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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 191943
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
343 PM EDT Thu May 19 2022

.SYNOPSIS...
-- Changed Discussion --
Weak low pressure approaches late tonight and passes through on
Friday. Bermuda high pressure sets up for the weekend. A cold
front passes through Sunday night, and remains nearly stationary
over the Mid-Atlantic into the new week. High pressure passes
to the north as the week progresses. A cold front approaches
late next week.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH FRIDAY/...
-- Changed Discussion --
The remnant MCV which passed across the region this and
associated morning is now offshore. A shortwave trough axis
across southern New England will also move away from the area
into this evening allowing for some transient subsidence this
evening and into the overnight period. A weak frontal boundary
will push southeastward into the area this evening. This will
result in a continued scattering out and eventually clearing of
clouds from this afternoon, however a couple showers can`t be
ruled out in the vicinity of the front through the early evening
hours. Expect westerly winds around 10-15 mph through early
evening as well.

Temperatures are expected to drop off fairly quickly this
evening and low temperatures should range from the low 50s north
of I-80 to the mid 50s to low 60s elsewhere. Winds will become
light and variable. Areas of fog are expected to develop
overnight, particularly across coastal areas of New Jersey and
into interior portions of northern and northeastern New Jersey.
Confidence is low on how dense the fog may become, but a Dense
Fog Advisory may need to be considered in a future update if
confidence on dense fog increases tonight for those areas.

Another shortwave trough and an associated MCV complex
currently moving east across the central Mississippi and lower
Ohio Valleys are expected to progress toward the region
overnight. The approaching wave will lift a more pronounced warm
front north through the area during the morning hours Friday.
Temperatures, dewpoints, and thus instability will rise as the
front lifts through the area as the day progresses. Meanwhile,
the broad synoptic ridging will begin quickly building
throughout the day and will continue building through Friday
night.

The latest CAM guidance suite indicates a wide variety of
outcomes related to how the remnant MCV progresses across the
region from the mid-morning and into the afternoon on Friday.
The strengthening ridge axis across the East Coast and western
Atlantic introduces a complex and low predictability scenario.
It seems that the strengthening ridge axis may be enough to
weaken/dry out the MCV or even push it north of the local
forecast area (into northeastern Pennsylvania and Upstate New
York). However, if the MCV slows down overnight and passes
across the region after daytime heating has allowed instability
to build, we could see a few thunderstorms become strong to
locally severe. In any case, the probability of convection has
undoubtedly increased enough to warrant a wholesale update and
increase to the PoP and weather forecast for the daytime period.

Aside from the convection potential on Friday, skies should
start out partly cloudy with scattered clouds expected much of
the day. The cloud cover will be more widespread if the MCV
holds together or restrengthens across the region. Any lingering
fog should mix out fairly quickly by late morning. Southerly
winds will increase to around 10-15 mph. Expect highs about 10
degrees above normal in the mid to upper 80s in most areas.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
-- Changed Discussion --
Weak low pressure passes north of the region Friday evening.
Any showers or thunderstorms should be over prior to sunset.
Meanwhile, Bermuda high pressure sets up off the Mid-Atlantic
coast with strong mid-level ridging along the Eastern Seaboard
and developing surface ridging as well.

Warm air and moisture advection will be underway Friday night.
Surface dew points climb into the mid and upper 60s through the
night. With sea surface temperatures still in the upper 50s to
around 60, can expect advection fog to form over the ocean and
to spread into coastal areas Friday night through Saturday
morning. Any fog on land should burn off with heating of the day
shortly after sunrise on Saturday.

A hot and humid air mass will be over the area this weekend,
but the hottest day will be Saturday. With abundant sunshine and
850 mb temperatures upwards of +20C, high temperatures away
from the coasts will climb into the mid and upper 90s. Surface
dew points will start out in the mid and upper 60s, but should
mix out into the low to mid 60s by Saturday afternoon. There is
not much wind aloft, and mixing does not look to be all that
impressive, so not expecting dew points to crash. Regardless,
the Heat Index will generally be in the mid to upper 90s, and
around 100 along the Urban corridor and into portions of
northeast New Jersey. For Delmarva and extreme southeast New
Jersey, Heat Index values have to be over 105 for a Heat
Advisory. It does not look as if the Heat Index will be quite
that high in those areas, so any Heat Advisories will be limited
to the Urban corridor and portions of northern New Jersey.
Along the coasts, highs will top off in the upper 70s to low
80s.

A warm and humid night is on tap for Saturday night. Some mid-
level shortwave energy approaches from the west in the afternoon
and evening, but will ride around the apex of the high. Any
convection should stay well north and west of the local area
during that time. Coastal fog redevelops Saturday night as
moisture advection continues and surface dew points rebound into
the mid and upper 60s.

A cold front begins to approach on Sunday. Clouds will spread
into the region ahead of the front, and the hottest air of the
air mass will push offshore. As a result, high temperatures will
be several degrees cooler compared to Saturday, generally in
the upper 80s to low 90s inland and in the 70s along the coast.

On Sunday, the cloud cover will help keep dew points elevated
in the afternoon. As a result, although surface temperatures
will be cooler compared to Saturday, the Heat Index will be high
once again. Max Heat Index values will be in the low to mid 90s
throughout, and in the mid to upper 90s along the Urban
corridor. A more localized Heat Advisory may be needed for
Sunday.

Surface high pressure sags a bit to the south on Sunday
afternoon as that cold front approaches, but mid-level ridging
remains strong along the coast. Mid and upper level energy rides
around the apex of the mid-level high north of the area, so
there is not much support for widespread convection with the
approach and passage of the cold front. Timing does not look
good, as the front does not pass through until late Sunday
night. Will carry chance PoPs to low-end likely PoPs for areas
north and west, but will only carry a chance for thunder.
-- End Changed Discussion --

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
-- Changed Discussion --
Cold front slowly works its way through the region Sunday
night. Not much in the way of mid-level troughiness. In fact,
the mid- level ridge remains over the area into Monday morning.
Although scattered showers are possible, not expecting much in
the way of convection, especially considering how warm and humid
it will be ahead of the front.

Cold front finally pushes offshore on Monday, but will become
nearly stationary south of the area and over the Mid-Atlantic
into the new week. Meanwhile, surface high pressure builds in
from the north. A fairly unsettled pattern sets up for most of
next week, as several weak waves of low pressure develop on that
stationary front. However, if the high is able to sag far
enough southward, that would help keep precip mainly focused on
southern areas. Either way, it is not looking like a washout for
most of next week, but chances are enough to keep at least
chance PoPs in the forecast for most of next week.

Highs will be around 15 degrees cooler Monday compared to
Sunday, and then temperatures will be on the cooler side of
normal for the rest of the week.
-- End Changed Discussion --

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

Through 00Z...Lingering MVFR ceilings will continue to scatter
out and lift. Westerly winds around 10 kts with gusts up to 20
kts possible. High confidence.

Tonight...VFR/SKC early, but some fog may develop after 06Z,
especially at ACY, MIV, TTN, and ABE. Winds light and variable.
Low confidence on timing and any associated restrictions with
the fog.

Friday...Once any morning fog dissipates, prevailing VFR
conditions are expected. However, a period of showers or
thunderstorms may move into the region after between 15-21Z.
Confidence on the occurrence of the showers or storms is low, so
PROB30 groups were introduced at some terminals to highlight
this potential. Southerly winds increasing to 10-15 kts with
gusts up to 20 kts. Moderate confidence overall.

Outlook...

Friday night...VFR overall. Fog may develop at KACY and
possibly KMIV with sub-VFR VSBYs. S wind 5 to 10 kt. Moderate
confidence.

Saturday through Saturday night...VFR. Reduced VSBY in fog at
KACY and possibly KMIV. S to SW winds 5 to 10 kt. High
confidence.

Sunday through Sunday night...VFR on Sunday, and then scattered
SHRA/TSRA will result in sub-VFR conditions in the evening and
at night. SW winds 5 to 10 kt, becoming NW late Sunday night.
Moderate confidence.

Monday through Monday night...Mainly VFR. NW winds 5 to 10 kt.
Moderate confidence.

Tuesday...VFR. E winds 5 to 10 kt. Moderate confidence.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
South to southwesterly winds will prevail tonight around 5-10
kts. Areas of fog are expected to develop overnight, some of
which could be locally dense reducing visibility to 1-3 NM. The
winds will increase to around 10-15 kts from the southeast
during the daytime Friday. Seas 2-3 feet. A period of showers or
thunderstorms is possible Friday morning or afternoon.

Outlook...

Friday night through Tuesday...Conditions overall will remain
below SCA criteria. S-SW winds generally 10 to 15 kt with 3 to 4
ft seas. The SW gradient will result in 15 to 20 kt winds
Sunday afternoon and evening, and seas may build close to 5 feet
as a cold front approaches. Winds shift to the NW behind the
departing front on Monday, and then an E wind develops for
Tuesday.

As a warm and humid airmass overspreads the colder waters
starting Friday night, reduced VSBYs in areas of fog are likely
through Sunday.
-- End Changed Discussion --

&&

.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...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$
Synopsis...MPS
Near Term...Staarmann
Short Term...MPS
Long Term...MPS
Aviation...MPS/Staarmann
Marine...MPS/Staarmann
Climate...WFO PHI