Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
356 am EDT sun Jul 31 2016
a frontal boundary will remain draped across portions of our area
today and tonight before gradually shifting offshore during Monday.
High pressure will then build across our area Tuesday through
Wednesday before shifting offshore Thursday. A cold front approaches
late Friday, then it is scheduled to settle across our region during
Near term /until 6 PM this evening/...
as of early Sunday morning the heavier shower/T-storm activity has
moved away from our forecast area. However there is some new
development over southeast PA which at this time of night must be
associated with some forcing for upward motion. For today, we are
still in a favorable position for more showers/T-storms ahead of a
slow-moving upper trof still over the Midwest. Model guidance shows
upward vertical velocity persisting over the mid-Atlantic today along with modest to
moderate instability with daytime heating. A slow moving frontal
boundary will enhance low-level convergence across the area. Pwats
should continue in the 1.5 to 2.0 inch range and thus heavy
downpours and localized flooding is possible again today.
Short term /6 PM this evening through 6 am Monday/...
for tonight, basically the same pattern aloft will continue,
although the surface front/trof is forecast to shift southeast to near the
New Jersey shore by Monday morning. Ongoing convection during the evening
should diminish somewhat overnight, but some activity may continue
into early morning with the upper trof still upstream.
Long term /Monday through Saturday/...
the synoptic setup is comprised of a trough in the northeast and mid
Atlantic that amplifies some into Tuesday before shifting offshore.
A ridge across the southern states builds north into the Great Lakes
Wednesday and Thursday, then a narrow ridge axis briefly moves
across our area Friday. A trough near Hudson Bay Friday into
Saturday extends into the Great Lakes, however an associated cold
front approaches late Friday and then settles across our area
Saturday. We used a model blend for Monday into Wednesday, then
mostly went with mostly a continuity/00z wpc guidance blend. Some
adjustments were then made however following additional
collaboration with our neighboring offices.
For Monday...an upper-level trough sharpens some across the region.
As this occurs, a weak area surface low pressure tied to a frontal
boundary will gradually shift offshore. This will take much of the
forcing with it, however the presence of the upper-level trough will
still provide some lift and therefore some convection is still
expected. The convection may be more focused inland for much of the
day, before shifting toward the coast early in the evening. The precipitable water
values remain near 2 inches and therefore included a heavy rain
mention. There could be a few strong thunderstorms during peak
heating, however the severe thunderstorm risk looks rather given
that the shear is not all that strong and lapse rates are not
forecast to be that steep. The convection should mostly trend
downward at night as the boundary stabilizes.
For Tuesday through Thursday...an upper-level trough axis should be
shifting offshore during Tuesday. However, if this is slower to
occur and enough moisture remains in place then a few showers/storms
could develop during peak heating. We then look for surface high
pressure to build in and be in place through Wednesday before it
shifts offshore Thursday. We are anticipating some lowering of the
dew points and also the temperatures. Some return flow however
starts to develop on Thursday, which should allow the dew points to
inch back up some.
For Friday and Saturday...high pressure to our south and east will
yield to a warm front lifting well to our north. This will help
assist in a more south-southwest flow as a cold front approaches
late day and at night. This front should settle across our area
during Saturday, however its forward progress could be slowed as the
main upper-level energy is forecast to track well to our north. Warm
air advection ahead of the front will allow for afternoon
temperatures to approach 90 degrees especially from the Interstate
95 corridor on south and east. The overall timing of the front will
govern any convective threat as it appears that a Lee side trough
may not be present. We continued slight chance to low chance pops
from west to east mostly Friday night and Saturday.
Aviation /07z Sunday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Conditions are mostly VFR to MVFR early this morning but are also
quite variable. Cigs are expected to lower to MVFR and possibly
IFR at all sites by sunrise but then gradually improve again to
VFR by mid-day. There will again be scattered showers and T-storms
around the area today which can produce locally poor conditions
especially this afternoon and evening. Winds will be light,
between 5 and 10 kt, except stronger around T-storms.
Monday...there is the potential for MVFR ceilings and/or
visibilities to start the morning, otherwise VFR with scattered to
broken cloud coverage. Some showers and thunderstorms will be around
and this will lead to mainly local and brief restrictions.
Tuesday through Thursday...VFR overall, with drier conditions
especially Wednesday and Thursday.
winds and seas will remain rather light through tonight. Southeast winds
should shift to SW over Delaware into southern portions of New Jersey waters as a
frontal boundary moves north. There will be scattered showers and T-
storms with locally gusty winds and poor vsbys.
Monday through Thursday...the winds and seas are anticipated to be
mainly below Small Craft Advisory criteria, as weak low pressure
shifts offshore late Monday and then high pressure arrives Tuesday
into Thursday. Scattered thunderstorms are expected Monday
especially toward late day, however the greatest concentration of
storms may end up being inland.