Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1100 am EDT sun Jul 5 2015
weak high pressure will build from the west today and east of the
region on Monday. A low pressure trough moving up the middle Atlantic
Coastal Plain will approach Monday night...and move across on
Tuesday. A cold front will then move through on Wednesday...then
stall just to the south on Thursday with weak waves of low
pressure moving along it. High pressure should return on Friday or
Near term /until 6 PM this evening/...
a band of cirrus has set up from northestern New Jersey into western Li. Forecast updated
for this. Also bumped up seas on the ocean. Otherwise...mostly
sunny skies with some fair weather cumulus and coastal sea breezes
developing this afternoon via weak thermal troughing.
High temperatures will be in the lower and middle 80s...warmest in NYC
metropolitan and the interior valleys. Afternoon sea breezes will keep
south coasts closer to 80.
There is a moderate to borderline high risk of rip current
development at the ocean beaches into this evening due to 3-4 feet
long period southerly swells and developing onshore flow this
Short term /6 PM this evening through Tuesday/...
the 06z NAM suggests we may have to watch for development of late
day showers somewhere over central New Jersey...that could slowly drift
into parts of NYC and Long Island tonight. This hinges on ideal
placement of mesoscale and thermodynamic features as forecast by that
model...including a low level Theta-E ridge and moisture
convergence in the inland thermal trough...topped by upper
divergence in the right entrance of an upper level jet streak
lifting north through that region as upper ridging starts to build
and push it northward. The 06z GFS and latest rap are slower to
build the upper ridge northward...which keeps the jet streak and
surface Theta-E ridge farther south toward southern New Jersey and
Philadelphia...without producing any precipitation as surface ridging from
offshore will be more likely to dominate there. Since the
aforementioned ingredients would have to line up perfectly...will
not mention in forecast...but it is Worth monitoring in the late day
and early evening.
Otherwise...tranquil and seasonably mild conditions tonight.
Patchy fog expected outside of NYC metropolitan with clear skies...light
winds...and increasing moisture.
Upper ridging will remain in control on Monday while a closed low
aloft moves toward the central Appalachians...with a weak surface
reflection east of the mountains. The high will provide another day
of mostly sunny skies and temperatures again in the lower and middle 80s.
The closed low will open up to a weak trough as it gets closer Monday
night. Deep layer ridging will give way to this trough...with
increasing chances for showers and perhaps an isolated thunderstorm from light snow shower
NE Monday night into Tuesday morning...then more numerous showers/thunderstorms
from NYC metropolitan north/west Tuesday afternoon via daytime
surface heating/destabilization and continued deep layer moisture
transport. With precipitable water increasing to near 2 inches...precipitation efficiency
(pw times 1000-500 mb mean rh) to 1.6 inches...and mbe vectors
under 5 knots...locally heavy rainfall is possible. Wind fields do
not look strong aloft so organized severe weather not expected...but some
pulse storms could produce locally gusty winds.
Onshore flow should greatly limit convective potential in the
afternoon across much of central/eastern portions of Long Island
and southern CT.
Long term /Tuesday night through Saturday/...
a cold front then moves in from the northwest Wednesday afternoon and
possibly clears the eastern zones by midnight...but there is still
some uncertainty regarding how far southeast the front moves before
stalling. Will cap probability of precipitation at high end chance Wednesday/Wednesday night...but this
might eventually need to be bumped up should models continue to
show roughly the same frontal passage time and increasing moisture. Enough
cape is present for a chance of thunderstorms...and with continued
high precipitable water...fairly light steering flow...and the cold front
becoming more aligned with this steering flow aloft...there is
again concern for heavy rain and training of cells storms that
could lead to least minor urban/small stream flooding.
There appears to be agreement among the global models that the
cold front stalls south of US during Thursday and weak wave of
low pressure moving along the boundary brings US a chance of rain
some time fro Thursday into Friday morning. Will go with low chance probability of precipitation
for most of this period...then high pressure should build back in
later Friday and Saturday with the likelihood of dry weather.
Aviation /15z Sunday through Thursday/...
high pressure builds in today and then gradually east
VFR today with few clouds through the day and into tonight. After
midnight tonight...expect patchy fog to develop with MVFR likely
and IFR conditions possible. Isolated LIFR cannot be ruled out.
Light and variable winds will give way to afternoon sea breezes.
Southeast seabreeze likely for kewr/kteb and S seabreeze expected for
the rest of the coastal terminals this afternoon. Winds lighten
Outlook for 12z Monday through Thursday...
Monday...VFR with S winds 10 to 15 knots. Sub VFR in patchy fog at night
Tuesday...mainly VFR. Chance thunderstorms...especially western areas. S winds.
Tuesday night...patchy fog possible.
Wednesday...mainly VFR with a chance of thunderstorms. SW flow.
Thursday...MVFR possible with a chance of showers. Flow becoming NE.
ocean seas still expected to remain just below 5 feet
today. 44017 has been steady at around 4.6 feet this morning. Updated
the forecast to indicate around 4 feet however. Winds and seas should
remain below Small Craft Advisory levels through the period...but will have to deal
with late night and morning patchy fog for the next couple of
nights...also possible thunderstorms with locally heavy rain and gusty
winds Tuesday through Thursday...mainly each afternoon/evening.
significant precipitation could occur at some point from the
during middle week. Tuesday and Wednesday both offer potential for at least
localized urban and poor drainage flooding as precipitable water increases to
near 2 inches...with generally weak steering flow.