Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1030 am EDT Tuesday Jun 30 2015
a warm front over the Ohio Valley is predicted to lift slowly
northeast into and through the forecast area tonight. It will
be followed by a slow moving cold front late Wednesday or Thursday.
That front is expected to stall just south of our region for the
remainder of the work week. Another cold front should pass
through our region on Independence day. A weak high pressure
system should follow on Sunday and move offshore as a warm front
approaches from the Ohio Valley on Monday.
Near term /until 6 PM this evening/...
latest radar trends indicate -shra with an occasional rumble of
thunder moving through the Poconos and Lehigh Valley as isentropic
lift and elevated instability precede a warm front in vicinity of Delaware Bay
at this time. As middle-level flow becomes more meridional in response to
shortwave trough approaching from the west...the wm front will make
slow progress north through the day. The main concern for today's
forecast is the potential for convection.
There is still a lot of uncertainty with regard to convective
potential. Approaching shortwave will provide a source of lift...as
best forcing occurs near the warm frontal boundary. Ample low-
level moisture is in place...as drier middle-level air advects in
aloft. The main uncertainty is instability...as lapse rates are
less than ideal...with perhaps even some capping. Sat trends
also indicate considerable cloudiness. Therefore ml Cape May
have a tough time reaching 1 kj.
Although instability is limited...bulk shear is 40 knots northwest of
I-95 along west/ ample low-level helicity...as 0-1 km shear reaches
20 knots. So there is severe potential today mainly northwest of I-95...especially
the Poconos and Lehigh Valley...W/ the main threat being damaging
winds and small hail given inverted-v profiles and favorable wbz
heights. Will also have to watch activity near the warm front...
where a supercell cannot be ruled out...particularly if greater
instability is realized. Flash flooding is also a concern mainly
northwest of I-95...where cells will have a tendancy to train.
Short term /6 PM this evening through 6 am Wednesday/...
a chance of scattered showers and thunderstorms will continue
through tonight as the warm front to our south lifts across the area
and additional short waves/vorticity impulses move across the area.
It is possible that there could be a break in shower activity for
some areas during a portion of the overnight in between short waves.
However, we expect activity to increase again toward the very early
morning hours Wednesday. There remains some instability through the
night and bulk shear may actually increase overnight, so there
remains the potential for some strong storms.
Lows tonight are a blend of mav/met MOS and mosguide.
Long term /Wednesday through Monday/...
there was about a 50/50 split between the GFS and WRF-nmmb
initialization at 500mb. Farther downward, the WRF-nmmb looked
better. Deep/dting the western Continental U.S. Ridge looks stronger, while the
eastern noam trough is broader. While the models agree on a continuation
of this overall synoptic pattern, they vary on details and
continue to find themselves in odd positions with the normally
slower European model (ecmwf) and WRF-nmmb considerably faster than the other
medium range models. As per pmdhmd we are leaning away from these
faster results and going more toward continuity. Regardless with
the current pattern remaining in place it is tough to confidently
predict much prolonged dry weather.
The start of the long term does have decent modeling consensus.
While the warm front should be lifting northeast of our cwa,
short waves interacting with the warm sector should re-generate
more showers and thunderstorms rather quickly on Wednesday morning. Cold
pocket aloft coupled with near neutral lower level thermal
fields keep predicted total totals at or around 50c.
Appropriately mixed layer convective available potential energy (above 1000j in delmarva) peak
during the morning and decrease as the afternoon progresses as
the cold pocket gets sheared. Highest probability of precipitation are in the morning with
a trail off as the day continues. Stronger shear and cape are
decoupled and (cape) may not ramp up fast enough given timing of
features for severe which looks better northeast of our County Warning Area. Air
mass supportive of middle to upper 80s for maximum temperatures most of our County Warning Area.
Given the brief flattening of the trough aloft, we did not carry
much of a chance of thunder into the night and no probability of precipitation anywhere
overnight. Stat guidance mins look reasonable.
On Thursday the frontal boundary is expected to stall just south of
our County Warning Area. From here the timing of impulses on the front start to
diverge. Regardless, the boundary is close enough to act as a
trigger with higher confidence (thus higher pops) in the southeastern
part of ur County Warning Area. Mixed layer convective available potential energy in Delaware-Maryland-Virginia reach the lower
1000s, but are relatively low farther to the northwest. Thunder
chances may be overstated. Thermal fields suggest a 2-3f drop off
in maximum temperatures from Wednesday.
Now the models really start diverging for Thursday night and Friday
with the GFS and can ggem emphasizing Friday with the European model (ecmwf) and
WRF Thursday night. Where models agree is that instability in our
County Warning Area is modest and there are higher chances south than north.
Timing resolution is too uncertain to forecast dry weather for
either period. We did steer higher probability of precipitation into Thursday night as the
gefs is slightly faster than the op GFS.
It does not become much clearer for Independence day with the European model (ecmwf)
forecasting a dry day and the can ggem having a total washout. Most
models are not indicating a surface low on the level of last Saturday,
so for now we kept the forecast for Independence day close to
continuity and Summer climatology and not sound like a total loss.
Sunday/Monday remain close to continuity. With both the GFS and ec
dry we have Sunday predicted to be the better of the two weekend
days and kept the chance for thunderstorms in for Monday as the
warm front is predicted to return.
Aviation /14z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
General VFR conditions will persist across the taf sites today,
although cloud cover will continue to increase and lower through the
day. Showers will be on the increase through the morning and into
the afternoon. With instability increasing today, there will be a
chance of thunderstorms. Any showers or thunderstorms have the
potential to temporarily reduce visibilities and/or ceilings. Winds will
generally be south to southeast, and could gust around 15-20 knots
later this morning into this afternoon.
A chance of showers will continue tonight, along with the chance for
scattered thunderstorms. Any showers or thunderstorms have the
potential to temporarily reduce visibilities and/or ceilings. There is a better
potential for lower visibilities overnight as a warm front lifts across the
area. Wind gusts will drop off by sunset, with a southerly flow
remaining through the night.
Wednesday...mainly VFR except MVFR or IFR conditions with
scattered showers and thunderstorms.
Wednesday night...mostly VFR with any precipitation chances decreasing
Thursday through Saturday...predominately VFR, but some
MVFR or IFR conditions during scattered showers and thunderstorms.
Impact outlooked to be greater for southern airports and terminals.
sub-Small Craft Advisory conditions will remain across the waters
today into tonight, although winds may gust around 20 knots at
times. Seas will remain around 3-4 feet. There is a chance of
showers and thunderstorms late this afternoon into tonight. Higher
winds and waves could occur with any showers or thunderstorms.
Wednesday and Wednesday night...seas on the ocean may approach Small
Craft Advisory criteria in pre frontal southerly flow, but there
is considerable uncertainty.
Thursday and Thursday night...winds and seas should remain below Small Craft Advisory
Friday through Saturday...seas on the southern ocean waters might
reach Small Craft Advisory levels pending the strength of the low
pressure system on the frontal boundary. Confidence is less than
based on our local forecast application using a 3 foot waves/8
second period and southeast wind around 12 knots, we will continue
with a moderate risk of rip currents for New Jersey and low for
the chart below shows rainfall statistics at our four big climate
sites through 6/29. The Columns are broken down by site, "por" (how
far records date back), June 2015 rainfall, normal June rainfall,
June 2015 rainfall ranking, as well as the wettest June on record.
Site por June normal rank wettest
Ilg 1894 12.46 3.50 2nd 13.66 (2013)
Acy 1874 8.04 2.81 2nd 8.45 (1920)
Abe 1922 7.02 3.86 6th 10.51 (1938)
phl 1872 7.23 3.08 10th 10.56 (2013)
At this time, it has been the second wettest June on record in
both Wilmington and Atlantic City. With today being the last day
in the month, current forecasts do not favor either site breaking
their all-time June rainfall record. However, it would only take
a heavy shower or thunderstorm to close The Gap, which is 0.41
inches in Atlantic City and 1.2 inches in Wilmington.