Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS61 KOKX 100434

Area Forecast Discussion
National Weather Service New York NY
1134 PM EST Mon Dec 9 2019

A cold front will approach into Tuesday and will move across 
late Tuesday into Tuesday night. Weak low pressure develops 
along the front offshore early Wednesday slowing down its 
eastward progress Wednesday. Arctic high pressure builds into 
the region late Wednesday through Thursday. The high moves off 
the northeast coast Thursday night. A low pressure system 
approaches from the southwest Friday and moves through the area 
Saturday and Saturday night. High pressure builds Sunday and 


Heaviest rain has moved east of the region coinciding with the
low level jet. Lighter rain will continue to move through for 
the next few hours as the warm front lifts north and weakens. 
The rain tapers off from west to east after 06z. There may be 
some spotty light rain or drizzle during the early morning 
hours, but no widespread rain is anticipated heading into the 
Tuesday morning commute.

Some fog is possible, but feel the relatively strong SW flow
will limit fog coverage. 

Temperatures will not drop too much from the upper 40s inland
and 50s elsewhere. 


The short term will feature the rainfall ahead of and along the
cold front Tuesday into Tuesday evening as well as the mixing 
with and changing to snow behind the cold front later Tuesday
night into Wednesday.

For this timeframe, used mostly a consensus of raw model
temperatures with some slight adjustments downward for Tuesday
night and Wednesday when colder air will be advecting into the
region on more of a northwest flow.

In the upper levels, a jet streak will be approaching and will
move in with its right rear quad by Wednesday morning, before
moving farther northeast. Mid level shortwave trough will be 
approaching Tuesday and then move across the region Tuesday 
night into Wednesday with the most positive vorticity advection 
staying north of the region. The most forcing for lift will be
late Tuesday night into Wednesday.

At the surface, the cold front approaches Tuesday and moves
across late Tuesday afternoon into Tuesday evening. Rain
continues through the day which could again be moderate at
times. Precipitation lingers behind the cold front for Tuesday
night into Wednesday and models have been pretty consistent
showing potential for 1 to 3 inches of snow for much of the
area, 3 to 4 inches across the interior, which is reflected in 
the current forecast. Initially, the changeover from rain to 
snow will be limited with accumulation especially if it is light
as ground temperatures will be above freezing. The snow 
accumulation occurs Wednesday morning when much of the region is
at freezing or below. Some slight rise in temperatures expected
during the day, low to mid 30s.

While the amounts of snow forecast are 1 to 4 inches, the timing
puts this during the Wednesday morning commute, making for
potentially hazardous travel conditions due to slippery surfaces
and reduced visibilities.

Weather becomes drier Wednesday afternoon into Wednesday evening
with a slow decrease in clouds as the shortwave trough starts to
lift north of the region.


Wednesday night through Thursday night the guidance is in good 
agreement with arctic high pressure building over the region and
then departing off the northeast coast. Well below normal 
temperatures are expected Wednesday night and Thursday. The 
upper flow becomes nearly zonal through Thursday night. 
Differences then develop with the next shortwaves impacting the 
area Friday into Saturday night. Split flow is expected to 
develop and the timing, and strength, of the northern and 
southern stream shortwaves differs. Regardless, the southern 
stream wave remains dominant, with warm advection increasing 
ahead of a developing warm front. The best chances at this time 
for snow and/or a rain snow mix will be across the interior 
Friday morning. Then timing of the warm up will determine the 
changeover to rain. Along the coast rain is expected. A lot of 
uncertainty remains with the strength of the northern stream 
shortwave and the interaction with the southern stream wave 
later Saturday into Sunday. The GFS is much farther to the north
and deeper than the ECMWF with the northern stream.

High pressure and colder weather returns Sunday into Monday.


A cold front over the Midwest will slowly approach the area through 
the day on Tuesday.

Generally IFR or lower conditions expected into Tuesday morning
before some improvement to MVFR is possible Tuesday afternoon.
The steadiest rain will continue to push east this evening,
coming to an end between 05-07Z. As it does so, visibilities at
the city terminals have improved to VFR, but expect this to be 
short lived as pockets of drizzle and/or fog linger through 
daybreak. A few showers are possible Tuesday morning, then 
another round of steadier rain is expected Tuesday afternoon in 
association with the approaching front. 

S winds 10-15 kt expected tonight, with gusts up to 25 kt
possible, primarily at city and coastal terminals. Winds and
gusts could be a few knots higher at eastern coastal terminals.
LLWS at all terminals through tonight. Winds shift to the SW at
around 10 kt during the day on Tuesday, then WNW by the end of 
the TAF period.

.Tuesday night...Winds shift to the NW behind the cold front. 
Rain transitions to snow from northwest to southeast.
.Wednesday...IFR or lower possible in snow in the morning,
improving to VFR late.
.Friday...MVFR possible in developing rain.
.Friday night-Saturday...IFR in rain or a wintry mix. LLWS 


Gale warning in effect for all ocean zones into early Tuesday
morning, but it is possible that winds stay below 34 kt. The
warning may need to be converted to an SCA. SCA remains in 
effect for non-ocean waters into early Tuesday. 

For Tuesday, SCA conditions remain on the ocean and continue 
through Tuesday night. SCA remains on much of the ocean 
Wednesday before dropping below SCA mid to late Wednesday 
afternoon west of Moriches Inlet.

SCA in effect for all waters. Main push of stronger winds to 
the east today, and gusts in S-SW flow getting close but not 
quite to 35 kt except on the ocean E of Moriches Inlet this 
afternoon. Gale warning starts on the ocean east of Moriches 
Inlet this afternoon. Rest of ocean, gale warning starts 
tonight. Gales remain on ocean until Tuesday morning and SCA 
remains on non-ocean waters until Tuesday morning. Gales subside
Tuesday with SCA remaining on the ocean. Tuesday expected to be
below SCA on non-ocean waters.

Increasing, and gusty, northwest flow develops Wednesday night 
behind departing low pressure. Marginal SCA conditions are 
expected to develop on the ocean waters Wednesday night and 
continue into Thursday morning.

With high pressure moving across the waters Thursday and 
departing Friday sub advisory conditions are expected. Then east
to southeast winds will increase ahead of the next low pressure
system moving in from the southwest Friday night. Once again, 
marginal SCA wind gusts are expected on the ocean waters Friday 
night through most of Saturday, while ocean seas will build 
significantly Friday night into Saturday.


Widespread rain will taper off early Tuesday morning. Another
area of rain will overspread the region Tuesday afternoon and
evening with the passage of a cold front. The rain mixes with
and changes to snow early Wednesday morning. No hydrologic
concerns are anticipated with this precipitation. 

Total liquid equivalent for the recent event from Monday morning
through Wednesday morning remains between 1 to 2 inches.

The next significant rain of up to an inch is expected Friday night 
through Saturday. Timing and rainfall amounts may change, so 
hydrologic impacts are uncertain at this time.


NYC NOAA Weather Radio Station KWO35 (162.55 MHz) is still
operating at reduced power.


MARINE...Small Craft Advisory until 6 AM EST Tuesday for ANZ330-335-338-
     Gale Warning until 6 AM EST Tuesday for ANZ350-353-355.



National Weather Service Glossary of Abbreviations