Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1218 am EDT Wednesday Jul 8 2015
a cold front in northwest Pennsylvania will sag slowly southeast
today, reaching southern sections of Pennsylvania and New Jersey
before stalling Wednesday night. Two areas of low pressure will
move east along the front and off the New Jersey coast, one early
Thursday and then another early Friday. Thereafter the front slips
slowly south of the Delaware-Maryland-Virginia during Friday. High pressure will
briefly move into the region for the weekend, before a warm front
moves to our north on Monday. A trough looks to persist over our
area through most of next week, as a result of a dominant ridge
over the Midwest.
Near term /through Wednesday/...
1122 PM estf: showers dissipating as they move east from central PA
and adjusted probability of precipitation/temperatures down slightly before the scheduled 1230 am
A fair, warm and humid Summer night...min temperatures 6 to 12 degrees above
normal. Still a chance of showers early today for the Poconos into
northwest New Jersey...depending on any showers that can remain active in their
eastward trek from the 0330z pit-unv area. Precipitable water increases overnight reaching
2 inches along and west of I-95 by 12z Wednesday. Instability aloft
also increases early today.
Today-Wednesday...a cool front is forecast to extend from the
Catskills across northeastern Pennsylvania to around Pittsburgh
early on Wednesday morning. The boundary is expected to sink
slowly into our northwestern counties as the afternoon progresses.
Showers either on going at daybreak near and north of I-80 or redevelop
during the midday/afternoon hours over east PA and north or central New Jersey.
Precipitable water 2.25 inches during the afternoon and evening along and southeast of I-95!
Yet MLCAPE not impressive...about 800j. 0-6km bulk shear decreases
during the day with westerly convective steering flow appearing to
slow to 15 to 20 knots by this Wednesday evening, and nearly parallel to
the slow moving front. This could mean narrow swath of large
rainfalls, if training can occur or reoccur, especially Delaware-Maryland-Virginia
or southeast PA and S New Jersey.
Maximum temperatures are dependent on remaining sunshine heating
and onset of showers at any location. For now, with about 18c at
850 to start the day and still 16-17c at 18z...think we should
nudge 90 in phl around 17z before any further rise in temperatures is
problematic with thickening cloud cover and development of
showers. Dewpoints at time of maximum temperature should be low enough to
prevent heat indices from rising to advisory threshold. Still a
hot and humid day vicinity I-95 sewd, especially with less wind than
Forecast maximum temperatures for Wednesday.., not yer decided on weighting the
various operational guidances.
Short term /Wednesday night/...
Wednesday night...evening convection probably dies out though there
is a chance of renewed showers/thunderstorms to our west advancing into
our area overnight. The surface cool front sags down to near Philadelphia
and Atlantic City by dawn Thursday. Humid. Precipitable water lowers .3 to .4
inches overnight but still a juicy 1.5 to 2 inches S of I-78 at
This forecast at 330 am will probably be a 50 50 blend of the 00z/8
NAM/GFS MOS guidance.
Long term /Thursday through Tuesday/...
hemispheric wave guidance shows deep southwesterly flow across the
eastern half of the U.S. At the start of the longterm period. By the
weekend the wavelength across the contiguous U.S. Becomes longer
allowing the southeast ridging to retrograde towards the central
U.S. This sets up a pseudo-high latitude Omega block, with our
region on the periphery of an East Coast trough. This pattern looks
to remain in place, while lifting and weakening a bit, going into
next work week, adding to our daily chances for showers and
Thursday - Friday night...the slow sagging cold front that
begins to cross the region on Wednesday looks to make it as far
south as Delaware-Maryland-Virginia on Thursday and remain nearly in place through
Friday. Multiple waves move along this boundary as it presses
southward adding to the increased chances for scattered showers
and embedded thunder. Guidance tries to advect in more instability
from the south on Thursday ahead of the front but the timing
doesn't look like it overlaps the frontal passage. That being said
precipitable waters will still be well above normal, possibly 2+ inches giving
US more localized flooding issues...same as it ever was. We
continue with the heavy rain wording in the forecast Thursday
night into Friday morning, but confine it to our northern
half...better lift/dynamics and some elevated instability to work
with. After what could be a Great Lakes mesoscale convective system passage Friday morning
across our north, the front continues to sag southward during the
day with isolated showers and thunderstorms possible across
Delaware-Maryland-Virginia...drying out behind the front across the north. It should
be noted that ffg across the northern zones is running quite low
with a lot of areas only needing 1.5 inches in an hour to cause
issues...something to watch.
Saturday...the aforementioned front should be farther to our south
this weekend while large scale subsidence takes over...the longwave
ridging retrograding all the while. We still expect Saturday to be
rain free but there could be lingering middle-level energy moving by to
our southwest that may touch off a few isolated to scattered showers
in our extreme southwest zones...have time to better define these
chances if any.
Sunday - Tuesday...warm front passage, from what was once the cold
front earlier in the period, moves back towards the north on Sunday
night into Monday. Cold front then nears from the northwest late
on Monday into Tuesday as troughing takes back over again.
Northwest flow aloft looks to prevail as central U.S. Ridging
amplifies. This may send several shortwaves through the region
from late Monday Onward...northern plains mesoscale convective system season.
Aviation /04z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Overnight...VFR high ceilings develop. Visibility may lower to 4-6 Michigan in haze
fog in a few locations. Light S-SW wind. Chance of showers toward
dawn near and north of I-80 (showers seen on radar over west and central
PA at 0330z).
Wednesday...VFR ceilings . Brief IFR conditions in mainly afternoon evening
showers and scattered tstms, especially kphl south. Gradient S-SW wind gust
15 kt, possibly 20 knots at 15z, but somewhat decreasing gustiness during
the afternoon except near thunderstorms where gusts 30-40 knots possible.
Wednesday night...VFR ceilings with MVFR visibility possible. Chance of showers.
Thursday...potential MVFR and IFR restrictions in showers and
thunderstorms, highest chances each afternoon and evening. West-
southwest wind gusts at or under 20 knots.
Friday - Saturday night...VFR. Winds at or under 10 knots, mainly
Sunday...mostly VFR. Some scattered showers and embedded thunder
no marine hazards foreseen at this time through Wednesday night, excepting
the possibility of mws or smw's for convective gusts 25-35 knots
late this afternoon/evening, especially Delaware waters and south of
Little Egg Inlet New Jersey (kacy).
Otherwise gradient south-southwest wind gusts 15-20 knots this morning may decrease
late today from north to south in New Jersey with the approaching cold front
then winds along the New Jersey coast should become some sort of northerly component
Sub-Small Craft Advisory winds and seas expected. Any wind gusts look to remain
below 20 knots, 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
4 feet 6 second with a 190 degree wind at 12 knots offers low risk for
both the New Jersey and Delaware coasts today. Outgoing afternoon tides will
locally enhance the rip currents but the lack of much long period
incoming swell keeps the risk generally low. Thunderstorms may
impact beach activities middle or late afternoon, especially S New Jersey.
Synopsis... drag 1218
near term...drag/iovino/Johnson 1218