Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
720 PM EDT Sat Apr 25 2015
a large upper level low pressure system will persist over the
northeastern United States into early next week. High pressure
builds across the region Tuesday night into Wednesday.
Meanwhile...low pressure over the Gulf Coast states will track to
the middle Atlantic coast by Thursday and continuing northeast into
the Atlantic through the end of the week. An upper level
disturbance may impact the area on Saturday.
Near term /until 6 am Sunday morning/...
forecast is on track. Just freshened up the hourly T/dew point and made
minor adjustments to the sky forecast with cirrus ohd and expected
to persist overnight. Otherwise...upper low elongates into
northern New England tonight...with shortwave energy over the
Ohio/Tennessee River valleys this afternoon/evening sliding to the middle
Atlantic coast by daybreak. This will result in the region being
in an area of weak high pressure between the Canadian maritime low
and low pressure sliding through the middle Atlantic coast.
Dry conditions tonight with potential for good radiational cooling
conditions with light winds. The caveat will be northern extent of
cirrus shield associated with shortwave to the south. Models are
generally keeping this cirrus shield skirting southern portions of
the region. So high potential for frost conditions across interior
lower Hudson Valley and CT areas tonight...with a slightly moderated
potential across interior NE New Jersey and eastern Li due to cirrus
potential. Will issue a frost advisory for tonight into early Sun
morning for these regions.
Short term /6 am Sunday morning through Sunday night/...
elongated upper trough over northern New England begins to pivots
south into central New England on Sunday...with weak surface trough
reflection developing along the coastal plain.
Daytime instability...steepening middle level lapse rates...and
convergence along surface trough should allow for scattered-broken after/evening
instability cumulus and isolated-scattered shower developing off the higher terrain
and sinking S/se. Highest coverage will likely be across CT in
vicinity of surface trough. Gusty winds possible with any showers
with inverted v sounding. Highs generally in the upper 50s to lower
Upper trough continues to sink southeast over the region Sunday night.
Diminishing surface instability and convergence should end any
shower activity...but middle-deck shield associated with trough appears
to sink south over the region. This should keep temperatures several
degrees milder Sunday night.
Long term /Monday through Saturday/...
a blocky pattern looks to dominate the first half of next week
across the Continental U.S.. a large persistent cutoff low pressure system is
forecast to plague the northeast US through Tuesday which will
result in generally mostly cloudy conditions and scattered showers Monday/Monday
night as spokes of vorticity within the cyclonic flow rotate through
This cutoff finally exits on Tuesday with ridging briefly building in
Tuesday night and Wednesday. Dry conds and partly cloudy skies are expected.
Model guidance remains divergent with how quickly the ridge axis
moves through and the next trough approaches. GFS is faster than the
ec. What both models do agree on is the phasing of a northern stream
shortwave with a cutoff low over the Southern Plains resulting in a
deep trough through the Mississippi Valley Tuesday night. The surface low
associated with the cutoff tracks through the Gulf Coast states to
off the North Carolina coast on Thursday and continues on a NE track
through Friday. However due to the differences aloft the ec is
stronger...slower and closer to the coast...but continues to remain
well S of the forecast area. Have kept schc probability of precipitation across the area Thursday
as several shortwaves dive down from the north during this time.
However...due to the uncertainty in the pattern earlier in the
forecast...this is very low confidence.
Temperatures will be near to slightly below normal levels through
Aviation /00z Sunday through Thursday/...
a trough of low pressure will give way to high pressure building
from the northwest.
Winds are expected to turn to the northwest...then north later
this evening. Only high clouds are forecast overnight. VFR.
During the day Sunday...another trough develops. Northerly winds
are expected in the morning...then winds will vary based on
location during the afternoon. Generally expect northwest winds for New Jersey
and lower Hudson Valley terminals...with potential west/SW or sea
breeze wind flow to the east on Long Island and southern CT. VFR with
broken cumulus and ac developing during the late afternoon. A few
showers will approach from the north...but generally VFR
conditions are anticipated through 00z.
Outlook for 00z Monday through Thursday...
Sun night...mainly VFR. Possible MVFR with showers early evening.
Monday-Monday night...possible MVFR with showers.
Thursday...possible MVFR with showers.
marginal Small Craft Advisory gusts across eastern Li sound and rough water near
The Race this afternoon...otherwise a weak pressure gradient will
keep sub-advsy conds across the waters through much of the period.
Marginal northwest gusts are possible late Monday night into Tuesday on the
eastern ocean waters as the gradient tightens.
significant precipitation is not expected through next week.
CT...frost advisory from 2 am to 8 am EDT Sunday for ctz005>008-
New York...frost advisory from 2 am to 8 am EDT Sunday for nyz067>070-079-
New Jersey...frost advisory from 2 am to 8 am EDT Sunday for njz002-004-103-