Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
100 am EDT Wednesday Jul 1 2015
a trough is expected to slowly move east through middle week. As it
does so, a warm front will lift into our region tomorrow, followed
by a cold front late Wednesday. That front is expected to stall
just south of our region for the remainder of the work week.
Another cold front could arrive Saturday night.
Near term /until 6 am this morning/...
we expanded the Flash Flood Watch to cover areas basically along
and north of the I-95/New Jersey Turnpike corridor. Flash flood
guidance is around 1.5 inches/hour and two areas of heavy rain are
heading toward the area. A line of showers/thunderstorms is
approaching from the west, and a large area of
showers/thunderstorms approaching from the south.
Patchy fog and stratus possible toward dawn.
Short term /6 am this morning through 6 PM Thursday/...
gradually improving weather...as both probability of precipitation and sky cover decrease
through the day...with maximum temperatures at or above average.
Any residual showers and scattered thunderstorms in New Jersey and Delaware should end by
early afternoon. Precipitable water decreases steadily during the day.
West to southwest winds gust to 20 miles per hour during the afternoon.
Long term /Thursday night through Tuesday/...
little change to the long term in order to focus on ongoing severe
Previous long term discussion...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 /06z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Overnight...mainly VFR scattered-broken at or above 5000 feet but with patches of
MVFR ceilings. Brief gusty winds to 30-35 knots in IFR thunderstorms through
08z. Southeast to south-southwest flow north to south through the warm frontal
boundary. Possible developing expanding patches IFR fog/stratus
after 08z if the showers dissipate. Please see tafs and observations
Wednesday...VFR scattered at or above 5000 feet with chance of leftover showers
and isolated thunderstorms in the morning to early afternoon hours NJ/de.
Winds become west to southwest and may gust to 20 knots during the
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.
Small Craft Advisory for Delaware Bay discontinued this evening. May need to add Small Craft Advisory for
hazard 5 feet seas for a few hours during the early morning hours along
the Atlantic coast, especially S New Jersey and Delaware coasts.
Wednesday night...seas on the ocean may approach Small Craft
Advisory criteria in pre frontal southerly flow, but there is
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 4 foot swell/7
second period and southwest wind around 11 knots, we continue
with a moderate risk of rip currents for New Jersey and low risk
for Delaware Wednesday.
kphl tip bucket not working and trace rain is incorrect this
evening. Possibly over an inch. We'll estimate today.
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 only today left 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.
kphl tip bucket erroneous and ticket out on it. Will be fixed
PA...Flash Flood Watch until 6 am EDT early this morning for paz054-
New Jersey...Flash Flood Watch until 6 am EDT early this morning for njz001-
Delaware...Flash Flood Watch until 6 am EDT early this morning for dez001.
Maryland...Flash Flood Watch until 6 am EDT early this morning for mdz008.