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Area forecast discussion 
National Weather Service New York New York
357 PM EDT sun Apr 19 2015

Synopsis...
high pressure moves offshore this evening. A warm front approaches
from the south through Monday morning and remains near the region
through the day. A cold front moves through on Tuesday. A series
of weak cold fronts and/or troughs of low pressure will move
through during the middle to late week period. Low pressure
passes well to the south next weekend.

&&

Near term /until 6 am Monday morning/...
high pressure will continue moving offshore this evening.
With winds off the cold ocean...temperatures will fall into
the 40s and low 50s after sunset. Developing low pressure system
across the southeast states will send a warm front towards the
area overnight. Clouds will increase...lower...and thicken
throughout the night as the upper level ridge axis slides
offshore.

Rain will likely hold off until after 06z when good
isentropic lift and warm advection ahead of the warm front move
into western zones. Expect rain to break out after 06z...and move
east across the rest of the area through day break. As lift and
moisture increase...rainfall rates will begin to pick up as well.

A blend of the mav/met guidance looks good for low temperatures
tonight...in the lower and middle 40s.

&&

Short term /6 am Monday morning through Monday night/...
subtropical plume of moisture will ride through the area Monday
morning into Monday afternoon. Precipitable waters will likely
fall between 1.25 and 1.50 inches...nearly 2 Standard deviations
above normal for this time of year making for a very moist
atmosphere. Rainfall will become moderate to locally heavy at
times with good isentropic lift ahead of the warm front. Low level
jet will also move across during the morning and early afternoon
hours aiding in enhanced lift. Moderate to locally heavy rain will
likely continue in early afternoon...tapering off from west to
east late afternoon as the low level jet and deepest moisture
shift east of the area. This rainfall could cause localized minor
flooding of urban and poor drainage areas. No flash flooding is
anticipated at this time.

The warm front may struggle to completely move north of the
region. It is likely to hang just south or over Long Island
in the afternoon. It may not be until Monday evening or Monday
night that the warm front briefly moves through as a wave of low
pressure along a cold front approaches. Increasing elevated
instability is depicted by thermodynamic soundings late Monday
afternoon into Monday night...so continuing to mention isolated
thunder. Showers will remain likely through the night as this wave
of low pressure and cold front approach.

Strong east-southeast-southeast winds are near the coast...20 to 25 sustained with
gusts to 35 miles per hour possible. The winds will be strongest as the low
level jet moves overhead in the morning and early afternoon. Winds
should diminish late in the day.

Temperatures on Monday will reach the upper 50s to lower 60s and
only fall into the lower 50s on Monday night.

&&

Long term /Tuesday through Sunday/...
aloft...the merging of the closed low with a digging northern stream
shortwave will produce a large trough over the western Great Lakes
region Tuesday. This closed low slowly moves to a position just
north of the Great Lakes by Wednesday.

At the surface...models indicate a cold front crosses the area...
moving to the east during the day Tuesday. Developing westerly flow
behind the front will aid in drying the atmosphere out. Surface low
pressure remains in Canada north of the Great Lakes region Tuesday
into Wednesday. The next cold front approaches Wednesday late in the day.

There is generally good model agreement on the large scale.

Any morning clouds and patchy fog quickly give way to clearing
Tuesday as westerly flow picks up. Statistical NAM/GFS MOS suggest
temperatures well into the 60s to around 70 Tuesday. This seems to agree
with expected temperatures aloft (caa) and expected mixing levels.

Thereafter...the cold front moves through resulting in scattered
showers late Wednesday and Wednesday night. Behind this
front...westerly flow prevails as the surface low remains located well
to the north. This slow movement due to the slow movement of the
upper low/trough through the period.

High pressure eventually builds to the west by the weekend. Another
area of low pressure passes well to the south late Saturday and
Sunday...associated with southern stream energy that ejects out of the SW
United States. Timing and positional differences noted in the GFS
and European model (ecmwf). Would not expect this low to make much northward progress
though given upper pattern and pesky stacked low near the Canadian
Maritimes.

As mentioned...near to slightly above normal temperatures Tuesday can be
expected. Then as heights lower and the area remains under the
influence of the large slow moving trough...temperatures will average below
normal through the remainder of the week. Followed wpc and gridded
MOS Wednesday through Sunday...which seems close to 12z mex
numbers.

&&

Aviation /20z Sunday through Friday/...
approaches from the southwest through Monday as high pressure
retreats to the northeast.

VFR at all terminals through at least 6z. Conditions then lower to
MVFR late tonight...then to IFR at western terminals by early Monday
afternoon. Some uncertainty on exact timing of category
changes...could be off +/- 2-4 hours.

Wind mainly ESE-se...except east kswf with speeds around 10 knots or less
this afternoon. Occasional gusts to 15-20 knots possible late this
afternoon. Winds then back to the east-southeast-east this evening...with a few
knots increase in speed. Winds increase more significantly after 6z
to 15-20kt with gusts up to 20-25kt probable...and then again after
12z with gusts up to 25-30 knots out of the ESE-se. Low level wind shear is expected at
all but kswf after 12z.

Confidence is higher in low level wind shear than in gusts. Could end up with gusts
only a few knots higher than wind speed.

Outlook for 18z Monday through Thursday...
Monday afternoon...IFR or lower in rain. Low level wind shear early. East-southeast winds 15-
25kt likely gusts to 20-25 knots likely early.
Monday night. IFR or lower probable. Isolated thunderstorm possible.
Tuesday...MVFR early...otherwise VFR. West-SW winds gusts 15-20kt
possible.
Tuesday night...VFR.
Wednesday-Wednesday night...MVFR possible in the afternoon and
night in -shra. SW-west-southwest winds g20-25kt possible.
Thursday-Friday...mainly VFR...with low chance MVFR in any
-shra. West-northwest winds g15-20kt possible.



&&

Marine...
Small Craft Advisory conditions will develop on the ocean/New York
Harbor/South Shore bays this evening with gusts up to 25 knots. Ocean
seas will also build to 5-7 feet during the night.

As a warm front approaches the waters...conditions on the waters
will deteriorate quickly. Widespread winds around 25 knots will gust
up t0 30 knots. With low level inversion and colder ocean
temperatures...confidence in seeing widespread gales is low. Have
continued to mention occasional gusts to 35 knots. If these gusts
occur...it will be over a short time period as a low level jet
moves overhead. Will continue with small craft advisories on all
waters on Monday. Seas will build 7 to 12 feet.

The strongest winds subside from west to east on Monday afternoon
and evening. Seas will continue to remain high through Monday
night.

As a cold front moves to the east of the waters Tuesday...westerly
winds will increase. In fact...a west flow...at times backing to the
SW and then veering to the northwest...is expected through the late week
period. A series of weak cold fronts or troughs of low pressure will
move through middle to late week. A fairly tight pressure gradient
remains in place.

Seas gradually subside over the ocean waters Tuesday...but do remain
elevated through the week as wave watch iii suggests.

&&

Hydrology...
significant rainfall will develop across the region late tonight
through Monday night as a warm front will set up near the region.
A cold front then moves through on Tuesday. Storm total rainfall
with this system will range from 1 to 2 inches with locally
higher amounts. This could cause possible minor flooding of urban
and poor drainage areas.

For details on specific area rivers and lakes...including
observed and forecast river stages and lake elevations...please
visit the advanced hydrologic prediction service /ahps/ graphs on
our web site.

&&

Tides/coastal flooding...
with strengthening east/southeast flow and high astronomical tides...will need
to watch departures over the next few high tide cycles. For
now...will issue a coastal flood statement for the western Long
Island Sound for tonight's high tide...and for Monday afternoon's
high tide.

For tonight...only a half a foot or less is needed for the western
portion of the Long Island Sound. Slightly more is needed for the
remainder of the area.

Astronomical tides are a little lower during the day Monday...but
winds do increase...leading toward additional storm surge
potentially. Again...will only issue a coastal flood statement for the
western sound for now.

The Monday night high tide could experience more widespread minor
coastal flooding...but will wait to see subsequent model runs to
determine if any future advisories are needed.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory from 11 PM this evening to 6 PM EDT
Monday for anz338-345.
Small Craft Advisory from 6 am to 6 PM EDT Monday for anz330-
335-340.
Small Craft Advisory from 11 PM this evening to 6 am EDT
Tuesday for anz350-353-355.

&&

$$
Synopsis...ds/pw
near term...ds
short term...ds
long term...precipitable water
aviation...maloit
marine...ds/pw
hydrology...ds/pw
tides/coastal flooding...

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