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Area forecast discussion 
National Weather Service New York New York
407 am EDT Tuesday Jul 7 2015

Synopsis...
high pressure offshore gives way to an approaching warm front today.
The front moves across today with a cold front moving through
Wednesday. The cold front stalls to our south Wednesday night
through Thursday night...with waves of low pressure riding along
it. Weak high pressure builds in Friday through Saturday...then
slowly slides offshore Sunday. A warm front slowly approaches from
the west Sunday night and Monday.

&&

Near term /until 6 PM this evening/...
not too much change with height fields...and hence not much synoptic
forcing today. On a large scale...upper level trough lifts becoming
diffuse. The larger signal is a strong upper level ridge
stretching from the south central U.S. Up along the eastern
Seaboard. The ridge axis is offshore as well as the surface high
pressure center.

Initially some low stratus and patchy fog in the morning
will quickly dissipate with diurnal warming. A warm front
is expected to move across today with accompanying winds
shifting from southeast to S-SW...further boosting warm air advection. A
mav/met/ekd blend yields high temperatures well within the 80s...upper
80s for urban northeast New Jersey.

Concerning showers and thunderstorms...low chances in the morning
with relatively higher chances in the afternoon. Precipitable
waters of near 1.6 to 1.8 inches will enable for locally heavy
downpours with the higher moisture content of the atmosphere
derived from the continued warm air advection.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
for tonight...instability lowers with the loss of diurnal warming
and without much synoptic forcing...any leftover showers or
thunderstorms will decrease...gradually diminishing in areal
coverage. Still expecting another round of late night/early morning
low stratus or patchy fog within the region. Therefore...used
mav/met/gmos and added one for lows considering the continued warm
air advection. The temperatures will be very mild and with dewpoints
also increasing...humidity will increase as well.

For Wednesday...after another round of patchy fog or low level
stratus...another very warm day in store. The core of the warmest
air at 850mb moves across within the first half of the day and then
lowers slightly for the remainder of the day. These 850mb temperatures will
be reaching up to near 18 degrees c. Highs at the surface well into
the 80s and near 90 for portions of NYC and northeast New Jersey as
daytime mixing occurs within the boundary layer.

Regarding the showers and thunderstorms...overall higher chances
Wednesday due to the cold front moving across the region plus some
additional positive vorticity advection at 500mb as well as an
approaching jet streak at 250mb. The jet streak will be well north
of the region but a little more in the way of shear will be seen and
this should provide a little more organization for thunderstorms.
High precipitable water values again with forecast readings approaching near 2
inches so heavy downpours will be a possibility with any
thunderstorms that develop. Highest likelihood north/west of NYC with
regards to convection.

&&

Long term /Wednesday night through Monday/...
the tri-state will experience unsettled weather Wednesday night into
Thursday night with a frontal boundary stalled out just to the S and
multiple shortwaves passing aloft. Wednesday night should see the
best chance for any evening showers and thunderstorms/overnight showers over
the S 1/2 of the County Warning Area closer to the front. Probability of precipitation increase to chance
everywhere Thursday and remain so into Thursday evening in response
to the passing of two distinct 700-500 hpa shortwaves. Precipitation
should taper off from west to east late Thursday night as the last
shortwaves exits to the NE.

With cape forecast to be minimal after Wednesday evening...through
Thursday night...limited thunder potential to slight chance from
late Wednesday night into Thursday night. This corresponds to
times when showalter indices where generally at or below 2
reflecting the potential for elevated convection.

The NAM/ECMWF/CMC all suggest that the heaviest rainfall should
occur with the last shortwave Thursday afternoon/evening...too soon
to latch onto such specifics...but with precipitable waters forecast
to be between 2-2.25 inches will have to monitor for that potential.

Refer to the hydrology section of the afd for potential impacts from
any rainfall Wednesday night-Thursday night.

For lows Wednesday night used a blend of mav/met/ecs guidance with
NAM 2-meter temperatures. Lows should be near to slightly above
normal. A blend of mav/met guidance...NAM 2-meter temperatures and a
mix down from 950 hpa per BUFKIT soundings was used for highs on
Thursday...with readings 5-10 degrees below normal due to cloud
cover and expected rainfall. A blend of mex/men/ekd/ece/ecm/wpc
guidance and NAM 2-meter temperatures was used for lows Thursday
night...with values forecast to be near to slightly below normal.

The region will be under west-northwest-northwest flow aloft Friday-Monday in between
a mean trough located over southeast Canada and a closed high that slowly
retrogrades from the deep south back towards the Texas Panhandle/New
Mexico by early next week.

With no shortwaves currently forecast to impact the area Friday-
Saturday night have gone with a dry forecast in this time frame.
From Sunday-Monday have slight chance probability of precipitation to reflect the
possibility that shortwaves going over the top of the Central Plains
ridge could impact the area. However...models have great difficulty
with the timing and strength of shortwaves in patterns like
this...so this is another reason why confidence in any particular
solution is low in this time frame.

For temperatures Friday-Monday used a blend of
mex/men/ekd/ece/ecm/wpc guidance...with values generally expected to
be near to slightly above normal.

&&

Aviation /08z Tuesday through Saturday/...
a warm front approaches from the southwest and lifts north of the
region today.

Early this morning...MVFR conditions lower to IFR in low stratus
and fog. Some LIFR conditions possible.

Chance of showers from 13z-20z today...especially along and west of
a klga-kswf line. Chance of thunder is also possible...however
chances are too low to include in the taf at this time.

Winds will be out of the southeast...generally 10 knots or less through
midday. This afternoon...some gusts into the teens or even lower
20 knots possible east of NYC.

..NY metropolitan enhanced aviation weather support...

Detailed information...including hourly taf wind component forecasts can
be found at: http://www.Erh.NOAA.Gov/zny/n90 (lower case)

Kjfk fcster comments: amendments may be needed early this morning
for changes in flight categories due to low stratus and fog.
Amendments may be needed late this morning and early afternoon for
timing of any thunderstorms. Occasional wind gusts possible this
afternoon to 20 knots.

Klga fcster comments: amendments may be needed early this morning
for changes in flight categories due to low stratus and fog.
Amendments may be needed late this morning and early afternoon for
timing of any thunderstorms.

Kewr fcster comments: amendments may be needed early this morning
for changes in flight categories due to low stratus and fog.
Amendments may be needed late this morning and early afternoon for
timing of any thunderstorms.

The afternoon kewr haze potential forecast is yellow...which implies
slant range visibility 4-6sm or greater outside of cloud.

Kteb fcster comments: amendments may be needed early this morning
for changes in flight categories due to low stratus and fog.
Amendments may be needed late this morning and early afternoon for
timing of any thunderstorms.

Khpn fcster comments: amendments may be needed early this morning
for changes in flight categories due to low stratus and fog.
Amendments may be needed late this morning and early afternoon for
timing of any thunderstorms.

Kisp fcster comments: amendments may be needed early this morning
for changes in flight categories due to low stratus and fog.
Amendments may be needed late this morning and early afternoon for
timing of any thunderstorms.

Outlook for 06z Wednesday through Sat...
Tuesday night...MVFR/IFR conditions possible.
Wednesday...shra/tstms possible with MVFR or lower conditions at times.
Thu-Fri...chance of showers with MVFR or lower conditions at times.
Sat...VFR.

&&

Marine...
seas currently on the ocean at near 2 feet. Wavewatch is predicting
3 feet for the same time. Therefore this positive bias in the wave
height was taken into account for the forecast. Basically 2 to 3 feet
seas today and a long fetch duration of southern flow will build
seas up to 4 feet by late tonight.

Winds within the boundary layer increase as well but with
warm air advecting aloft...will have difficulty mixing down to the
surface especially tonight. Therefore gusts will be closer to 20
knots with any 25 knots gusts being occasional. Hence...Small Craft Advisory conditions
are not expected to be met. It is not totally out of the question
but did not have enough confidence with these marginal conditions
to hoist Small Craft Advisory with this forecast.

Nearly the same conditions persist into Wednesday but continuing to
stay below Small Craft Advisory.

A relaxed pressure gradient over the region Wednesday night-Saturday
should keep winds to 10 knots or less over all waters. Seas will be 1
feet or less on the non-coastal ocean waters and 4 feet or less on the
coastal ocean waters as a result Wednesday night-Saturday.

&&

Hydrology...
Summer convection is forecast for today and Wednesday (more
likely) afternoons. With precipitable water values near 2
inches...heavy rainfall is possible. With the convection also
being rather slow moving...localized urban and poor drainage
flooding could occur...with a low probability of flash flooding.

Precipitable waters Wednesday night are forecast to be around 1.75-2
inches and increase to around 2-2.25 by around midday Thursday and
continue to remain high into Thursday evening. As a result there is
the potential for locally heavy rainfall with any stronger
convection Wednesday night-Thursday evening. There is some
indication though that there could be some organization of the
convection...making the potential for heavy rainfall more
widespread. While it is too early to specify any rainfall
amounts...there is the potential for at least minor urban/poor
drainage flooding Wednesday night...with a low chance of flash
flooding as well Thursday/Thursday evening. Will highlight the
threat of flash flooding County Warning Area wide in the severe weather potential statement.

&&

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

&&

$$

Synopsis...jm/maloit
near term...jm
short term...jm
long term...maloit
aviation...British Columbia
marine...jm/maloit
hydrology...jm/maloit

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