Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 221904
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
304 PM EDT Mon May 22 2017

.SYNOPSIS...
Weak low pressure is developing on a warm front from the Delmarva
Peninsula into southern New Jersey today. A cold front approaching
from the west will merge with the warm front just off the mid
Atlantic coast tonight. Low pressure in North Carolina Tuesday will
pass east of the mid Atlantic coast Tuesday night. Weak high
pressure is left behind over our area Wednesday. Stronger low
pressure organizes in the Ohio Valley Wednesday night sending its
associated fronts through the mid Atlantic states late Thursday or
early Friday as the low moves into New England. High pressure should
follow for the weekend.


&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
An occluded frontal boundary approaching the area from the west this
afternoon and evening is expected to move across the area tonight.
The associated warm front is expected to stay to our south as an
area of low pressure moves off the Delmarva coast later this
evening. North of the warm front and low pressure, there will
continue to be showers moving across the area, with the heaviest
rainfall across southern New Jersey and Delware late this afternoon.
The majority of the showers are expected to dissipate this evening
and overnight.

There will be plenty of moisture around through tonight, especially
before the frontal boundary pushes through the area. As winds become
light and variable, it is possible that some fog may develop. How
thick it becomes is uncertain as there is some vorticity forecast to
move across the area, and positive low level lapse rates, so there
could be enough weak lift and turbulence to prevent it from become
widespread dense. So no Dense Fog Advisory is planned at this
time.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
The frontal boundary that moves across the area overnight is
expected to stall to our south. An area of low pressure is forecast
to move along this boundary from the south, as the first low
pressure lifts to the northeast. The low pressure, nor the frontal
boundary, is expected to make its way back into our area during the
day, however there will be a chance of showers to lift across
portions of the area later during the day on the north side of the
low. The greatest chance for showers will be across southern
Delmarva and souther New Jersey. With no instability forecast, we do
not expect any thunderstorms across our area.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
DRAFT DRAFT DRAFT for the 330 PM discussion:

**Flood potential may exist where its rained more than 2 inches
 today in SNJ and the Delmarva**

12Z NAM not applied for this discussion. Its not off to a good
start for today.

500mb: 500mb: A sharpening and unusually strong high amplitude
trough in the nations midsection will closed off and weaken as
it moves to new England Friday, with ridging to follow this
weekend. The next trough will be organizing in the Great Lakes
region early next week.

Temperatures: Calendar day averages Wednesday-Saturday near
normal warming Sunday and Monday to nearly 5 above normal,
ahead of the next trough.

Forecast basis: a 50 50 blend of the 12z/22 GFS/NAM MOS for
Tuesday night through Wednesday night,  then the 12z/22 GFS
MEX MOS for Thursday with the 15z WPC guidance for Thursday
night-next Monday. Any substantial deviations from the basis
above, will be noted:

The dailies...

Forecaster confidence is below average on details through Friday
morning.

Tuesday night through Wednesday...Depending on the path of
the next coastal...a risk of rain south and probably dry north.

Thursday...Looks wet in warm air advection.

Friday...After any early morning showery rains depart with the cold
frontal passage...a breezy west wind should develop with
afternoon warming.

Memorial Day weekend...Warming will continue in the lower levels
with a strengthening west to southwest flow as high pressure
starts to build in from the southwest. Showers may approach from
the west late Monday but for now...we`ll consider that possibility
as a low probability of occurrence prior to sundown Monday
evening the 29th.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.

IFR conditions remain across the TAF sites this afternoon as low
clouds and rain continue across the area. There has been some breaks
in the low level clouds, revealing some slightly higher cloud decks
across the area, so it is possible that there could be some
temporary MVFR conditions develop. But with the amount of moisture
around the area, we expect the lower clouds to fill back in.

An occluded cold front is forecast to move across the area overnight
tonight. As this front moves across the area overnight and toward
daybreak Tuesday, it is possible for conditions to improve to MVFR
from west to east. It is entirely possible that conditions may
improve to VFR during the day Tuesday, especially for ABE and RDG.
But we will keep MVFR conditions further south across ILG, PHL, PNE,
and TTN. IFR conditions remain in the forecast for ACY and MIV as
there is the possibility they may be affected by an area of rainfall
that lifts into our southern areas north of an area of low pressure
to our south.

Generally east-southeast winds will continue across the TAF sites
this afternoon north of the warm front to our south. However, winds
are expected to become light and variable this evening and
overnight. As the occluded frontal boundary moves across the area,
winds will become north-northwest to north-northeast. Speeds through
the next 24 hours are expected to be 5-10 knots or less.

OUTLOOK...
DRAFT for the 330 PM issuance.

Forecaster confidence on details is below average Tuesday night
through Friday morning.

Tuesday night...VFR conditions north and possibly the entire area
but a risk of MVFR/IFR in rain vicinity KMIV/KACY. Light
northeast wind.

Wednesday...VFR except possible MVFR/IFR conditions during the
morning KMIV and KACY. East to northeast wind gusts to 15 mph.

Thursday...VFR CIGS with periods of MVFR/IFR in showers and isolated
thunderstorms. easterly winds probably becoming southeast to
south at night.

Friday...Improving conditions after any early morning showers end
with mainly VFR expected. Westerly wind gusts to 20 kt possible
in the afternoon.

Saturday...VFR.  Westerly wind gusts to 20 kt.

&&

.MARINE...
Winds and waves will remain below Small Craft Advisory levels
tonight through Tuesday. Wind directions will begin out of the
southeast this evening and overnight, before becoming north-
northwest to north-northeast late tonight into Tuesday as an
occluded front moves across the area.

OUTLOOK...
Draft for the 330 PM issuance.

Forecaster confidence on this outlook section is below average
Tuesday night through Friday morning.

Tuesday night and Wednesday...Leftover SCA for hazardous seas
possible...mainly the DE Atlantic coastal waters. Otherwise
northeast to east wind with gusts generally under 20 kt.

Thursday...SCA probable for the well organized Ohio Valley low.
East to southeast winds build the seas to b between 5 and 8
feet on the Atlantic waters.

Friday...SCA may continue for leftover Hazardous seas on the
Atlantic portion of our coastal waters.  Westerly wind develops
with gusts to 20 kt.

Saturday...Small chance an SCA for westerly nearshore gusts of
20 to 25 kt.

&&

.HYDROLOGY...
1137AM: DOX and DIX STA (DP)/STP (LEGACY) are underestimating
rainfall. Ditto MRMS. We are using FFMP HPE. PNS for 1.75 inch
or greater amts will post soon as we are seeing numerous reports
of 1.5 to 2.5 inch rainfall since 230 this morning. At this
time...DIX STP (Legacy is performing best vs its DP). DOX
STP/STA are almost identical and far too low.

The Flood Advisory updated statement (FLS) will post soon. At
1PM we will consider extending the NJ portion and cancel the MD
DE portion.

The Flood Advisory for generally nuisance potentially travel
slowing/altering poor drainage street flooding continues. This
advisory is because of overrunning along and just north of the
warm front that shows light southerly flow in the warm sector
and light northeast flow just north of the boundary. PWAT is
near 1.75 inches. 12z NAM is off to a poor start.

&&

.TIDES/COASTAL FLOODING...
DRAFT for 330 PM discussion:

Astronomical tides are at some of their highest of the year this
Wednesday and Thursday evenings. Some onshore flow will contribute
positive departures and its probable that a few locations along
the Atlantic coasts of DE and NJ will exceed the minor coastal
flood advisory threshold. It only takes about .6 to .7 feet
above high tide to reach the threshold. It`s all in the details,
which are yet to be confidently determined. This mornings
12z/22 NAM does not loom to be off to a good start. We will
eight its guidance less than other traditionally used models.
for now the SIT and ETSS modeling forecasts minor with a small
chance of a moderate episode if prior to high tide onshore is
strong enough for enough duration.

&&

.CLIMATE...
Record daily rainfall at ACY has a good chance of exceedance.
1.19 inches is the daily record set in 1909. as of 1205 PM 1.13
inches...appears well on its way to a record for this date.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

Synopsis...Drag
Near Term...Robertson
Short Term...Robertson
Long Term...Drag
Aviation...Drag/Robertson
Marine...Drag/Robertson
Hydrology...
Tides/Coastal Flooding...
Climate...



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