Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
443 PM EDT Sat may 30 2015
high pressure will remain over the western Atlantic through this
evening. A cold front approaches tonight...moves into the region
Sunday...and pushes south Sunday night. Waves of low pressure
track over or just south of the area Monday into Tuesday. High
pressure will then build in from the north late Tuesday into
Wednesday...and shift to the south Thursday into Friday.
Near term /until 6 am Sunday morning/...
a few showers and thunderstorms will develop or advect across the northwest
interior late this afternoon into early evening. Surface cape values of
1500-2000 j/kg noted across this area this afternoon with convective
initiation taking place across east PA. Weak shear fields will keep
this activity pulsey...but cant rule out a strong storm. Convection
likely dissipates this evening as it moves east with loss of daytime
heating and with a strong marine layer working northwest of the
NYC/New Jersey metropolitan this afternoon/evening.
Otherwise...region will be on western periphery of western Atlantic
ridging with deep trough digging into Mississippi and Ohio River
valleys...and a strong northern stream shortwave tracking into
At the surface...an associated slow moving cold front will approach
the region from the west. The northern stream shortwave will push
the northern part of this cold front into central New York tonight. Weak
vorticity aloft...low level jet forcing...and elevated instability late tonight
could support isolated rain showers/thunderstorms and rain activity ahead of the front
tonight...best chance n&w of NYC metropolitan.
Otherwise...an unseasonably warm and humid night with lows generally
in the 60s...near 70 NYC/New Jersey metropolitan.
Coastal stratus/dense fog likely once again tonight with moist
airmass overriding the comparably cooler waters. Sref probs are
not that high for tonight...but more widespread coverage of low
probs than what it was showing for this morning.
A high risk of rip currents at the Atlantic Ocean beaches continues
Short term /6 am Sunday morning through Sunday night/...
region will continue to be on the western periphery of western
Atlantic ridging with deep trough digging into the Mississippi and
Ohio River valleys.
At the surface...models in pretty good agreement with a cold front
sinking into northern portions of the region Sunday after/evening in the
wake of a strong northern stream shortwave sliding through Quebec.
The cold front...a possible warm front approaching from the south
associated with a weak surface wave approaching from the west...and
vorticity energy riding in the upper flow should act as trigger/focuses
for numerous showers and thunderstorms developing sun after in a marginally
unstable environment across the lower Hudson Valley...SW CT and
NE New Jersey...NYC metropolitan. Main threat appears to be heavy downpours and
potential for localized urban flash flooding with any training
thunderstorms as steering flow aligns with the front and precipitable waters
pool to 1.5 to 2 inches ahead of the front.
Overall severe threat appears to be sparse and low...mainly across
NE New Jersey/lower hud...as increasing cloud cover and convective
activity should temper instability in areas of increasing shear
farther north. Potential for rotation if any severe storms do
develop...with increased low level shear/helicity in vicinity
ahead of the surface wave and in vicinity of frontal boundaries.
Models coming into better agreement with cold front sinking through
the region Sunday night as strong Canadian high pressure noses in
from the N/NE. Waning instability should decrease coverage and
intensity of thunderstorms in the evening. Shower and isolated embedded
thunderstorm threat in the vicinity of the cold front as it pushes
through...likely transitioning to stratiform in its wake. Highest
probability for shower and embedded thunderstorm activity in the evening and rain
overnight will be across the NYC/New Jersey metropolitan...SW CT and lower hud
valley with low level jet forcing to the NE of the surface wave and more in
the way of vorticity energy...and possible some weak elevated
Highs on Sunday will be in the upper 70s to lower 80s...warmest
across NE New Jersey. Cooler and less muggy Canadian maritime airmass
advects in Sunday night.
There will be a moderate risk for rip currents at ocean facing
beaches on Sunday.
Long term /Monday through Saturday/...
frontal boundary becomes nearly stationary over or just south of
the area early this week. Several areas of low pressure will develop
over the Delaware-Maryland-Virginia area and track to the northeast Monday through
Tuesday. High pressure builds into the region behind the front
Wednesday and Thursday.
Will carry likely probability of precipitation for Monday and Monday night...and then likely
probability of precipitation on Tuesday for the eastern half of the County Warning Area as the final low
departs. Could have some embedded thunderstorms from time to time
during the day Monday and Tuesday.
Highs Monday and Tuesday will top off in the 60s to around 70...and
then temperatures warm back up through the 70s for the middle-week period.
Low pressure will impact the area late in the week and for the first
half of the weekend. Will carry chance probability of precipitation for now.
Aviation /21z Saturday through Thursday/...
high pressure gives way to a cold front on Sunday.
Southerly flow will be at its strongest for the day now through approx
sunset. Kjfk/kisp could see a brief period of low level wind shear after dark as surface
winds die off but remain at 30-40 knots only a few hundred feet above ground level.
Cannot rule out a shower/thunderstorm near kswf. A brief shower could also
pass through kjfk/klga/kewr/kteb/khpn until shortly before sunset as
showers form off a nearby sea breeze.
Expect a return of low stratus and fog with IFR conds late tonight
into middle morning Sunday. LIFR conds may be possible at
kjfk/kisp/kbdr/kgon. Showers and a few thunderstorms with MVFR and local IFR
visibility are then possible late Sunday morning into the early afternoon
from NYC metropolitan north/west.
Outlook for 18z Sunday through Thursday...
Sunday afternoon-Tue...chance of low stratus with IFR ceilings
developing late each night and morning. MVFR to IFR conds also
possible at times in showers/tstms.
Tuesday night...becoming VFR.
wind gusts of 25 to 30 knots expected across the western ocean
waters...western Li sound...Lower Harbor...and South Shore bays of
Li with a developing coastal jet this evening. 4 to 5 feet seas likely
on the ocean waters late this afternoon into evening. Small Craft Advisory for this
afternoon into evening for these locations. Elsewhere winds and seas
remain just below small craft levels into tonight.
Dense fog possible once again tonight across ocean waters and
southern and eastern nearshore waters.
With a prolonged southerly flow ahead of an approaching cold
front...marginal Small Craft Advisory seas possible on all ocean waters late tonight
into Sunday night. Confidence not high enough for an Small Craft Advisory at this
point with observed long period southeast swells running about 1 feet below
wna. Will let evening/overnight shift re-eval.
Seas on the ocean waters remain at or above 5 feet for the first half
of the new week...and then seas will begin to subside on Wednesday.
A persistent easterly flow for the start of the new week could gust
to 25 knots from time to time.
Tranquil conds return for Wednesday and Thursday.
between 1/2 to 1 1/2 inches of rain likely for much of NYC
metropolitan...NE New Jersey...lower hud valley...and southern CT Sunday afternoon
through Sunday night with slow moving cold front approaching.
Locally higher amounts of 2 to 3 inches are possible with any
training convection...which would pose a flash flooding threat. The
probability in any given location is low. Of note...sbu WRF is
indicating potential of locally 3 to 5 inches during this 24 hour
Rainfall amounts will taper down to 1/4 to 1/2 inch across eastern
Li and southeast CT...with more stable marine airmass limiting convection.
An additional 1 to 2 inches of rain possible Monday through
Tuesday. Locally higher amounts will be possible with any
thunderstorm activity. Minor urban/poor drainage/small stream
flooding would be most likely during this time.
Marine...Small Craft Advisory until 11 PM EDT this evening for anz335-