Scientific Forecaster Discussion
fxus61 kokx 230829
Area forecast discussion
National Weather Service New York New York
429 am EDT Fri Jun 23 2017
a warm front moves well north this morning. A cold front
approaches tonight and moves across the area Saturday. A series
of frontal boundaries will move across the tri-state area
Sunday through Tuesday. A large area of high pressure builds in
Near term /until 6 PM this evening/...
region will be between Bermuda ridging and deepening northern
stream longwave trough across the north central US today...with
one distinct southern stream shortwave riding northeast this
morning and then several weaker vorts riding northeast later
today. At the surface...a warm front washes out/pushes north of
the region this morning...with likely pre-frontal trough
development in the Lee of the Appalachians this afternoon.
Deep southwest flow with sub-tropical connection will result
in an increasingly moist and humid airmass working into the
The initial shortwave rides north through the region this morning
into early afternoon. Low level jet forcing weakens as this activity works
towards the region...but a marginally unstable and moist airmass in
place should support scattered shower and isolated thunderstorm
activity to work northeast through the region. Overall appears
to be a marginal instability with moderate shear
situation...which presents a low probability of an isolated
strong to severe storm.
In the wake of this shortwave...potential for partial clearing and
additional destabilization late this afternoon/early evening across
NYC Metro and points n&w. Although moderate instability/Uni-
directional shear levels could exists during this time...appears to
be lack of a distinct focus or trigger for convection until the
evening. In fact...subsidence and weak mid-level capping may
limit convective activity across the region until late. Based on
instability/shear environment there is a threat for isolated
strong to severe storms during this time...conditional on
sufficient heating and development along any differential
heating boundaries or elevation.
Otherwise...considerable cloudiness and convective debris today
will keep temps in the lower to mid 80s for most of the region.
If enough breaks in the clouds materialize...temps could rise
into the upper 80s across NYC Metro and points n&w.
Short term /6 PM this evening through 6 PM Saturday/...
northern stream longwave trough continues to deepen into the
upper Mississippi River valley and Great Lakes through the
period...with the shortwave remnants of Cindy shearing northeast
towards the region late tonight into Saturday morning. At the
surface...a cold front over the Great Lakes will slide east
towards the region tonight...with the remnant circulation of
Cindy riding NE towards the region along the front.
Leading edge of southern stream shortwave energy and pre-
frontal trough approach the region this evening. Will have to
watch for convection developing over central/eastern PA this
afternoon...and whether line segments can translate east in the
moderate mid- level flow into the lower Hudson Valley/NE New Jersey
before instability begins to wane. A conditional low threat for
severe winds gusts exists mainly northwest & west of NYC if this activity
The parade of shortwaves late evening into the overnight and
tropical airmass will keep a threat for iso convection with
heavy downpours overnight. Coastal stratus/fog development
possible with high dewpoint airmass advecting across east Li/southeast
CT late today/this evening.
Main concern during this period will be approach of cold front
and remnant low of Cindy late tonight/Saturday morning.
Environment presents a threat for flash flooding along and just
to the south of the path of this low...with precipitable waters in excess of
2+ inches and corfidi vectors indicating potential for slow
moving or back building convective elements. Also can't rule out
an isolated severe wind/tornado threat if any mesoscale convective system type activity
develops in a weak instability but high shear/helicity and low-
Drying conditions in the wake of the cold front and Cindy
circulation Saturday afternoon...with highs in the mid to upper
A high risk of rip current is likely Saturday with building
southerly swells and wind waves.
Long term /Saturday night through Thursday/...
nwp is in agreement that a broad upper level trough will remain east
of The Rockies into early next week. The 500 mb flow then flattens from
west to east as a cutoff low pres system moves through the western
Canadian provinces...eventually consolidating with a vortex over
northern Quebec. This will sharpen the trough with its axis passing
through Tue night followed by weak ridging for the remainder of the
In terms of sensible weather...not a whole lot to talk about. A
few cool frontal boundaries will pass through the local
area...the first Sunday aftn/eve with just a chance of isold
showers. Mid level warming will keep instability in check so no
tstms in the forecast.
The second boundary approaches on Monday and is very slow to
move through the area. It may become hung up...before pushing
east Tue night. Despite a decent shortwave and being in the rrq
of a 120+ kt upper jet...moisture looks very meager...thus have
kept the forecast dry. Moisture is still limited on Tue...but
there could be enough for isold showers/tstms in the aftn.
Dry and seasonable weather then returns for the remainder of the
Aviation /08z Friday through Tuesday/...
a warm front approaches the region overnight, and lifts nwd
thru the area Friday.
Mainly VFR overnight, however there is a chance that some areas
of IFR develop for a few hours, especially east for kgon and
kisp. Pockets of MVFR are possible again on Fri with cigs
around 2500 ft. There is also some potential for eastern
terminals to briefly go to MVFR in the late afternoon due to
low stratus. For now the tafs indicate VFR because coverage is
in question and too uncertain at this time. More widespread sub
VFR conditions are expected late in the taf period after 0z
Saturday (see outlook below).
There will be a chance of isold-sct shwrs thru the day (friday),
with the best potential for thunderstorms aft 20z, particularly
in areas along and W of the Hudson River.
Sea breeze flow will lessen overnight, and veer to the SW as the
flow weakens. The sea breeze may attempt to back winds closer to
the S again aft 16z Fri.
Outlook for 00z Saturday through Tuesday...
Friday night...MVFR or lower in shra/tsra. IFR or lower
conditions possible in stratus/fog for eastern terminals for the
first half of Friday night.
Saturday...MVFR or lower possible in shra/tsra. S/SW winds.
Saturday night-Sunday night...VFR. Northwest winds...becoming W/SW.
Monday...VFR. Slight chance of afternoon shra/tsra. SW winds.
Tuesday...VFR. Chance of afternoon shra/tsra. SW winds.
southerly winds increase to marginal Small Craft Advisory on the ocean this
afternoon...and likely continue into tonight. Occasional gusts
to 25 kt possible on nearshore waters this afternoon. Ocean
seas likely building to Small Craft Advisory levels this afternoon...and likely
further build to 4 to 7 ft tonight. Winds subside and
Saturday...but southerly swells are expected to keep ocean seas
at 4 to 7 ft on Sat.
The other hazards for mariners will be rounds of
showers/thunderstorms this today into Saturday morning, and
potential for dense fog development on the ocean waters and
eastern Li nearshore waters this afternoon and continuing into
Seas begin to subside Sat night...but could take until Sun morning
to drop below Small Craft Advisory levels east of Moriches Inlet. A weak pressure
field is then expected to prevail through Tue...keeping conds at sub-
localized minor urban and poor drainage flooding is possible
with showers and thunderstorm activity this morning into the
first half of tonight.
There is a threat for flash flooding late tonight through
Saturday morning from a likely complex of showers and
thunderstorm associated with a frontal wave (remnants of cindy)
moving through the areas. Uncertainty exists on the
exact track of this wave...which could be from the northern mid-
Atlantic to southern New England.
Otherwise, no other hydrologic concerns.
astronomical tides are running very high, especially during the
evening high tide cycles today and Saturday.
Less than 1 ft of surge is needed during these evening high tide
cycles for minor flooding, and in some cases less then 1/2 ft.
The expected S/SW flow is not favorable for surge, but a
background anomaly will likely be enough for minor coastal
flooding of the most vulnerable coastal locales along the South
Shore bays of western Long Island, along Jamaica Bay, and along
western Long Island Sound during this time.
kokx weather radar is scheduled for maintenance starting today June
23rd for a period of 3 days.
Marine...Small Craft Advisory from noon today to 2 am EDT Sunday for