Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 220643

Area Forecast Discussion
National Weather Service Mount Holly NJ
243 AM EDT THU SEP 22 2016

High pressure will continue to build over the region and become
established over our area through Friday with the remnants of Julia
drifting offshore. A backdoor cold front will then move through
the region early Saturday and be followed by another high pressure
system building in from the northwest early next week. By the
middle of next week, a cold frontal boundary will move toward the
region from the west.


Early this morning...cirrus bands, mostly thin with radiational
cooling shallow fog expected by 6 am in parts of e PA and nw NJ.

Today...Considerable sunshine with remaining bands of thicker cirrus
thinning midday. Max temps 8-13 degrees above normal...greatest
positive departure in the northwest portion of our area vcnty KABE
and KMPO. light wind becomes east this afternoon around 10 kt with
scattered gusts near 15, especially coasts.

Forecast a max temp of 86F in PHL and confidence is very high
that the max will fall in the range of 85-87F.

KABE and KSMQ should be warmest with max temps around 87F,
possibly even 88.

Forecast basis started with a 50 50 blend of the 00z/22 GFS/NAM


Clear or mostly clear with radiational cooling and a few patches
of fog possible late at night, the usual countryside suspects of
ne PA and nw NJ.

Forecast basis started with a 50 50 blend of the 00z/22 GFS/NAM
MOS. I did lower that blend by 3-5F to fcst mins in the
countryside lower than guidance but within a couple of degrees of
the coolest GFS 2m temps (09z) which has widespread 48F Northampton/
Warren and Sussex counties in ne PA and NW NJ.


Friday through Friday night:

High pressure will continue become established across the region
on Friday. Some cloudcover ahead of an approaching frontal boundary
may keep low temperatures slightly higher Friday night. Friday
looks like the last of the anomalous early fall heat for at least
a little while with temperatures well into the 80`s. Modeled
boundary layer temperatures indicators of surface temperatures
match well with MET/MAV and ECMWF statistical guidance.

Saturday through Monday night:

A cold front will move from northeast to southwest across our
region. Our coolest airmass of the season will advect in as
another high pressure system dives southeast from Canada. Enough
lift and moisture may be present for a temporary increase in cloud
cover and isolated showers on Saturday otherwise continued dry
conditions. temperatures will be much cooler for the weekend.
Some indications in ensemble guidance have a slightly delayed
frontal passage which may allow for Saturday to get into the 80`s.
However, we will stick with the mean timing of early Saturday with
the operational and ensemble guidance for the frontal passage.

Much cooler air, a first real taste of fall with lows in the 40`s
and 50`s with highs in the 60`s and 70`s. Less spread with
temperatures Sunday and Monday with the ensemble guidance.

Tuesday through Wednesday:

The backdoor frontal boundary coupled with a mid-level ridge to our
west look to setup an omega block which will likely slow the
approach of the next cold frontal boundary or weaken as it moves
east. As is usually the case in the 5-7 day time period uncertainty
is present on the exact timing of this feature.

The UKMET, CMC and some ensemble data weaken the front before it
approaches our area. On the other spectrum, the GFS and GEFS are
much faster bringing it through around Tuesday. Given this spread
and questions if the front makes it to our area, will keep a dry
forecast. Low and high temperatures should slightly warm each day
unless the high pressure system sets-up just to our north. In that
case an easterly flow could slow the approach of a warmer airmass
expected ahead of the next front.


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

Early this morning...VFR bands of cirrus with small chance of
MVFR fog KABE/KMIV but not in the TAF due to low confidence. light
north wind or calm.

Today...VFR bands of cirrus thinning. Wind becoming east northeast
around 10 kt this afternoon with scattered gusts around 15 kt.

Tonight...VFR but may degrade to areas of ifr or mvfr fog after
06z, vcnty KMIV/KACY and KILG where a little more shallow moisture
available. Nearly calm wind.


Friday through Friday night: VFR.Varibale winds becoming west-
southwest but staying under 10 knots.

Saturday through Monday: VFR. An isolated shower possibile on
Saturday. Northerly winds around 10 knots Saturday afternoon with
gusts up to 20 knots then staying under 10 knots Sunday and Monday.


A Small Craft Advisory for hazardous is in effect from Noon today
to 6 am Friday. Have pulled back a bit on the extensiveness and
duration of SCA conditions and converted to Haz seas. Forecast
seas are a little less than previous guidance. The 18z GWES prob
for >6 ft is southeast of our area, and pulling eastward faster
early Friday. We dont have 44009 data to measure seas so we rely
on BTHD1.

Elsewhere for the Atlantic waters a 2 to 4 foot easterly swell of
11 seconds occasionally 6 seconds through tonight. De Bay a few
gusts 20 kt today.

Water temperatures continue above normal.


Waveheights will start in the four to five feet range and should
slowly decrease on Friday. GWES guidance indicates a fairly high
confidence for seas to reach five feet Thursday night and early
Friday. So have issued an SCA which goes through 18z Friday. This
ending time may be slightly long but allows for wiggle room if
waveheights respond slower, typical of easterly flow. For the
weekend into early next week seas and winds are expected to remain
below SCA criteria.


There is a moderate risk for the formation of dangerous rip
currents along the NJ shore and Delaware Beaches today, mostly
driven by a 2-3 foot ese swell of 11 seconds and additional
onshore wind wave created by an east northeast wind gusting 15
kt. Swim only in the presence of a lifeguard.

Friday...A generally low or low enhanced risk is forecast.

Weekend...There is a pretty good chance of a moderate risk for the
formation of dangerous rip currents on at least one of the weekend
days as a 4 to 5 foot ESE swell from Tropical Cyclone Karl arrives
along with a gusty northeast wind.


We`ll rereview the forecast monthly outcome at 5 am.


MARINE...Small Craft Advisory for hazardous seas from noon today to 6
     AM EDT Friday for ANZ454-455.


Near Term...Drag 242
Short Term...Drag 242
Long Term...Gaines
Aviation...Drag/Gaines 242
Marine...Drag/Gaines 242
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