Area Forecast Discussion
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FXUS61 KOKX 301959
Area Forecast Discussion
National Weather Service New York NY
359 PM EDT SAT JUL 30 2016
Low pressure slowly approaches from the Ohio Valley through Sunday.
This low slowly tracks along a frontal boundary that becomes nearly
stationary through central New Jersey to south of Long Island
Monday. Waves of low pressure track along the boundary Monday and
Monday night. High pressure begins to build toward the region
Tuesday, and moves over the area Wednesday. The high then slides
off the northeast coast Thursday. A cold front approaches Friday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Showers and embedded thunderstorms have continued to develop,
mainly west of the New York City metro. This trend will continue
into the evening, although expect the activity to continue to
stratify into a larger area of showers with isolated thunder as
CAPE decreases. This activity is forming ahead of an approaching
low pressure over the Ohio Valley with increasing low level warm
Have increase PoPs to categorical this evening across NE NJ and
the Lower Hudson Valley, but this may need to be pushed further
east across the metro and possibly western Long Island and SW CT
if latest radar trends continue. The main concern is locally heavy
rainfall as PWATs are running between 1.7 and 1.9 inches per
latest SPC mesoanalysis.
As the activity translates eastward across southern CT and eastern
LI, there should be a downward trend in intensity as the
airmass is more stable and the surface high just to the east.
There may be a lull in showers around midnight, but there is
decent agreement among latest NWP model guidance that warm
advection increases further as a warm front associated with the
low sets up near the region towards daybreak. Low level winds also
increase which should supply deep moisture and lift for coverage
of showers/isolated storms to expand.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
While not a strong low level jet, there is decent agreement among
the latest NWP guidance for 25-35 kt of low level flow helping to
enhance overrunning precipitation Sunday morning. The warm front
will continue to lie near the region as well with the low slowly
moving eastward across PA along this boundary. Showers and a few
thunderstorms should be moving across the region in the morning
from west to east. There is some uncertainty in where the heaviest
rainfall will ultimately end up occurring, with highest confidence
at this time from the city north and west. There will also be some
shortwave energy moving around the broad trough over the Ohio
Valley which could further support showers and a few storms.
Best warm advection axis shifts to the eastern portion of the area
in the afternoon, so there may be a lull in activity across the
west. However, this may present an opportunity for some breaks in
the clouds and some increasing instability for redevelopment of
showers/storms. Likely PoPs continue into the early evening mainly
along and west of the Hudson River.
Locally heavy rainfall continues to be the main threat with any of
the heavier showers and thunderstorms.
Frontal boundary looks to set up south of Long Island Sunday night
with weak waves of low pressure riding along it, so the potential
for a few showers continues through the night, but coverage should
be less that during the day.
.LONG TERM /MONDAY THROUGH SATURDAY/...
Ridging remains over the country with a near zonal flow continuing
along the Canadian/US border as shortwaves move through during the
Monday into Monday night a trough will be moving through the
northeastern and upper midwestern states, as a series of shortwaves
move through the trough. At the surface a frontal boundary will be
nearly stationary somewhere in the vicinity of the Ohio Valley into
the mid Atlantic states and south of Long Island. The location of
the frontal boundary will be affected by on going convection this
weekend into the beginning of the week.
Current indications are that a series of broad lows move along the
boundary Monday into early Tuesday. Monday morning instability is
marginal with isolated thunder possible. With daytime heating and
Monday and another wave moving through chances for convection will
be increasing. Moisture will be a little more limited Monday into
Tuesday as moisture from the Gulf of Mexico is cutoff. However, some
storms could produce locally heavy rain.
The upper trough axis slides through the region early Tuesday with
the last wave exiting offshore Tuesday morning. Upper ridging then
builds into the east through Thursday.
A rather vigorous shortwave will be coming onshore of the Pacific
northwest early next week and will track along the northern US,
digging a trough into the upper midwest and Great Lakes by the end
of the week. Deepening surface low pressure will send a cold front
toward the area Friday into Saturday as the ridge moves offshore.
Humidity will be increasing for Friday and Saturday as a deep
southwesterly flow sets up.
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
SHRA/TSRA developing over NJ and lifting to the east. Activity
will become more widespread going into this afternoon, and impacts
to KNYC terminals are expected to develop between 19-21Z. Over
Long Island, some SHRA/embedded TSRA developed along the sea
breeze, and those should taper off in the next hour or so.
Expecting SHRA/TSRA for many of the terminals through this
evening, and then there should be a lull from around 04-06Z
through 08-10Z. SHRA develop again towards Sunday morning, and
will persist through the day. Conds will drop to MVFR with local
Persistent onshore, SE flow expected into Sunday. For outlying
terminals, winds will go LGT/VRB tonight.
.OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY...
.Sunday afternoon...MVFR or lower in SHRA.
.Sunday night-Monday Night...Chance of showers and possibly a
tstm. MVFR or lower conditions possible.
.Tuesday...Mainly VFR, although isolated showers are possible.
Low pressure approaches the waters from the Ohio Valley through
Sunday. The flow may increase Sunday with gusts up to 20 kt
possible on the ocean waters. Otherwise...winds and seas will
remain below SCA levels through Sunday night.
A frontal system is expected to be in the vicinity of the forecast
waters Monday with waves of low pressure tracking along a nearly
stationary front Monday into early Tuesday. Winds and seas likely
remain below small craft advisory levels.
High pressure builds into the waters Tuesday and remains Wednesday.
The high then shifts off the coast Thursday. Sub advisory conditions
are expected through Thursday night.
Showers and embedded thunderstorms will bring an average of one
half to around one inch of rainfall with the highest amounts along
and west of the Hudson River. Any thunderstorms can produce
localized higher amounts. Minor urban flooding will be the main
threat within heavier showers/thunderstorms.
A quarter to one-half inch of rainfall is possible Monday into
early Tuesday morning with locally higher amounts. The greater
rainfall totals are expected across the lower Hudson Valley into
southern Connecticut. However, with uncertainty as to the track of
low pressure confidence in the rainfall totals is low.
Dry weather returns Tuesday and continues through the midweek