Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
415 PM EDT Friday Aug 1 2014
a frontal boundary hovers near the region through the
weekend...with low pressure riding the front to the north and
east. High pressure builds in briefly beginning of next
week...with a cold front approaching for middle week.
Near term /until 6 am Saturday morning/...
on going showers and thunderstorms this afternoon with a passing
shortwave triggering initial convection along sea breeze
boundaries. Outflow from current precipitation leading to further
development of showers and isolated thunderstorms...mainly over NE New Jersey into the
lower Hudson River valley. With the atmo having been worked over
this afternoon...expecting more along the lines of showers...with maybe
embedded thunderstorms into the evening. Weak flow aloft...generally
around 10 kts...leading to little if any movement with these
storms. As such...the flooding threat...particularly flash
flooding potential in the heavily urban areas of NE New Jersey...will
continue through 00z.
Aftr this day time convection...attention then turns to precipitation
potential during the overnight hours heading into Sat. At the
surface...stalled frontal boundary to the east will attempt to
back near the area...though remaining just offshore by 12z Sat.
Meanwhile...low pressure forms along the front near the middle
Atlantic and will ride the front...approaching from the south and
west by the morning...ushering in a very moist airmass ahead of
it. Aloft...mid/upper level trough axis swings through the
Midwest...continuing to position the northeast under the passing
of multiple shortwaves. Overall...the pattern is suggestive of
multiple rounds of precipitation forming with each shortwave providing the
forcing aloft to trigger the next round. Thinking there should be
a brief period of dry weather this evening once the afternoon convection
dies down...with the next round of precipitation moving up from the south
by around 02/03z...then spreading to the north for the remainder
of the night. Minimal instability keeps just shower wording in the
forecast for now.
Temperatures near normal for tonight...using blend of met/mav with
persistent cloud cover and precipitation.
Short term /6 am Saturday morning through Saturday night/...
surface low rides the front just to the south of Long Island
Saturday into Sat night...bringing yet another round of precipitation to
the region. Upper level trough continues progressing to the
east...with the axis remaining west of the region through at least
Sat night. Surge of deep moisture will be ushered in...so
expecting periods of moderate to potentially even heavy rain
throughout the day. Question remains for the potential for
thunder however. Winds turn to the east Sat...and with a more
marine influenced...moist environment in place...soundings indicating
little to no instability and unimpressive shear. As such...have
included isolated thunderstorm mention to the south where likely probability of precipitation are in
place...but overall confidence is that Sat will turn to be more
of a heavy rain...none thunder day earlier on...becoming more
periodic or even completely tapering off late afternoon into the evening.
Models in decent agreement with the precipitation during the day.
However...by Sat night...some discrepancies on just how long the
precipitation lingers. 12z NAM more of the outlier with persisting precipitation all
night...versus the general consensus which suggests a period of
dry weather before the next round of precipitation by Sunday morning with the
surface low passing further to the south. Am hesitant to completely
change probability of precipitation at this time with the path uncertainty...so will remain with
slight chance then chance wording for Sat night until the models gain a
better handle of the situation.
Temperatures cooler on Sat with the combination of an easterly
flow...cloud cover and precipitation. Have highs and lows a few degrees
cooler than normal...siding more to the mav guidance.
Long term /Sunday through Friday/...
a shortwave weakens at the base of a 500mb trough axis as it
approaches the forecast area...eventually passing through Sunday
night into Monday morning. This will help slowly nudge the offshore
frontal boundary farther out to sea.
Some synoptic lift will be present through Monday with the right
entrance of an upper jet streak in the vicinity. Less certain are
the timing and position of low-middle level shortwaves that pass
through/nearby the County Warning Area before the trough axis aloft passes through.
Probability of precipitation therefore capped at chance...which is close to what a model
blend would produce. Best overall chances of rainfall would be
Saturday night into Sunday morning and closer the offshore frontal
boundary. Monday could even turn out to be completely
dry...especially if the European model (ecmwf) is correct with the trough axis
passing through Sunday night and a lack of low-middle level shortwaves
trailing it on Monday. Do not have enough confidence to remove probability of precipitation
altogether on Monday...so have left the previous forecast of slight
chance/chance probability of precipitation.
Weak high pressure probably keeps Tuesday and Thursday dry...but a
cold front and cyclonic flow aloft could bring an isolated
shower/thunderstorm to the area on Wednesday.
Clouds and an onshore flow will hold high temperatures on Monday
below normal...highs otherwise near normal for the rest of the long
Aviation /20z Friday through Wednesday/...
convection across NE New Jersey and the lower Hudson will continue to
diminish over the next hour or two. Thereafter...an isolated shower
or thunderstorm is possible through early this evening. .
S/southeast winds will prevail around 10 knots through early this evening.
Winds will then gradually back around late tonight to the east/NE as a
frontal wave approaches from the south.
A period of MVFR ceilings/visibilities with mainly light rain is forecast Sat
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: brief period of MVFR ceilings possible this after.
Winds may vary from 150 to 180.
Klga fcster comments: winds may vary from 150 to 180.
Kewr fcster comments: winds may vary from 150 to 180.
Kteb fcster comments: winds may vary from 150 to 180.
Khpn fcster comments: isolated thunderstorms in the vicinity may
impact airfield through 21z. Winds may vary from 140 to 160.
Kisp fcster comments: brief period of MVFR ceilings possible this after.
Outlook for 18z Saturday through Wednesday...
Saturday-Sat night...rain showers with MVFR or lower conds likely. Low
probability for thunderstorms and rain.
Sun-Sun night...shra/tsra possible...MVFR or lower conds
Monday-Wednesday...VFR. MVFR possible in isolated rain showers/thunderstorms in the
with a weak pressure gradient over the waters...sub-Small Craft
Advisory conditions are expected on the waters through Tuesday. An
approaching cold front could potentially increase winds and seas
to Small Craft Advisory levels by Wednesday.
on going flash flooding and urban flooding threat across
northeast New Jersey late this afternoon into the early evening where
between 2 and 3 inches have fallen.
Urban and poor drainage flooding threat will persist into Monday
with multiple rounds of showers expected with a passing surface
low through the region. The combination of slow movement and a
very moist airmass could result in periods of moderate to heavy