Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
243 am EDT sun Jul 31 2016

Synopsis...
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 this morning/...
an area of heavy rain producing showers will move across the
eastern half of Orange County the next hour, otherwise activity
is forecast to be scattered through most of the night.

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 this morning through 6 PM Monday/...
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 night through Saturday/...
ridging remains over the country with a near zonal flow continuing
along the Canadian/US border as shortwaves move through during the
upcoming week.

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 /06z Sunday through Thursday/...
multiple waves of low pressure will ride along a frontal boundary
situated south of the area through Monday. The front works north
as a warm front this morning before stalling near or just south of
the region this afternoon.

Showers will be possible at almost anytime, but are forecast to
be more widespread from 09z to 18z today, developing from SW to
NE. Thereafter, the activity should be more scattered in nature.
Isolated thunderstorms are also a possibility, but confidence of
occurrence and in timing is too low to mention in the tafs.

Widespread MVFR/IFR conditions throughout the period.

Southeast flow expected through today, then backing to the east tonight,
generally 10 kt or less. Coastal locations may be slightly
stronger.

Outlook for 06z Monday through Thursday...
Sunday night-Monday night...chance of showers and possibly a
tstm. MVFR or lower conditions possible.
Tuesday...mainly VFR, although isolated showers are possible.
Wednesday-Thursday...VFR.

&&

Marine...
winds and seas forecast on track and no changes were made at this
time.

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 Small Craft Advisory 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.

&&

Hydrology...
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
period.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...none.

&&

$$
Synopsis...ds/met
near term...BC/ds/met
short term...ds
long term...met
aviation...dw
marine...ds/met
hydrology...ds/met

National Weather Service Glossary of Abbreviations