Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
1104 PM EDT Friday may 29 2015

Synopsis...
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
on Thursday.

&&

Near term /until 6 am Saturday morning/...
challenge overnight is development and possible expansion of low
stratus and patchy fog.

Earlier...public reported fog just out over the water in Moriches
Bay...and various web cams along the South Shore of Long Island
indicated fog moving in with lowering visibilities. Fok reporting fog.
Hrrr and narre continue to show higher probs of visibility below 1
mile over eastern zones...although they have backed off a bit from
earlier runs. Already have a dense fog advisory for some of the
marine zones. Will continue to watch for eastern Li and southeast CT.
Combo of onshore flow and low level radiational cooling under
mainly clear skies should promote the expansion of stratus and fog
north/west...into the rest of Long Island and southern CT after
midnight and possibly all areas late tonight.

Strengthening winds though off the deck may preclude widespread
fog.

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 NYC.

&&

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.

There is a high risk of rip currents at the Atlantic beaches
Saturday. Strongest rip currents would occur during the afternoon
as the southerly winds increase.

&&

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
evening hours.

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 /03z Saturday 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.

VFR will lower to MVFR/IFR and below in low
stratus/fog...especially kisp and kgon. More uncertain farther
west...IFR potential late at kjfk and potential for MVFR for other
terminals north and west.

Conditions improve to VFR after 13z Sat. There will be a chance
of showers and a slight chance thunderstorms late Sat afternoon through
Sat evening with MVFR possible...but confidence too low to include in
taf at this time.

The timing has uncertainty and categorical changes could be off by
2-4 hours.

Outlook for 03z Sunday through Wednesday...
Saturday night-Tuesday morning...gusty S winds up to 20 knots Sat
night but perhaps at more occasional frequency. MVFR or lower at
times in showers. Thunderstorms possible Saturday night-Sunday
night.
Tuesday afternoon/night...becoming VFR.
Wednesday...VFR.

&&

Marine...
poor visibilities for many areas tonight in fog. Dense fog for some of
the waters in effect.

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.

&&

Hydrology...
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.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...dense fog advisory until 10 am EDT Saturday for anz330-340-345-
350-353.
Small Craft Advisory from 2 PM to 11 PM EDT Saturday for
anz345-350-353-355.

&&

$$
Synopsis...jc/Goodman
near term...Goodman/pw
short term...Goodman
long term...jc
aviation...jm
marine...jc/Goodman/pw
hydrology...jc

National Weather Service Glossary of Abbreviations