Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 241407
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1007 AM EDT SUN JUL 24 2016

.SYNOPSIS...
High pressure will remain in control over the area until a weak
warm front returns back to the north and east by late tonight.
This cold front is expected to approach from the northwest Monday
before slowly moving into the area Monday night. The front may
stall over the Delmarva or nearby to our south midweek as high
pressure builds in from the north. Another front may affect the
area late this week into next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A weak cold front that moved through the area last night was located
to our south across the southern half of VA. High pressure centered
to our north was building into the forecast area in wake of this
front.

The term cold front may be somewhat misleading as the air is
nominally cooler behind the front; certainly not enough to break
the ongoing heatwave. High temperatures across most of the area
will be in the mid 90s today (80s across the hilly terrain in
northeast PA and northwest NJ as well as at the beaches). However,
the post-frontal airmass will be drier with dewpoints dropping
into the low 60s and even 50s. Therefore, humidity won`t be much
of a factor today across most of the area with the heat index
similar to the dry-bulb temperature. The one exception will be
central/southern DE and adjacent eastern MD, where the surge of
drier air will not make much advancement that far south with more
of an onshore component to the flow today (either easterly or
westerly winds will advect higher dewpoints inland this afternoon
with bay breezes. Forecast heat indices in these southern most
zones will range from 98-102F for this afternoon, just shy of heat
advisory criteria.

Although an offshore flow will develop later today in eastern PA and
western NJ, the onset of it will be delayed late enough in the day
and the winds will be light enough to allow the sea breeze to move
inland this afternoon. Hi-res model guidance indicates the bay/sea
breeze front reaching the I-95 corridor prior to sunset (6-8 PM).
Winds will shift from W-SW to S-SE once the sea breeze passes
through.

12Z RAOBs from IAD, OKX and PBZ captures a strong mid-level
subsidence inversion overhead. Forecast soundings as well as
modified RAOB soundings indicates this inversion should cap
convection today, especially in the absence of deeper organized lift
over the area.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
The evening will start off precipitation free, but as we go through
the night, the frontal boundary to our south will begin lifting
northward, while a short wave/vorticity impulse approaches from the
west. This short wave is expected to interact with the lifting
frontal boundary and create isolated/scattered showers or
thunderstorms during the overnight hours. The best chance for any
precipitation overnight looks to be the northern two-thirds of the
area.

There could also be some patchy fog north of the lifting warm
frontal boundary overnight with a warm and moistening airmass moving
northward.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
The main impact will be the heat and humidity for the early part of
the week. Expect high temperatures in the mid to upper 90s across
the area Monday.  This, combined with a very humid airmass will push
heat index values above 100 degrees for most of the area. A weak
cold front will push across the region late Monday and Monday night.
This will spark off the next round of showers and thunderstorms with
the potential for some to become severe.

This cold front will slide to our south by Tuesday, bringing some
slight moderation in temperatures and humidity levels. Still expect
temperatures in the lower to mid 90s with heat indexes that approach
100. Much of the area should stay dry Tuesday and Wednesday, with
just extreme southern New Jersey and the Delmarva with the threat of
thunder due to the proximity to the stalled frontal boundary
lingering across the mid-Atlantic. The slight downward trend of heat
and humidity levels will continue on Wednesday with temperatures
generally staying in the lower 90s.

The front starts to approach back from the south as a warm front by
Wednesday night into Thursday. A couple of weak waves of low
pressure may develop and then ride up along this boundary giving us
a couple of chances for shower and thunderstorm development for the
latter part of the week.  There does not look to be much in the way
of a pattern chance into next weekend, so expect the warm, humid and
unsettled weather to continue through the end of the week and next
weekend.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

There is some patchy light fog this morning, mainly at MIV and other
rural areas, but this will lift and burn off around/shortly after
sunrise. The rest of the day will be VFR. It is possible that some
patchy fog could develop again overnight tonight into Monday
morning. Also, there is a chance for isolated/scattered showers or
thunderstorms overnight tonight.

Winds are light and variable at many locations this morning, but
where they have a direction, they are more northwest and will likely
become north to northeast later this morning. Winds are expected to
become more south to southwest during by midday as high pressure
weakens as it tries to move across the area.

outlook... VFR much of the time. Scattered (mostly) late
afternoon and evening showers and thunderstorms may limit
cigs/vsbys at times through the period. The best chance for this
will be Monday afternoon and evening and then again on Thursday.

&&

.MARINE...
Sub-small craft advisory conditions will continue today and tonight
across the area. There is a chance of showers or thunderstorms late
tonight into Monday morning.

outlook...
Mostly a period of sub-sca conditions expected. Scattered
showers and thunderstorms will create locally higher winds and seas
through the period. Best chance for this will be Monday afternoon
and evening and Thursday.

&&

.CLIMATE...
Yesterday, July 23rd, was the hottest day in quite some time (3 to 4
years) at several of our climate sites:

Philadelphia:  The max temperature of 97F yesterday was the highest
temperature observed at PHL airport in three years (since July 19,
2013 when it was also 97F).

Reading:  The max temperature of 98F yesterday at RDG airport was
the highest reading in four years (since July 18, 2012 when it was
100F).

Trenton:  The max temperature of 96F yesterday at Trenton was the
highest temperature recorded at the site in three years (since July
18, 2013 when it was also 96F).


The forecast high temperature for Philadelphia tomorrow, Monday,
July 25th is currently 98F. The last time the temperature reached or
exceeded 98F at PHL was three years ago on July 18, 2013. The last
100-degree day at PHL occurred four years ago on July 18, 2012.


Record high temperatures today through Thursday are below. Except
maybe ABE, we`ll fall short of record highs today. We may tie or
break daily record highs tomorrow at several of our climate
sites.


Site    24th      25th      26th       27th       28th
----    ----      ----      ----       ----       ----

PHL...  98-2011   96-1899   101-1892   101-1940   100-1941

ABE...  95-1999   95-1999   98-1940     98-1955    97-1949

ACY...  100-2011  99-2010   96-2011     99-2005    98-1999

ILG...  98-2011   96-1987   99-1894    100-1894   101-1894

TTN...  98-1910   97-1999   99-1892    100-1894   101-1894

GED...  99-2011   99-2010   97-2012     98-2005    99-1949

RDG...  96-2010   96-1999   99-1940     98-1955    99-1941

MPO...  91-1914   90-1999   89-1949     91-1955    93-1949

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 11 AM to 6 PM EDT Monday for PAZ060>062-101-
     103-105.
     Excessive Heat Warning until 6 PM EDT Monday for PAZ070-071-
     102-104-106.
NJ...Heat Advisory from 11 AM to 6 PM EDT Monday for NJZ001-007>010-
     012>014-016-020>027.
     Excessive Heat Warning until 6 PM EDT Monday for NJZ015-
     017>019.
DE...Heat Advisory from 11 AM to 6 PM EDT Monday for DEZ002>004.
     Excessive Heat Warning until 6 PM EDT Monday for DEZ001.
MD...Heat Advisory from 11 AM to 6 PM EDT Monday for MDZ008-012-015-
     019-020.
MARINE...None.

&&

$$
Synopsis...Klein/JK
Near Term...Klein
Short Term...Robertson
Long Term...JK
Aviation...Robertson
Marine...Robertson/JK
Climate...Klein


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