Scientific Forecaster Discussion
fxus61 kphi 261942
Area forecast discussion
National Weather Service Mount Holly New Jersey
342 PM EDT Wed Apr 26 2017
a weakening coastal low near Long Island will move slowly northeast
overnight. A cold front will move across the area late Thursday
night and early Friday morning before another cold front crosses
Saturday night. A warm front is then expected to lift north across
the area Sunday night, followed by another cold front Monday night.
High pressure is then expected for the middle of next week.
Near term /until 6 am Thursday morning/...
rest of today...ceilings slowly lifting with some breaks in overcast
or brightening and temps ever so slowly warming as the vertically
stacked low pressure system off the New Jersey coast heads east. There
may still be some spotty mist or an isolated shower/ sprinkle
into this evening, mainly NE New Jersey.
Tonight....where it clears...fog may form right away...otherwise
a deck of clouds may persist much of the night near 2000 or 3000
ft that would prevent significant fog and stratus formation during
the night. Confidence on stratus-fog formation, expansion/reformation
is below average but we have maintained it in the fcst..using the
ups crossover tool. Fcst was was a 50 50 blend of the 12z/26
GFS/NAM MOS. Fcst mins are 8 to 12 degrees above normal.
Short term /6 am Thursday morning through 6 PM Thursday/...
mostly cloudy to start...but all model tsections fcst a much
brighter and warmer day... with a decent amount of afternoon
sunshine so have used the 12z/26 GFS/NAM MOS blend for the fcst
basis. Fcst temps are 7 to 13f above normal. Max T at phl may
reach 82 or 83.
Long term /Thursday night through Wednesday/...
a cold front associated with low pressure moving north through
eastern Canada is expected to cross the region Thursday night, then
move off the coast Friday morning. Mainly scattered showers are
expected at this time, primarily from midnight through 6 or 7 am. A
southerly flow aloft will maintain low temperatures in the mid to
upper 40s and high temperatures in the upper 70s to low 80s, above
normal for this time of year. The daytime hours on Friday will
feature mainly dry weather has high pressure briefly builds into
By Friday night, another frontal boundary is forecast to begin
approaching the area from the northwest as it crosses Pennsylvania
and New York. The front will sag south through the area during the
day Saturday, bringing with it some additional shower activity, then
stall to our south Saturday night into Sunday. The subsequent
onshore flow will cool temperatures down to the 60s north and low
70s south on Sunday,but with mainly dry conditions. This front is
then expected to lift back north as a warm front Sunday night into
Monday morning, with an increasing chance of showers as the day
wears on with the approach of a cold front from the west late in the
day. Showers and thunderstorms may accompany this front...especially
later Monday night into Tuesday morning. Instability in the warm
sector ahead of this front could even produce shower and
thunderstorm activity as early as Monday afternoon. High
temperatures in the 70s are expected on Monday.
The front will move offshore by Tuesday morning, but a secondary
surface trough may move across the area during the day. With a short
wave/vorticity Max moving across the area during the day, there
could be some isolated showers across northeastern Pennsylvania and
northern New Jersey. Cooler temperatures are expected through mid
week, with lows generally in the 50s and highs in the 70s.
Aviation /20z Wednesday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Rest of this afternoon...cigs 1000 to 2500 feet continue to improve-
rise-lift. Light north to northeast wind.
Tonight...probably MVFR cigs to start but may deteriorate to IFR
conditions in St/fog with a nearly calm wind sometime between
06z and 12z/27. Please see tafs for details.
Thursday...IFR or MVFR conds in St/fog to start the day, probably
improves to VFR sct-bkn clouds aoa 3500 feet during the afternoon.
Wind becoming southeast to south with mid afternoon gusts 15-20kt.
Thursday night...generally VFR. A chance of showers overnight
which could temporarily reduce conditions to MVFR.
Friday...VFR conditions expected.
Friday night...VFR early. Patchy fog and low ceilings may develop
Saturday...becoming VFR during the morning, then a chance of
showers during the afternoon. Conditions may temporarily be
reduced with any showers.
Saturday night-Monday...low clouds and fog may develop
overnight Saturday and continue into Sunday leading to reduced
conditions. There will also be a chance of showers.
the Small Craft Advisory hazardous seas continues through
Thursday. Waves (virtually all se swell at 10-11 seconds) are
currently around 7 ft and will gradually subside through
Thursday. How much marine fog develops the next day or so.?
unsure...so fcst the fog conservatively for now.
Thursday night...Small Craft Advisory for hazardous seas
through Thursday night.
Friday...winds expected to remain below advisory levels, but
seas may remain elevated to advisory levels.
Friday night-Monday...winds are expected to remain below
advisory levels. Seas may approach 5 feet at times, but mostly
remain around 4 feet.
tides fcst near advisory threshold this evening. Holding off on
an advisory for now but may need to issue for minor coastal
flooding around 6 or 7pm if departures do not further decrease.
We will continue to monitor the high tide this evening since it
will be the higher one that occurs with a new moon. If the water
does not drain away from the coast fast enough, we could see
some localized minor flooding at that time.
presuming our forecast temps these last 5 days of April are accurate,
we are assured of a top 3 warmest April on record in much of our
forecast area. Sunday is the critical day for determining record
Below: April projected within the top April avg temps, the
normal for April and the period of record (por).
Phl normal 54.0 por 1874
Abe normal 49.9 por 1922
56.6 projecting record
Acy normal 51.7 por 1874
57.2 projecting record
Marine...Small Craft Advisory for hazardous seas until 6 am EDT Friday
near term...drag 342