Area Forecast Discussion
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FXUS61 KOKX 010816
Area Forecast Discussion
National Weather Service New York NY
416 AM EDT FRI JUL 1 2016
A warm front approaches from the south today, followed by a cold
front crossing the Tri-State tonight. High pressure will
build in for the holiday weekend. Low pressure may track close
enough on Monday night and early Tuesday to spark a few showers
and thunderstorms, then fair weather will return through Thursday
followed by low pressure for next weekend.
.NEAR TERM /THROUGH TONIGHT/...
** MARGINAL TO SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
TRI-STATE THIS AFTERNOON AND EVENING **
A 850-500 hPa trough moves across the Great Lakes today,with the
trough axis pushing across the area tonight.
Ahead of it, winds veer from the SSE-SE at the surface to SW-WSW
at 500 hPa, with a Bulk shear of 30-40kt. In addition to the speed
and directional shear, 1000-2000 J/kg of CAPE is forecast over
most of the region (only 500-1000 J/kg over Eastern Long Island
and coastal SE CT). Furthermore the region will be under the
surface theta-e ridge and have a 25-30kt 950 hPa jet pass just to
the south. Given the shear, CAPE, abundant low level moisture and
forcing from the low level jet and an approaching warm front (and
cold front by late afternoon), the ingredients exist for strong to
severe storms across the Tri-State from mainly this afternoon into
this evening. Bulk Richardson numbers in the 15-40 range, along
with hodographs suggest potential for some isolated supercells
and possibly some bowing segments as you get towards late
Consistent with this, SPC has placed NYC, NE NJ, the Lower Hudson
Valley and most of Fairfield County in a slight risk for severe
thunderstorms, and the remainder of the CWA in a marginal risk.
The main threat is from damaging winds, with a secondary threat
from large hail. In addition, given the anticipated low level
helicity, as evidenced by Vorticity Generation Parameter from
around 0.25-0.5 and Energy Helicity Index of 1 to 2.5 across
mainly the W 2/3 of the CWA (highest over NE NJ/Lower Hudson
Valley), LCLs forecast down to around 800-900m there is a small
chance for tornadoes, highest west of the Hudson River.
In addition to the severe threat, with the abundant low level
moisture, there are some potential hydrologic concerns as well.
Refer to the hydrology section of the AFD for details.
The threat for storms falls off fairly rapidly from west to east
this evening (maybe lingering into the first part of the overnight
hours far eastern zones), as the surface cold front reflection of
the upper trough pushes to the east.
Highs today were based on a blend of MAV/MET/ECS guidance, NAM
2-meter temperatures and a mix down from 975-900 hPa per BUFKIT
soundings. Highs should be near normal.
Lows tonight were based on a blend of MET/ECS/MAV guidance and NAM
2-meter temperatures, with values forecast to be near normal.
.SHORT TERM /SATURDAY/...
Saturday will feature rising heights aloft, as the aforementioned
upper trough lifts to the northeast. The low-mid levels dry out
fairly quickly, so should see minimal, if any cloud cover - except
for maybe some diurnal cumulus over mainly higher elevations over
far N/W portions of the CWA.
Highs on Saturday were based on a blend of MAV/ECS/MET guidance,
NAM 2-meter temperatures and a mix down from 825-775 hPa per
BUFKIT soundings. Highs should be near to slightly above normal.
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Saturday Night through the day Monday will feature fair weather with
near normal temperatures as high pressure moves slowly east across
the area. Day time heating will develop inland troughs that will aid
the development of weak sea breezes both Sunday and Monday afternoon.
Monday Night through Tuesday Morning, forecast models show a weak
upper level short wave advecting east along the southern edge of
the polar jet stream. There are enough differences in model track
guidance to include at least a 20% POP for widely sct TSTMS after
8 pm during Monday evening with both the latest operational runs
of the ECMWF and the NAM forecasting measurable QPF across NYC
during this time. If the track becomes suppressed and remains
further south of the area, fair weather will occur. If the track
lifts further north, then heavier showers and TSTMs could occur.
Tuesday Afternoon through Wednesday Night will feature fair weather
with day time temperatures averaging slightly above normal in the
mid to upper 80s across the NYC Metro area.
Thursday through Friday, two successive troughs of low pressure
may cause mainly diurnal widely sct TSTMs during each afternoon as
humidity increases in an uncomfortable maritime tropical air mass
with day time highs in the mid and upper 80s.
.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
A cold front approaches late today and passes through this
VFR, however there will be chance of tempo or prevailing cigs of
2000-3000FT after around 14Z, primarily east of the city, but may
include the city terminals as well.
Showers will be possible starting 12-14Z, but will be most likely
for a few hours starting 20-21z for most terminals. TSTMs possible
with westerly gusts over 40KT during this period as well. Winds
otherwise SSE mostly 10-15KT most of the day.
.OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY...
.Friday Night...VFR NW gusts to 20 kt possible late.
.Saturday-Sunday Night...VFR. NW-W flow Saturday and WSW-SW flow
Sunday. Gusts up to 20KT for both days. Winds diminish at night.
.Monday Night-Tuesday...Mainly VFR. Slight chance for
** STRONG TO SEVERE THUNDERSTORMS LIKELY OVER THE WATERS AROUND
LONG ISLAND THIS AFTERNOON AND EVENING **
A light to moderate pressure gradient over the waters around Long
Island through Saturday will keep sustained winds to 15 kt or
less. Some gusts to around 20 kt are possible due to an
approaching/passing cold front from late this afternoon into
Saturday. Seas should run 4 ft or less, and waves 2 ft or less
through Saturday as well.
Saturday Night through Monday...Winds and seas are forecast to
remain below Small Craft Advisory/SCA levels of 25 knots across
local coastal waters and 5 feet across Atlantic Ocean Coastal waters.
Monday Night through the day Tuesday...Winds and seas may reach SCA
levels as a wave of low pressure tracks east, passing just south of
the Atlantic Ocean coastal waters. This low may bring showers and
TSTMs along with reduced VSBY. Stay tuned to forecast updates.
Around 1/3-2/3 of an inch of basin average precipitation is
expected into this evening. However with precipitable waters
forecast to be around 1.75 inches, and the potential for strong
convection, locally heavy rainfall is possible. Areas receiving
locally heavy rainfall could experience minor flooding of
urban/poor drainage areas. With a forecast storm motion of
20-30kt, storms should be moving fast enough to minimize the flash
flood threat, unless localized training occurs.
It should be dry from late tonight into Monday.
From Monday night through early Tuesday, there is a chance of
rain depending on the future track of low pressure passing south
of the local area, with amounts ranging from 0 to 1 inch plus.