Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
439 am EDT Wednesday may 27 2015

Synopsis...
high pressure slides farther offshore today. A cold front
approaches from the west tonight...then crosses the area on
Thursday...sliding to the south Thursday night. Meanwhile...high
pressure will remain off the Atlantic coast. A stronger cold front
will then impact the area from Sunday into early next week.

&&

Near term /until 6 PM this evening/...
main focus today is how much convection develops in response to a
weak 700-500 hpa shortwave...currently stretching from upstate SC
into Ohio...that crosses the area this afternoon is at continues to
weaken. Should also be able to achieve some lift over the lower
Hudson Valley/NE New Jersey as the seabreeze intersects a weak thermal
trough forecast to set up there this afternoon.

With forecast convective available potential energy over the lower Hudson Valley/NE New Jersey/SW CT on
average of 1500-2500 j/kg...25-30kt of 0-6km shear and the region
in the right rear quadrant of a 85kt 300 hpa jet...have the
potential for some isolated to scattered severe thunderstorms over
this area. Bulk Richardson numbers generally 25-50 do support the
possibility of a discrete supercell...with mainly multicellular
convection. The severe threat is generally consistent with Storm Prediction Center/S
area of marginal and slight risk of thunderstorms over the area.
Not quite so sure about the marginal risk over NYC...as seabreeze
could stabilize things before any convection arrives there. For
that reason will only highlight the severe threat in the severe weather potential statement for
the lower Hudson Valley/NE New Jersey and SW CT at this time. However
cannot completely rule out a severe thunderstorm moving into NYC.
The main threat would be for strong gusty winds. There is also the
threat for locally heavy rainfall with any stronger
convection...refer to the hydrology section of the afd for
details.

For now appears most if not all of Long Island and
southeast CT should be too stable in the low levels due to marine
influence to keep any convection at Bay...however due to proximity
due have slight chance probability of precipitation in north Middlesex...North Nassau and northwest
Suffolk counties this afternoon as well.

For highs today used a blend of mav/met/ecs guidance with NAM
2-meter temperatures and a mix down from 975-850 hpa per BUFKIT
soundings. Highs should be 5-10 degrees above normal.

There is a moderate risk for the meteorological enhancement of rip
current development at Atlantic beaches into this evening.

&&

Short term /6 PM this evening through 6 PM Thursday/...
could see storms linger into the evening across the northwest 1/2 of the
County Warning Area...otherwise should be dry tonight absent any notable forcing.
It will be notably humid...with dewpoints mainly in the lower to
middle 60s. Lows tonight were based on a blend of NAM 2-meter
temperatures with ecs/met/mav guidance...with values around 10-15
degrees above normal. There is some potential for fog
tonight...depending on exactly where/how much it rains this
afternoon. Noting that fog has not materialized the past few
nights...do not have the confidence to continue with patchy fog
in the forecast for tonight.

Models differ on coverage/extent of convection with a cold front
on Thursday. Also differ on timing with the GFS/European model (ecmwf) faster than
the NAM/CMC-reg. Noting 700-500 hpa flow has a fairly decent
perpendicular component to the front...leaned towards the faster
timing of the GFS/European model (ecmwf) for probability of precipitation. With a weakening front
though...did not feel comfortable going with higher than chance
probability of precipitation at this time...and kept southeast Suffolk County at slight chance.
Probabilities are highest over the northwest 1/2 of the County Warning Area where the
instability is highest.

With slightly less cape - 1000-2000 j/kg over the interior than
today...and the best dynamic forcing forecast to the north of the
region...do not think there is as much of a threat for severe
weather. Though an isolated or two strong to severe storm cannot
be completely ruled out.

For highs Thursday used a blend of mixing down from 975 to 825 hpa
per BUFKIT soundings with NAM 2-meter temperatures and a mixture
of ecs/mav/met guidance. Highs should be around 10-15 degrees
above normal. It would not be surprising if a few locations in NE
New Jersey and/or northern portions of NYC came in with a high at or just
above 90.Dewpoints on Thursday should be a tad lower than
today...mainly in the upper 50s...so heat indices should peak out
in warmer areas in the middle 80s.

&&

Long term /Thursday night through Tuesday/...
a weak cold front will move across the area Thursday night before
dissipating offshore on Friday. Little to no precipitation is
expected with the front. Heights build aloft Friday into Saturday.
Any convection Friday or Saturday will be isolated...diurnal in
nature...and likely well inland. Will keep the forecast dry for now.

Main question in the long term will come during the second half of
the weekend and start of the new week as a cold front approaches.
The 00z operational GFS still remains the faster and more more
aggressive solution. Will continue to run with the slightly slower
00z European model (ecmwf)...which does not bring the front through until Sunday
afternoon/night. Will continue to introduce some low chance probability of precipitation
late Saturday afternoon and night as some showers and thunderstorms
could develop out ahead of the front itself.

Both model solutions keep the front in the vicinity of the forecast
area into early next week...resulting in chance probability of precipitation for Monday and
Tuesday.

There is the potential for an organized rainfall event late in the
weekend into early next week as the cold front moves into the area.

Conditions will remain unseasonably warm through Sat...then cools
down Sunday into Monday behind the cold front.

&&

Aviation /09z Wednesday through Sunday/...
a weak cold front will approach the region today...and dissipate
over the area Thursday.

Mainly VFR this morning...however there is the potential for some
pockets of stratus and br which could bring MVFR. Any MVFR Burns
off by 13-15z except kgon where there is the potential that it
could linger most if not all of the day. Otherwise...afternoon thunderstorms
likely to develop across the lower Hudson Valley after 18z. The
activity may hold together to impact areas roughly along and west of
a khpn-kewr line.

MVFR or lower at times tonight with stratus and possibly fog.

S to SW flow through the taf period. Highest speeds this afternoon into
early evening...especially in vicinity of kjfk where sustained around 20kt
expected.



..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: low probability for MVFR ceilings through 14z.

Klga fcster comments: low probability for MVFR ceilings through 14z.

Kewr fcster comments: low probability for MVFR ceilings through 14z.

The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.

Kteb fcster comments: no unscheduled amendments expected.

Khpn fcster comments: no unscheduled amendments expected.

Kisp fcster comments: no unscheduled amendments expected.



Outlook for 06z Thursday through Sunday...
late tonight...MVFR or lower at times with SW flow.
Thursday...morning MVFR or lower. Scattered thunderstorms possible in vicinity of a weakening
cold front. SW flow diminishing and possibly becoming northwest or vrb.
Friday...VFR with light NE winds veering through the day.
Sat...morning MVFR or lower possible. Chance showers and thunderstorms in the
afternoon and overnight with MVFR or lower. Strong southerly flow.
Sun...possible improvement to VFR. NE winds.

&&

Marine...
seas should remain at or above 5 feet over at least the southern
portion of the coastal ocean waters through tonight...so have
continued the Small Craft Advisory there.

Once again appears the sea breeze will be strong enough to bring
gusts to around 25 knots to the coastal ocean waters and to New York
Harbor and the South Shore bays of Long Island. Have issued a
Small Craft Advisory for those two zones from noon until midnight
as well. On the sound and eastern bays of Long Island...gusts
should peak out at 20 knots this afternoon/evening...with maybe some
occasional gusts to 25 knots.

For Thursday for now it appears seabreeze should be weaker...and
the pressure gradient slightly more relaxed...so expecting sub-Small Craft Advisory
conditions on all waters.

Have adjusted wavewatch down 1 feet today-Thursday...as it has
generally been over forecasting wave heights at the buoys by
about that amount.

There will be a brief period of offshore winds Thursday night behind
a dissipating cold front. Then...marginal small craft conditions on
the ocean waters will be possible Friday through Sunday with a
moderate southerly flow.

&&

Hydrology...
there is the potential for basin average of around 1/4 an inch of
rainfall across the lower Hudson Valley/NE New Jersey/SW CT this
afternoon/evening...with lesser amounts...down to zero elsewhere.

Noting precipitable waters forecast to be around 1.75 inches and
storm motion forecast to be around 10 knots...there is the potential
for slow moving storms that produce locally heavy rainfall in any
stronger convection. This could lead to minor flooding of
urban/poor drainage areas.

On Thursday there is the potential for less than 1/4 of an inch of
basin average rainfall. However...with storm motion of around 10
knots and precipitable waters around 1.25 inches...there is the
potential for slow moving storms producing locally moderate to
heavy rainfall. This could result in the minor flooding of
urban/poor drainage areas...especially if it occurs over areas
receiving locally heavy rainfall today.

There is the potential for an organized rainfall event late in the
weekend into early next week as cold front moves into the area.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory until 6 am EDT Thursday for anz350-353-
355.
Small Craft Advisory from noon today to midnight EDT tonight
for anz338-345.

&&

$$
Synopsis...BC/maloit
near term...maloit
short term...maloit
long term...British Columbia
aviation...jmc
marine...BC/maloit
hydrology...BC/maloit

National Weather Service Glossary of Abbreviations