Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
145 am EDT Sat Aug 2 2014
a frontal boundary over the Atlantic coast and low pressure to
the south will impact the area into Monday. High pressure will
then build in on Tuesday. A cold front will pass through
Near term /until 6 am this morning/...
bumped up probability of precipitation across the area as per latest radar observation and new
guidance. By daybreak...rain likely for a good portion of the County Warning Area.
Elevated instability is lacking...and thinking is that any
chance of thunder would be close to the low pressure center moving
north along the stalled boundary offshore. Will therefore leave
thunder out of the forecast.
Rainfall mostly moderate in nature...but brief heavy downpours are
also possible. Based on latest flash flooding guidance and radar
trends...looks like the areas of NE New Jersey and adjacent areas that had
seen flash flooding earlier should be good through at least the
rest of the night...so no Flash Flood Watch will be posted at this
Short term /6 am this morning through 6 PM Sunday/...
next focus of rain will be the stationary front backing in from
the east with the western Atlantic high pressure expanding
slightly westward. Some model differences exist on the timing of
when the precipitation will reach the area with the 01/12z NAM the
slowest and driest for the day on Saturday. Highest precipitation amounts
will be Long Island and southeast CT with the front positioned
just to the south of the island. Have increased pop to
likely/categorical in the morning...as showers should still be
able to develop with upper jet and middle level shortwave
enhancement. As well...deep moisture streaming from the south will
be in place so any showers will produce locally heavy rainfall.
Very low confidence on any thunder for Saturday. Little to no
instability or shear...just moderate lift. Expect showers to be very
tropical in nature and maybe an isolated lightning strike or two.
Wind profiles aloft are again light so training of cells is likely.
Guidance for highs on Sat is lower than previous...possibly due to
the models coming into agreement for a rainy day. Will lower
highs a few degree from previous forecast...with lower and middle 70s.
Long term /Sunday night through Friday/...
a shortwave weakens at the base of a 500mb trough axis as it
approaches the forecast area...eventually passing through Sunday
night into Monday morning. This will help slowly nudge the offshore
frontal boundary farther out to sea.
Some synoptic lift will be present through Monday with the right
entrance of an upper jet streak in the vicinity. Less certain are
the timing and position of low-middle level shortwaves that pass
through/nearby the County Warning Area before the trough axis aloft passes through.
Probability of precipitation therefore capped at chance...which is close to what a model
blend would produce. Best overall chances of rainfall would be
Saturday night into Sunday morning and closer the offshore frontal
boundary. Monday could even turn out to be completely
dry...especially if the European model (ecmwf) is correct with the trough axis
passing through Sunday night and a lack of low-middle level shortwaves
trailing it on Monday. Do not have enough confidence to remove probability of precipitation
altogether on Monday...so have left the previous forecast of slight
chance/chance probability of precipitation.
Weak high pressure probably keeps Tuesday and Thursday dry...but a
cold front and cyclonic flow aloft could bring an isolated
shower/thunderstorm to the area on Wednesday.
Clouds and an onshore flow will hold high temperatures on Monday
below normal...highs otherwise near normal for the rest of the long
Aviation /06z Saturday through Wednesday/...
a frontal boundary will remain southeast of the region through the
forecast period. One wave of low pressure moves along the front
this morning...with another approaching tonight.
A period of moderate to locally heavy rain expected across NYC/New Jersey
metropolitan terminals and points east this morning with MVFR conditions.
A period of IFR conds possible across eastern terminals.
Improving conds this afternoon as rain lifts to the NE with ceilings
likely rising to VFR from west to east. Ceilings may remain MVFR across
kisp/kgon into tonight.
MVFR conds possible to return in light rain once again late
tonight. Increasing probability of this from klga/kjfk and points
Winds backing northeast this morning as the wave of low pressure
approaches.The wind will then remain from the east to northeast
through the remainder of the forecast.
Outlook for 06z Sunday through Wednesday...
late tonight...rain showers with MVFR or lower conds
possible...particularly eastern terminals.
Sun-Sun night...shra/tsra possible...MVFR or lower conds
Mon-Wed...VFR. MVFR possible in isolated rain showers/thunderstorms in the
there is a growing chance that minimal Small Craft Advisory criteria could be
briefly met Sat afternoon as a wave of low pressure rides up the
coast along a nearly stationary front. Otherwise...sub-sca conds
are expected through Wednesday.
highest areal rainfall totals through Sat night of an inch or more
are expected over Long Island and far southeast CT. Heavy downpours are
possible this weekend into Monday via numerous showers and slow
movement/training of cells. This could once again result mainly in
urban/poor drainage flooding.