Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
919 PM EDT Friday may 29 2015
high pressure will reestablish itself off the East Coast tonight
into Saturday. A cold front is forecast to move across our region on
Sunday, then stall across the area Monday into Tuesday, as a wave of
low pressure moves along it. High pressure will build to our north
early next week, before moving into the area Wednesday into Thursday.
Near term /until 6 am Saturday morning/...
no big changes with the estf update. NAM verified the best with
upstream and Delaware-Maryland-Virginia convection and corroborates current no precipitation
forecast for tonight. Still looking out for the development of
some low clouds and patchy fog overnight. Narre and hrrr guidance
suggesting more of a low cloud impact than fog on the Mainland, so
no big changes were made to the extent of fog presently in the
grids. Temperatures are running a bit warmer than expected
northwest and cooler than expected southeast. With lower dew
points in the former, these discrepancies should dampen out over
the next couple of hours.
An area of high pressure remains off the eastern Seaboard, with
an upper level ridge also extending over the East Coast states and
out over the Atlantic waters. Light winds through the course of
Friday day have shifted from an easterly direction to more of a
southeast flow, and some return moisture with dewpoints slowly
creeping upward has been observed.
Otherwise then through the overnight, the other main element to
watch will be the possibility for some patchy fog or perhaps a few
lower clouds to form, mainly from along the coast and into eastern
portions of our forecast area. While confidence is only moderate at
best on this occurring at this time, we did keep a mention of patchy
fog in the forecast for these areas as light southeast to south
winds will continue through the night and dewpoints rise into the
60s. Overnight minimum temperatures were a blend of met/mav
guidance, and we anticipate lows in the 60s across the region.
Short term /6 am Saturday morning through 6 PM Saturday/...
during the daytime Saturday, our forecast area will be on the
western periphery of lingering offshore high pressure and an upper
level ridge. In addition, a cold front is expected to be approaching
slowly from around the eastern Great Lakes, with a Lee-side trough
possibly developing to the west of our region around the
Appalachians. These factors, along with some increasing daytime
instability, will likely be enough for some isolated to perhaps
scattered showers/thunderstorms to develop from late morning through the
afternoon. Overall, we focused highest probability of precipitation across our western
zones. Muggy conditions will be felt across the area, with dewpoints
into the 60s. Maximum temperatures were a blend of met/mav guidance
with continuity, and we anticipate highs to reach into the 80s for
most of the region, except some cooler 70s along the coast and into
Long term /Saturday night through Friday/...
the region will be under the influence of a southwest flow aloft as
a middle-level trough transits the Great Lakes and northeast Continental U.S. Sun
through Wednesday...while an attendant cold front moving into the region on
sun becomes quasi-stationary over the middle Atlantic through early next
week...as the trough gradually amplifies causing the middle-level flow
to become parallel to it. The flow should become more zonal with
weak ridging by Wed-Thu...with fair weather expected to return. Temperatures...
west/the exception of Monday and Tuesday...should be near seasonable normals.
The main concern during the long term portion of the forecast is
the potential for convection on sun and heavy rainfall early next
week. A cold front will approach Sun afternoon...with an anafront-type
setup...as the bulk of the precipitation is expected to the north and west.
Ml cape values reach 2-3 kj...while the most favorable bulk shear
is along and just west of the front. Model soundings indicate an
environment most favorable for gusty winds with any thunderstorms
that occur. Heavy rainfall is also possible...given precipitable waters of 1.5
inches /1-2 Standard dev above normal/ as well as sluggish storm motion.
The front stalls over the middle Atlantic region late sun/early Monday
and this leads to an overrunning regime...as low pressure develops
along it during the Monday-Tuesday time frame. The main uncertainty here
is with regard to the placement of the overrunning...as the models
trend further north...given the tendency toward a more amplified
trough. The potential exists for 1-2 inches of rainfall...which
could lead to flooding problems due to dry antecedent conditions
but there is a high amount of uncertainty at this time.
Aviation /01z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
00z tafs are a bit more pessimistic overnight. There has been
recent hourly modeling trends of a growing consensus of a
borderline MVFR/IFR ceiling forming toward morning throughout our region
with ceilings tending to be IFR near/at the coast. Confidence is
moderate inland, but high at coastal airports and terminals.
Rest of this evening...VFR no cig, mainly cirrus. Lowest
confidence kacy as they should be first to observe the stratus.
South to southeast winds becoming lighter and averaging less than
Overnight...low MVFR to IFR ceiling forming and spreading throughout
most of the region. Closer to midnight at the coast and later
at night inland. Visibilities becoming MVFR, IFR at kmiv. If low
clouds do not form, greater chances for IFR visibilities at more rural
airports. Light south winds.
Saturday morning...becoming VFR with no ceiling developing between 13z and
15z. Visibility likely improving first to VFR. South winds increasing to
around 10 knots.
Saturday afternoon...VFR with a gustier south wind. Wind gusts
in final forecast group more likely to occur in afternoon.
Scattered showers and thunderstorms will develop, but most likely to
occur north and west of terminals. Confidence too low to include.
Lowest confidence of exclusion at kabe.
Sat night...MVFR possible in low clouds and fog near the
coast...especially Acy and miv.
Sun...MVFR likely in rain showers and thunderstorms and rain during the afternoon and evening hours...
Sun night through Monday night...MVFR in shra/tsra...low clouds...and fog.
Tuesday...MVFR in shra/tsra...with gradual improvement to VFR
sub-advisory conditions will continue for the coastal waters and for
Delaware Bay through tonight, with generally light southeast winds
becoming more southerly as the night progresses. Some fog may
develop over the waters during the overnight and advect to the
coast, causing locally reduced visibilities.
Reduced visibilities in fog is possible early Saturday for the
waters, otherwise sub-Small Craft Advisory conditions are expected through the
morning. Marginal Small Craft Advisory conditions may be reached Saturday afternoon
and evening, with wind gusts approaching 25 knots, especially for
the northern coastal waters. However, confidence was not high enough
at this time to issue a Small Craft Advisory. We will allow the next
shift to re-evaluate incoming data.
Sat night through Tuesday...Small Craft Advisory conditions possible through the entire
period...as a cold front stalls over the waters on Sunday and low
pressure develops along it early next week. At this time...highest
confidence in seas meeting Small Craft Advisory thresholds.
new weblink, works best on firefox. Displays the forecast graphic et cetera.
The initial rip current risk for the New Jersey coast on Saturday
is moderate while for the Delaware coast the initial rip current
risk is low. This follows our long time in house procedure. The
gridded procedure splits New Jersey in half with the moderate risk
in ocean and Monmouth counties. In general looks like predicted
winds are stronger progressively farther north along on the
waters. This will be tracked and reaccessed overnight.
may 2015...a top 5 warmest on record for large portions of our area.
All overnight and forecast information checked through 830 am
today - Friday may 29.
Conservative values listed below from our 5 am sft and cooling the
near midnight Sunday night may 31 low temperature due to northerly flow cold air advection Sunday
Allentown will probably average very close to 65.9 or 6 degrees
above normal. Por back to 1922. At least 5th warmest on record.
Philadelphia will probably average close to 69.7 degrees or 5.8
degrees above normal. Second warmest on record.
Number 3 would be 69.2 in 2004.
Atlantic City may 2015 65.9 or 66.0 or 4.8 to 4.9 above normal
and probable #2 or #3 por back to 1874
Wilmington Delaware solid por back to 1916 locked into #4 warmest
2015 around 68.0
No available monthly historical data for kmpo kged kttn and krdg.