Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
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FXUS61 KPHI 261401
Area Forecast Discussion
National Weather Service Mount Holly NJ
1001 AM EDT Wed Oct 26 2016
High pressure centered in eastern Canada today will shift eastward
tonight and Thursday. Low pressure is then forecast to track from
the upper Ohio Valley tonight eastward to southeastern New England
Thursday night. This will pull a warm front across our area Thursday
morning, following by a cold front Thursday night. High pressure
briefly builds in during Friday before shifting to our south over
the weekend. Low pressure and an associated cold front should then
move through later Sunday with high pressure returning Monday into
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --High pressure centered over southern has been building slowly
southeast across the mid-Atlantic region overnight and into this
morning. The air mass aloft is rather dry with generally downward
VV resulting in mostly clear skies for today. Some high level
clouds to the west may begin spreading into east PA and vicinity
this afternoon. With limited heating from the late October sun,
current temps seem on track to reach forecast highs in the lower
to mid 50s this afternoon, except for 40s in far northwest NJ and
With overnight temperatures below freezing in many locations, the
growing season is judged to be over for the following counties. In
Pennsylvania: Berks, Lehigh, Northampton, Chester, Montgomery and
Bucks. In New Jersey: Morris, Hunterdon, Somerset, Ocean,
Burlington, Camden, Gloucester, Salem, Cumberland and Atlantic.
Growing season ended earlier this month for Carbon and Monroe
counties in PA, and for Sussex and Warren counties in NJ. No
additional Frost Advisories or Freezing Warnings will be issued
for these areas.
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.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
The low will continue to track further east overnight, reaching
north central or northeastern Ohio by morning. Still quite a bit of
uncertainty as to how far east the precip shield will move
overnight. At this point, think it will mostly be confined to the
Poconos in our region. Mid level clouds should move over the region
by late this evening, which should help to limit radiational
cooling. In addition, surface winds will be northeasterly by this
time which could further limit radiational cooling. NAM MOS and GFS
MOS seem to be downplaying these factors with lows much lower than
the deterministic models. I went a bit above the MOS guidance as I
do think these factors should lead to temps being a bit higher than
what we are seeing this morning. Still, locations in the Poconos and
NW NJ could drop below freezing.
Based on the latest model soundings, it looks to be more of a rain
or freezing rain event (depending on the surface temperature at the
time that precipitation begins), though can`t rule out some snow
mixing in. For more details on precipitation type, see the long term
.LONG TERM /THURSDAY THROUGH TUESDAY/...
The synoptic setup is comprised of a trough that amplifies across
the Northeast during Thursday before exiting on Friday. An active
but progressive pattern looks to be in place, therefore a ridge
quickly moves across the area to start the weekend before the next
trough arrives. This trough should also amplify as it arrives in the
Northeast Sunday but then exits Monday. Some ridging is then
forecast to return Monday into Tuesday. The forecast challenge is
mostly centered on Thursday as strong warm air advection with a warm
front will be clashing with lingering cold surface high pressure to
the north and northeast. This should keep in colder air for a time
in the lowest levels across the north, opening the door for a period
of mixed precipitation.
For Thursday and Friday...A potent short wave will amplify an upper-
level trough from the Great Lakes to the Northeast during Thursday
before shifting east Friday. This will drive surface low pressure
from the upper Ohio Valley to start Thursday then to the
southeastern New England coast Thursday night and Friday morning.
The associated wind fields will respond and enhance the downstream
warm air advection. It still looks like a decent shot of overrunning
precipitation overspreads at least the northern half of the area
during the morning hours, on the nose of a 40-50-knot 850 MB jet. As
this occurs, strong high pressure at the surface to the north will
gradually give way however it will keep some cold air trapped for a
time in the lower levels. This should allow for a wintry mix to
occur mainly across the Poconos to far northwestern New Jersey,
although if the precipitation arrives fast enough then some brief
mixing may occur into the Lehigh Valley. The forecast soundings
indicate mostly a sleet/freezing rain to rain scenario, however
there is a decent amount of dry air in the lowest levels to start.
This may allow for enough cooling of the column initially for snow
to occur at the onset. The warming does look quick though therefore
we continued with the idea of any snow to quickly change to sleet or
freezing rain then to rain. Any accumulations of snow/sleet and
freezing rain look to be light. The extent of the cooling into early
Thursday morning will depend on how fast the clouds increase and
thicken. Given the idea of some icing, a winter weather or freezing
rain advisory may be needed for the far northwestern zones. However
given some uncertainty with the timing we held off for now.
Farther to the south, there may not be much rain for awhile Thursday
until a cold front arrives late in the day. Overall though the
precipitation may become more showery through the day. Some
instability looks to develop during the course of the day especially
for the southern areas, however the prospects of deeper convection
looks low given marginal instability and weak mid level lapse rates.
Therefore no thunder was included at this time. The cold front
crosses the area Thursday night with some cooling taking place and
some increase in the winds. For Friday, surface low pressure is
forecast to strengthen as it tracks to the northeast from coastal
New England. This will allow for a tightened pressure gradient and
as mixing improves, Friday should feature a gusty northwesterly wind
(which then diminishes early in the evening).
For Saturday and Sunday...Some upper-level ridging migrates across
the area with surface high pressure centered to our south. A trough
in the Midwest will slide eastward with downstream warm air
advection occurring. This will send a warm front north of our area
later Saturday, then a surface low generally tracks just to our
north later Sunday pulled a cold front across our region. We should
be within the warm sector as a result, with a surge of much warmer
air Sunday ahead of the cold front. If thicker clouds and any
showers can hold off then Sunday could feature temperatures well
into the 70s for a good part of the area especially from the I-95
corridor on south and east. This could be held back some though
given the potential for the cold front to arrive during the
afternoon and cap the overall warming. Much of the forcing looks to
be tied along and north of the surface low track, with perhaps a
broken band of showers with the cold front. At this point,
instability looks to be low enough and therefore thunder was not
added to the forecast. Cooler and breezy conditions arrive behind
the cold front.
For Monday and Tuesday...As a trough shifts east to start Monday
some ridging arrives. This allows surface high pressure from the
north to build across our area Monday before shifting offshore
Tuesday. A similar setup looks to be taking shape for Tuesday as low
pressure tracks up across the Great Lakes sending a warm front to
our north later Monday, then a cold front arrives Monday night into
Tuesday. Given the general quick progression of the systems,
moisture return may tend to be limited and therefore any POPs were
kept on the low side.
.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
VFR conditions should continue through at least 09Z. Increasing
clouds, and ceilings lowering to 10K ft AGL are possible after 00Z.
After 09Z, lower clouds and precip will start to move in from the
southwest. Through 12Z, only KRDG and KABE have a risk of seeing
precip, and with it possibly MVFR ceilings and visibilities.
Winds will be light...less than 10kt, but wind direction will shift
from northwesterly through much of the day today to northeasterly
Thursday...Conditions lower to MVFR or IFR with a period of rain
moving across the area. The greater chance of a steady rain is near
and north of KPHL. A wintry mix should occur in the morning north of
KABE. The rain tapers off in the evening with conditions improving
to VFR. Southeast winds near 10 knots Thursday shifting to west-
southwest early in the evening, then becoming northwest 10-15 knots
and potentially gusty during the night.
Friday...VFR overall. Northwest winds 10-15 knots with gusts to
about 25 knots, diminishing early in the evening.
Saturday and Sunday...Generally VFR. A cold front moves through
later Sunday with a wind shift to the northwest.
Along the coastal waters, gusts above 20 kt will be possible through
the morning, but should remain below SCA criteria and continue to
decrease through the day. On the Delaware Bay, winds should
generally stay less than 20 kt. Seas should be below SCA criteria
today and tonight.
Thursday and Friday...Southerly flow increases Thursday with a warm
front with advisory conditions looking to be reached later in the
day. There is a window of opportunity Thursday evening where gusts
could reach gale force as a low-level jet moves through, however
this is during a warmer airmass which may limit the mixing. Small
Craft advisory conditions should continue at night and Friday behind
a cold front as cooler air moves in. The winds and seas should then
settle Friday night.
Saturday and Sunday...The conditions are anticipated to be mostly
below Small Craft Advisory criteria.
-- Changed Discussion --PA...None.
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