Scientific Forecaster Discussion
fxus61 kokx 291136
Area forecast discussion
National Weather Service New York New York
736 am EDT Sat Jul 29 2017
low pressure tracks well south of Long Island today, and well
east of the area tonight. Meanwhile high pressure builds to the
northwest through Monday, and moves offshore Tuesday and
Wednesday. A cold front approaches from the northwest.
Near term /until 6 PM this evening/...
with high pressure to the northwest and subsidence increasing
across the region, especially across the northern and western
forecast area, the low moving off the Delmarva, along with the
precipitation shield, was having tough time moving farther to
the north. Also, in the northeast flow dew points have dropped
into the 40s and 50s across much of the area, so lower levels
have dried and any precipitation falling into this lower dry
layer will not reach the ground.
A very sharp gradient in the precipitation shield associated
with the coastal low moving off off the Delaware-Maryland-Virginia is evident in
the radar returns and observations. Adjusted probabilities
through this morning to increase gradient and cut back on the
northern extent of precipitation.
Surface high pressure and mid and upper level ridging north of
the low and upper trough will keep the low from tracking to much
farther to the north through today. Also with the low moving
off the coast through today areas to the west will have
precipitation ending 14z to 15z, so will be a short period of
precipitation as well. A northeast flow will keep cool
conditions across the region with temperatures below seasonal
There is a high risk of rip currents at Atlantic beaches today.
Short term /6 PM this evening through 6 PM Sunday/...
surface and mid level high pressure builds into the region from
the west and northwest tonight through Sunday as the upper
level trough shifts farther to the south as height rise across
the northeast and mid Atlantic regions.
Long term /Sunday night through Friday/...
aloft, upper trough will slowly drift east Sunday night through
Monday, weakening in time. Weak flow behind this trough
prevails Tuesday through Wednesday. Then upstream trough
amplifies as it slowly tracks east, extending across the Great
Lakes region and the Ohio Valley, with lowering heights the
result for our area late week.
At the sfc, waves of low pressure ride along a stalled front well to
the southeast Sunday night into Monday. High pressure builds to
the west. Daily sfc troughs develop mid week, then a cold front
makes progress toward the area Thursday and Friday.
As for sensible weather, dry conditions expected through Wednesday,
with perhaps an isolated afternoon/early evening shower/thunderstorm
Tuesday and Wednesday. This would be mainly across the interior.
Showers and thunderstorm chances increase just a bit Thursday and
Friday with the approach of the front/trough.
Temps will remain around seasonal norms, with perhaps readings a few
degrees above early to mid week. In general, do not foresee large
swings in temps with this expected pattern.
Aviation /12z Saturday through Wednesday/...
low pressure tracks south and east of Long Island today and
Northern extent of the rain shield made it as far north as
kewr/kjfk/kisp. Additional low level convergence has triggered a
few showers across southern CT and into the lower Hudson
Valley, likely impacting khpn and possibly kbdr next hour or
two. Rain threat should end at all terminals by mid to late
Ceilings finally dropping to low VFR and still expect to see a
period of MVFR at some of the terminals this morning into early
aftn before lifting above 3k ft. There is the possibility that
NYC terminals remain VFR, or experience MVFR for a shorter time
than forecast. VFR returns all terminals around 18z.
NE winds will increase this morning and gradually back to the north
early this evening. Gusts may exceed 30 kt at times 16z-22z at
the Metro terminals. Winds then diminish tonight.
Outlook for 12z Sunday through Wednesday...
Tuesday-Wednesday...VFR. Slight chance of a shower or
thunderstorm northwest of NYC each afternoon.
forecast on track and no changes made at this time.
Low pres passes south and east of Long Island today and
tonight. NE winds increase this morning with Small Craft Advisory conds
developing on all waters and gales on the ocean early this aftn.
There could be some 35 kt gusts on Li sound at times and have
mentioned this in the forecast...just not confident it will be
frequent. Strongest winds and highest seas will be during the
aftn and eve. Directions back to the north early this eve and will
start to diminish after sunset. Have backed up the end time of
the gales to 06z tonight with an Small Craft Advisory replacing it.
No change to the non-ocean waters headlines...but Small Craft Advisory may
linger a few hours longer than forecast.
Northeast flow Sunday diminishes as high pressure builds to the
west, and waves of low pressure pass well to the east. Gusty
winds remain on the ocean Sunday with rough ocean seas lingering
into Sun night.
For the early to mid week period, sub Small Craft Advisory conditions are
anticipated across the area waters as high pressure remains to
a light rainfall is expected today, mainly along the coast, with
amounts ranging from nothing across the lower Hudson Valley and
interior southern Connecticut to about 1/10 of an inch across
northeastern New Jersey eastward across Long Island. No
hydrologic impacts are expected.
No significant hydrologic impacts are expected Saturday night
New York...high rip current risk through this evening for nyz075-080-081-
Marine...Small Craft Advisory until midnight EDT tonight for anz335-338-
Small Craft Advisory until 6 am EDT Sunday for anz330-340.
Gale Warning until 2 am EDT Sunday for anz350-353-355.