Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
536 am EDT Friday Aug 1 2014
several weak surface troughs will move into the area today, before
high pressure over the western Atlantic pushes an offshore warm
front northwestward across the East Coast this weekend. Several
disturbances will move northeast along this boundary through the
weekend. Another cold front will then move across the area late
Tuesday into Wednesday.
Near term /until 6 PM this evening/...
an active weather pattern will be ramping up in the near and short
term. First...a short wave trough currently over the Carolinas will
move over the region by 18z. There is currently an area of mostly
stratiform precipitation associated with this trough. However...as
this trough propagates northeast...it will encounter drier air
especially in the middle an upper levels. Thus...expect clouds, but not
necessarily widespread precipitation to move into the region early in the
day. What showers and storms do move into the region should be
limited in coverage, at least at first. It does appear that there
will be enough instability to support thunderstorms. The NAM even
shows ml cape values near 1000 j/kg. However, it seems that the NAM
is overly aggressive with low level moisture return, and thus too
high on the instability. Also, the persistent cloud cover should
help to keep surface temperatures down slightly, further limiting
instability. Thus, the GFS seems to have a better handle on this
aspect, with ml cape values generally less than 500 j/kg.
Short term /6 PM this evening through 6 am Saturday/...
right on the heals of the first short wave trough today, a second
upper level short wave trough approaches the region. This, coupled
with the moist southerly and southwesterly flow, and a slow moving
warm front which approaches the region late tonight, will mean
increased precipitation chances for much of the region. This is especially
true for the eastern half of the region which should have slightly
better lift, and see precipitable water values climb to near 2
inches by late in the period.
Long term /Saturday through Thursday/...
overall the medium range is on par with one another with the
synoptic features through early next week. The early part of the
longterm period, this weekend, is still viewed as an average to
slightly below average confidence, inland, as the timing and
placement of several smaller impulses and coastal baroclinic zone
Saturday...starting to see some better consensus, though still not
great, and according to the 01/00z data the non-NCEP members have jumped
more towards the NCEP guidance in keeping the baroclinic zone and
its subsequent surface waves more offshore...ec included. The gefs
has been pretty consistent the past few nights while the ec
ensembles have been trending less confident in the middle-levels and at
moreso at the surface. Precipitable waters increase upwards 1.5 to 1.75 inches by
Saturday evening with greater amounts east of the Delaware River.
Upper level jet dynamics with the right entrance region sitting
across the middle-Atlantic and ample sub-tropical moisture available
for the passing waves to tap into, we could be looking at a heavy
rain potential...greater chances east of the river closer to the
coast and frontal boundary. Temperatures will struggle to get out of
the 70s in a lot of places with lots of cloud cover, rain, and
easterly flow. The metmos seemed too low, as it usually GOES crazy
with stratus when rain is forecasted. Any breaks in the clouds for
an hour or two could easily boost some locations into the low-80s.
Sunday...there looks to be a drier period, at least the first half
of the day before a stronger middle-level wave nears from the west
during the afternoon hours...this is the kicker vorticity lobe. Cold pool
interaction aloft and minimal surface heating should be enough for
scattered showers with very isolated convection. Again, frontal
boundary still close to the region so we have likely probability of precipitation across
southern Delaware-Maryland-Virginia and along the New Jersey coast. Temperatures may end up
being a degree or two warmer than Saturday with possibly more breaks
in the clouds.
Monday...depending on the timing of more middle-level shortwaves, or
lack thereof, Monday could end up being a mostly dry day. Ec does
not show much forcing while the GFS keeps a few impulses shearing
through. Gefs paints a pretty broad area of at least chance probability of precipitation and
given the uncertainty at this point did not want to change too much
during the timeframe...continue chance probability of precipitation with moderating
Tuesday - Thursday...continuing cyclonic flow aloft may be enough
for isolated shower activity each afternoon, otherwise a mostly dry
forecast is expected this timeframe. Weak front may cross on
Wednesday with our best chances at scattered activity. Temperatures
moderate even more and should end up being normal.
Aviation /10z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Mostly VFR conditions are expected through the taf period. Still
expect to see some patchy br through 15z, primarily for kmiv, krdg,
kabe, kpne and kttn. The bigger question will be timing of rain showers and
thunderstorms and rain. Very low confidence on the timing of any rain showers and thunderstorms and rain
through the day today, but if any do move over terminals through
the day, expect VFR conditions even with the precipitation.
Coverage through 00z is expected to be too limited to include in
the tafs at this time. After 00z...chance for rain showers increases.
There may remain isolated thunderstorms and rain after sunset, but expect the risk
for lightning to decrease by late evening. For the period between
00 and 12z, expect rain showers to be more widespread especially for
locations along and east of the Delaware River, including kphl,
kpne, kttn, kilg, kmiv, and kacy. MVFR visibilities will be
possible with any overnight rain showers.
Saturday - Sunday...mostly VFR with scattered showers and isolated
thunderstorms possible each afternoon. Heavy rain may occur closer
to the coast. MVFR/IFR conditions likely in showery activity.
Easterly flow in place. Medium confidence.
Monday - Tuesday...VFR. Isolated showers possible on each afternoon.
expect winds and seas to remain below Small Craft Advisory today and
tonight with winds staying near or below 20 knots and seas between 2
and 3 feet.
Friday - Tuesday...sub-sca conditions are expected across our
waters this period.
the risk of rip currents will increase to moderate today as the
winds shift to southeasterly.