Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
726 am EDT Sat Mar 28 2015
low pressure well east of the New Jersey coast deepens and tracks
northeast through tonight...reaching the Canadian maritime. High
pressure builds into the region tonight into Sunday...followed by
a series of frontal systems that will impact the area through the
Near term /until 6 PM this evening/...
low pressure was centered well east of the Delaware-Maryland-Virginia...southeast of
the benchmark...this morning and continues to track northeast
through today as the broad and nearly full latitude upper trough
moves east toward the coast. The precipitation shield has now
spread a little farther to the west into central and eastern Long
Island...and into Middlesex and New London counties of Connecticut.
A vigorous vorticity maximum was rotating into the trough and was moving
off the North Carolina coast as seen on the water vapor.
Precipitation will become more widespread early this morning...and
especially across the east as this vorticity maximum moves through the
eastern potion of the trough. Have limited the westward extent of
higher probability of precipitation today. All model profiles indicate light snow for the
event. With the low a little deeper and closer to the
region...northwest flow has increased along with gusts.
Short term /6 PM this evening through 6 PM Sunday/...
the upper trough moves over the region by 00z Sunday with the
intensifying vorticity moving south and east of the region. This
deepens the surface low which will pass south and east of the 40n
70w benchmark. Again enough cold air will be in place behind this
low for the precipitation to be all light snow. With the low
passing well to the south and east have cut back of the westward
and northward extent of the probability of precipitation with inland areas receiving
little precipitation. Liquid to snow ratios around 1 to 10 and
with around a third of an inch mainly across New London
County...could see 2 to 3 inches of snow here...and close to wpc
snow amounts. Precipitation ends slowly from west to northeast
late in the day and into tonight as the surface low tracks
northeast toward the Canadian maritime and the upper trough axis
moves off the coast 06z to 12z Sunday...with heights quickly
building. Sunday remains dry with upper ridge axis over region by
00z Monday...and the surface high sliding to the south.
Long term /Sunday night through Friday/...
a progressive...yet amplified flow is being advertised by the global
models through next week. Initially...a series of fast moving Pacific
systems ride over top the ridge over western North America...
dropping southeast across central Canada and into the NE quarter of the
nation. However...toward the end of the week...there are timing and
magnitude differences with Pacific energy moving into the West Coast of
the lower 48. The 12z European model (ecmwf) focuses on a trailing second piece of
energy...thus slowing down the frontal system at the end of next
week. For the time...will maintain a low chance of rain showers Thursday
and Friday with the possibility that this system may be slower than
The other system that may be noteworthy is a clipper low that the
12z GFS takes just north of NYC and Li Tuesday night...while the European model (ecmwf)
is significantly farther south emerging off the middle Atlantic coast.
The latter scenario has some support from the gefs. This could raise
concerns for some wintry weather...especially inland. For now...going
with an all rain forecast based on climatology and model uncertainty.
A much weaker cold front will move across the area Monday with
perhaps a few showers.
After an unseasonably cold start on sun with highs 40 to 45...both
highs and lows will rebound to near seasonable levels. The one
caveat is a farther south storm track Tuesday night into Wednesday.
Aviation /11z Saturday through Wednesday/...
surface low pressure will pass well to the south and east today.
Meanwhile...an upper level disturbance and weak surface low
pressure trough will move across the region.
VFR conditions at most terminals to start. Ceilings at kgon are MVFR
and are expected to fall to to IFR by 15z. Ceilings are expected to
fall to MVFR at kisp and kbdr in snow between 12z-14z.
Precipitation should generally be snow through the event except at
kgon where the precipitation has started as rain. Runway accumulation of
1-3 inches is forecast for east of NYC.
The rest of the terminals should remain VFR through much of the
taf period...although a brief period of MVFR is not out of the
question in any light snow that develops.
Winds increase as the pressure gradient tightens with the
offshore low deepening and gusts should develop. Expect gusts into
the 20-25 knots range. A few occasional gusts could exceed 25 knots.
Outlook for 12z sun through Wednesday...
Monday...VFR. West winds g20kt.
Tuesday night...chance of MVFR conditions with any rain showers.
forecast on track...wind and gusts a few knots higher than
forecast with the low off the Delaware-Maryland-Virginia and deepening quickly.
A Small Craft Advisory on the ocean waters remains with seas 5 feet
or more...in addition as low pressure passes south and east today
while deepening...wind and gusts will increase to small craft
levels across all the forecast waters. Gusty northwest small craft
wind continues into tonight as the low moves into the Canadian
maritime and high pressure builds to the west. Small craft gusts
may linger into early Sunday morning across the eastern
waters...however gusts diminish as high pressure builds to the
The small craft on the ocean waters was extended through Sunday
for lingering seas...and the small craft on the remainder of the
waters remains in effect tonight.
Waves diminish to sub Small Craft Advisory on Sunday...but build to above Small Craft Advisory
criteria on a southerly flow late Sunday night into Monday ahead
of an approaching warm front. Winds mainly over the ocean waters
will gust to 25 knots late Sunday night into Monday night. Winds and
waves will diminish on Tuesday as the pressure gradient relaxes
with weak high pressure building in. There is the potential for
marginal Small Craft Advisory conditions Tuesday night into Wednesday morning depending on
the track and intensity of low pressure near the waters. Leaning
toward sub-Small Craft Advisory conditions at this time.
a few hundredths to a third inch liquid equivalent quantitative precipitation forecast is
expected through tonight...with little to none across portions of
the lower Hudson Valley and into northeastern New Jersey and the
highest amounts across the Twin Forks and New London County. The
precipitation falls as snow.
No significant widespread precipitation is forecast Sunday into
Rivers and streams are expected to remain below bank full...but
increased river/stream flow across the lower Hudson Valley and
southern Connecticut will continue ice breakup and movement into
this weekend. Isolated ice jams are possible...which if they
occur...could result in localized flooding. Since ice jam flooding
is unpredictable and sudden...interests along ice covered rivers
should monitor National Weather Service forecasts for the latest information.
For details on specific area rivers and lakes...including
observed and forecast river stages and lake elevations...please
visit the advanced hydrologic prediction service /ahps/ graphs on
our web site.
Marine...Small Craft Advisory from 4 PM this afternoon to 6 am EDT
Sunday for anz338.
Small Craft Advisory from 6 PM this evening to 6 am EDT Sunday
Small Craft Advisory until 6 PM EDT Sunday for anz350-353-355.