Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 191445
Area Forecast Discussion
National Weather Service Mount Holly NJ
1045 AM EDT Sun Mar 19 2017
Low pressure will strengthen as it tracks to the southeast of
Cape Cod during today, then high pressure builds in tonight and
Monday. A weak cold front moves through the area Monday night
and stalls to our south, then low pressure tracks along it to
our south while a stronger cold front arrives Tuesday night.
Strong high pressure builds in from the northwest Wednesday
before shifting off the Mid Atlantic coast Thursday night. A
warm front will move into our region later Friday into Saturday
as low pressure tracks toward the Great Lakes region.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --A mid level low is forecast to sink southward across eastern
Virginia before passing off the coast this afternoon. Meanwhile,
A surface low pressure OUT AHEAD OF THE UPPER LOW iS on its way
farther out to sea.
One last bit of lingering showers can be found across Coastal
Cape May county NJ and Sussex county DE. These showers should
diminish over the next few hours as drier air arrives behind the
departing low. Clearing has begun across the north and will push
southward this afternoon.
A northeast wind around 10 to 15 MPH with gusts near 20 MPH is
forecast to back to the north and northwest today.
Maximum temperatures are expected to range from the middle and
upper 30s in the Poconos to the upper 40s in much of northeastern
Maryland and Delaware.
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.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
Surface high pressure is forecast to build into our region from
the west for tonight. We are expecting a mostly clear sky along
with a diminishing northwest wind.
Low temperatures are anticipated to favor the 20s in eastern
Pennsylvania and New Jersey, and the lower 30s on the upper
.LONG TERM /MONDAY THROUGH SATURDAY/...
Synoptic Setup and Summary...A closed low will continue to
shift away from the East Coast Monday as some ridging builds in
from the west. An upper- level trough then amplifies from
central to eastern Canada Monday through Tuesday with this also
extending across the Northeast through Wednesday. This will sent
a couple of cold fronts through our area, with the second one
being stronger. Some energy within the flow looks to develop a
wave of low pressure on the initial front as it stalls west-east
to our south Monday night and Tuesday. A round of precipitation
looks to slide across our southern areas Tuesday night, with
perhaps some enhancement as the secondary cold front catches up.
A shift in the pattern may then allow stronger ridging in the
East Friday as a trough amplifies across the Plains and Midwest.
The pattern will offer some warming, but also some shots of
colder air. A more pronounced warm-up should occur Saturday as
the warm sector of low pressure advancing toward the Great Lakes
should expand northeastward. We used a model/continuity blend
for Monday through Tuesday night, then blended in the 00z WPC
Guidance thereafter. Some adjustments were then made following
additional collaboration with our neighboring offices.
For Monday and Tuesday...A closed low will continue to move
farther offshore Monday giving way to some ridging into the East
Coast. This will allow some warming ahead of a weak cold front.
This front is being pushed by a trough that is amplifying from
central to eastern Canada, although much of the forcing looks to
be focused farther to the north and west. A band of showers
should be with the front to our west, although these may begin
to weaken as they arrive into our area Monday night. The front
becomes stalled in an east-west fashion Tuesday just to our
south. As some energy tracks along a tightening thermal gradient
along this front, an area of precipitation looks to develop
eastward along with surface low pressure. This feature looks to
track to our south Tuesday night and early Wednesday, however
the overrunning on the north side of the thermal boundary may
extend into portions of our southern zones for a time. A
secondary cold front will be arriving from the northwest, with
colder air in its wake. Cold high pressure will be building
southeastward from the Great Lakes, however it may be delayed
until after this surface wave along the front shifts offshore.
Therefore, precipitation type is more uncertain at this time
however we will continue to indicate some snow or rain/snow mix
overnight Tuesday. PoPs were increased some a bit northward for
a time Tuesday night.
For Wednesday and Thursday...Low pressure is forecast to
quickly shift offshore early Wednesday allowing for clearing. A
developing trough into the Plains results in downstream ridging.
This will drive strong surface high pressure from the Midwest
and Great Lakes regions Wednesday to right over our area
Thursday. This will result in a brisk northerly flow Wednesday
then less wind on Thursday. The high will be shifting offshore
Thursday night setting the stage for a return flow to occur in
advance of the next system. A colder airmass will in place once
again for both of these days.
For Friday and Saturday....A potentially strong trough in the
Plains to the Great Lakes will shift eastward. This will drive
surface low pressure from the Central Plains Friday to near the
central Great Lakes and upper Ohio Valley Saturday. There are
some mixed signals with how quick the associated warm front
lifts northward and if it clears our region. A lower amplitude
system would offer the warm front getting hung up over our area
as low pressure moves more east instead of north=northeast, and
therefore cooler air along with more precipitation. Given the
uncertainty with the details this far out, we went with an even
blend of continuity and the 00z WPC Guidance. There should be
some warm advection showers or a period of rain preceding the
warm front and therefore some PoPs were maintained especially
starting later Friday. If any precipitation moves in faster
Friday before temperatures can warm, some snow or mixed
precipitation is possible across portions of the northern zones.
.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Another hour of MVFR at KACY and KMIV before VFR conditions
return for the afternoon.
VFR conditions are anticipated from this afternoon into tonight.
Scattered clouds are expected for this afternoon with a clear
sky for tonight.
A northerly wind is forecast to range mainly from 10 to 15
knots with gusts around 20 knots today. The wind is expected to
be northwest at 5 to 10 knots for tonight.
Monday..VFR. Northwest winds 10 knots or less.
Monday night...A period of MVFR conditions possible with
showers as a weak cold front moves trough.
Tuesday and Wednesday...A low pressure system tracks to our
south Tuesday night and early Wednesday and should produce a
period of mostly rain mainly south of PHL with MVFR/IFR
conditions. Otherwise, VFR. Northerly winds Wednesday may gust
to 25 knots.
Thursday...VFR with light winds as high pressure is over the
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We will continue the marginal Gale Warning until 2:00 PM this
afternoon for our ocean waters and for Delaware Bay as low
pressure moves slowly away from the coast. We will keep the
Small Craft Advisory for the upper part of Delaware Bay in
effect for the same time period. The wind is forecast to
diminish gradually during the afternoon and nighttime hours with
Small Craft Advisory conditions expected on our ocean waters
during that period.
Wave heights on our ocean waters should favor the 6 to 9 foot
range today, and the 5 to 7 foot range for tonight. Waves on
Delaware Bay are expected to be 2 to 5 feet today and 1 to 4
Monday and Tuesday...The conditions are expected to be dropping
below Small Craft Advisory criteria Monday, and then remaining
below for Tuesday.
Wednesday...Northwest winds increase along with colder air
arriving. This should result in wind gusts to around 25 knots,
then these conditions diminish at night as high pressure starts
to arrive from the west.
Thursday...The conditions are anticipated to be below Small
Craft Advisory criteria as high pressure is over the region.
MARINE...Gale Warning until 2 PM EDT this afternoon for ANZ431-450>455.
Small Craft Advisory until 2 PM EDT this afternoon for ANZ430.