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Area forecast discussion 
National Weather Service New York New York
446 am EDT Tuesday Mar 31 2015

Synopsis...
low pressure near Chicago early this morning will move to near
Pittsburgh this afternoon...then to near Baltimore early this
evening and finally pass southeast of Long Island later tonight.
High pressure will build to the south from Wednesday into
Thursday. A cold front will approach from the northwest Thursday
night...then move slowly across Friday and Friday night.
Another cold front will approach on Saturday...then push to the
south into Sunday...and stall near the area into Monday.

&&

Near term /until 6 PM this evening/...
observation at 07z indicated the surface low was near Chicago Illinois...with
3-hrly pressure falls in its advance suggesting a path east-southeast toward
Pittsburgh PA by early afternoon. This also suggests the slightly
northern low track forecast by the NAM may verify better today...and
in fact this forecast leaned more heavily on a NAM/European model (ecmwf) blend as
opposed to the faster and slightly farther south GFS. As
usual...the NAM is probably too slow with overrunning precipitation and
hangs onto evaporative cooling aloft too long...so started
increasing pop to chance in NYC and NE New Jersey by 15z-16z...gradually
increasing thereafter to likely/Cat across the entire County Warning Area by late
afternoon. Per a blend of 00z NAM 2m and met MOS
temps/dewpoints...think high temperatures most areas will rise no higher
than the upper 30s/lower 40s...with the warmest temperatures today
occurring mainly in southern CT where clouds and precipitation will take
longer to arrive. The above guidance blend also suggests temperatures
will remain cold enough for an all snow event in the highest
elevations north/west of NYC...and a snow/rain mix transitioning
to snow evening elsewhere north/west. This system should be a
quick hitter...with strong 700 mb-8 frontogenesis north of the low
track producing accumulations of 2-3 inches in the highest
elevations of 2-3 inches by the evening commute. Have issued a
Winter Weather Advisory for western Passaic County where confidence in
higher quantitative precipitation forecast and an all-snow event is greatest. This advisory could
eventually be expanded into Orange/Putnam counties if the above-
mentioned forcing trends farther north than expected.

Temperatures elsewhere will cool toward evening via combo of evaporative
cooling from falling precipitation...and expect most of southern CT and
Long Island to see all snow or a snow/rain mix this evening...with
accumulations there of about an inch...mainly on grassy and colder
elevated surfaces. NYC metropolitan may see a few snowflakes...but with
little to no accumulation expected.

Precipitation should taper off after midnight as the associated 800 mb low
and middle level trough pass to the east...with clearing skies from
west-east. Lows should range from the lower 30s in vicinity of NYC...to
25-30 most elsewhere...to some lower 20s in the valleys well
north/west of the city.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
expect dry weather on Wednesday...with perhaps some broken clouds during late
morning and early afternoon from NYC west a weakening upper trough
moves across. Highs should be mostly in the middle 40s... which is
5-8 degree below average.

&&

Long term /Wednesday night through Monday/...
deep layered ridging builds over the area Wednesday night and
Thursday...with associated subsidence keeping things dry. For lows
Wednesday night used a blend of mav/met/ecs guidance with values
expected to be a few degrees below normal. For highs on Thursday a
blend of mixing down from 975-925 hpa per BUFKIT soundings...with
NAM 2-meter temperatures and a blend of mav and met guidance was
used. Highs should be a few degrees below normal.

The deep layered ridge axis slides to the east Thursday
evening...allowing for low-middle level moisture to rapidly increase in
its wake. Passage of a surface warm front to the north and weak 700 and
500 hpa shortwaves should produce sufficient forcing to warrant
chance probability of precipitation throughout...mainly after midnight. Also...NAM/GFS/ECMWF
also show showalter indices in the 0 to 2 range...warranting a
slight chance of thunder to reflect potential for elevated storms.
Region also will be in the right rear quadrant of 135+kt 300 hpa
jet...and have a west-southwest 50-60kt low level jet pass near the area as
well.

Increase probability of precipitation to likely Friday ahead of cold front...with stronger
shortwaves forecast to pass through...a coupled upper jet structure
forecast to evolve...and expected persistence of low level jet.
Have also continued with slight chance of thunder on Friday as
well.

Some differences between the models on timing of cold frontal
passage...with the GFS faster than the European model (ecmwf) and CMC. Have leaned
towards slower solution...noting general progressive bias to the
GFS. As a result carry chance probability of precipitation into Saturday morning.

500 hpa trough axis slides over then to the east of the area
Saturday and Saturday night. The low levels though should be
sufficiently dry to preclude any precipitation.

A clipper type low with a fairly potent shortwave moving
with the base of a700-500 hpa north stream trough passes to the NE
Sunday...with its associated cold front pushing through...then
stalling near or just to the S of the area by late Sunday. The
region will then be under west-northwest to zonal flow aloft Sunday night and
Monday. For now went with a dry forecast Sunday night/Monday...but
there is the possibility that shortwaves embedded in the flow aloft
could act on the frontal boundary stalled near by. However...at this
time do not quite have confidence in this occurring to place in the
forecast.

For temperatures Thursday night-Monday used a blend of
mex/ece/ecm/wpc guidance with NAM 2-meter temperatures blended in
Thursday night as well. Temperatures should be above normal Thursday
night-Friday night...then below normal Saturday-Monday.
However...departures should not be very large...generally less than
10 degrees.

&&

Aviation /09z Tuesday through Saturday/...
low pressure approaches from the west today and passes S of Long Island
tonight.

VFR until this afternoon when ceilings lower and precipitation overspreads the region.
The precipitation starts as a mix of rasn or all rain...then changes to
snow into the evening.

LIFR possible in the 22-04z time period when potential will be
highest for 1/2sm snow.

Improvement from west to east tonight.

Winds veer through this afternoon...then vrb direction becomes NE as the
low approaches the metropolitan. The NE flow then veers to the northwest as the
low passes east of the region.

..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: no unscheduled amendments expected.

Klga fcster comments: some variability in wind direction can be
expected through 14z.

Kewr fcster comments: no unscheduled amendments expected.

The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.

Kteb fcster comments: no unscheduled amendments expected.

Khpn fcster comments: no unscheduled amendments expected.

Kisp fcster comments: no unscheduled amendments expected.

Outlook for 06z Wednesday through Saturday...
Tuesday night...VFR with northwest flow 10-15kt.
Wednesday-Thursday...VFR.
Thursday night-Friday night...MVFR in rain showers.
Saturday...sub VFR possible in showers early...then VFR late.

&&

Marine...
Small Craft Advisory continues on the ocean waters...with seas 5 feet this morning.
There may be a lull this afternoon ahead of approaching low
pressure...but then have high confidence that Small Craft Advisory criteria will be
met again late tonight into Wednesday...with wind gusts in north-northwest flow up
to 30 knots and seas building to 5-6 feet in the wake of the
low passage.

After a lull from Wednesday night into Thursday...persistent
southerly flow coupled with S swell should build seas on the
coastal ocean waters to Small Craft Advisory levels late Thursday and Friday. Small Craft Advisory
level gusts are also possible on the coastal ocean waters from
late Thursday into Friday as well.

At this time it appears The Harbor/sound/bays of Long Island
should experience sub-Small Craft Advisory conditions Tuesday
night-Friday.

&&

Hydrology...
quantitative precipitation forecast of 2 to 4 tenths of an inch expected this afternoon and
evening...with some of this in the form of snow especially inland.
There is also potential for about 1/3 to 1/2 inch of rain from
late Thursday into early Saturday.

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.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...Winter Weather Advisory from noon today to midnight EDT
tonight for njz002.
Marine...Small Craft Advisory until 6 PM EDT Wednesday for anz350-353-
355.

&&

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

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