Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 251054
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
654 AM EDT Fri Jun 25 2021

.SYNOPSIS...
High pressure over the Canadian Maritimes through the weekend will
slide southward, becoming a Bermuda High through the middle of the
week. A slow moving frontal boundary will move through the Great
Lakes this weekend, approaching our area late next week.

&&

.NEAR TERM /THROUGH SATURDAY/...
High pressure prevails through the rest of the evening as marine
stratus is just pushing in over the coast. As the sun comes up
we can see the marine layer on visible satellite and its
basically sitting over Atlantic/Camden/Gloucester counties
this morning. BUFkit soundings suggest that the clouds over the
shore will likely hold on through much of the morning before
finally eroding. Either way, with the weak wave of low pressure
starting to pull away towards the north and east, we`ll see
another day of mostly dry weather and closer to normal temps
through this afternoon.

Patchy drizzle will be possible falling out of the low stratus and
we`ve already gotten several reports along the Shore of drizzle. I
think this wanes heading into the middle of morning as we start to
see some of the dry air from the ridge mix down.

Southerly flow will start to push higher dew points over the region
and we should start to see another round of summer type weather late
this afternoon. The warm air continues overnight as temps only fall
into the low 70s/ upper 60s setting the stage for a warm day on
Saturday. A very weak upper level wave tracks through over central
PA into NY during the afternoon on Saturday and may provide enough
lift to see some light showers develop over the Poconos, Lehigh
Valley, and parts of NW New Jersey. There will be abundant low level
moisture across the region so fog remains possible, however given
the modest boundary layer flow, and modified Richardson numbers
projected to be less than 0.2 I think we`ll be looking at low
stratus clouds instead of widespread fog.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
The high will be located over the Canadian Maritimes Saturday night
but will start to slide southward, becoming more of a Bermuda High
by Sunday night.

Generally expecting this period to be dry, though there will be a
chance for some showers or thunderstorms Sunday afternoon as a
shortwave crosses to the north of the region. Chances look slim at
best right now but the best chances for any convection is north
and west of the I-95 corridor.

Return flow around the high to our northeast will keep us in a south-
southwest regime, which will continue the influx of moisture and
heat to our region. Overnight lows will be in the upper 60s to lower
70s both nights with daytime highs on Sunday rising into the upper
80s to lower 90s. Cooler temps in the low to mid 80s are expected
along the immediate coast and in the southern Poconos. With all of
the moisture in place, there will be the potential for fog
development each night.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
This period will feature Bermuda high pressure to the east of the
region and a slow moving frontal boundary to the west. With the
forecast area sandwiched between the two features, we will generally
see a return flow across the area with a south to southwest wind
through the middle of the week. This will allow for increasing
moisture and increasing temperatures.

Guidance continues to show a prolonged period of 850mb temps rising
into the mid and upper teens, which translates into max temps in the
low to mid 90s. The heat hangs around through at least Thursday as
the front slows and possibly stalls near or over our area. Dew
points are where we will really start to feel the heat though. Dew
points will remain in the upper 60s to lower 70s. With all that
moisture in place and no where for it to go, we will feel the
stickiness factor rise and heat index values will rise into the mid
to upper 90s, especially for Monday through Wednesday. The potential
for heat headlines is increasing for the early week period for the
urbanized I-95 corridor and possibly the nearby surrounding suburbs.
A pre-frontal trough sets up near or across the forecast area which
may serve as a focus for mainly diurnally driven showers and
convection each day, with increasing chances as the front pushes
closer to our area. With several shortwaves rotating through the mid-
level flow, we should have enough lift across the region to support
convective development. The key will be to see just how much
instability is across the area each day. The risk for heavy rain
will also be in play as PWATs near (possibly exceed) 2 inches across
the region. Additionally, with such moist air over the region and
generally light winds, especially at night, it seems likely we will
have fog develop, though exactly where and how dense is yet to be
determined.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Today...VFR prevailing for all sites west of the MIV/ACY.
MVFR/IFR over the coast will be slow to erode but by late
morning expect VFR for all taf sites. Winds will start to pick
up in the morning to around 5-10kts out the south, with a more
southeasterly component near the coast. High confidence.

Tonight...VFR generally expected to start with MVFR/IFR low
stratus developing for most sites late. Fog may be possible but
generally stratus will be favoured over fog. Winds should be
southerly and light overnight. Moderate confidence.

Outlook...

Saturday...VFR expected through the day as any MVFR ceilings lift in
the morning. Showers will be possible for the Lehigh Valley late in
the afternoon which could reduce flight conditions. Winds remain out
of the south throughout occasionally gusting to 15kts.

Saturday night through Tuesday... Mainly VFR. Fog/stratus possible
each morning. Afternoon showers and thunderstorms possible. South to
southwest winds around 5 to 10 knots with gusts around 15 to 20
knots possible. Moderate confidence.

&&

.MARINE...
Through Saturday...Sub SCA conditions expected through the period
although winds make get close to 25 kts late Saturday.  Seas will be
between 3-4 feet generally on a 5-7 second period with onshore flow
generally 10-15kts.

Outlook...

Saturday night through Monday...Mainly sub-SCA conditions expected.
A brief period of gusts near 25 knots is possible Saturday night and
Sunday, mainly across the northern and central New Jersey coastal
waters. Southeast to south winds 10 to 15 knots with gusts around 20
knots. Seas 2 to 4 ft.

Rip Currents...

Given the long period swell remains and the flow is becoming more
onshore, we`ve opted to continue with a MODERATE risk for dangerous
rip currents today.

Saturday the risk will remain the MODERATE generally only for the
afternoon low tide cycle. The risk will likely be low in the morning
and late at night however the low tide during the middle of the day
is enough to warrant a MODERATE risk.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will be high the next couple of days due to the
recent full moon and the continued onshore flow. Some minor tidal
flooding is possible with this mornings high tide, mainly along the
southern New Jersey and Delaware coasts. However, we are not
expecting any advisory level flooding to occur.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...Meola
Near Term...Deal
Short Term...Meola
Long Term...Meola
Aviation...Deal/Meola
Marine...Deal/Meola
Tides/Coastal Flooding...WFO PHI


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