Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 241911
Area Forecast Discussion
National Weather Service Mount Holly NJ
311 PM EDT Sat Sep 24 2016
High pressure north of the Great Lakes will build to the south
and east towards the Northeast this weekend, and will be centered
over New England by Monday morning before moving offshore by
Monday night. A cold front approaches Monday night and passes
through the region on Tuesday. Low pressure then dives into the
Northeast for the midweek period, eventually departing as high
pressure builds in from the west for the end of the new week.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Cloud cover is slowly eroding from north to south, and will
continue to do so into this evening and overnight as drier air
moves into the area. We expect mostly clear skies overnight, and
winds will become light and variable most places as high pressure
begins to nose its way down from the north. This will allow for
good radiational cooling to take place, and a seasonably cool
night is expected across the area with near normal temperatures.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
High pressure will continue to affect the area from the north
through Sunday. Mostly clear skies, except some cirrus through the
day, are expected. Temperatures will remain pretty close to
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Quiet conditions for the start of the long term period, and then
a period of unsettled weather for the midweek period before high
pressure returns for next weekend.
High pressure centered just to the north of the local forecast
area Sunday night will drop into New England by Monday morning.
With clear skies, a dry airmass, and a light pressure gradient
over the area, can expect strong radiational cooling for areas
away from the urban centers. For most areas, the coldest temps of
the season, and in quite some time, will occur. Temps across the
Pocono Mountains and into northern NJ will be the coldest,
dropping into the upper 30s to near 40. Some patchy frost is
possible prior to daybreak. For the rest of the region, lows will
generally be in the 40s, but the ocean will keep coastal areas
several degrees warmer, generally near 50. MD/DE zones, as well as
the Philly metro area, will also have the warmest temps.
High pressure over New England on Monday continues to drift to
the south and east during the day. Meanwhile, a cold front will
push through the OH/TN Valleys, and will end up west of the
Appalachians by Monday evening. Mid and high clouds will build in
from the west ahead of that front, but based on latest latest
models, precip should hold off until Monday night. Another mild
day on tap for Monday with highs in the mid 60s in the mountains
to the north and in the low to mid 70s elsewhere.
Warm front lifts north through the region Monday evening ahead of
that cold front, and increasing low level moisture will spread
into the region. Surface dewpoints will climb into the upper
50s/low 60s, and resulting PWATs will range from 1.75-2". As a
result, can expect occasionally moderate to possibly locally heavy
rain at times as the front passes through the region Monday night
into Tuesday morning. Front may get hung up just offshore, and
this may keep showers in the forecast for eastern zones through
the afternoon, while conditions dry out to the west.
Thereafter, there is considerable uncertainty in the forecast for
the midweek period. Surface low pressure along with an upper
trough will track across Canada, ending up over the Great Lakes on
Tuesday. The uncertainty lies in where that trough will end up,
but models suggest that at least the base of the trough, if it is
not a closed low, will end up either right over the Mid-Atlantic
area or just to the south. Several waves of surface low pres will
develop around this upper trough and pass just south and east of
the region. For now, will keep slight chance PoPs in the forecast
from Wednesday through Friday. Latest ECMWF keeps the closed upper
low over the area into the weekend while the GFS has it offshore
and has high pressure building into the area.
Temps will be near or slightly below normal through the period.
.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Cloud cover is slowly eroding from north to south as drier air
settles into the area. Some MVFR CIGS will continue for a couple
of more hours, before VFR conditions return. Once they return, VFR
conditions will prevail through Sunday.
North-northeast winds around 5-10 knots will continue this
afternoon into this evening. Many places will become light and
variable overnight, but where any wind remains, should switch to a
north-northwest direction. Winds will likely switch back to a
north-northeast direction around daybreak for the morning hour
Sunday, before switching back to a northwesterly direction for the
Sunday night...VFR. Light winds.
Monday...VFR. South winds possibly gusting to 20 KT late in the
Monday night through Tuesday...MVFR with the potential for IFR or
lower in SHRA as a cold front works across the region. Improvement
possible Tuesday afternoon over western areas, but conditions will
be slow to improve over eastern areas.
Wednesday through Thursday...Predominantly VFR, but occasional
showers may briefly reduce CIGs/VSBYs.
A Small Craft Advisory will remain in place as seas are expected to
remain around 5-6 feet. Winds have dropped below 25 knots, and
should remain below advisory levels through Sunday. However, wind
may gust around 20 knots at times.
Sunday night...Long period swells associated with Tropical Storm
Karl will persist, but ocean seas will average 3-4 feet.
Monday through Thursday...Cold front approaches on Monday and
moves across the waters Monday night through Tuesday morning.
Strong southerly flow may result in 25-30 KT wind gusts during
that time, in addition to 5-6 foot seas. Sub-SCA conditions then
expected Wednesday and Thursday.
Both long period swells and building seas suggest conditions may
be more representative for a moderate risk of rip currents.
A moderate risk for the formation of dangerous rip currents will
likely continue into Sunday with long-period southeasterly swells
from Tropical Storm Karl expected to impact the eastern seaboard.
The high temperature yesterday, September 23rd, at Allentown, PA
(KABE) was 90 degrees. While this did not set a daily high
temperature record, it marked the second latest 90-degree day in
the calendar year at KABE since 1970. During this span, the only
other date that reached 90 degrees this late in the year was
October 8, 2007.
Note: A high temperature of 90F on October 8, 2007 was also the
latest occurrence of a 90-degree day in a calendar year on record
for KABE. Allentown historical climate records go back to 1922.
MARINE...Small Craft Advisory until noon EDT Sunday for ANZ450>455.