Scientific Forecaster Discussion
fxus61 kphi 250819
Area forecast discussion
National Weather Service Mount Holly New Jersey
419 am EDT Tue Jul 25 2017
a cold front will continue to move south of the region today. High
pressure eventually builds in from the Great Lakes tonight and
Wednesday morning before moving offshore Wednesday afternoon and
night. A warm front approaching from the southwest on Thursday is
expected to stall over the area Thursday night and Friday.
Meanwhile, a wave of low pressure tracking along the boundary will
move through the mid-Atlantic states. The front should progress
south and east of the region Friday night once the low moves
offshore. High pressure returns for the weekend and into early next
Near term /until 6 PM this evening/...
the cold front which brought the showers and tstms to the area last
night has moved offshore. Lingering patches of low clouds/fog and
some drizzle are across the area early this morning. Drier air will
arrive across the area later today, but with the onshore low level
flow and the upper trough moving across the area, it may take until
afternoon for breaks develop in the clouds. We'll keep the fcst
mostly cloudy early today then bring in improved conditions for the
afternoon. Across the western parts of the area, there is not
much lower clouds, with the drier air already in these areas, so
conditions will be better there this morning. High temperatures will
be in the 70s across the north and low 80s over Philadelphia and
Delmarva. The high will occur late in the day however. Winds will
remain mostly east or NE at around 10 mph.
Short term /6 PM this evening through 6 am Wednesday/...
high pressure will be across New York and NE tonight. The onshore flow
over our area will result in cloudy periods, but no precipitation is
expected. It will remain seasonably cool with lows in the mid/upper
50s over the north areas and low/mid 60s over srn New Jersey and much of
Long term /Wednesday through Monday/...
long term forecast remains mostly unchanged as most of this
shift was focused on short-fused products (convective and flood)
and monitoring (e.G., Radar and river gauges).
The next round of active weather for our area looks to be Thursday
night through Friday night with another threat of heavy rainfall and
severe thunderstorms. Global model guidance is in fairly good
agreement regarding the synoptic pattern (a wave of low pressure
tracking eastward along a stationary front through the mid atlantic)
and timing of the heaviest rain falling on the calendar day Friday.
Both the wpc excessive rainfall outlook and Storm Prediction Center severe thunderstorm
includes our area in a slight risk for d3. There is quite of bit of
support from operational guidance (and its ensembles) quantitative precipitation forecast fields for
2-4 inches of rainfall. The wet antecedent conditions will heighten
the concern for flooding with this event. Will continue to mention
both potential hazards in the severe weather potential statement.
Outside of the late-week event, the long-term period looks to be
quiet and void of any significant heat (possibly below 90f for
the next seven days).
Aviation /08z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
IFR ceilings have developed across the area behind the earlier
convection across the area. Even if the overcast breaks up a bit, fog
will likely form across the area. Accordingly, most of the tafs have
poor conditions this morning with a transition back to VFR probably
happening 13z-15z across the area. The synoptic onshore flow will
likely keep enhanced moisture over the area today and tonight. We
will have mostly cloudy skies with VFR cigs over the area much of
the afternoon and early evening. A change back to MVFR is possible
tonight, but confid in this is medium at best.
Wednesday-Thursday...potential for MVFR cigs with moisture
trapped below subsidence inversion, particularly outside of peak
heating (e.G., Early morning and night time).
Thursday night-Friday night...potential for MVFR or IFR
restrictions with moderate to heavy rainfall. Chance for thunderstorms and rain as
Saturday...slowly improving conditions to VFR in wake of the
previous storm system. Breezy north-NE winds possible early in the
the cold front has moved offshore and high pressure will build in
from the north today. Winds should remain mostly east or NE on the
waters today and tonight. Winds will likely remain short of Small Craft Advisory
levels, although there will probably be S few gusts over 20 kts at
times. Seas should mostly be in the 3-4 ft range. We will hold
the Small Craft Advisory flag for now, but may reconsider for 630 am if seas
continue to build. Fair weather expected across the waters today and
Wednesday-Thursday...winds and seas below Small Craft Advisory criteria.
Thursday night-Saturday...Small Craft Advisory may be required for SW winds near
25 kt ahead of an approaching low pressure system Thursday
night and Friday, then NE winds behind it Friday night and
a moderate risk for the formation of dangerous rip currents is
expected for the New Jersey beaches in Atlantic, Ocean and
Monmouth counties owing to an underlying longer period swell and
a relatively strong northeast wind (15-20 mph). Farther south
along the coast, where the winds will be lighter and backed out
of the north or northwest, the risk is lower.
astronomical tides tonight will be lower than the past few. Onshore
flow will continue however. There will probably be higher than usual
water levels tonight, but it will probably come short of minor tidal
flooding levels. No statements will be issued with this package.