Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
938 PM EDT Wednesday Oct 1 2014
high pressure will continue to work in from the north tonight before
sliding to our east by Friday. A very potent cold front sweeps
through Friday night into Saturday morning followed by another brief
respite of high pressure through Monday. Then a series of impulses
look to affect the region through at least mid-week.
Near term /until 6 am Thursday morning/...
no major changes to the forecast this evening. An area of low
pressure aloft continues to spin to our northeast and will slowly
drift into New York and New England coastal waters tonight. An abundance
of low level moisture will continue to advect into the area
around the low, which will keep mostly cloudy to overcast skies
with a slight chance of light rain/sprinkles or drizzle for the
early part of tonight. The latest GFS and NAM keep the majority of
barely measurable precipitation across our northeastern and coastal
areas for the early part of the night while the hrrr dissipates
most activity through the night before it gets here. So we will
keep the highest probability of precipitation across the coastal areas where there are
currently reflectivities and the northeastern areas where some
light precipitation may move in later.
Most of our County Warning Area we are expecting to become mostly cloudy (or stay
cloudy) as the forecast soundings are pretty moist below 850mb. To be
consistent, this would preclude much mention of patchy fog and
also continuing to side with the higher stat guidance for min
Short term /6 am Thursday morning through 6 PM Thursday/...
going with a quicker modeling trend to ending the precipitation chances based
on the faster 500mb low movement. Precipitation chances in morning only.
Models indicating convective temperature being reached and more low
level moisture than even today. We are not going to be fast to
increase sunshine because of this. On the other hand any channelized
positive vorticity advection is done by the middle of the afternoon. Full sun macros
suggesting maximum temperatures about 5f above stat guidance. That stat
guidance drop off looks reasonable given afternoon predicted convective
temperatures are around 70. An indicator of possibly faster clearing
tomorrow would be if winds back further toward the northwest than
Long term /Thursday night through Wednesday/...
operational models are in pretty good agreement with the large scale
features through the weekend. The potential for phasing of a strong
northern and southern stream system to our west that carves out a
very large and deep closed low/trough across the Upper Middle-west by
late Friday night will be the main driver for a majority of the
long term period. A few breaks in the action are expected with weak
ridging, but overall we will remain unsettled through middle next week.
Friday...guidance has been running a bit slower with breaking the
middle-level ridging down and therefore keeps US mostly dry during the
daytime hours. Easterly flow will keep US damp with lots of cloud cover
in place. Temperatures climb into the low-70s. Strong cold front
nears from the west late Friday night with showers beginning to
overspread. The lack of instability, with its nocturnal passage,
should limit the amount of thunder, if any, though there is ample
lift with this system to possibly see a few taller updrafts.
Saturday...the front continues to barrel through the region early.
Pretty hefty heights falls with very robust upper level dynamics,
500mb jet nearly 70kts, and a negatively tilting trough axis are
prime ingredients for heavy rainfall...possibly even a narrow cold
frontal rain band. Too early to have higher confidence on the narrow
rain band but the models are indicating a sharp wind shift with the
strong frontal convergence zone lifting, low equilibrium levels, and
tremendous upper level momentum...even with the lack of surface
instability. Either way these showers will be soakers as we tap into
the Gomex/Atlantic moisture streaming from the south and east.
Antecedent conditions are still pretty dry across the region so not
expecting anything out of the Ordinary to occur with the possible
heavier rain. Post frontal winds look to be strong as well with a
decent isallobaric component and strong cold air advection.
Temperatures should be dropping throughout the day so we could be
looking at a late morning high.
Sunday...cold front off to the east with troughing establishing
itself to our west and a crisp cool airmass in place. A dry day is
on tap with temperatures in the upper-50s to low-60s.
Monday - Wednesday...a series of upper level waves rotate through
the base of the trough to our west. This allows for chances of
showers each day though timing of the waves is nearly impossible at
this juncture. Temperatures should climb back towards normal.
Aviation /01z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Conditions vary from site to site, from VFR to MVFR. There is an
abundance of low level moisture associated with the low pressure
aloft located to our northeast. This will keep the chance for
occasional MVFR ceilings for a few more hours, before we expect all
sites to lower to MVFR overnight. Winds should be northeast at 5
to 10 knots.
On Thursday we expect an improvement to VFR by late morning/early
afternoon, similar to Wednesday. Winds should be mostly north to
northeast with speeds of around 10 knots.
Friday...mostly VFR. Rain, heavy at times late, overspreads the area
from the west. Reduced visibilities and ceilings in heavy showers.
Easterly winds back southeast.
Saturday...MVFR/IFR early in heavy rain, trending VFR. Winds
continue to back to the west-northwest becoming gusty.
seas at buoy9 are around 4 to 5 feet, about a foot over wave watch
guidance. Unfortunately buoy65 remains ots. Wave watch guidance
continues to be quite robust with the swells and even if this GFS
based run is too slow, seas should remain at or above Small Craft
Advisory criteria into Thursday. Not as confident about the winds
getting there as the jet may pass east of our coastal waters.
Because of the latter, no small craft advisories will be issued for
Friday...Small Craft Advisory conditions will likely persist on our
waters through early Friday as we continue with the easterly onshore
flow. Seas will continue to run around 5 feet. Winds begin to back
towards the south-southeast by late Friday ahead of the next cold
Saturday...strong cold front moves through. Winds back towards the
west-northwest later in the day and with stronger cold air
advection occurring, we could see a return to Small Craft Advisory conditions.
Gusty winds in the heavier rain showers...mostly in the morning.
Sunday...residual Small Craft Advisory wind gusts drop off by late morning. Seas
should also drop below Small Craft Advisory conditions to around 3-4 feet.
with persistent breezy northerly and north northeasterly winds
tonight into tomorrow, tidal departures by tomorrow afternoons high
tide should range from 0.5 to 1 feet above astronomical tide. This
should result in tides below minor flooding thresholds. However, we
will continue to monitor the departures over the next high and low
Marine...Small Craft Advisory until 6 am EDT Friday for anz450>455.