NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at May 21, 8:10 AM EST, 2 hours 50 minutes earlier.
Area forecast discussion, May 21, 8:10 AM EST, 2 hours 50 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
910 AM EDT Sat May 21 2022
.SYNOPSIS...
A Bermuda high pressure pattern will develop for Saturday and Sunday
with the Mid Atlantic region on the northwestern periphery of the
high. A strong cold front will move through Sunday night as low
pressure passes to our northwest, with the front slowly settling
offshore on Monday. High pressure builds in for Tuesday and
Wednesday, then a frontal system may approach the area later next
week.
&&
.NEAR TERM /THROUGH TONIGHT/...
Fog continues to burn off, and dense fog has lifted. Therefore,
the Dense Fog Advisory that was in effect until 10 am has been
cancelled.
Otherwise, attention will turn to the heat. There has been
little change in the temperature forecast, with the longstanding
idea of a very hot day remaining intact. The general idea with
the latest update was that max temperatures generally dropped a
degree or two, while dew points were nudged up a little,
rendering essentially no change to the heat index forecast.
These were largely cosmetic changes, but were made in
consideration of what happened on Friday. With fairly widespread
rainfall, there is more leftover moisture to contend with,
likely leading to a greater than previously expected latent
heating versus sensible heating component today. This could keep
the temperatures just a bit lower and also cause them to rise
more slowly, especially in northern portions of the area where
fog is a factor this morning. But it will also increase the
humidity, again especially in northern areas. So widespread heat
index values in the upper 90s to around 100 are still expected.
No changes were made to the Heat Advisory. While there is a
large amount of elevated instability present today, a strong
capping inversion will assure a dry forecast.
Tonight continues to look very mild also. With the dew points
staying up and a light southerly flow continuing, lows will only
fall into the upper 60s and low 70s, providing little relief from
the daytime heat. There may be a bit of patchy fog again tonight
such as near the coast and/or in the typically prone valleys. But
the signal is much weaker than Friday night, and for now, have opted
to leave the mention out.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Another hot day is expected on Sunday as a cold front approaches
the region from the west. The temperature forecast for Sunday is
rather tricky as a lowering in highs is forecast, but how much
relief from the heat is still somewhat uncertain. In the mid-
levels of the atmosphere, the 500 MB sub-tropical ridge will
begin to decay and be shunted southeast. At the same time
though, compressional warming ahead of the approaching cold
front can bee seen with only a modest decrease in 1000/850 MB
thicknesses forecast. The biggest question for Sunday will be
how quickly the cold front and associated convection takes to
arrive. The upper level disturbance responsible for the cold
front will also be heading rapidly northeast and shearing out.
This type of setup usually favors a slower cold front passage.
Given the above, have kept high temperatures above guidance or
lower 90s for most of the area Sunday. This puts heat index
values right at criteria for the Urban Corridor Sunday. Since
this is the first heat event of the season, will go ahead and
extend the heat advisory through Sunday.
Late Sunday afternoon into evening a surface cold front will
progress east through the region triggering showers and
thunderstorms. Mean 850/ 300 MB flow is rather weak with the
cold frontal passage at only about 20/30 kts. Instability on the
other hand is rather robust with ML CAPE values of ~2000 J/kg.
These higher CAPE values are greatest across eastern PA though,
with instability decreasing towards the NJ coast. Thanks to the
relatively weak steering flow and shear values, mostly
multicells are expected. The primary threats with these storms
will be damaging wind gusts (thanks to the potentially high
equilibrium levels and modest DCAPE values) and heavy rainfall.
Sunday night into Monday the cold front will push off the NJ
coast with showers and thunderstorms exiting the region. Behind
the cold front, much cooler and drier air will filter into the
region as dewpoints fall into the upper 40s. Expect temperatures
much cooler Monday with highs only in the lower 70s.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
A general warming trend in temperatures is expected through the long
term period as mid-level heights again start to rise across the
eastern United States. Meanwhile, across the western United States
heights will rapidly fall as an upper level low begins to wrap up on
Tuesday. Latest ensemble and probabilistic guidance is in fairly
good agreement that the upper level low will slowly approach the
area by Friday with precipitation chances slowly rising by the end
of the period.
The long term will open up on Tuesday with surface high pressure
centered over southern Quebec with the low level boundary located
across southern NC. Some of the latest probabilistic guidance is
showing the front stalling further north across VA with
precipitation possible across southern DE. This solutions appears to
be more on the tails of the distribution. The latest ensemble
guidance tends to support more of a dry forecast for Tuesday. Have
trimmed back PoPs for Tuesday and confined the slight chance of
precipitation to far southern DE. Temperatures Tuesday will be
rather pleasant for late May with highs right around 70 degrees with
partly cloudy skies.
On Wednesday, the surface high pressure over Quebec will slowly
start to translate towards the Canadian Maritimes and then offshore.
This means Wednesday will be the last day of lower dewpoints and
below normal temperatures before the warm up commences. Thursday
into Friday the upper level low over the western United States will
be well on its way east towards the Ohio River Valley. As this
occurs, a surface cyclone over MO will head north towards MI with a
warm front pulling north across the area Thursday. The closed upper
level low will then begin to become absorbed back into the upper
level flow and track northeast. As this occurs, another cold front
will approach the area from the west bringing the chance of showers
and thunderstorms back to the region.
&&
.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Through 12z... Variable condition are expected. A weak boundary is
oriented west to east across the area, running roughly through PHL.
From PNE northward (north of the boundary), areas of low CIGs and
fog will likely bring IFR or lower conditions. PHL may be just far
enough south to remain VFR, but cannot rule out a period of MVFR or
perhaps briefly lower through daybreak. For southern portions of the
area, mainly VFR conditions are expected. Winds mostly light and
variable, but favoring east-northeast over the northern half of the
area (north of the boundary), and south-southwest over southern
areas. Moderate confidence.
Today... Becoming VFR across the entire area as any remaining fog
dissipates. Southwest wind 5 to 10 kt. High confidence.
Tonight... Mainly VFR. Some patchy fog development is possible, but
appears it would be much less widespread than Friday night, and may
not form at all. Winds remaining southwest around 5 kt. Moderate
confidence.
Outlook...
Sunday...VFR initially ahead of an approaching cold front.
Showers and thunderstorms will then push across the terminals
from west to east late Sunday afternoon into evening.
Restrictions in visibility will be likely in any stronger
showers and thunderstorms. Southwest winds 5-10 kts, with gusts
15-20 knots. Confidence is high for most of this period, but
low on any one terminal experiencing showers and thunderstorms.
Confidence is higher that KRDG and KABE will observe
thunderstorms with restrictions in visibility. Winds will then
turn from the north 10-15 kts behind the front.
Monday... Some possible MVFR restrictions possible in the
morning with a recovery to VFR expected later in the morning.
Northwest winds 5 to 10 kts gradually shifting to northeast
overnight. Moderate confidence.
Tuesday... VFR. Northeast to east wind 5 to 10 kts, a little
breezier at the coast. Moderate confidence.
Wednesday... Mainly VFR. East to southeast wind 5 to 10 kts.
Moderate confidence.
&&
.MARINE...
Through tonight... Sub-SCA conditions are expected. South-
southwest winds 10 to 15 kt. Some gusts near to a little above
20 kt are possible especially this evening and early tonight.
Seas 3 to 4 ft. Areas of fog are also possible today especially
for the Atlantic coastal waters of central and northern New
Jersey. In those areas, a Marine Dense Fog Advisory is in effect
until 1PM today. Trends will be monitored in the event the
advisory needs to be expanded in area or time.
Outlook...
Sunday and Sunday night...Winds and waves mostly remain below
advisory levels through the period. However, winds could
approach advisory levels for a brief period Sunday
afternoon/evening. Wind will be south to southwest Sunday,
shifting to north behind the cold front.
Monday-Wednesday... No marine headlines are currently
anticipated. Offshore winds early on Monday, becoming onshore
later Monday into Tuesday and through midweek. Seas of 2 to 4
ft expected.
Rip Currents...
There is a LOW risk for the development of dangerous and life
threatening rip currents at NJ and DE beaches today and Sunday.
&&
.CLIMATE...
A hot and humid air mass is forecast to overspread the region
this weekend. The hottest day will be Saturday. Here is a list
of the high temperature records for Saturday and the record high
temperatures for the month of May.
Locations 5/21 Record High Temps May Record High Temps
--------- ---------------------- ---------------------
Philadelphia, PA 95 in 1934 97 in 1991
Reading, PA 96 in 1996 96 in 1996/ 1962
Allentown, PA 92 in 1934 97 in 1962
Mount Pocono, PA 87 in 1911 94 in 1911
Trenton, NJ 94 in 1934 99 in 1986/ 1911
Atlantic City (airport), NJ 93 in 1996 99 in 1969
Atlantic City (marina), NJ 85 in 1934 95 in 1925/ 1895
Wilmington, DE 95 in 1996 98 in 1895
Georgetown, DE 94 in 1996 98 in 1991
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory until 6 PM EDT Sunday for PAZ070-071-102-104-106.
Heat Advisory until 10 PM EDT this evening for PAZ101-103-105.
NJ...Heat Advisory until 6 PM EDT Sunday for NJZ008-010-012-015-
017>019.
Heat Advisory until 10 PM EDT this evening for NJZ009-013-020-
027.
DE...Heat Advisory until 6 PM EDT Sunday for DEZ001.
MD...None.
MARINE...Dense Fog Advisory until 1 PM EDT this afternoon for ANZ450-
451.
&&
Synopsis...Haines/O'Brien
Near Term...MPS/O'Brien
Short Term...Haines
Long Term...Haines
Aviation...AKL/Haines/O'Brien
Marine...AKL/Haines/MPS/O'Brien
Climate...WFO PHI