Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 211942
Area Forecast Discussion
National Weather Service Mount Holly NJ
342 PM EDT WED SEP 21 2016
High pressure will continue to build southeastward over the region
tonight and become established over our area through Friday with
the remnants of Julia well offshore. A backdoor cold front will then
move through the region on Saturday and be followed by another high
pressure system building in from the northwest early next week. By
the middle of next week, a cold frontal boundary will move toward
the region from the west.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Thick cirrus remains over much of the area this afternoon but a
gradual thinning of these clouds will occur through this evening and
especially overnight. Areas to the south and east may continue to
see continual cloud cover overnight with thinning occuring more
towards tomorrow morning.
Aside from the clouds, tonight looks to be a fairly nice night. The
airmass continues to dry out, with the exception of the far
southeastern areas, and fog should be less of an issue overnight but
we may still see some patchy fog occur.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Thursday will be similar to today but with an easterly flow, it
might end up a degree or two cooler but areas along the coast will
be closer to 5 degrees cooler today. Temperatures across the region
will generally be around 80 to 85 with mid to upper 70s along the
The remnants of Julia may keep the clouds around our southern areas
for a bit longer into Thursday but it looks like the bulk of the
showers will remain to the south and east of the area.
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Thursday night through Friday night:
High pressure will continue to build into the region Thursday
night and become established across the region on Friday.
Favorable conditions for radiational cooling are expected Thursday
night with lows in the 50`s and low 60`s. Some cloudcover ahead of
an approaching frontal boundary may keep low temperatures slightly
higher Friday night. Friday looks like the last of the anomalous
early fall heat for at least a little while with hell well into
the 80`s. Modeled boundary layer temperatures indicators of
surface temperatures match well with MET/MAV and ECMWF
Saturday through Monday night:
A cold front will move from northeast to southwest across our
region. Our coolest airmass of the season will advect in as
another high pressure system dives southeast from Canada. Enough
lift and moisture may be present for a temporary increase in cloud
cover and isolated showers on Saturday otherwise continued dry
conditions. temperatures will be much cooler for the weekend.
Some indications in ensemble guidance have a slightly delayed
frontal passage which may allow for Saturday to get into the 80`s.
However, we will stick with the mean timing of early Saturday with
the operational and ensemble guidance for the frontal passage.
Much cooler air, a first real taste of fall with lows in the 40`s
and 50`s with highs in the 60`s and 70`s. Less spread with
temperatures Sunday and Monday with the ensemble guidance.
Tuesday through Wednesday:
The backdoor frontal boundary coupled with a mid-level ridge to our
west look to setup an omega block which will likely slow the
approach of the next cold frontal boundary or weaken as it moves
east. As is usually the case in the 5-7 day time period uncertainty
is present on the exact timing of this feature.
The UKMET, CMC and some ensemble data weaken the front before it
approaches our area. On the other spectrum, the GFS and GEFS are
much faster bringing it through around Tuesday. Given this spread
and questions if the front makes it to our area, will keep a dry
forecast. Low and high temperatures should slightly warm each day
unless the high pressure system sets-up just to our north. In that
case an easterly flow could slow the approach of a warmer airmass
expected ahead of the next front.
.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Tonight...mainly VFR conditions expected. Cirrus will remain around
the region tonight but is expected to thin out from northwest to
southeast. Winds will become calm to light and variable this
evening, remaining light through the overnight hours. Patchy MVFR
fog is possible late tonight but with a drying airmass it seems less
likely to occur.
Thursday...VFR conditions expected. Any early morning fog should
dissipate fairly quickly. Northeast to east winds around 10 knots or
less are expected with a slight shift towards the southeast late.
Thursday night through Friday night: VFR.Varibale winds becoming
west-southwest but staying under 10 knots.
Saturday through Monday: VFR. An isolated shower possibile on
Saturday. Northerly winds around 10 knots Saturday afternoon with
gusts up to 20 knots then staying under 10 knots Sunday and Monday.
A Small Craft Advisory is in effect from 14z Thursday through
Tonight...Sub-advisory conditions are expected to continue on the
area waters tonight. Seas may near 4 feet by late tonight.
Winds will remain around 15 to 20 knot through early evening
before starting to subside a bit overnight.
Thursday...An east to northeast wind will increase through Thursday
afternoon with gusts around 20 knots. However, seas will build
in the easterly flow and are expected to exceed 5 feet along the
Delaware and southern New Jersey coast around late morning and
continue into Thursday night. As a result, we have issued a Small
Waveheights will start in the four to five feet range and should
slowly decrease on Friday. GWES guidance indicates a fairly high
confidence for seas to reach five feet Thursday night and early
Friday. So have issued an SCA which goes through 18z Friday. This
ending time may be slightly long but allows for wiggle room if
waveheights respond slower, typical of easterly flow. For the
weekend into early next week seas and winds are expected to remain
below SCA criteria.
Today...low enhanced risk NNJ and Moderate risk SNJ and DE for the
formation of dangerous rip currents, in part dependent on a 1 ft 12
second ESE swell from Tropical Cyclone Karl arriving and in part
dependent on the strength of the onshore flow.
Water temperatures have reverted to significantly above normal and
so while swimming off the NJ and DE beaches these next several warm
days will be fun... be aware that rip currents can be dangerous to
your health. There were rescues this past weekend and a beach
drowning with the cause as yet, unknown. The point: odds favor being
safest swimming within sight of a life guard.
Thursday and Friday...A generally low or low enhanced risk is
Weekend...There is a pretty good chance of a moderate risk for the
formation of dangerous rip currents on at least one of the weekend
days as a 4 to 5 foot ESE swell from Tropical Cyclone Karl arrives
along with a gusty northeast wind.
September is well on its way to a top 10 warmest September through
most of our forecast area, and...for the 3rd consecutive month!
So while there may be a 2 or at most, 3 day string of below normal
temperatures between Sunday and Tuesday, that is not likely to be
enough to prevent a third consecutive top ten warmest month for
much of the NWS Mount Holly forecast area. In this case a probable
second consecutive top 5 warmest month in the period of record for
PHL and ABE and possibly ACY too.
We`ve run the actual numbers through the 20th, our forecast from
today through the 28th and then the GFS2m max/min as seen on the
The following are the predictive sampling of reliable long term
Philadelphia: Projects a 74 degree average or about 5 degrees above
the monthly normal of 69.1. This will probably be a #4 or #5 warmest
September on record for Philadelphia.
Philadelphia September average temperature rankings
74.0 -2016 #4
Philly ranked #7 warmest July followed by a warmest ever August
(in the POR dating back to 1874).
Atlantic City: where there can be greater variability due to the
sea breeze cooling during the afternoon and the radiative cooling
at night, is still projecting around a 71.5 degree monthly average
temperature, or 4+ degrees above the monthly normal of 67.2. Odds
are locking into a top 4 to 8 warmest September in the period of
record dating back to 1874. Atlantic City recorded a #7 warmest
July and warmest ever August.
73.3 - 1961
72.8 - 1881
72.3 - 1931 and 1930
71.7 - 1921
71.6 - 2015
71.5 - 2016 and 1933
71.3 - 2005
Allentown: projects to a monthly average of near 69.9 degrees, or
almost 6 degrees above the monthly normal of 63.9 and a highly
probable 3rd to 5th warmest September on record. Allentown ranked
8th warmest July and #2 warmest August.
70.8 - 1961
70.3 - 1980
69.9 - 2016
69.7 - 2015
69.4 - 1931
Allentown and Philadelphia have so far recorded only 1 day below
normal through the first 20 days of September, TTN only 2 days
below normal and RDG 3 days below normal.
Rainfall: The rains of earlier this week were welcome. Still only
ACY and GED of our long term climate sites are above the monthly
normal. Multiple weather forecast models indicate little or no
rain here for at least the next 7 days. The only good news, is
that evaporative rates will be a little smaller due to the
climatology of lower temperatures and shortening days.
MARINE...Small Craft Advisory from 10 AM Thursday to 2 PM EDT Friday