Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
648 PM EDT sun Jul 13 2014

Synopsis...
a slow moving cold front will approach from the west tonight and
then dissipates across the area on Monday. A secondary frontal
system will impact the area Tuesday into Wednesday. High pressure
returns for the end of the week before another frontal system
approaches for the weekend.

&&

Near term /until 6 am Monday morning/...
Severe Thunderstorm Watch in effect until 9 PM for Orange and
Putnam counties. Thinking is that sufficient cape exists that as
an upper shortwave approaches...a few severe thunderstorms may
develop. Much of the activity should stay to the north but
Orange/Putnam are still prime for a few isolated storms.

The first cold front for the week is now in western portions
of New York and PA will send a line of showers and thunderstorms into
the far western zones of the lower Hudson Valley toward early
evening...then works east toward the NYC metropolitan/western Li/SW CT
between 8 and 11 PM. Weak shear and marginal instability will
likely lead to dissipation as the convection approaches the coast.
Brief heavy downpours will be possible.

Synoptically...an anomalously strong upper low north of the upper
Midwest and Great Lake states will descend southeast through the upcoming
week sending multiple frontal boundaries into the area. This
coupled with deep-layered moisture...moderate instability...and
strengthening wind shear will result in several episodes of
convection with heavy rainfall and isolated severe weather.




Warm...muggy conditions will prevail with lows in the 70s.

&&

Short term /6 am Monday morning through Monday night/...
the ingredients are coming together for a potential moderate to
heavy rainfall episode Monday after/evening as a dissipating frontal system
across the region interacts with deep moisture...moderate
instability...and strengthening deep-layer shear. There is always
some uncertainty with the timing and precise location where the
heaviest rain will occur...primarily due to where the stalled
boundary resides. The best chance at this time looks to be just
north and west of NYC in the after...with the convection working
into coastal locations during the evening hours. This episode
looks to dissipate toward the late night/early morning hours Tuesday.
The potential exist for localized heavy rainfall with rainfall
rates in excess of an inch an hour. Uniform westerly flow may also
allow for training of showers and thunderstorms. Based on latest
ffg guidance a Flash Flood Watch is not being issued at this
time... but this does not mean there will not be localized
flooding. In addition...this first event will likely serve as the
primary for potential flooding on Tuesday.

Furthermore...upper air soundings indicate long narrow convective available potential energy
supporting slow rising updrafts...conducive to heavy rainfall in
deep moist air masses. While hail will not be a threat...the shear
supports potential wet microbursts and perhaps small line segments.

Stayed close to guidance with highs in the low to middle 80s...and
lows generally in the 70s. Dew points will also be around 70
making for muggy conditions.

&&

Long term /Tuesday through Sunday/...
the main cold front slowly approaches on Tuesday with rain likely
through the day. Global models have slowed down their precipitation timing
since yesterday and keeps rain in the forecast through at least
Wednesday morning.

Tuesday remains warm with a moist southerly flow and continuing precipitable waters of
1.5 to 2 inches through the afternoon and evening. The chance of
severe thunderstorms is lower than Monday while the threat of flash
flooding increases. Less cape is in place but still enough mu
cape....around 1500 j/kg interior...to keep thunderstorms in the
forecast. Shear increases slightly for Tuesday as well. Cannot rule
out a severe thunderstorm or two but the threat is low. With the
rain that will fall Monday...the additional rainfall will rapidly
increase the flash flooding threat as Tuesday progresses. Tuesday
also has greater lift with the cold front along with upper jet
dynamics which will help create the higher rainfall amounts. See the
hydrology section for additional information on rainfall amounts.

As the front progresses east...probability of precipitation decrease west to east with rain
lingering through Wednesday afternoon for the eastern part of the area.
High temperatures drop to near normal values starting on Wednesday and continuing
through the weekend as the deep upper trough continues moving
northeast. Broad high pressure builds in at the surface and remains
through the Friday. Low temperatures will be near to slightly below normal
values.

As the high pressure area shifts east on Saturday...another frontal
system will move north and impact the area for the weekend.

&&

Aviation /00z Monday through Friday/...
high pressure continues moving offshore as a slow moving cold front
approaches from the west through the taf period.

Winds generally 180-210 degrees this evening 10 to 15 knots with
gusts 20 to 28 knots. Gusts will gradually diminish after
00z...although thunderstorms could provide brief gusty winds.

Showers/thunderstorm chances increase early evening for kswf.
Shower/storms should spread east later this evening into city
terminals between 01z and 04z. Activity expected to diminish as it
heads further east overnight.

More stratus/fog will be possible tonight with MVFR or lower
conditions before improving on Monday morning.

Showers and thunderstorms will become likely Monday afternoon.

Outlook for 00z Tuesday through Friday...
Tuesday-Wednesday...scattered to numerous shra/tstms. Stronger thunderstorms
during this time frame could produce periods of MVFR or lower
conditions...locally heavy rainfall...and gusty winds. Conditions
improve late Wednesday.
Thursday...VFR.
Friday...VFR.

&&

Marine...
marginal Small Craft Advisory conditions forecast across all waters this evening...then
just for the ocean waters late tonight into Monday. High seas may
linger into Monday night. A persistent southerly flow/fetch out
ahead of multiple frontal boundaries will allow for the building
seas through the first part of the week.

A second cold front approaches the waters on Tuesday and moves
through by Wednesday afternoon. The prolonged southerly flow will
keep ocean seas above 5 feet through Wednesday afternoon. Winds on all
waters should stay below 25 knots. After the front moves
through...sub Small Craft Advisory conditions expected on all waters through the
week.

&&

Hydrology...
a significant rainfall is possible beginning Monday afternoon and
continuing into early Wednesday. Total rainfall through this
period is expected to range from around 2 to 3 inches with
locally 3 to 4 inch amounts possible.

The heaviest rainfall is expected to occur Tuesday morning into
Wednesday morning. The flash flooding threat will be highest on
Tuesday due to the rainfall that will fall on Monday and the
continued moist southerly flow.

For the Tuesday-Wednesday time frame with the heaviest rainfall...continued
the increase in quantitative precipitation forecast from the previous shift. There are some
operational models indicating higher amounts than currently forecast
but confidence is too low to increase more than forecast.

&&

Tides/coastal flooding...
astronomical high tides remain high due to the recent full moon of
Saturday morning. The high tide cycles this evening will be similar
to what occurred Saturday night with tidal departures 2 to 3 tenths
of a foot above the astronomical high tide. This will bring some
locations to just under the minor coastal flooding thresholds during
the high tide cycle...around 10 PM along the South Shore and
midnight to 1 am Sunday in the Long Island Sound. However with a
strengthening...and persist onshore flow today along with a
southeast swell...tidal departures may run a little higher and bring
some locations...especially along the South Shore back bays...to or
just above minor flooding thresholds tonight. With low confidence of
widespread minor coastal flooding occurring and the high tide cycle
tonight will not issue any statements at this time.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory until midnight EDT tonight for anz330-335-
338-340-345.
Small Craft Advisory until 6 PM EDT Monday for anz350-353.
Small Craft Advisory until 6 am EDT Monday for anz355.

&&

$$
Synopsis...ln/dw
near term...ln/dw
short term...dw
long term...line
aviation...BC/ds
marine...ln/dw
hydrology...ln/dw
tides/coastal flooding...

National Weather Service Glossary of Abbreviations