Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
129 am EDT Tuesday Sep 16 2014
offshore high pressure will give way to an approaching low
pressure area and cold front tonight. These will move across and
weaken Tuesday morning with high pressure returning Tuesday night.
High pressure is then in control for the remainder of the week and
into the weekend.
Near term /until 6 am this morning/...
minor adjustments made with this update...mainly to temperatures and
Clouds will continue to stream in from the middle and high levels.
This will be ahead of a southwesterly jet streak in the upper
levels as well as a digging shortwave moving in from the Great
Lakes. This will have an associated cold front at the surface.
Lows were a blend of mav/met/ecs...yielding a range from the
upper 40s to lower 60s.
Probability of precipitation increase late...especially after 08z from west to east with
light rain showers moving in from the west. Went with coverage
wording and activity is expected to be numerous near NYC and north/west
but more scattered farther east. Might need to lower probability of precipitation with the
next update based on latest guidance and observed trends.
Short term /6 am this morning through 6 PM Wednesday/...
these light rain showers will continue through Tuesday morning
but models are showing a consistent trend of breaking up and
lowering the quantitative precipitation forecast as the front tracks eastward during the day
Tuesday. The jet streak will be exiting quickly so the forcing for
lift will be lost and the front at the surface will weaken...leaving
a weak pressure gradient with high pressure building in thereafter
on Tuesday night from the west.
Overall conditions may end up drying out earlier than forecast.
Wind direction is also southwest to west with light wind
speeds...so this will allow for less moisture to get entrained
into the front as it moves near.
Maximum temperatures Tuesday were a blend of 2/3 nam12 and 1/3
gmos...accounting for lower temperatures due to wet ground from
rainfall...allowing for more insolation to go into the evaporation
of water. The cold front will exit east of the area and weaken
later Tuesday morning. The more westerly flow behind the cold
front should allow for high temperatures to be similar to
Monday...with values in the upper 60s to lower 70s.
For Tuesday night...the clouds will be decreasing as high pressure
builds in and with a decreasing pressure gradient and decreasing
geopotential height gradient aloft...winds will remain light.
However...they will be from the north and advecting in cooler air.
Went with a blend of mav/met guidance for lows which yield a range
from the middle 40s to middle 50s for much of the region. This will be
several degrees cooler than the previous night.
There is low risk of rip currents on Tuesday...but due to an
increasing swell from distant hurricane edourd...this could be
elevated to a moderate risk late in the day.
Long term /Wednesday night through Monday/...
broad upper trough over the northeast remains in place through
Friday with high pressure building in at the surface and no
precipitation forecast. A weak shortwave moves through on
Thursday with just a brief increase in clouds expected. The trough
will keep temperatures cool at normal to just below normal values.
Chilly overnight lows Wednesday-Thursday night with light winds will drop
values into the 40s for interior locations and lower to middle 50s
NAM/mosguide blend was used for temperatures through Thursday with a
mosguide/wpc blend thereafter. Very little change from previous
forecast overall with temperatures.
Temperatures warm to near normal values Sat-Monday as heights rise ahead
of a trough approaching from the west. 20/00z European model (ecmwf) run was an
outlier in relation to precipitation on Saturday. 20/12z has come into line
with the GFS/CMC lending to a dry day on Saturday. A cold front well
to the west will be approaching through the weekend but with a
strong high pressure area to the east...expect precipitation to hold off
until Sunday night at the earliest. Moisture will begin to build in
ahead the front on Saturday so expect a partly sunny sky.
Aviation /06z Tuesday through Saturday/...
a trough of low pressure passes across the area this morning...with
high pressure building to the west late.
VFR conditions are expected...and any rain will be light. Scattered
showers are expected after 9-11z...through about 14-16z or so. Then
clearing will take place. Please see individual terminals forecasts
Wind direction forecasts may be problematic today. Light
winds...mainly out of the south or southwest early this morning will
vary as the trough nears. A brief shift to the west or northwest is
possible before winds settle back to the west or southwest this
afternoon. Then a wind shift will occur late in the day to the northwest.
Speeds generally remain light today.
Outlook for 06z Wednesday through Saturday...
Thursday night-Friday...VFR. NE-east wind g15-20kt possible.
even with increasing swell from tropical cyclone Edouard...winds
and seas will remain below Small Craft Advisory levels through Tuesday night with
an overall weak pressure gradient in place.
High pressure will be in control of the weather across the waters
Wednesday-Sat with mainly sub Small Craft Advisory criteria expected. With an offshore low
passing to the east...swells increase Wednesday with ocean seas possibly
reaching 5 feet through Thursday morning. As well...winds increase
slightly Thursday night into Friday and seas could once again rise
again to 5 feet.
rainfall amounts of less than a quarter of an inch are forecast
late tonight through Tuesday morning. Mainly dry conditions are
forecast thereafter through the weekend.