NWS - Mount Holly Forecast Discussion
830
FXUS61 KPHI 160930
AFDPHI
Area Forecast Discussion
National Weather Service Mount Holly NJ
530 AM EDT Fri May 16 2025
.SYNOPSIS...
A warm front lifts north across the area this morning. Periods of
showers, thunderstorms, and humidity continue through Saturday ahead
of a strong cold front that passes through late Saturday afternoon
into Saturday evening. High pressure builds into the area on Sunday
and persists into Tuesday before another period of unsettled weather
returns Wednesday into Thursday.
&&
.NEAR TERM /THROUGH TONIGHT/...
525 AM...It`s relatively quiet across the area at the moment as
weak ridging is briefly moving through. The main concern is
areas of dense fog and so as a result, much of the area is under
a Dense Fog Advisory through this morning. Otherwise, our
attention turns to an MCS located upstream to our west. At this
time it has started to weaken some (compared to what it was
yesterday evening) as it begins to move into NW PA and western
NY though it`s still producing quite a bit of lightning. This
MCS is located ahead of the triple point associated with a large
and deep area of low pressure centered near Minnesota.
As we get into the day today, our attention will turn to the
MCS as it will be continuing to weaken but is likely to move
into the area from west to east sometime beginning around the
mid to late morning over our western most counties in eastern PA
and reaching the I-95 corridor shortly there after as it should
continue to be pretty quick moving. There remains some
uncertainty regarding how strong it will be at this time as it
moves into our area. But given that ML CAPE values will be
increasing to 1000+ j/kg with bulk shear values around 35 to 40
knots certainly the potential is still there for severe weather.
As a result, there has been little change to the outlook from
the Storm Prediction Center as areas basically from near
Allentown PA to Trenton NJ south and southwestward remain in a
SLIGHT risk for severe weather with a MARGINAL risk to the
north. Damaging winds and large hail look to be the biggest
threats but a brief tornado or two cannot be ruled out. Finally,
given how wet it`s been and that these storms will be capable
of producing very heavy downpours, localized flooding will also
be possible.
As we get further into the day Friday towards the afternoon and
early evening, the forecast becomes a little more uncertain.
Following the initial round of showers/storms with the MCS
there are indications that more scattered convection develops as
we go through the afternoon. This later convective development
could on the one hand be aided by residual boundaries from the
earlier convection but could also be mitigated if the MCS takes
longer to move through since this would give the atmosphere less
time to recover. Otherwise, the morning fog will have been
broken up with the first round of convection moving through and
we may even see some sunny breaks or partial sunshine for a time
in the afternoon. But again, this could fuel convective
redevelopment and this second round of storms could also be
severe. It will be a warm and very humid day with highs
generally ranging from the mid to upper 70s north to the low to
mid 80s south. Right near the shore though it will be a bit
cooler.
For Friday night, there may still be some convection ongoing into
the evening but this should diminish with time leading to another
brief lull. Once again, there could be some low clouds, mist, and
fog that form due to the continuing moist environment. The action
won`t be over though because by later Friday night the main slug
of energy more directly associated with low will be approaching
and this could bring another MCS into the area sometime either
overnight Friday night or Saturday morning. There remains a lot
of uncertainty on this though. Otherwise, it will be a mild,
muggy night with lows mainly in the 60s.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Mid/upper level low over the Great Lakes will pivot east on Saturday
as a vigorous shortwave tracks across the Mid-Atlantic with
northwest flow developing in its wake on Sunday. At the surface, an
area of low pressure will slide across Ontario/Quebec by Saturday
night before meandering near Nova Scotia on Sunday. A strong cold
front will pass through the area late Saturday afternoon into
Saturday night.
To start out Saturday, a MCS originating from the lower Ohio Valley
is progged to approach our area on Saturday morning. The overall
nature of this feature depicted by the latest CAM guidance is that
it will be decaying or even dissipate as it approaches our area. A
few showers and thunderstorms may be possible through the morning
hours especially north and west, but since this feature is mesoscale
driven, it`s very difficult to depict where this feature may be come
Saturday morning. Skies should be partly to mostly cloudy through
the morning however, before clearing out by early afternoon.
Temperatures will climb into the 80s for most areas with dew points
in the low to mid 60s making it feel quite uncomfortable outside.
The cold front will continue to make its way east through the
afternoon where isolated to scattered thunderstorms will re-develop
by the afternoon. In addition to the better forcing, we`ll have
MLCAPE values around 1000-1500 J/kg, DCAPE around 900 J/kg, and
modest shear as indicated by point forecast soundings. These
parameters will support damaging winds being the primary concern and
possibly some severe hail. A brief tornado also cannot be ruled out
as some low level shear will be in place. This is in line with the
Storm Prediction Center which keeps the entire area in a Slight Risk
(Level 2/5). Unfortunately, this threat is conditional and entirely
dependent on the morning MCS and how it evolves, so the forecast may
vary significantly by this time tomorrow. Nonetheless, the cold
front will push off the coast by Saturday night and the threat for
storms wanes in addition to the loss of daytime heating.
Sunday is looking like the better half of the weekend as tranquil
weather returns with the upper trough moving further east. Partly to
mostly cloudy skies are expected with dry conditions and lower
humidity. Perhaps an isolated shower is possible north and west, but
general thinking is most of the area will stay dry. The one thing to
note is winds will increase as diurnal mixing occurs as the area
lies wedged between systems resulting in a tightening pressure
gradient. Wind gusts up 30-35 mph will be possible. Gusts will
diminish into Sunday night under mostly clear skies. Despite the
windy conditions, high temperatures should mainly be in the 70s
(with 60s in the Poconos).
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
By Monday, low pressure over the Canadian Maritimes will begin to
move further east into the North Atlantic. At the same time, high
pressure will settle over the Mid-Atlantic before moving offshore on
Tuesday. Aloft, the area will be situated under northwest flow in
wake of exiting upper trough. All in all, a tranquil weather period
is in store with mostly clear skies, light winds and dry weather.
By Tuesday night and through the middle of the week, our attention
will turn to our next weather system which will take aim at the
area. Global and ensemble guidance both feature a deep upper trough
moving into the Great Lakes/Northeast region around the middle of
the week with a potential coastal low developing before moving up
towards New England. This would indicate another period of unsettled
weather with periods of rain starting as early as Tuesday night,
and more so on Wednesday and Thursday. Still quite a ways out from
this potential, so have generally stuck with NBM guidance and capped
rain chances at chance (~30-50%).
In terms of temperatures, we`ll encounter temperatures around
average on Monday, before dipping below average for Tuesday through
Thursday as the area remains situated within the deep upper
trough.
&&
.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Today...Restrictions to IFR/LIFR fore most sites to start the
day then some improvement to MVFR expected between 14-17Z.
However, around this time there will be a complex of showers and
storms moving through as it moves in from the west but still
some uncertainty on the details including how strong it will be
at this time. Winds light and variable early in the day becoming
SW 5 to 10 knots in the afternoon. There could be some
additional showers/storms that form in the mid to late
afternoon. Moderate confidence.
Tonight...Any showers/storms diminish through the evening with
with the potential for low cigs and low visbys once again due to
stratus, mist and fog. Low MVFR or IFR appears likely. More
showers and storms could move in late. S to SW winds around 5
knots. Low confidence.
Outlook...
Saturday through Saturday night...Primarily VFR expected. Scattered
showers and thunderstorms likely, especially during the afternoon
and early evening. Any shower or thunderstorm may cause temporary
sub-VFR conditions, gusty winds and/or visibility restrictions.
Sunday through Tuesday...VFR. Gusty winds up to 25-30 kt possible on
Sunday. Otherwise, no significant weather expected.
&&
.MARINE...
Areas of dense fog over the waters likely to be an issue through the
first half of Friday. Beyond this time, increasing chances for
showers/storms over the waters in the afternoon. Generally sub SCA
except any storms could produce locally strong winds.
The risk for some showers/storms over the waters continues Friday
night along with the potential for low visbys due to fog.
Outlook...
Saturday through Saturday night...No marine headlines expected.
Sunday through Sunday night...SCA conditions possible due to wind
gusts up to 25 kt.
Monday through Tuesday...No marine headlines expected.
&&
.TIDES/COASTAL FLOODING...
The Coastal Flood Advisory for northwestern Burlington and lower
Bucks Counties has been extended until 8 AM Saturday. Minor
coastal flooding is expected with the early morning high tide
this morning and on Saturday. It`s possible minor coastal
flooding may occur on Sunday as well, where further extensions
may be needed.
For areas of the lower tidal Delaware River near Philadelphia
may encounter spotty minor coastal flooding through Saturday,
but should fall short of advisory levels.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Dense Fog Advisory until 11 AM EDT this morning for PAZ054-055-
060>062-070-071-101>106.
Coastal Flood Advisory until 8 AM EDT Saturday for PAZ106.
NJ...Dense Fog Advisory until 11 AM EDT this morning for NJZ001-
007>010-012>027.
Coastal Flood Advisory until 8 AM EDT Saturday for NJZ019.
DE...Dense Fog Advisory until 11 AM EDT this morning for DEZ001>004.
MD...None.
MARINE...Dense Fog Advisory until noon EDT today for ANZ430-431-450>455.
&&
$$
SYNOPSIS...DeSilva/Hoeflich
NEAR TERM...Fitzsimmons
SHORT TERM...DeSilva
LONG TERM...DeSilva
AVIATION...DeSilva/Fitzsimmons
MARINE...DeSilva/Fitzsimmons
TIDES/COASTAL FLOODING...
NWS PHI Office Area Forecast Discussion
End NWS - Mount Holly Forecast Discussion