Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
135 am EDT Sat Jul 26 2014
high pressure will shift offshore tonight into Saturday. A warm
front moves through Saturday night...followed by a cold front
Monday. The cold front moves across Monday night. High pressure
then builds in behind the cold front by middle week next week.
Near term /until 6 am this morning/...
forecast remains on track. Will make minor adjustments based on
latest surface observation.
Otherwise...surface high pressure remains over the area as an upper
level disturbance passes through the region.
S/SW flow over the area will result in increased moisture over the
region through the overnight. Lows will be close to normal. Patchy
fog will develop away from the city.
Short term /6 am this morning through 6 PM Sunday/...
for Saturday...there will be a moderate risk of rip currents along
Atlantic facing beaches.
An approaching upper level jet will lead to surface pressure falls
across the east. Models generally suggest a corridor of favorable
surface convergence developing across New Jersey and west of NYC where
thunderstorms should initiate late in the afternoon as cinh
erodes. High temperatures will be a few degrees warmer than the previous
day...primarily across the interior where the maritime influence
will not be felt.
By Saturday night into Sunday morning...a warm front will finally
move northeastward/poleward through the forecast area. A
concurrent short wave aloft will aid in thunderstorm development
overnight into the morning. As low level moisture increases and
west-northwest flow aloft advects steeper middle-level lapse rates
into the region...instability will increase overnight. The
increased instability combined with 30-40kt of 0-6km shear may be
sufficient for isolated small hail. Although a weak inversion will
exist around 850 hpa...a briefly rotating storm and/or weak
tornado near the warm front...especially along the South Shore of
the NYC boroughs and Long Island cannot be ruled out.
Additionally...precipitable water values near 1.85 inch indicate heavy rain
potential in any thunderstorms that develop.
Long term /Sunday night through Friday/...
relatively active weather pattern featured in the long term and has
been present at other times this Summer...an upper level trough will
be setting up across the northeast. This lingers through much of the
long term period.
At the surface...a parent low moving across southern Quebec into
northern New England will have an associated warm front moving
across early Sunday. The associated cold front will stay north and
west of the region through the rest of Sunday and Sunday
night...with an area of low pressure approaching the area along the
With some patchy fog and convection Sunday morning...there could be
a brief respite before another round of convection develops with
afternoon heating. Sref probability of precipitation were preferred here as they have been
consistent from run to run showing higher probability of precipitation across NYC and the
interior. We will be in the warm sector. The convection will spread
eastward at night across the rest of the region including the
There will be higher layer precipitable water Sunday and Sunday night with around
1.5 to 1.7 inches from southwest atmospheric flow. The flow is
parallel from lower to middle levels. Therefore...there could be
training of cells and some cells could produce heavy downpours.
In terms of shear 0-6km...25-30 knots Sunday along with cape of
1000-1500 j/kg will allow for stronger convection to develop. The
winds in the boundary layer will be more on the light side...mostly
below 30 knots...so severe possibility seems marginal at the moment.
But any helicity increase from perhaps more veering low level
profiles as well as any increase in the shear...would increase the
The wave of low pressure moves northeast of the region Monday and
this will eventually drag a cold front across Monday night.
Again...there could be another lull in activity before the next
batch of convection develops and moves in. This will be associated
with the cold front.
Shear 0-6km will be a little higher Monday with deepening trough
moving in with magnitude increase of about 5-10 knots compared to
previous day. Colder air aloft will be moving in. Cape though is a
little more limited and this is likely related to less moisture from
a little more westerly flow.
After this...weather pattern begins to stabilize with heights
building as the upper level trough begins to lift north of the
region. At the surface...high pressure will begin to build in from
The high pressure continues to build in and the upper level trough
amplitude continues to weaken with time through the rest of this
period. This will allow for a dry airmass to encompass the region.
Temperatures will not deviate too much from normal.
Aviation /06z Saturday through Wednesday/...
high pressure gives way to a surface trough and warm front that will
approach from the west.
Mainly VFR conditions are expected. Increasing middle and high level
clouds are forecast. An isolated shower or thunderstorm is possible
mainly west of NYC terminals this afternoon. However...activity
would be too isolated to include in the forecast at this time.
Brief sub VFR conditions are possible in any shower or thunderstorm.
Southwest winds 10 kts or less this morning will become south 10 to
15 kts this afternoon. A few gusts up to 20 knots are
possible...however gusts will not be frequent to include in the
Outlook for 06z sun through Wednesday...
tonight-Mon...VFR with a chance of rain showers/thunderstorms with MVFR or lower
relatively tranquil conditions expected across the waters through
Saturday. Increasing southerly flow ahead of a warm front Saturday
night is expected...with southerly winds continuing Sunday into
Monday ahead of a cold front. Winds shift behind the cold front
Monday night into Tuesday.
Seas build Saturday night in response to the increasing south
flow. Small Craft Advisory seas are forecast to begin Sunday afternoon and continue
through Monday night before subsiding below going into Tuesday. Wave
watch iii output could be too fast with increasing seas so future
forecasts may have this Small Craft Advisory potential beginning more Sunday night
as opposed to Sunday afternoon.
unsettled weather with scattered to numerous showers/thunderstorms are
forecast Saturday night through Monday. Any of these storms have the
potential to produce heavy downpours. Significant uncertainty still
exists with timing and amounts though. It looks like the higher
potential for heavy rain is Sunday and Sunday night with higher
precipitable waters of 1.5 to 1.7 inches across the region.