Scientific Forecaster Discussion
fxus61 kokx 170619
Area forecast discussion
National Weather Service New York New York
119 am EST Wed Jan 17 2018
low pressure develops along the mid Atlantic coast tonight and
then passes near or just east of Long Island on Wednesday before
moving up the coast into the Canadian Maritimes Wednesday
night. High pressure will then build to the south through Friday
and move into the western Atlantic this weekend. A cold front
then passes through Monday night into Tuesday morning.
Near term /until 6 am this morning/...
no significant changes were made to the forecast with this
update except to delay precip timing a bit from NYC on east. It
looks like precip will Blossom after 06-08z as the upper trough
dynamics interact with the developing secondary low. No changes
were made to the winter weather headlines.
Light snow continues to fall across northwest Orange County. Starting
to see reflectivity increase as better dynamics begin to move
into this area. Steadier precipitation will continue to
overspread from the west through the night and then Blossom
across the rest of the area towards day break.
Have taken an initial look at the 00z nam12, 00z 3-km NAM and
they generally support the current forecast. Quantitative precipitation forecast may be a bit
lower than previous runs, but overall looks close. The latest
hrrr also is in general agreement with the ongoing forecast.
The biggest challenge continues to lie with the northward
extent of the warmer air and how far the rain/snow line works.
Despite temperatures currently running a bit cooler than
previously forecast in the NYC Metro area, a surge of warmer air
at the surface to just above 925 mb is anticipated. This is due
to a prolonged period of S-southeast winds ahead of the developing low.
The transition of energy from upper trough/weakening primary low
is to the secondary low is slow such that an inverted trough is
expected to extend back into the Hudson Valley of New York.
This should allow the rain snow line to make it about 10-20
miles north and west of I-95 corridor in New Jersey to near or
just south of a line from hpn to dxr.
Temperatures will remain nearly steady overnight and even slowly
rise. Lows will range from the upper 20s in the interior to the
mid 30s along the coast.
Short term /6 am this morning through 6 PM Thursday/...
low pressure near Long Island in the morning lifts northeast
during the day and up into the Canadian Maritimes by Wednesday
night. Precipitation shuts down across most of the area by late
morning/early afternoon and perhaps ends as period of snow at
the coast. Even if the changeover to snow occurs a bit faster
than indicated in the city/at the coast, limited duration of
precipitation on the backside of the low will limit any
accumulation. Highs will top out in the mid to upper 30s with
northwest winds developing on the backside of the storm. Gust up to 20
mph develop late in the day and possibly linger into first half
of the night.
Cold air will follow for Wednesday night with lows in the teens
inland and around 20 at the coast. This is slightly below
Long term /Thursday night through Tuesday/...
surface high pressure will build to our south on Thursday and
Friday. Meanwhile, an upper trough shifts through with some
shortwave energy Thursday night into Friday. Moisture looks
insufficient for any pcpn, so dry weather is expected. Highs a few
degrees below normal for Thursday, returning to near normal on
Friday. Ridging aloft will then keep the weekend dry with warming
Low pressure enters the Great Lakes region Sunday night, eventually
tracking through Quebec on Tuesday. Some warm advection precipitation may
reach some of the northern zones Sunday night into Monday morning,
which could be in the form of a wintry mix. A cold front otherwise
approaches with increasing chances of rain during the afternoon and
night. Some timing differences still exist among the global models
with the cold front passage, so have capped pops at chance through
Tuesday morning. Rain chances otherwise diminish Tuesday afternoon
with dry weather likely returning Tuesday night. Temperatures Sunday
through Tuesday will remain above normal.
Aviation /06z Wednesday through Sunday/...
a developing coastal low with move north towards the region this
morning, tracking just southeast of Long Island early on today,
and then into the Canadian Maritimes this evening.
Conditions expected to lower to IFR early this morning as
precipitation develops across region.
Expect all snow at kswf with LIFR conds, which may be moderate at
times between 07z and 13z. Between 5 and 7 inches of snow expected.
Rain expected to develop for NYC/New Jersey Metro terminals and kbdr after
midnight, likely mixing with snow towards daybreak, and then
changing to all snow after 11-13z. IFR conditions with a quick
coating to 2 inches of slushy snow likely for NYC terminals, with 1
to 3 inches for kewr/kteb/kbdr during the morning push. Low
potential for these amounts to be about one inch higher, with LIFR
Khpn likely to have a mix of rain/snow early this morning, before
changing to all snow with LIFR conds towards daybreak, with 2 to 4
inches of snow likely. Low potential for this amount to be about one
All rain expected for kisp/kgon.
Precip taper off from west to east Wed morning into early afternoon, with
conditions improving to VFR.
East/NE winds for coastal terminals less than 10 kt overnight, becoming
north/north-northwest for all terminals towards daybreak. Winds become west-northwest with
gusts 20 to 25 kt Wed afternoon continuing into Wed eve push, likely
averaging just right of 310 magnetic.
Outlook for 06z Thursday through Sunday...
late tonight-Thursday night...VFR. West-northwest winds g20-25kt on Thursday.
Friday...VFR. West-SW winds g20kt possible.
Small Craft Advisory in effect for the ocean waters as seas remain 4-5 ft. Ocean
seas increase a bit more tonight. Flow returns to a northwest direction
and begins to gust late on Wednesday.
Small Craft Advisory conditions continue on the ocean for Thursday through Friday
morning, then sub-advisory conditions are expected for a brief
period Friday afternoon and night. Winds and seas then pick up with
marginal advisory conditions on the ocean during Saturday and
Saturday night. A weaker pressure gradient then returns relatively
tranquil conditions for Sunday.
no significant hydrologic impacts are expected.
NYC National oceanic and atmospheric administration weather radio station kwo-35 (162.55 mhz) is off the
air for an extended period of time.
CT...Winter Weather Advisory until 1 PM EST this afternoon for
New York...Winter Weather Advisory until noon EST today for nyz069-070.
Winter Storm Warning until noon EST today for nyz067-068.
New Jersey...Winter Weather Advisory until noon EST today for njz002-004-
Marine...Small Craft Advisory until 6 am EST Thursday for anz350-353-