Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1106 am EDT Tuesday Jul 7 2015
a warm front lifts to the north this morning...with a pre-frontal
trough developing over western portions of the tri-state this
afternoon. A cold front approaches from the northwest
tonight...crosses the area Wednesday. The front stalls to our
south Wednesday night through Thursday night...with waves of low
pressure ride 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/...
have updated forecast to include a slight chance for showers
for the entire area this morning. Some light showers have
developed under a marine stratus deck along/ahead in vicinity of of the
warm front across southern CT and eastern Long Island. Isolated showers
are also occurring west of the Hudson River.
Otherwise...a weak 700-500 hpa shortwave approaches western
zones by late afternoon. As it draws near...have increasing
chances for showers and thunderstorms...with highest probability of precipitation over northwest
zones. Precipitable waters of near 1.6 to 1.8 inches will allow
for locally heavy downpours. Refer to the hydrology section of the
afd for any potential impacts.
High temperatures will be well within the 80s across much of the
area...and upper 80s for urban northeast New Jersey.
There is a moderate risk of the meteorological enhancement of rip
current development at area Atlantic beaches today.
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 /15z Tuesday through Saturday/...
a warm front lifts north of the region today...with a cold front
approaching late tonight into Wednesday morning.
Conds have improved to VFR across NYC/New Jersey metropolitan terminals...but
slower imprvement to VFR expected across northern and eastern
terminals. Kgon may take until late afternoon to improve to VFR.
Isolated-scattered showers through this afternoon...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. Ccfp forecast of low confidence/sparse coverage of
thunderstorm across NYC/New Jersey metropolitan and northwest terminals looks good.
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. Seabreeze will likely have trouble
getting into kewr/kteb this afternoon as SW flow picks up
aloft...but will be close.
Light S/SW winds knots tonight. VFR likely across NYC/New Jersey metropolitan
terminals tonight. Patchy fog possible across interior terminals.
MVFR/IFR ceilings/visibility possible across eastern terminals after
06z...likely at kgon.
New York 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: low probability of isolated thunderstorm this afternoon.
Sustained wind of 20 knots possible late this after/early evening.
Klga fcster comments: low probability of isolated thunderstorm this afternoon.
Occasional wind gusts possible this afternoon to 20 knots.
Kewr fcster comments: low probability of isolated thunderstorm this afternoon.
Low probability of southeast seabreeze making it into kewr after 20-21z.
The afternoon kewr haze potential forecast is yellow...which implies
slant range visibility 4-6sm or greater outside of cloud.
Kteb fcster comments: low probability of isolated thunderstorm this afternoon.
Low probability of southeast seabreeze making it into kewr after 20-21z.
Khpn fcster comments: low probability of isolated thunderstorm this afternoon.
Kisp fcster comments: timing of improvement of ceilings to VFR may be 1-2
hours too slow
Outlook for 12z Wednesday through Sat...
Wednesday-Thursday evening...shra/tstms possible with MVFR or lower
conditions at times.
Late Thursday night-Sat...VFR.
dense fog has developed on the central and eastern ocean...Peconic
and gardiners bays...and eastern sound. Have therefore issued a
dense fog advisory until 17z. Will continue to monitor trends into
the morning as the fog could linger further into the afternoon.
Wavewatch currently running around 1 feet high...so have adjusted
seas downward 1 feet. This is a fairly typical bias for wavewatch in
S-SW flow. Basically 2 to 3 feet seas today and a long fetch
duration of southern flow will build seas up to 4 feet by late
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 likely to be met.
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.
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.
Marine...dense fog advisory until 1 PM EDT this afternoon for anz330-