Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
617 am EST Sat Nov 28 2015
a cold front will move southward through the region today and
tonight. The front will push south of our area Sunday and Monday as
high pressure builds in from eastern Canada and New England. The
boundary will eventually return back northward as a warm front on
Tuesday while an area of low pressure tracks across the Great Lakes.
A cold front should move through the area as the low lifts into
southeastern Canada on Wednesday. High pressure builds in from the
west late in the week.
Near term /until 6 PM this evening/...
some very patchy fog is present across southern New Jersey and the
Delaware-Maryland-Virginia regions. However, due to the very patchy nature, the fog will
left out of the grids. Any fog should burn off very quickly this
morning. High clouds will be moving southeast into the region with
a cold front to our northwest this morning the 6:30 am update did
reduce cloud cover some across New Jersey and Delaware taking into account
current trends. Temperatures will start off in the 40's to low
By this afternoon, a cold frontal boundary will gradually move
southeast into the region. Moisture will be limited along the front
but enough lift looks present for some scattered rain showers along
the frontal boundary. The rain showers could possibly reach the
Lehigh Valley, Poconos and northwest New Jersey in the afternoon with the hrrr and
rap not ruling out a stray shower or sprinkle this morning. Some
minor adjustments were made with the 6:30 am update on probability of precipitation but
the general expectation is for scattered showers this afternoon northwest
of phl increasing in coverage tonight further south. Fairly good
model agreement on the frontal timing, although slightly slower
than what was modeled 24 hours ago. With the front not arriving
till the afternoon, the remainder of the region should be dry with
an increase in clouds throughout the day from north to south. High
temperatures will be closer to noontime across the Poconos and
northern NJ, only near 50 then falling into the upper 40's. More
in the way of sunshine will be in place with with some warm air advection ahead
of the front for the Philadelphia area and points southeast. This
will lead to another day with highs in the 60's, likely a hair
above met/mav guidance as well.
Short term /6 PM this evening through 6 am Sunday/...
the frontal boundary continues to slowly move south taking
with it the highest chances of rainfall to the Philadelphia
metropolitan area and points south. However, quantitative precipitation forecast throughout the near and
short term periods looks rather meager under 1/4th of an inch on
the operational models, the sref and wpc guidance. Colder air will
begin to funnel in behind the front, perhaps a hair slower/warmer
than indicated with met and mav guidance given recent trends to
slow the frontal passage. Right now any moisture looks to depart
before temperatures get close to freezing in the higher elevations
north and west. Even if that were not the case, temperature
advection will be slower at 925 and 850 mb which would result in
freezing drizzle and not snow.
Long term /Sunday through Friday/...
the best lift aloft is expected to move offshore on Sunday.
Meanwhile, the front will move south of US into southern Virginia as high
pressure builds in from eastern Canada. Accordingly, any leftover
anafrontal rain should diminish in intensity/coverage and likely
shift south of the Mason-Dixon line on Sunday. Northerly winds behind
the front will draw colder air into our region. Highs will only be
in the 40s in NE PA/northwest New Jersey and lm50s elsewhere, which is actually
right at climatology for the end of Nov.
The center of high pressure will progress into northern New
England by Monday. Depending on how far south the high builds,
isolated light rain showers or sprinkles may linger into Sunday
night or Monday in southern Delaware and adjacent eastern Maryland. Kept slight
chance probability of precipitation in for these far southern zones Sunday night and dry for
Monday. An onshore flow early in the week will keep conditions
A closed low over the Central Plains on Monday is forecast to move
eastward into the Great Lakes Tuesday-Wednesday before moving
off the New England coast either Wednesday night or Thursday.
Strengthening southerly flow ahead of the low will produce an
overrunning setup along and to the north of the old frontal
boundary to our south. This should result in precipitation returning to
the area either late Monday night or Tuesday as the warm front
lifts northward toward US. If the precipitation comes in before sunrise,
then models indicate a potential fowill be away from most of the taf sites with the exception of
kmiv. Patchy fog will continue at kmiv until 12z or so.R light
freezing rain or freezing drizzle briefly at the onset in the
sheltered valleys along and north of I- 80 (where the retreating
cold air near the surface is typically last to scour out due to
the orography). Will keep this threat out of the severe weather potential statement this far out
since it seems like a very low probability scenario but still
bears watching. Rain chances should continue until the cold front
passes through the area, which is Wednesday according to the 00z GFS
and Gem and Wednesday night based on the European model (ecmwf).
High pressure builds in from the central Continental U.S. Wednesday night
through Friday. Temperatures will likely be at or slightly below normal
late in the week as a shot of colder air follows the midweek cold
frontal passage. Aside from maybe an isolated snow shower or flurry in the
Poconos on Wednesday night (when the upper trough swings thru),
expect a dry ending to the week.
Aviation /11z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
VFR conditions with some middle and high level clouds. Localized fog
has been near kmiv the last few hours and may linger for another
couple of hours. Local tools continue indicate the highest chance
for patchy fog will be south of the remainder of the taf sites.
Conditions are forecasted to favor VFR today with ceilings
lowering gradually. We have indicated a transition to MVFR
ceilings at krdg and kabe during the afternoon with the arrival of
of some scattered showers. This timing is a few hours later for
kphl, kttn and taf sites further southeast. IFR conditions are
even possible from middle evening on tonight, more uncertainty at this time
to include with the 12z tafs. Thinking some of the indicators
looked at may a bit to aggressive lowering ceilings tonight.
Winds will remain at or under 10 knots and gradually shift from
the southwest to west then more northerly throughout the day
Sunday...low clouds with ceilings may yield MVFR and possibly IFR in
southern terminals (ilg-miv-acy) initially daybreak Sunday morning.
Gradual improvements in ceilings to VFR are expected from north to
south during the day. North-NE winds at or below 10 knots.
Sunday night...predominately VFR west/ clearing skies.
Monday and Monday night...an onshore flow may be accompanied by
marine stratus moving inland. Miv and Acy would be most vulnerable
of the taf sites to MVFR ceilings in this setup. Rain may also
overspread the area from the SW late Monday night.
Tuesday and Tuesday night...periods of MVFR and IFR with rain
likely. Light Ely winds become southeasterly late.
Wednesday...attm, the rain may linger into at least the morning.
There are model differences for the afternoon, with some solutions
indicating improving conditions during the afternoon while other
slower solutions delay the improvement until Wednesday night. It
will occur with a cold frontal passage. The frontal passage will also be accompanied
by a wind shift from southerly to westerly.
winds will remain below Small Craft Advisory criteria through Saturday night.
However seas we remain around five feet through today before
falling to around four feet tonight. An Small Craft Advisory continues through 23z
for the high seas. There is a possibility that seas may be
slightly delayed falling below five feet tonight with the
persistent east-southeast swell. For now though, both wavewatch and nwps have
seas falling below five feet by this evening, so will not extend
the Small Craft Advisory.
Sunday...winds and seas below Small Craft Advisory thresholds.
Sunday night through Tuesday night...increasing northeasterly winds 15-20 knots
will accompany a pressure surge Sunday night into Monday morning.
Looking at forecast soundings, there is not really much of a gust
potential in this setup so getting 25 knots gusts are questionable.
However, seas in the coastal Atlantic will likely increase to 4-7
ft, so a Small Craft Advisory will likely be warranted through early next week.
Wednesday...southerly winds will increase ahead of a front, then sharply
turn westerly behind the front late. A Small Craft Advisory may be needed.
kdix radar is currently inoperable. Technicians have been notified
about the outage. The return to service time is unknown at this
Marine...Small Craft Advisory for hazardous seas until 6 PM EST this
evening for anz450>455.