Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 010150
Area Forecast Discussion
National Weather Service Mount Holly NJ
950 PM EDT Sun Apr 30 2017
High pressure offshore will cause a warm front to lift across the
area Monday morning. Low pressure will will move from the upper
Great Lakes region Monday through southern Canada Tuesday. It
will cause a cold front to cross our area Monday night. An area
of high pressure will move over the area during the middle of
the upcoming week. More low pressure will bring unsettled
conditions for Thursday and into the early part of next weekend.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
930 PM ESTF: Adjusted temps/dews downward overnight based on
current reality. Drizzle in the fcst in central NJ now and
spread it north to blend with the previously fcst drizzle late
at night further north. Fog wont form til late at night. too
much wind and dewpoint spread at 01z/01 (as of this writing).
Strong warm front extreme s DE at 01z (sank swd a few miles
since 22z) with dewpoints mid 60s along and south of the front
overrunning the 50s air temp across NJ.
As the flow aloft increases through the night along with warm
air advection, some lift looks to be generated although this
should be on the weaker side. Some guidance wants to produce
some showers mainly across the northern areas. We included a
slight chance PoP at this point starting a little later this
evening, however the forecast soundings indicate stratus with
perhaps some drizzle occurring overnight especially across the
central to northern areas. It is these areas that may experience
more fog overnight as the low levels saturate within a
southeasterly low-level flow north of an incoming warm front.
While some dense fog is possible overnight, it is not a
certainty given increasing flow and some weak short wave energy
moving through. Depending on the movement of the warm front
overnight, the clouds may thin out across parts of the southern
areas leaving some fog behind.
Low temperatures were mostly a blend of MOS and continuity. The
hourly temperature, dew point and wind grids through at least early
this evening were adjusted based on some of the high-res model
guidance. This included initially showing warmer inland temperatures
for many locales.
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
An upper-level ridge will be to our east as a closed low tracks into
the Great Lakes by the end of the day. This will allow for
increasing southwesterly flow including a low-level jet. This along
with an increase in warm air advection will assist in pushing a warm
front to our north during the morning. This will allow for areas of
low clouds and fog (perhaps drizzle) to dissipate/end from south to
north. This process should occur fairly quickly during the morning
as the strengthening wind field promotes mechanical mixing.
As the lower clouds/fog dissipate, boundary layer heating will occur
faster and this will promote deeper mixing especially from late
morning onward. This is expected to result in breezy conditions
particularly for the coastal plain in the afternoon, with gusts to
about 30 mph. The combination of warm air advection, deeper mixing
and a southwesterly flow will allow for after temperatures to get
into the upper 70s to lower 80s for much of the region. In addition,
the dew points will be gradually increasing.
The aforementioned closed low tracks into the Great Lakes region
toward late in the day, with surface low pressure with it. An
associated cold front will be approaching our area late in the day,
with nearly all the forcing associated with it. Given the deep
southwesterly flow, a lee side trough does not appear to develop. As
a result, we slowed down the PoP increase from west to east with
much of the area tending to be dry through the day. There should be
a strong to potentially severe convective line approaching our
western zones late in the day, however this may not arrive until the
early evening hours. High temperatures were a MOS blend with some
upward adjustments given the anticipated better afternoon mixing
(much closer to the warmer GFS MOS).
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
There will be two weather systems of significance in the longer
range part of the forecast. First, Monday night a strong cold front
will be in the process of crossing the Middle Atlantic / Northeast.
The front will be preceded by warm and humid air and this will
cause abundant showers and some tstms to accompany the front. While
widespread severe weather is not expected, the front may have some
stronger tstms. The SPC Day 2 outlook which covers into Monday
night had higher probabilities just west of our area. Once the front
passes through, colder air will be over the area Tuesday. A couple
afternoon showers N/W are possible Tue/Tue evening.
A dry period from Tuesday into Wed night with temperatures close
seasonal normals. Highs Wed will be in the low 60s north and upper
60s around metro Philadelphia and over Delmarva.
The second system will bring rains and clouds for Next Thu and with
the slow nature of the system, these rains could persist into early
next weekend. Both the 12Z GFS and EC models are showing a slowly
moving upper/sfc low moving across the area from the SE states. The
low could bring soaking rains to much of the area with some models
already showing 1-3 inches across our CWA through this period. This
will be the system to watch this week. Temperatures will be near pr
a little below normal with numerous clouds expected.
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Tonight...Ceilings are expected to lower everywhere to IFR
(locally LIFR in st/fog toward 08z) as a warm front in far
southern DE slowly lifts north after midnight. Some drizzle
should develop, however the extent of this is less certain at
this time and is primarily forecast in the north and central
parts of NJ. Visibilities are currently forecast to lower into
the 1-4SM range but patchy 1/4-1/2sm fog is possible, especially
NJ coastal plain as the the 18z NARRE by 05z. Some improvement
may take place toward morning especially at MIV and ACY as the
warm front shifts northward. east to northeast winds gusting 12
to 20 kt knot should subside overnight.
Monday...IFR/MVFR conditions to start at most terminals, then
improving to VFR by late morning. MIV and ACY could have little to
no clouds, but may start with some fog. South to southwest winds
increasing to near 15 knots with mainly afternoon gusts to around 25
knots (highest gusts may be from TTN-PHL/PNE-ILG on south and
Mon night...Widespread lower cigs and vsbys with showers and sct
Tue thru Wed night...Mostly VFR.
Thu thru Fri...Lower cigs/vsbys with showers and tstms.
A front stalled just to our south this afternoon will shift northward
as a warm front Monday morning. Warmer air and eventually an
increase in low-level moisture will lead to some fog tonight and
early Monday. Some of this could become dense (1NM or less),
however some increase in wind from south to north may prevent
this from becoming widespread. The onshore flow will gradually
shift to south and then southwest late tonight and especially
Monday and increase as the warm front moves through. This will
initially build the seas late tonight but especially during
Monday. There will be much warmer air overspreading the area
Monday and this should tend to shift the strongest winds closer
to the coast where mixing is most efficient. Wind gusts up to 30
knots are anticipated, and this should occur on Delaware Bay as
well therefore a Small Craft Advisory was added starting at
16z. The Small Craft Advisory for the coastal waters starts at
10z as seas should be near 5 feet at this time.
Mon night/Tue/Tue night...Ongoing SCA. Showers and tstms Mon
night. Fair weather Tue and Tue night.
Wed thru Thu...SCA diminishing Wed morning then sub-SCA.
Thu thru Fri...SCA expected. Showers and tstms.
**Record warmest April on record in part of our area**
RER`s..record event reports wont post til Monday morning at the
Max temps checked through 5P today and only the mins this
evening ending at 1 AM will adjust the average maybe 1 tenth of
PHL normal 54.0 POR 1874
59.5 2017 this still could slip .1 degree if the low this
evening is colder than 53.
23 of the past 25 months have been above normal. The last
long duration cold period was Jan-March 2015.
ABE normal 49.9 POR 1922
56.8 Record! Could still be 56.7 if this evenings low is below
24 of the past 25 months have been above normal with the last
long duration cold period was Jan-March 2015.
ACY normal 51.7 POR 1874
only 4 of the past 25 month have record below normal
temperatureswith the last long duration cold spell, Jan-Mar
MARINE...Small Craft Advisory from 6 AM Monday to 8 PM EDT Tuesday for
Small Craft Advisory from noon to 8 PM EDT Monday for ANZ430-
Near Term...Drag/Gorse 950