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Area forecast discussion 
National Weather Service New York New York
236 PM EDT Thursday Mar 26 2015

Synopsis...
a cold front passes tonight. A weak trough moves through Friday
night into Saturday...behind the departing low. High pressure
builds in Sunday. Another frontal system moves through
Monday...followed by high pressure for Tuesday. A frontal system
will approach late Wednesday into Thursday.

&&

Near term /until 6 PM this evening/...
forecast updated mainly for marine headlines. With lift supplied by a
low level jet and plenty of moisture in place...rain pushes in
from the south into early afternoon. This lift...combined with
some elevated cape and marginally unstable middle level lapse
rates...could result in an isolated rumble of thunder as well.
Better overall chances of thunder would be over the eastern half
of the area...but will leave in mention of thunder across the
entire area. Expecting patchy/areas of fog as well...and some of
this fog could be locally dense. Not enough confidence in
widespread dense fog to go with a dense fog advisory at this
point. But this will need to be watched...especially over the
eastern half of the County Warning Area where relatively higher dewpoints advect
from off the cold area waters.

Other concern is for localized flash flooding...particularly over
eastern CT where rainfall this afternoon could be briefly heavy due
to convection...and coinciding with where snow melt can contribute to
runoff. Overall threat is low...so no watch is planned for this.

Used a NAM/mav MOS blend for high temperatures...which brings them
above normal.

&&

Short term /6 PM this evening through 6 PM Friday/...
a cold front slowly passes through with more rainfall. Still enough
elevated cape to mention isolated thunder...but mainly for the
evening. Models have trended slower with the end time of
rainfall...so even by daybreak Friday...will carry likely probability of precipitation for a
good portion of the County Warning Area. Probability of precipitation then gradually lower into Friday
afternoon....with at least the western half of the County Warning Area at a high
chance of remaining dry during the afternoon. Cold advection behind
the cold front will be delayed somewhat...so highs will manage to
average near 50.

&&

Long term /Friday night through Wednesday/...
broad upper level trough remains over the East Coast Friday night
into Saturday with the trough axis moving east of the region late
Saturday night into Sunday. Cold air advection on Saturday will mean
lower thicknesses and colder temperatures...generally 30s region-
wide. Shortwave energy will rotate through the upper trough while at
the surface a weak trough remains behind departing low pressure. The
combination will provide enough lift with lingering low level
moisture. With colder air in place...most of the area will see snow
showers Saturday morning...changing over to rain showers by late
morning into the afternoon. Precipitation lingers into Saturday
night.

Surface high pressure builds in for Sunday...then moves off the
coast Sunday night. Ridging aloft over the northeast along with
deepening low pressure moving into the Great Lakes will allow for
warm advection ahead of the low. Temperatures will warm into the
40s. Looks like any precipitation from this system will hold off
until Monday morning.

Cold front moves through Monday. There is limited moisture to work
with...so will continue with just slight chance probability of precipitation.

With lower amplitude upper flow systems quickly move east. As a
result...high pressure builds Monday night into Tuesday. Some
uncertainty for the area of low pressure that approaches for
Wednesday. For now...will keep slight chance probability of precipitation for Wednesday.
Another frontal system approaches late Wednesday night into
Thursday...with a warm front moving through the area during this
time period.

&&

Aviation /18z Thursday through Tuesday/...
a warm front will become stationary over the area this afternoon.
A cold front will then move across tonight.

Warm front appears to have moved into NYC metropolitan and Long
Island...but do not expect it to make much more northward
progress. Showers and isolated thunderstorms accompany the front...with
impacts expected at kjfk/kisp within the next hour.
Otherwise...moist southerly flow moving over cold ocean waters
should help maintain IFR/LIFR conditions into this evening before
cold frontal passage...with low level wind shear as strong low level jet passes overhead.

Cold frontal passage should occur at NYC metropolitan from 02-03z...and farther
east at 03z-04z...with S flow shifting NW-NNW. Followed GFS lamp
guidance with quick improvement to MVFR at NYC metropolitan after
frontal passage...but this may be a little too quick. Held onto IFR/LIFR
conds at the CT/Long Island terminals for a few hours after frontal passage.
There is some uncertainty as to flight Cat later tonight into Friday
morning...at this time decided to side with more pessimistic guidance but
there could be periods of VFR.

..NY metropolitan enhanced aviation weather support...

Detailed information...including hourly taf wind component forecasts can
be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)

Kjfk fcster comments: unscheduled amend possible for changes in
flight category. Cold frontal passage by 03z...but IFR conds could
persist until 05z-06z.

Klga fcster comments: unscheduled amend possible for changes in
flight category. Cold frontal passage by 03z...but IFR conds could
persist until 05z-06z.

Kewr fcster comments: unscheduled amend possible for changes in
flight category.

Kteb fcster comments: unscheduled amend possible for changes in
flight category. Cold frontal passage by 02z...but IFR conds could persist
until 04z-05z.

Khpn fcster comments: unscheduled amend possible for significant
changes in flight category.

Kisp fcster comments: unscheduled amend possible for changes in
flight category.

Outlook for 18z Friday through Monday...
Friday afternoon...becoming VFR.
Friday night-Sat...chance of MVFR conds with any rain or snow
showers. North winds g15-20kt.
Sat night-.Sunday night...VFR.
Monday...VFR. SW winds 15g20kt...becoming west-northwest at night.
Tuesday...VFR. Northwest winds 15-20g25-30kt...diminishing at night.

&&

Marine...
a cold front moves across the waters tonight before becoming
nearly stationary across the ocean waters on Friday.

The pressure gradient will tighten today...and Small Craft Advisory
conditions will develop on the ocean and South Shore bays this
afternoon. Winds fall below Small Craft Advisory conditions on the sunset bays
tonight...but seas will remain elevated on the ocean waters through
at least Friday.

Waves remain at or above 5 feet Friday night into Saturday with a
strong northwest flow between departing low pressure to the east and
high pressure building to the west. Also...gusts on the ocean waters
may approach small craft for a while Saturday.

The flow Sunday night into Monday becomes west then southwest as
high pressure moves east and another low approaches. Wind and waves
will be above Small Craft Advisory criteria for Monday through Tuesday. Gale force
winds are possible Monday night into Tuesday. Waves come down below
5 feet on Tuesday. Winds stay above Small Craft Advisory through Tuesday night.

&&

Hydrology...
an additional 1/2 to 3/4 inch of rain is expected through Friday.
Thereafter...significant precipitation is not expected Friday night
through the beginning of the new week.

The rainfall and snow melt will result in minor to moderate rises
on rivers/streams across mainly southern Connecticut and lower
Hudson River valley during the late week period...possibly into
this weekend.

Currently rivers and streams are expected to remain below
bank full...but the mild temperatures and increased river/stream flow
will increase ice breakup and movement during the next few days.
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.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory until 6 PM EDT Friday for anz350-353-355.
Small Craft Advisory until midnight EDT tonight for anz345.

&&

$$
Synopsis...jc/jp
near term...jmc/jc
short term...jc
long term...jp
aviation...Goodman
marine...jmc/jc/jp
hydrology...jc/jp

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