern parts of the forecast area Thursday and Thursday night.
The NAM does have a bias of tracking lows to far north in the last
24-36 hours of model runs. So this forecast did not fully jump on
the board with the slower moving further north frontal idea. It
will be cooler as well with a somewhat more refreshing air mass
coming in behind the front. Rain chances may linger on Friday in
Saturday through Monday night: another warm front will push
northward into the region later in the weekend. So the somewhat
cooler and less humid air mass will get replaced by another round
of hot and humid weather early next week. Did trend temperatures
than the ensemble guidance by early next week. The ensemble
guidance probability of precipitation were also lowered in this forecast given normal 5-7
day forecast uncertainties.
Aviation /16z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
As the wind shifts more southwesterly, conditions improve to VFR
scattered-broken at or above 3500 feet. Ceilings rise further to at or above 5000 feet early
this afternoon then clear from SW to NE later in the day as the
precipitable water drops. Scattered IFR showers and isolated thunderstorms in the 16z-
21z time frame, mainly along and northwest of I-95. A couple of these
storms may produce a gust to 35 knots.
Gradient southwest wind gusts 15-20 knots at all sites during the
Tonight...VFR clear this evening then a deck of broken ceilings at or above 5000
feet arrives north of I-78 (near kabe and krdg) after 04z/8 associated
with a decaying band of convection ahead of the eastward moving cold
Wednesday through Thursday night: potential MVFR and IFR
restrictions in showers and thunderstorms, highest chances each
afternoon and evening. West-southwest wind gusts at or under 20
Friday through Saturday night: VFR. Winds at or under 10 knots,
sub-Small Craft Advisory conditions expected through this evening. Atlantic seas may
increase to the hazardous 5 feet threshold late tonight but no Small Craft Advisory
at this time since during warm air advection, guidance tends to have a
high bias on the seas.
Winds will become SW today and increase to 15 to 20 knots late today
sub-Small Craft Advisory winds and seas expected. Any wind gusts look to remain
below 20 knots, more southwesterly through Wednesday night then
more northerly through Saturday night. Seas around four feet on
Wednesday and Thursday. The highest chance of thunderstorms is
Wednesday afternoon and evening then again later Thursday.
forecasting a low risk today using a 3 feet 5 second southerly
swell this afternoon or early this mornings 2 feet 9 second. Combine
that with a southerly wind that increases to 12-13 knots this
afternoon and we get a low risk along our waters.
We cannot overemphasize...low risk does not mean no risk.
Transitory and recurrent rip currents occur every day. Play it
smart and swim safely in the presence of a lifeguard who knows
what they're doing if a Rescue is needed. They are there instantly
to save lives instead of be notified to later recover.
Tide going out this afternoon Fosters a possible enhanced low
risk for the formation of dangerous rip currents, especially
combined with an increasing south wind.
Media communication of the increased rip current danger swimming
away (outside) from the watchful eyes of lifeguards is very
important. Raising awareness can be a lifesaver, for all Ages but
even more so for the vulnerable 10-29 age males that comprise the
preponderance of rip current related fatalities. Interviews can be
conducted. Just contact US.