Scientific Forecaster Discussion
fxus61 kokx 270549
Area forecast discussion
National Weather Service New York New York
149 am EDT Thu Jul 27 2017
high pressure moves off the mid-Atlantic coast through Thursday. Low
pressure forms late Friday over Virginia and passes south of
Montauk Saturday morning which likely brings rain to the region.
Canadian high pressure builds from the north late Saturday into
early next week.
Near term /until 6 am this morning/...
only minor adjustments needed to reflect current temperature and
dew point trends. Mid and high level clouds will continue to
increase from the west overnight ahead of an approaching short
Lows around 65 in the New York Metro - near 60 elsewhere (around 5
degrees below climo). Could have some valley fog towards
morning over the interior, but with the increase in high level
moisture, decided to not including it.
Short term /6 am this morning through 6 PM Friday/...
weak frontal boundary sags down and over the region Thursday
evening. Have continued with low chance tstms with Storm Prediction Center lowering
the region to marginal after collaboration with local National Weather Service offices.
Ensemble of nwp suggest about 1000 j/kg of MUCAPE and Li's of -1
to -4 c of Li. Shear is only around 30 knots and most show
subsidence in the 850-700 hpa layer. Thus the lowering of pops
and severe potential.
Pops increase overnight as front sags southeast. Instability
then has a synoptic support from the frontal passage and most
nwp supports scattered convection.
Upper 70s to around 80 based on consensus of MOS for highs and
around 70 for lows Thursday night using warmer NAM MOS based on
clouds and scatted precipitation.
There will be a moderate risk of rip currents at area beaches.
Long term /Friday night through Wednesday/...
the long term period starts off with unsettled weather Friday,
Friday night and the first half of Saturday as low pressure passes
south of the forecast area.
At this time, looks like showers and thunderstorms will occur on
Friday. There is the potential that some rain could be heavy at
The showers should transition to more of a stratiform rain event
Friday night into Saturday morning, once again with some rain
potentially being heavy, especially during the first half of Friday
night. Winds will increase, especially across Long Island and
southern CT, as the low intensifies Friday night and Saturday. Gusts
into the 30 mph range is possibly, and can not rule out a few gusts
to 40 mph.
As of right now, average rainfall amounts for this event are
expected to range from 0.50-1.00 inches across the lower Hudson
Valley and southern CT and from 1.00-1.70 across the northeast NJ,
NYC and Long Island. Locally higher amounts will be possible. These
amounts are likely to change, as we fine tune the exact track of the
The low moves east on Saturday. The rain comes to an end Saturday
morning as high pressure builds in from the north.
High pressure remains over the region through the first half of next
week, providing dry and seasonable conditions.
Aviation /06z Thursday through Monday/...
a weakening cold front approaches from the northwest as high
pressure continues to slide offshore.
Mainly VFR through the taf period. There is a low chance of
MVFR or lower conditions in valley fog early this morning at
kswf, although high clouds should help limit this potential. In
addition, there is the potential for showers and thunderstorms
to impact the northernmost taf sites late this afternoon, which
could result in a brief period of MVFR conditions. Chances are
too low to include in the tafs at this time however.
Light and variable or light southerly winds will return out of
the south at generally 10 kt or less by mid to late morning.
Outlook for 06z Friday through Monday...
Thursday night-Friday...chance MVFR ceilings early Friday
morning, otherwise VFR.
Friday night-Saturday...MVFR or lower possible, with showers
and possibly a tstm. NE winds g20-30kt on Saturday, mainly at
the coastal terminals.
tranquil into Friday. Winds and seas gradually build to
advisory levels Friday night and into Saturday night as low
pressure passes over the area waters. Expect a strengthening
north-NE flow, with the potential for gales Friday night into
Saturday. Winds will subside below advisory level on Sunday,
however it may not take until Monday for seas to fall back below
5 ft as high pressure builds in.
heavy rainfall is possible Friday afternoon into the night
across the New York Metro and Long Island. Urban and poor drainage
flooding is possible.