Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
347 PM EDT Friday may 29 2015
high pressure will remain over the Atlantic through Saturday
afternoon. A cold front will approach Saturday night...and move
through on Sunday. The front will stall just to the south as weak
low pressure rides along it. High pressure will then build in from
the north late Tuesday into Wednesday...and shift to the south
Near term /until 6 am Saturday morning/...
after a mostly sunny afternoon...with only a few cumulus over interior
southeast CT and thin high clouds from NYC north/west...attention will
turn to development of low stratus and patchy fog tonight.
Patch of low clouds 20-40 nm S of Suffolk County has been slowly
expanding. Combo of onshore flow and low level radiational
cooling under clear skies will promote its expansion north/west
after dark...to the South Shore of Long Island and possibly
coastal southeast CT by late evening...then into the rest of Long Island
and southern CT after midnight and possibly all areas
late tonight. Low temperatures will be in the upper 50s across eastern Long
Island and southeast CT...lower 60s most elsewhere...and middle 60s in vicinity of
Short term /6 am Saturday morning through Saturday night/...
morning low clouds should be slow to burn off especially across
Long Island and coastal CT. Surface ridging and southerly flow should
keep the air mass stable over most of the County Warning Area from NYC east...
while enough late day instability may develop well north/west of
NYC ahead of an advancing weak shortwave to spark isolated-scattered
showers and possibly a thunderstorm. Afternoon coastal sea breezes will be
enhanced by a tight pressure gradient...and could again see gusts
20-30 miles per hour late in the afternoon especially across Long Island.
High temperatures should be 80-85 inland and in the 70s along the coast.
Convective potential should wane Sat evening with loss of daytime
heating...then could see scattered showers and possibly a thunderstorm late at
night as a cold front approaches. Prefer slightly slower/drier
frontal approach per NAM/European model (ecmwf) vs faster/wetter GFS...and so have
scaled back guidance pop...with only chance late at night mainly
inland. Low temperatures should be in the lower and middle 60s.
Long term /Sunday through Friday/...
cold front slowly crosses through the County Warning Area through on Sunday with
showers becoming likely. Cape is sufficient for a chance of
thunderstorms. With the cold front becoming aligned with the upper
flow along with a relatively slow storm motion forecast...will need
to keep an eye out for the potential of training cells and at least
minor urbanized/small stream flooding during the afternoon and
The cold front stalls to our south...then a wave of low pressure
forms along it...passing over or just south of US on Tuesday. Models
disagree on how quickly this happens with European model (ecmwf) continuing to be the
slowest with the passage. Have gone with likely probability of precipitation through Monday
night before tapering to chance on Tuesday. Might eventually need to
increase probability of precipitation for Tuesday...especially over eastern zones. Elevated
cape will be just south of US...so no mention of thunder from late
Sunday night through Tuesday.
After near-normal highs on Sunday...Monday and Tuesday should be
below normal with rain/clouds/onshore flow.
Will maintain a dry forecast for Wednesday...favoring the more
progressive models. High pressure builds in behind the departing
low. Higher confidence that Thursday will be dry with the center of
the high passing through. Temperatures returning to normal. Friday likely
remains dry as well with the high offshore and the next cold front
well off to the northwest.
Aviation /19z Friday through Wednesday/...
high pressure remains offshore through Saturday with a cold front
approaching from the Great Lakes. This will keep the area under a
prolonged period of southerly flow.
Forecast dilemma resides in the extent and magnitude of
stratus/fog development tonight. Latest Sat imagery shows area of
stratus 40-50 miles south of Li. This will begin returning north
this after as winds becomes southeast...and may reach the South Shore
between 00z and 03z. The offsetting factor with be the amount of
dry air over land. Thus...have delayed IFR/MVFR conditions until
after 06z tonight...and then quickly improve to VFR after 12z 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: timing of stratus along the South Shore
could move in earlier this evening.
Klga fcster comments: no unscheduled amendments expected.
Kewr fcster comments: no unscheduled amendments expected.
Kteb fcster comments: no unscheduled amendments expected.
Khpn fcster comments: no unscheduled amendments expected.
Kisp fcster comments: timing of stratus along the South Shore
could move in earlier this evening.
Outlook for 18z Saturday through Wednesday...
Saturday afternoon...most likely VFR. Chance of MVFR in
showers/thunderstorms mainly to the north/west of city terminals. Gusts
to 20-25kt possible with sea breeze.
Saturday night-Tuesday morning...MVFR or lower at times in
showers. Thunderstorms possible Saturday night-Sunday night.
Tuesday afternoon/night...becoming VFR.
quiet conds through early Sat afternoon. Coastal sea breezes
enhanced by a tightening pressure gradient should then help
generate frequent gusts up to 25 knots along the near shore waters
south of Long Island late Sat afternoon into Sat evening...so
have raised Small Craft Advisory for the ocean and the South Shore bays.
Ocean seas may flirt with 5 feet late Sat afternoon and Sat night.
With sustained winds remaining mostly 15 knots or less held them
at 4 feet.
Small Craft Advisory conds will probably be on the ocean waters Sunday and Sunday
night...however there could be an extended period during this
time frame where the criteria is not being met. East winds otherwise
increase on Monday with Small Craft Advisory conds probable on most of the waters.
Winds then subside on Tuesday...but a lingering swell may keep
ocean seas at Small Craft Advisory levels through the day...and probably through
most of Wednesday as well.
forecast rain amounts from Sunday through Monday night currently
range from 1.5 to 2.5 inches. As usual...locally higher amounts will
be possible due to scattered thunderstorms. These thunderstorms are
more likely to occur Sunday afternoon and evening. There is a threat
of flooding...but minor urban/poor drainage/small stream flooding
would be more likely. Flash flooding is not out of the question
Sunday afternoon and night...but confidence is not high enough to
include in the hazardous weather outlook...especially with antecedent
dry conditions for the past month or so.
Marine...Small Craft Advisory from 2 PM to 11 PM EDT Saturday for