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Area Forecast Discussion (AFD)

Issued by Philadelphia/Mt Holly (PHI)

FXUS61 KPHI 221922

Area Forecast Discussion
National Weather Service Mount Holly NJ
322 PM EDT Mon Apr 22 2019

Low pressure well off the coast will continue to slowly track 
northward through tonight, and be off the New England coast Tuesday. 
Low pressure then tracking to our north Tuesday night into Wednesday 
will pull a cold front across our region. A weak area of high 
pressure returns by later Wednesday, then a few cold fronts move 
through from late Thursday into early Saturday. High pressure 
briefly arrives to start the weekend, however another cold front may 
move through late Sunday into Monday.


Surface low pressure lies about 150 miles east of Atlantic City and 
appears to be tightening up a bit as it drift to the north and east. 
The low should be centered near Cape Cod by late this evening, then 
begins to move out to sea towards daybreak.

Bands of rain are wrapping around the low and spreading from 
northeast to southwest into most of New Jersey and parts of 
southeast Pennsylvania. Rain is mainly light, and the heaviest of 
the precip, generally in northeast New Jersey, will result in as 
much as 1/4" QPF.

As the low departs, high pressure builds in from the west. Skies 
clear out during the overnight hours. Although some dryer air will 
begin to spread east, surface dewpoints do not look to drop off that 
much. With lingering low-level moisture, some patchy fog is likely 
to develop, especially in the outlying areas, in the pre-dawn hours.

Lows tonight will range from the 40s in the southern Poconos to the 
low 50s.


Surface high pressure with H5 ridge builds over the area Tuesday 
morning, and then slides offshore late in the day. Warm Air 
Advection due to southwest flow will usher a warm airmass into the 
region with highs some 10-15 degrees above normal, topping off in 
the mid to upper 70s, and around 80 along the urban corridor from 
Trenton to Wilmington. Temperatures will be cooler along the coasts. 

Afternoon sea breezes will develop as well, and the cooler air off 
the ocean results in cooler temps behind the sea breeze.

Weak low pressure will begin to approach late in the day, and some 
showers and thunderstorms will develop out ahead of the attending 
cold front. Some of those storms may get into far northwest parts of 
the southern Poconos late in the day.


Summary...Several cold fronts are advertised to cross our region 
through this time frame. This will offer several chances for 
showers, however the overall flow regime looks to be progressive.

Synoptic Overview...An upper-level trough will slide east from the 
Great Lakes region later Tuesday and cross the Northeast Tuesday 
night into Wednesday morning. The flow aloft then turns more zonal 
for a time, before the next trough in the northern stream amplifies 
eastward across the Great Lakes region. This feature may phase with 
a southern stream short wave trough as it gets to the East Coast by 
late Friday. The next system looks to quickly arrive later in the 
weekend to early next week.

For Tuesday night and Wednesday...An upper-level trough is forecast 
to cross the Northeast Wednesday morning, taking surface low 
pressure with it. These features pass north of us while an 
associated surface cold front crosses our region early Wednesday 
morning. The bulk of the forcing is forecast to remain removed from 
our area, and the ascent associated with the cold front looks to be 
on the weaker side. While some showers look to occur Tuesday night 
into Wednesday morning, it looks like much of the activity weakens 
or dissipates with a southern and eastern extent. The cold air 
advection behind the front does not look to be all that strong, and 
therefore while temperatures will drop back some it will still be 
mild Wednesday overall. The passage of the cold front and low 
pressure to our northeast though will result in a tightening 
pressure gradient for a time. This combined with deeper mixing 
during the day Wednesday will result in a gusty breeze at times 
before settling down Wednesday night as weak high pressure builds in.

For Thursday and Friday...A weak surface high slips offshore, and 
while a dry Thursday (daytime) is anticipated a return flow will 
setup allowing moisture to start increasing northward. An upper-
level trough in the northern stream may start to interact with a 
southern stream system Thursday night. The warm air advection and 
increasing isentropic lift will result in the clouds to increase by 
late Thursday, with the potential for showers to be on the increase 
Thursday night. If enough interaction occurs, there could even be a 
period of steady rain Thursday night. The showers looks to continue 
for at least the start of Friday, however the main cold front is 
forecast to shift offshore by late afternoon. This timing however 
could change depending on the phasing of the two systems. A 
secondary cold front may move through Friday night, however this 
looks to be dry as the main forcing and deeper moisture is offshore.

For Saturday and Sunday...High pressure briefly builds in for 
Saturday, however another short wave trough is forecast to move 
across the Great Lakes region Saturday night and Sunday. This will 
pull a cold front across our area later Sunday although moisture may 
be limited and the main forcing moves by to our north. The front may 
then start to stall to our south Sunday night.

For Monday...As the flow aloft in the East becomes more zonal, a 
frontal zone should be stalled to our south in an east-west fashion. 
As some energy ejects out of the southern Plains and around a ridge 
building across the Southeast U.S., a round of warm air advection 
induced showers/thunder may arrive in parts of our area mainly late 
Monday. This will all depend on the timing and strength of the short 
wave energy and associated warm air advection as the main trough 
looks to hang back across the southern Rockies.


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

This evening...Mostly VFR, but some MVFR CIGs possible through 00Z. 
Some light rain at the TAF sites, but VSBY restrictions not 
expected. N-NW winds 10-15 kt with 18-23 kt gusts.

Tonight...VFR. MVFR VSBY in BR possible in the pre-dawn hours at 

Tuesday...VFR. SW winds 5-10 kt. Afternoon seabreezes at

Tuesday night and Wednesday...VFR ceilings overall. Some showers 
should be around, then drying and clearing during Wednesday. 
Southwest winds 10 knots or less, becoming west-northwest Wednesday 
and increasing to 10-15 knots with gusts up to 25 knots.

Thursday and Friday...VFR during the day Thursday, then MVFR or 
lower possible with showers and some thunderstorms Thursday night 
into Friday. Light northwest to southwest winds Thursday, then 
becoming west-northwest around 10 knots Friday.

Saturday...VFR. West-northwest winds 10-15 knots.


Seas have dropped below 5 feet on the ocean, so will cancel the SCA. 
Sub-SCA conditions on tap for the rest of tonight and for 

Tuesday night and Wednesday...The conditions are anticipated to be 
below Small Craft Advisory criteria overall. A short duration of 
westerly wind gusts to near 25 knots may occur later Tuesday night 
into Wednesday morning behind a cold frontal passage. In addition, 
some gusts may near 25 knots at times nearshore Wednesday afternoon.

Thursday and Friday...The conditions are anticipated to be below 
Small Craft Advisory criteria.

Saturday...West-northwest winds turn somewhat gusty, however it 
should remain below Small Craft Advisory criteria.


The KDIX radar remains out of service as technicians continue to
troubleshoot the ongoing issues. Surrounding radars include,




Near Term...MPS
Short Term...MPS
Long Term...Gorse