Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
246 am EDT Wednesday Jul 30 2014
weak high pressure will slowly build offshore through tonight.
A frontal boundary over the western Atlantic will gradually work
west toward the coast through this weekend..with multiple waves of
low pressure tracking along it. Weak high pressure will then
return early next week.
Near term /until 6 am this morning/...
still seeing broken patches of high-based stratocu inland...also in
NYC and along the South Shore of Long Island. Showers have
developed offshore in convergence zone associated with a weak
trough. Radar shows the associated convergence boundary remaining
offshore...so do not expect any of these showers to drift
Low temperatures should range from the lower 50s inland and in the Long
Island Pine barrens...to 60-65 in and near NYC. Dry air remains
in place with dew points in the 50s.
Short term /6 am this morning through 6 PM Thursday/...
models in closer agreement as to amount of available moisture and
low level instability this afternoon to lead to showers as a weak
shortwave passes. 29/21z sref mean still suggests possibility of
sprinkles in Orange County from middle to late afternoon...at this time opted
to keep forecast dry. Even if any showers do manage to make it into
Orange...middle level cap should inhibit thunder.
Deeper middle level moisture should slowly edge into areas from NYC
north/west tonight...with mostly cloudy skies there and partly cloudy to
the east. Forcing for showers will be lacking as shortwaves
pivoting around a closed upper low in Ontario/Quebec will be weak
and passing just to the northwest.
A better and more widespread chance for showers will come on Thursday
as a stronger shortwave pivots around the closed low...and there
may be enough instability to support an isolated thunderstorm per NAM forecast
soundings. Have scattered coverage across nearly the entire County Warning Area despite
onshore flow...as marine layer does not look strong enough to
inhibit convection except far eastern sections of Long Island and
Long term /Thursday night through Tuesday/...
a highly amplified anomalous summertime pattern features a trough
across eastern North America...with ridging out west and across the
western Atlantic. This blocking pattern will result in the
aforementioned trough gradually filling and working east at the end of
the period as an upstream kicker moves into central Canada. There
are clearly timing differences amongst the global model suite with
how quickly this occurs...as well as with an offshore frontal
boundary that retrogrades west in response to height rises along the
eastern Seaboard Thursday into Sat. The latter of which could bring a
bout of steady rains into the region Friday night into the Sat. The 12z
European model (ecmwf) and 12z ggem remain the most aggressive solutions. The
potential is there foe a significant rainfall event...but there
remains a decent amount of uncertainty with the location of the
frontal wave and the boundary.
For Thursday into Friday...high pressure will be situated to the east with a
return southerly flow. Air mass remains fairly dry in the low-levels with
only marginal instability and weak to moderate shear. Overall chances
for convection are low during this time with the best chances being
in the after/evening hours in the hills northwest of NYC...driven by differential
heating. Rain chances then increase with the approach of the
offshore front and multiple waves of low pressure. Once again
though...the solutions vary on the proximity of the front.
For early next week...weak high pressure will build in on the heels
of the departing upper trough. The ggem and GFS both are slower with
the progression of the trough. Thus...convection could linger into Monday
with a weak trough/cold front moving through.
Temperatures should be near average Thu-Fri...then a little below average this
weekend via cloud cover and greater pop...then returning to near average
on Monday. Humidity levels will also NE on the increase with dew points
rising into the 60s.
Aviation /06z Wednesday through Sunday/...
weak high pressure remains over the region.
VFR. Light and variable winds overnight...lasting into Wednesday morning.
Sea breezes then develop this afternoon and pass through some
terminals. Winds generally SW to S 10kt or less.
Outlook for 06z Thursday through Sunday...
Thursday-Friday...isolated showers/thunderstorms possible in the
afternoon/early evening. VFR outside of any showers/tstms.
Saturday-Sunday...mainly VFR...IFR conditions possible in scattered
wind and seas remain below advisory levels through Wednesday
Conditions should remain quiet from Thursday though early next
week with an approaching offshore front this weekend and then weak
high pressure early next week.
mainly dry conditions expected through Wednesday night.
No significant rainfall is then expected from Thursday through
There is the potential for heavy rainfall during this weekend.
Too much uncertainty at this time for specifics.