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Area Forecast Discussion (AFD)

Issued by Philadelphia/Mt Holly (PHI)

FXUS61 KPHI 240126

Area Forecast Discussion
National Weather Service Mount Holly NJ
926 PM EDT Sat Mar 23 2019

High pressure will slide to the south and east of the area on 
Sunday. A low pressure system will track to the north of the area 
dropping a cold front through the region Sunday night into Monday. 
Another low develops along this boundary and crosses to the south of 
the area Monday night into Tuesday. High pressure then builds into 
the region on Tuesday and then remains in control of the weather 
through the remainder of the week. Another system may affect the 
area over the weekend.


High pressure stretching from the Ohio Valley southeast to the 
coastal section of the Carolinas will continue to propagate 
southeast overnight. Consequently, the pressure gradient has
already decreased significantly from what we have seen the past
two days. As a result of the decreasing pressure gradient and
nocturnal wind decoupling, we have seen winds drop off to 10 mph
or less in many places. This trend should continue overnight.

With dewpoint depression values between 10 to 15 degrees, very 
dry air and light winds will result in ideal radiational cooling
conditions, with expected lows in the low to mid 20s north and 
upper 20s to low 30s south, which is 5 to 10 degrees below 
normal for this time of year.


As high pressure slips off the Carolina coast, the combination of a 
developing southwesterly flow at the surface and zonal flow aloft, 
will bring warmer temperatures to the region. Expect highs in the 
low 50s in the north, and low 60s in the south, which is 5 degrees 
or so above normal for this time of year. Westerly winds in the 5 to 
10 mph range will become southwesterly as the day wears on. Skies 
will be mostly sunny in the morning, with increasing cloudiness 
during the afternoon ahead of the next system heading this way.


Sunday night through Monday...A cold front will drop through our 
area Sunday night into Monday morning. Not a lot of moisture 
available with the frontal passage but some showers will be possible 
as the front makes its way into the area. An area of low pressure 
develops along this frontal boundary and will travel along it as the 
front pushes to the south and east. The low remains centered to the 
south of the region as it makes its way towards the coast. This 
second low has more moisture associated with it and we should see 
some showers move across our southern areas through Monday and 
Monday night. While the precipitation will end from northwest to 
southeast, colder and drier air will filter into the region. If the 
precip doesn't cut off before the colder air arrives, then we may 
see some mixing with snow before the precip fully ends. But with the 
drier air moving in fairly quickly (which is what the guidance 
continues to show) the precipitation will largely be confined to the 
southern portions of the forecast area as we move through Monday 
afternoon and into Monday night. 

Tuesday through Friday...Any lingering precipitation over Delmarva 
should end early on Tuesday as dry air moves into the area. High 
pressure will build in from the west on Tuesday. The high settles 
just to the northeast of our area and remains there through the 
week. We should have dry conditions through the week and generally 
light winds, which should result in good radiational cooling at 
night. High temperatures will start off on the cool side (in the 
40s) but as we go through the week, they will moderate quite a bit 
and be pretty warm (into the 50s/60s) by the time we reach the 

Saturday...The next low pressure system is slated to move through 
the region over the weekend. With warm temperatures expected when 
the precipitation arrives, anticipate that we will have an all rain 
event. Precipitation in advance of the main system will start to 
arrive early Saturday and then gradually spread across the forecast 


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY and surrounding areas.

TONIGHT...VFR under a clear sky. Northwesterly winds are 
expected to remain around 10 knots or less overnight. 

SUNDAY...VFR with west winds 5 to 10 knots, becoming southwest 
during the afternoon.


Sunday night...Mainly VFR conditions expected. Increasing cloudiness 
overnight with showers possible towards daybreak. West to southwest 
winds around 10 knots or less.

Monday...Mainly VFR conditions expected with MVFR possible in 
showers. Northerly winds around 10 knots.

Tuesday and Wednesday...VFR conditions expected. North to northeast 
winds around 10 knots on Tuesday, becoming east to southeast 
around 10 knots or less on Wednesday.


Northwesterly winds continue to subside. Therefore, the Small
Craft Advisory has been cancelled for the Delaware Bay, Delaware
Coastal waters, and southern New Jersey coastal waters. The SCA
remains in effect for the central and northern NJ coastal
waters, though even here, gusts are expected to drop below 25 kt
after midnight.

Sunday and Sunday night...winds turning southerly while dropping 
below SCA criteria at 10-15 knots. Waves 2 to 4 feet.

Monday and Monday night...sub SCA conditions with westerly winds 
turning north to northeasterly as a cold front drops southward. 
Waves near 1 to 3 feet during the day, but building to 2 to 4 feet 
through the overnight Monday. 

Tuesday and Tuesday night...winds approaching SCA criteria out of 
the north at 20 to 25 knots, with gusts of 25 to 30 knots, 
especially for the southern zones. Waves building to 3 to 5 feet. 

Wednesday through Thursday...winds remain below SCA criteria and 
northeasterly winds from 10 to 15 knots. Seas, however, remain on 
the high side, possibly at SCA levels, from 3 to 5 feet for the 
southern zones Wednesday. Waves should drop to 2 to 4 feet by 
Thursday morning though.


MARINE...Small Craft Advisory until 4 AM EDT Sunday for ANZ450-451.


Near Term...Johnson/Miketta
Short Term...Miketta
Long Term...Meola