Scientific Forecaster Discussion
fxus61 kokx 250608
Area forecast discussion
National Weather Service New York New York
108 am EST Sat Nov 25 2017
high pressure off the mid Atlantic coast weakens tonight into
Saturday. A cold front approaches Saturday and moves through
Saturday evening. High pressure builds in Sunday through
Tuesday. Another cold front will move across on Wednesday. High
pressure builds briefly Wednesday night then lifts north of the
area as the next storm system approaches on Friday.
Near term /until 6 am this morning/...
minor changes were made to dewpoints and larger changes made to
hourly temperatures. It is just a matter of surface emissivity
and how the light onshore flow trends along the coast. Weaker
flow will allow more radiational cooling. Lows from previous
forecast were not changed too much overall. Clear sky conditions
are still expected.
Upper zonal flow gradually becomes southwesterly tonight as a
ridge moves into the western Atlantic and a northern stream
trough digs into the upper Midwest. Meanwhile a southern stream
shortwave will be pickup by the trough and moved into the
western Atlantic. This will spin up a weak surface low that
moves to off the North Carolina coast by 12z Saturday. The
atmosphere will remain dry, and surface wind will be light with
good radiational cooling tonight. This will lead to a wide
range of overnight lows. There will be weak warm advection from
around 950 to 850 mb, but with little moisture or lift, clouds
are not expected.
Short term /6 am this morning through 6 PM Sunday/...
late in the day Saturday a cold front will be approaching as the
associated low moves into eastern Canada. The northern stream
trough moves to the East Coast by Saturday night with weak lift.
There may be a few showers by late in the day into the far
western zones. Lift will increase Saturday night as a rather
strong vort Max rotates into the based of the upper trough and
then, with progressive flow, quickly moves into the western
Atlantic. Again moisture will be limited. So will keep
probabilities in the slight chance to chance categories. Cold
air will be lagging behind before the precipitation ends so
expect all liquid, light, precipitation. And with the quick flow
precipitation will end before 11z Sunday.
Long term /Sunday night through Friday/...
high pressure will build in from Sunday through Tuesday with a
warming trend into Tuesday, near seasonal normals.
A frontal system is then expected to move across the area on
Tuesday night. Moisture associated with the frontal passage is
expected to dissipate as it approaches the area. Kept the local
area precipitation free during this period. Temperatures on
Wednesday will continue to be above normal with high in the low
to mid 50s.
High pressure builds briefly on Wednesday night and into
Thursday before moving north of the area. Another storm system
is forecast to move across the area on Friday. Temperatures on
Thursday and Friday will be near normal for this time of year.
Aviation /06z Saturday through Wednesday/...
a cold front approaches from the Great Lakes today, moving
across this evening.
VFR today. There is a low chance of shower activity and MVFR
conditions Saturday evening with frontal passage.
S/SW winds today, with occasional gusts into the mid teens
possible for south coastal areas. Windshift from ssw>w/west-northwest
(around 310 magnetic) this evening. Gusts of 15 to 20 kt
possible for NYC/New Jersey Metro terminals late this evening in wake
Outlook for 06z Sunday through Wednesday...
late tonight...VFR, outside of an isolated rain/snow showers.
Northwest wind g20-30kt developing.
Sunday...VFR, outside of an isolated am rain/snow showers for
eastern terminals. Northwest winds g25-30kt with isolated gusts to 35
Sunday night...VFR. Nw>w winds g15-20kt.
Monday-Monday night...VFR. West/northwest winds g15-25kt, diminishing
Tuesday-Tuesday night...VFR. SW winds g15-25kt.
Wednesday...VFR. W>nw winds g15-20kt.
as high pressure south of the ocean forecast waters weakens
tonight and one low moves off the southeast coast as another
moves through southern Canada, the pressure gradient force will
increase through tonight. This will allow for southwest wind to
increase. However, winds and gusts are expected to remain below
small craft levels tonight through Saturday. Capped the ocean
waves at 4 feet as nwps was running around 1 foot too high
compared to current conditions. And with southwest flow tends to
be too high, so again capped waves at 4 feet into Saturday
night. There is a chance that late Saturday night waves do build
to 5 feet briefly in northwest gusts winds behind a cold front.
Expected ocean gusts to be marginally around small craft levels
in the cold advection behind the front late Saturday night. So,
will begin an advisory at 06z Sunday.
Small Craft Advisory conditions forecast on Sunday as a northwest flow increases
across all ocean waters to 25 to 30 kt. Small Craft Advisory conditions could
continue on the ocean into Sunday night and maybe into Monday
morning, then fall below Small Craft Advisory conditions later on Monday and into
Tuesday. Seas might rise to Small Craft Advisory conditions again Tuesday night
and into Wednesday ahead of the next frontal system.
no hydrologic impacts expected.
Marine...Small Craft Advisory from 1 am to 6 PM EST Sunday for anz350-