Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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059
FXUS61 KPHI 191133
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
633 AM EST Mon Feb 19 2018

.SYNOPSIS...
A strong warm front will lift through our area tonight as low
pressure heads from the Ohio Valley into the Quebec by midweek.
The associated strong cold front will ease southeast through our
area Wednesday night. Thereafter, strong high pressure builds
to our north Thursday and to the Maritimes by Saturday while a
warm front forms to our southwest. Low pressure heads into the
northeast USA next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
An area of showers associated with a weak shortwave/vorticity
impulse will slide into the area early this morning, but should
continue to weaken as they make their way into the area. We have
added some POPS to almost everywhere this morning, especially
the southwest portions of the CWA where the showers will hit
first. Otherwise, no additional changes to the overall forecast
at this time.

High pressure that controlled the weather overnight has pushed
offshore and will center itself south of the Canadian Maritimes
today. This will set up a return flow across the east coast
today, with a warm front located well to our south. The front
will be lifting northward through the day, but it will not make
it into the region during the daytime hours. Moisture will be on
the increase across the area through the day, so clouds will
increase through the morning and into the afternoon. A couple of
short wave/vorticity impulses will be moving across the area
later this afternoon. The lift from these impulses, combined
with the enhanced moisture across the area lifting north of the
warm front will lead to a period of light rain this afternoon,
especially for portions of northeastern Pennsylvania and
northern New Jersey. It is possible that portions of southern
New Jersey, as well as southern Delaware and Maryland could
remain dry. But we will keep a chance of rain in the forecast as
there could be a few showers. While temperatures are below
freezing this morning for most areas, by the time the
precipitation arrives, temperatures will be above freezing, so
no wintry precipitation is expected.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
The short wave and lift that will help create the rain this
afternoon will be lifting out of the area during this evening.
Therefore the rain is expected to tapper off and lift to our
north during the evening hours. The warm front to our south will
continue lifting to the north overnight, but it is not expected
to lift all the way through by daybreak Wednesday. There will
be an inversion developing across the area, and moisture is
expected to get trapped in the low levels north of the warm
front. This will likely lead to areas of fog and low stratus
overnight tonight into early Tuesday morning. Where ever the
warm front does lift through, the fog may begin to dissipate;
this would most likely be southern New Jersey and southern
Delaware and Maryland. It is possible that some patchy dense fog
may develop, but winds may be elevated enough in many locations
to prevent widespread dense fog from developing. It is also
possible that some drizzle may develop as well, especially where
the fog becomes thickest.

Very late in the night, toward the early morning hours Tuesday,
as a bubble of enhanced area of Theta-E lifts across coastal
areas of Delaware and New Jersey, there is indication by the
models that some light showers may develop. So we`ve added some
POPS late in the overnight/early morning hours for the coastal
areas.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
**Record warmth likely Tuesday and everywhere on Wednesday**

Hazards: Possible ice Thursday, and then again Friday into
Saturday near and north of I-80.

500 MB...an anomalously warm strong ridge along the east coast
prevails with a positive tilt trough back to the western USA,
ejecting short waves northeastward. One short wave dents the top
of the ridge Thursday. Subsequently another 1 or 2 disturbances
ride into the northeast states by the weekend at the same time
a blocking pattern becomes evident in Greenland with -NAO
development.

Temperatures: As we head toward a top 10 warmest February on record,
multiple records are anticipated this coming week. The climate
section has the record temperatures for Tuesday and Wednesday, and
also the record rainfall for ACY which may be rewritten this
weekend. Calendar day average temperatures Tuesday will be
20-25F above normal, 25-30F above normal Wednesday, then
substantial differences develop between the warmer GFS and the
colder ECMWF. The GFS continues 15 above normal Thursday, near 8
above Friday, 15 above Saturday and Sunday. The ECMWF is much
cooler with only about 10 above Thursday, 5 to 7 above Friday,
10 to 15 above Saturday and less than 10F above Sunday. With
blocking developing this weekend, i am favoring the colder EC
solution and this forecast in my opinion for Thu-weekend is not
cold enough across the board.

Forecast basis: Unless otherwise noted used a 50 50 blend of
the 00z/19 GFS/NAM MOS Tuesday-Wednesday (except mostly warmer
GFS temps). Thereafter the 00z/19 GFS MEX MOS Wednesday night-
Thursday and the 06z/19 WPC 12 hr max/min pop, 6hr td/wind/sky
with all the temps blended colder using the GGEM/ECMWF 2m
temps.


The dailies...

Tuesday...Record warmth likely (forecasting record equaling or
exceeding at 5 stations including ACY, PHL, ILG GED MPO). The
NAM in southwest flow tends to hold onto too much low lvl
moisture, thereby forecasting too cool. My primary concern with
temps is over the remaining rapidly melting snow cover of ne PA
and NNJ which should for the most part be depleted. Morning
fog/low clouds should give way to increasing afternoon sunshine.
Southwest wind gusts 20 mph during the afternoon. Confidence:
Average, the limit is stratus capping potential warmth.


Wednesday...After any predawn reforming of stratus/spotty fog, a
mostly sunny record warm day is expected with southwest wind
gusts 20-25 MPH. A couple of locations may approach all time
February records with 13C at 850 MB. Showers are now confined to
mainly ne PA late in the day. Confidence: Well above average.
Records should be exceeded at all stations and while this
forecast may be 2 or 3 degrees on the warm side, have taken into
acct the typical cool bias within a day of cfp on sw flow. A
564 1000-500 thickness. In some locations, the record could be
exceeded by 4 to 7 degrees.

Also, the numbers posted this morning are within 3 degrees of
all time Feb records at ILG TTN GED RDG MPO. So no guarantee of
getting that close but the forecast is the best estimate. If we
are correct on GED`s 77, that would equal their all time Feb
record set February 25, just last year.

Wednesday night...a cold frontal passage but probably too late
to prevent record warm daily mins for Wednesday as well. There
could be a few showers with the front, mainly I78 north. All the
record warm mins are in the Climate section. Confidence:
Above Average.


Thursday...(max temps for the day at 1201AM!) Cloudy and much colder
with a gusty north-northeast wind developing and a period of cold
rain likely. It`s possible sleet or freezing rain will occur
along the northern fringe from ne PA through far northwest NJ
but not enough confidence to grid-fcst at this time.
Confidence: Above Average.


Thursday night...a period of clearing is possible as a subtle
ripple of low pressure along the front that brought the rain
Thursday zips off the coast and allows the front to sag well
south of our area. Confidence: Average.


Friday-Saturday-Sunday...Provocative in multiple ways. Once
cold air gets in, its hard to dislodge with high pressure to the
north and northeast. We will be at the top of the ridge with
short waves not forcing much lowering of surface pressure but
sending periods of precipitation east north east into our area.
It looks like there will have to be some icing occuring in ne PA
and nw NJ, especially high terrain n of I80 Friday morning Its
possible this could turn into a subtle ice storm depending on
the duration of the icing. Have lowered guidance temps from the
00z/19 values and suspect am not cold enough in ne Pa and nw NJ
for most of this 3 day period. Confidence: Average.

Also, I am not starting a hydro section today, but there is
potential for a couple of inches of rain Friday-Sunday, in
pieces. That could be pushing a few small streams to near
bankfull. See and follow WPC D4-7 guidance for both qpf and
winter the next couple of days. MMEFS will soon extend into the
weekend for other review.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...VFR conditions with light and variable winds will start
the day off as high pressure moves out to sea. Some showers may
affect the TAF sites this morning as an area of showers moves in
from the southwest. Any steady wind direction will be from the
east to southeast this morning. Winds will increase out of the
south- southeast through today around 5-10 knots. Clouds will
increase through the day, and lower to MVFR and possibly IFR by
this afternoon. As a warm front lifts toward the region,
rainfall is expected to move into the area by this afternoon,
and could affect all TAF sites. The most likely sites to be
affected for the longest period of time by rain will be ABE and
RDG.

Tonight...Conditions expected to continue to lower to IFR
overnight as a warm front lifts into the region. The front is
not expected to make it all the way through the area through
daybreak however. North of the warm front, IFR conditions with
low clouds, fog, and possibly drizzle are expected. South of the
warm front, the fog and low clouds may lift. Winds will be
mostly south to southeast north of the warm front, then turn
south to southwest south of the warm front with speeds generally
around 5 knots or less.

OUTLOOK...

Tuesday morning...Leftover IFR conditions expected in low clouds and
fog.  Southwest wind.  Confidence:  Average.

Tuesday afternoon and evening...Mainly VFR.  Southwest wind gusty 20
kt.  Confidence:  Above Average.


Tuesday night and Wednesday morning...Patchy low clouds and fog with
some IFR conditions possible.  Southwest wind.   Confidence: Average.


Wednesday afternoon...Mainly VFR. Gusty southwest wind 20 kt.
Confidence:  Well above Average.


Wednesday night...VFR with a chance of showers vcnty KRDG/KABE/KTTN
and wind shift from southwest to northwest-north near or after
midnight.   Confidence:  Well above average.


Thursday...VFR with possible MVFR conds in a period two of
rain. a Gusty north to northeast wind developing of 15-20 kt.
Confidence: Above average.


Thursday night...VFR.  Northeast wind.  Confidence:  Above Average.


Friday...VFR to start but deteriorating to MVFR or IFR conditions in
rain. Northeast wind to start becoming east or southeast at
night. Confidence: Above Average.

&&

.MARINE...
Conditions will remain below Small Craft Advisory levels
through tonight. Winds will remain 10-15 knots as high pressure
pushes to the east, and a warm front lifts toward the area
overnight. Seas will build some overnight, but may only reach 3
to 4 feet. Areas of fog and drizzle are likely to develop this
evening and overnight as warm, moist air moves across the waters.
There may even be some showers later today and into tonight as
well.

OUTLOOK...
Tuesday through Wednesday...Wind speeds and wave heights are forecast
to remain below the Small Craft Advisory criteria. A 3 to 4 ft southerly
5 second wind wave group will be predominant in the Atlc coastal waters.
Patchy fog may develop over the coastal waters. Confidence: Well
above Average except less certainty on fog.

Thursday through Friday...An SCA, especially for seas may be
needed for the Atlantic waters due to persistent northeast flow.
Confidence: Average.

&&

.CLIMATE...
Record high temperatures are possible on Tuesday and Wednesday.

Tuesday, February 20:

Atlantic City...70 in 1930

Philadelphia....70 in 1939

Wilmington......71 in 1930

Allentown.......68 in 1930

Trenton.........70 in 1930

Georgetown......68 in 2002

Mount Pocono....59 in 1930

Reading.........72 in 1930


Wednesday, February 21:

Atlantic City...74 in 1930

Philadelphia....72 in 1930

Wilmington......70 in 1953

Allentown.......67 in 1953

Trenton.........70 in 1930

Georgetown......71 in 2014

Mount Pocono....60 in 1930

Reading.........71 in 1930


A record warm minimum temperature may be set for Atlantic City
on Tuesday. The current record is 44 in 1949.


The following are the record warm minimum temperatures for
Wednesday, all which should be exceeded.

ABE 46-1981
ACY 49-1954
PHL 49-2002
ILG 47-2002
RDG 48-1930
TTN 48-2002


The all time February max temps may be approached on Wednesday
at ILG, TTN, GED RDG MPO. All the all time monthly max`s are
listed below:

ACY 77 2/25/30
PHL 79 2/25/30
ILG 78 2/24/85
ABE 77 2/24/17
TTN 76 2/25/30
GED 77 2/25/17
RDG 77 2/24/17
MPO 70 2/25/30

Our expectation is that ACY will exceed the previous all time
record rainfall for February, by the end of the weekend. The
record is 6.50 inches in 2010. #2 is 1958 with 5.98 inches.

And...adding only half an inch to PHL and ILG will put both
locations in the top 9 ranking for Feb rainfall.


Have rechecked the monthly projection at PHL and the avg temp
continues at 41.0 or 5.3F above avg which is 8th warmest on
record, if it holds. Add or subtract a degree to the
average/departure and the ranking changes from 3rd to 11th. The
forecast 5.3F departure is ~2f warmer than the current
departure. I`d expect similar for the rest of our area...a bit
less in the north which will have better chances for colder air,
and a bit more warming in the south where the positive departure
as of yesterday was already 5F above normal, heading for 7+. So
all in all it appears we`re heading for a top 10 warmest
February. Last year was the warmest on record, a whopping 3+F
degrees warmer than our current projection.

&&

.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
Climate...Drag



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