Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1231 am EST Sat Dec 20 2014
high pressure builds in from the west and moves over the northeast
into early next week though skies remain mostly cloudy. Multiple
waves of low pressure will then impact the area Tuesday into
Wednesday. The first being a weak coastal low that moves off the
middle Atlantic coast Monday night into Tuesday...followed by a much
stronger system that tracks up into the Great Lakes by middle week.
Near term /until 6 am this morning/...
00z sounding has strong inversion with base around 880 mb and
plenty of moisture trapped beneath. Lots of strato cumulus around
scattered to broken...and expected to become more widespread
broken to overcast as inversion remains. Still leaning toward the
NAM for moisture profiles.
Forecast on track with just some minor adjustments to near term
hourly temperatures and wind.
Short term /6 am this morning through 6 PM Sunday/...
high pressure continues to build into the region as flow veers more
Continue with the clouds as NAM soundings indicate a deepening of
the isothermal layer. Also - weak insolation with a 25 degree sun
angle (winter solstice is Sunday 603 pm).
Low level moisture deepens further Saturday night as flow veers
more northeast and upper shortwave approaches. Nwp has been
persistent in some very light precipitation off to the east. Have dropped
probability of precipitation in favor of a chance flurry after midnight.
Have again adjusted temperatures up slightly from MOS based on extensive cloud
Long term /Sunday night through Friday/...
models remain in good overall agreement with a fast Pacific flow across
the country briefly becoming amplified into a full latitude trough
over the middle section of the country by Tuesday. This will result in
multiple waves of low pressure impacting the area in the Monday-Wednesday
timeframe before drying out on Thursday. Thermo profiles are warm enough
to support all rain events. The one exception being flurries and/or
sprinkles Sun morning in associated with a weak short wave trough.
A large dome of high pressure will pass to the north and east of the
area sun into Monday...as a southern branch storm system forms along
the southeast coast and takes a track to off the middle Atlantic coast Monday
night. This system gets caught up with the overall large scale
amplification of the upper air pattern. There is decent warm
advection with cold air damming across the NE. Even so...boundary
layer temperatures appear to be warm enough for an all rain event. Rain
develops late Monday after and continues into Tuesday...generally on the
light side with up to half an inch possible.
The second low will be a more substantial system as strong Pacific jet
energy carves out a full latitude trough over the middle section of the
country by Tuesday...sending a frontal wave NE across the Tennessee and Ohio
valleys Tuesday into Wednesday...eventually wrapping up into a deep low over
the Great Lakes Christmas eve/day. This will result in strong warm
advection ahead of the cold frontal passage Wednesday evening. There has been
a slower trend with the frontal passage. An additional one to one
and a half inches of rainfall is possible. This will be over a 12
hour period. So not expecting any significant flooding hazards.
In comparison to recent model runs...the potential for strong winds
Wednesday continues to diminish as the low-level jet is weaker and
displaced farther east.
Temperatures will moderate from near normal levels on sun to 10 to
15 degrees above normal Tuesday-Wednesday with a deep-layered southerly flow out
ahead of the amplifying upper trough. Conditions return back to
seasonable levels at the end of the week.
Aviation /06z Saturday through Wednesday/...
high pressure gradually builds east into New England through tonight.
Ceilings expected to continue to vary between scattered-broken 3000-3500 feet
through this morning as moisture remains trapped under an inversion.
Eastern terminals may see a period of clearing overnight into Sat
morning based on upstream drying seen on satellite...while stratus
may become more widespread across city and western terminals. Low
confidence on coverage of stratus through this morning.
Increasing chances for widespread broken MVFR ceilings this afternoon into
320-350 magnetic winds continue to veer to the north and decrease
early this morning. Light north-NE winds less than 8 knots during th day
Outlook for 06z sun through Wednesday...
late tonight...MVFR ceilings likely...with light snow showers possible
for eastern terminals. Light northeast winds.
Sunday...MVFR ceilings...with light snow/rain showers possible for
city/coastal terminals. Light northeast winds.
Monday...MVFR or lower possible in east-southeast flow. Chance of rain.
Monday night-Tue...IFR likely at times in rain...ceilings and visibilities. East-southeast
winds 10-20 knots.
Tuesday night and Wednesday...high impact event possible...IFR likely with
heavy rain and gusty southeast winds 25kt+ shifting to SW late Wednesday.
northwest wind remains around 15 knots with minimal gusts a few kts
higher. The wind was slowly diminishing as the surface pressure
gradient weakens as high builds in from the west. The high
will then gradually build through Saturday. Tranquil conditions
prevail through the weekend.
Tranquil conditions continue on sun. Winds and seas build on
Monday with a tightening pressure gradient. Small Craft Advisory conds then likely
follow Monday night and Tuesday ahead of multiple waves of low pressure
off the East Coast.
no Hydro impacts expected into early next week.
1/4 to 1/2 inch of rain is possible Monday afternoon through Tuesday
as low pressure passes south of Long Island. No hydrological impacts
Rain on Wednesday/Wednesday night may average 1-1.5 inches across the region.
Minor urban flooding is possible.