Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
154 PM EDT Sat Jul 26 2014
high pressure will move further out to sea today as a warm front
approaches from the southwest. This front will lift through the
area Sunday with a cold front approaching Sunday night. A wave of
low pressure expected to develop on the cold front...lifting
through New England on Monday as the front slowly slides across.
High pressure then builds in behind the front by the middle of
Near term /until 6 PM this evening/...
shortwave energy will continue to track eastward across Li/CT
through early afternoon...with middle-deck and scattered sprinkles.
An isolated light shower is possible across eastern Li/southeast CT..
partial clearing expected across NYC metropolitan and points west by late
this afternoon in wake of shortwave as seen on by satellite.
Otherwise...high pressure off the middle Atlantic coast will continue
eastward today with a mean trough persisting aloft. Environment
doesn't look great for afternoon convection...particularly in wake
of shortwave...but can't rule out isolated development off the
higher terrain of eastern PA working into areas west of the Hudson
region late in the day/early evening. Appears convective activity
across southern New Jersey should remain south of the region...where
higher Theta-E air resides.
High around normal levels in the lower to middle 80s.
There is low risk of rip currents along Atlantic facing
beaches into early this afternoon...becoming moderate late today
into this evening with increasing southerly winds from sea breeze
Short term /6 PM this evening through Monday/...
a warm front approaches tonight and lifts through Sun morning. The
combination of a middle level shortwave and the left exit region of a
90kt h250 jet will result in increasing chc's of rain showers/thunderstorms across
the area late tonight into Sun morning. Uncertainty in probability of precipitation and
sky behind the warm frontal passage. If there are any breaks in the clouds
we'll warm up fast and could hit 90 in metropolitan NY/NJ. Any sun will
also result in destabilization during the afternoon and could trigger
additional storms...some of which could reach severe limits. Muggy
conds will become noticeable and persist until the cold front
pushes through sometime Monday night.
This is where the forecast gets interesting with the focus turning
to a weakening cutoff low dropping through the upper Midwest
tonight...the Great Lakes sun and pivoting through New England on Monday.
Some of the model guidance is indicating a secondary area of low
pressure developing over central New Jersey Sun night...while others keep the
parent low in control further north and west. Considerable spread remains
amongst the guidance with regards to timing and track of the low.
The 00z NAM is the worst case scenario with the low tracking NE
from central New Jersey to Massachusetts with 60+kt of 0-6km bulk shear (~15kt 0-1km
shear)...approx 1k j/kg of SBCAPE...400-500 m2/s2 of surface-1km
helicity and an local below 1k feet around 06z Monday. This would be
sufficient for rotating storms. However if this secondary low does
not develop the most severe storms should remain further north and west.
Needless to say...still some fairly big uncertainty in how much of
an impact this will be...but since there is the threat for severe weather
have added enhanced wording to the forecast Sun afternoon and night.
Precipitable waters increasing to near 2 inches also indicate the potential for
heavy rain in any thunderstorms.
Front is slow to move across the area on Monday...and the potential
for more rain showers/thunderstorms will continue Monday afternoon.
Long term /Monday night through Friday/...
upper trough/cutoff low persists into the middle of the week with
weak high pressure in control at the surface. Schc/chance rain showers/thunderstorms Monday
night/Tuesday as a result. Weather pattern begins to stabilize with
heights building as the upper level trough begins to lift north of
the region during the second half of the week. At the surface...high
pressure will begin to build in from the west.
The high pressure continues to build in and the upper level trough
amplitude continues to weaken with time through the rest of this
period. This will allow for a dry airmass to encompass the region.
Temperatures will not deviate too much from normal.
Aviation /18z Saturday through Thursday/...
weak high pressure and surface trough nearby remain into this
evening. A warm front approaches tonight and passes through Sunday
VFR through this evening. SW to S winds 10-15kt this afternoon...dim
5-10kt tonight. A few gusts up to 20kt are possible into early
evening...however not frequent enough to include in the tafs.
Showers Sunday morning with a chance of thunderstorms. Additional rain showers/thunderstorms
possible Sun afternoon.
Outlook for 18z sun through Thursday...
Sun afternoon...mainly VFR. Isolated/scattered shra/tstms.
Sun night...rain showers and scattered thunderstorms. Chance tempo sub-VFR.
Monday...mainly VFR. Chance shra/tstms. Chance tempo sub-VFR.
sub Small Craft Advisory conds today...with south winds increasing Sunday and Sunday
night out ahead of low pressure and associated cold front. Seas
build as a result late Sunday into Sunday night and remain rather
rough Monday. Small Craft Advisory headlines may be needed
eventually for the Sunday night through Monday time frame across
the ocean waters.
Winds gradually shift to the west behind the slow moving front late
Monday and Monday night...and speeds diminish somewhat.
West or northwest winds can be expected Tuesday and Wednesday.
Rough seas subside Tuesday and Wednesday.
unsettled weather with scattered to numerous showers/thunderstorms are
forecast late tonight through Monday. Any of these storms have
the potential to produce heavy downpours. Significant uncertainty
still exists with timing and amounts though. It looks like the
higher potential for heavy rain is Sunday afternoon and Sunday night
with higher precipitable waters of 1.5 to 2 inches across the region.