Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
929 PM EDT sun Jul 5 2015
weak high pressure will shift off the coast tonight and Monday. A
warm front is forecast to lift northward and through our region
Monday night into Tuesday morning. Another frontal boundary is
expected to arrive on Wednesday, then the front is anticipated to
meander in or near our region Wednesday night into Friday as low
pressure moves along it. Weak high pressure may try to build down
from the northwest next weekend as the front remains nearby.
Near term /until 6 am Monday morning/...
a well defined upper-level low moving across West Virginia this
evening will continue to lift northeast through the night, however
it may weaken some. This is assisting in pulling moisture northward
with mainly high level clouds across our area at this time. However the
model guidance shows a precipitable water surge occurring overnight with an increase
to 2.00 inches by morning. This is combination with some warm air advection and
also some increase in lift with the aforementioned upper-level low
may result in some showers. This looks to be mostly across portions
of the Delaware-Maryland-Virginia to perhaps our far western zones.
The probability of precipitation were tweaked a bit to show a little faster increase to chance
across the far southern areas overnight. The coverage/timing is a
bit uncertain given the best lift looks to be to our west. The
ongoing convection though in Virginia will need to be watched as it
is gradually lifting northward. Otherwise, an increase in clouds
through the night with the chance of some low clouds/fog. The best chance
of the latter appears to be our western zones given the light
upslope component to the low-level flow within a moistening
The hourly grids were adjusted based on the latest observations,
then the lamp/lav guidance was blended in. No major changes were
made to the low temperatures at this time.
Short term /6 am Monday morning through 6 PM Monday/...
an area of showers will bring the best chances of rain to the Delaware-Maryland-Virginia
and western sections of the area during the day. It is possible that eastern areas
remain dry, but will carry very low probability of precipitation in these locations later in
the day. Overall the average quantitative precipitation forecast appears to be on the lower side,
however local downpours /higher quantitative precipitation forecast/ can occur given precipitable water values
forecast to be about 2.00 inches. High temperatures will be in the middle to
Long term /Monday night through Sunday/...
the middle level ridge that was over the western states is forecast
to disappear for the new week as low pressure meanders off the
California coast, moves inland and fills. The middle level flow east
of The Rockies is expected to become somewhat zonal, resulting in
another potentially active week for our region. The western ridge
is anticipated to return next weekend.
It continues to appear as though a wavering frontal boundary to
our south will return northward as a warm front on Monday night.
The boundary is expected to pass through our region from Monday
night into Tuesday morning. As a result, we may see some low
clouds and patchy fog and haze, along with a chance of showers or
A middle level short wave trough is forecast to be located over the
upper Ohio River valley and vicinity on Monday evening. The
feature will drift eastward and it is expected to pass over our
region on Tuesday afternoon. The increase in moisture and the
development of instability due to daytime heating along with the
middle level trough passing overhead could result in the development
of scattered showers and thunderstorms on Tuesday afternoon. The
greatest potential appears to be in eastern Pennsylvania and
northern and central New Jersey where mixed layer cape values are
forecast to rise around or just above 1000 j/kg.
The timing of additional impulses in the nearly zonal middle level
flow during the middle and late week period becomes a bit of a
challenge after the initial middle level trough passes on Tuesday
afternoon. While it seems that convection will occur in parts of
our area on Wednesday, and perhaps on Thursday and Friday, as
well, the exact location of the greatest potential remains a low
Presently, it looks as though our highest chance for severe
thunderstorms may be on Wednesday afternoon and evening with the
arrival of the front from the northwest. The forecast wind
profiles for that time period suggest that if convection develops
it could become organized. Cape values in excess of 1000 j/kg are
The latest general timing of the main surface low riding along
the frontal boundary brings it across our region on Thursday
night. As is the case with the middle level features, the timing of
the surface wave remains in question. We will keep a chance of
showers and thunderstorms for Thursday into Thursday night, with
mainly a slight chance of showers and thunderstorms for Friday.
Precipitable water values are forecast to rise near or above 2
inches during the middle and late week period. Any thunderstorms
could bring heavy downpours along with localized flooding of
roadways and areas of poor drainage. Also, we will keep an eye on
the flash flooding potential especially if certain areas are
affected by heavy rainfall on more than one day.
The guidance differs with the forecast for next weekend. The main
question concerns whether the frontal boundary will be pushed far
enough south to allow weak high pressure to build into our region
from the northwest and north. As a result, we will continue to
carry either a low or slight chance for precipitation.
Daytime temperatures are anticipated to be within a few degrees
of normal for the period from Monday night through Sunday.
Nighttime temperatures are forecast to be solidly above normal.
Aviation /02z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...VFR overall with an increase in clouds. Some MVFR ceilings
and/or visibilities should develop late especially in the kabe to
krdg areas. Light southerly wind becoming light and variable. Some
showers are possible closer to daybreak nearing krdg to kilg,
however confidence is on the lower side.
Monday...any MVFR conditions should lift early, otherwise mainly
VFR. Some showers and thunder are anticipated to develop, mainly
south and west of kphl. Since coverage and overall timing is a bit
uncertain, used a vcsh for now at inland terminals. Light and
variable winds, becoming south-southeast up to 10 knots.
Monday night and Tuesday morning...conditions possibly lowering
to MVFR or IFR in low clouds, haze and fog especially during the
late night and early morning hours. A chance of showers and
Tuesday afternoon and Tuesday evening...mainly VFR with a chance
of showers and thunderstorms.
Tuesday night and Wednesday morning...conditions possibly
lowering to MVFR or IFR in low clouds, haze and fog especially
during the late night and early morning hours.
Wednesday afternoon through Thursday night...a chance of showers
and thunderstorms which may cause conditions to lower to MVFR or
IFR at times.
no marine headlines are anticipated through the near and short term
Monday night through Friday...no marine headlines are