Scientific Forecaster Discussion
fxus61 kokx 291149
Area forecast discussion
National Weather Service New York New York
749 am EDT Sat Apr 29 2017
a weak front moves through the area this evening, with high pressure
briefly returning for Sunday. A warm front will then move northward
through the area on Monday, followed by a cold front from the west
Monday night into early Tuesday morning. Weak high pressure will
return for the remainder of Tuesday into Wednesday. A frontal system
approaches from the southwest Thursday and moves along the coast
through late week.
Near term /until 6 PM this evening/...
minor updates this morning to adjust for ongoing showers and
thunderstorms moving across Long Island this morning. Brief
heavy downpours and frequent lightning will be possible,
especially along the South Shore. Storms should move east of the
area by mid morning.
Otherwise, calm winds may lead to localized patchy fog outside
of any precipitation, though with a shallow inversion expect
any fog to dissipate quickly after sunrise. By afternoon, a few
gusty winds will be possible, along with a steady increase in
mid-upper level clouds. West downslope flow with little marine
influence will aid in well above normal temperatures ranging
from the 70s to near 80 closer to the coast, and around the mid
Short term /6 PM this evening through 6 PM Sunday/...
a few showers and thunderstorms may approach portions of
southeastern New York and northern New Jersey late in the evening, but
otherwise dry conditions are expected. As the cold front
gradually moves south of the area, flow will turn more north-
northeasterly leading to a low-level inversion and the potential
for more cloud development keeping low temperatures slightly
above climatological normals. The upper ridge centered off the
southeast coast will build northward through the Sunday, and in
combination with the onshore flow should act to strengthen the
low-level inversion. A general lack of overall forcing for
ascent along with the inversion should limit
precipitation/thunderstorm chances, though if low-level cloud
cover thickens sooner than forecast some light drizzle will be
possible. Daytime temperatures will be cooler than Saturday,
with highs closer to climatological normals.
Long term /Sunday night through Friday/...
onshore flow will continue into Monday morning, with increasing
chances of light rain and/or drizzle with a developing stratus
deck. By afternoon, a warm front will move through the area with
skies briefly clearing from south to north ahead of an
approaching cold front. The front moves through Monday night
with rain and a chance of thunderstorms giving way to clearing
skies, gusty west winds and seasonable temperatures by Tuesday
afternoon. The gusty west flow and cooler temperatures will
continue into Wednesday as a secondary trough of low pressure
moves through. By Thursday, divergence aloft associated with an
elongated mid-upper low across the central US will aid in the
development of an attendant surface low across the southeast
that will gradually move northeastward through Friday. The
prolonged period of south-southwest flow will advect moisture
into the region, with increasing chances for precipitation
through the weekend.
Aviation /12z Saturday through Wednesday/...
a weak cold front pushes through the area today, followed by
high pressure building down from southeastern Canada through tonight.
VFR through the taf period, with possible exception of a brief
period of MVFR visibilities at kjfk and kisp through 13-14z.
Winds become SW-west-southwest around 10kt by mid morning. The winds
continue to veer to the west-west-northwest with gusts around 15-20kt by
around midday. By late afternoon/early evening the winds become
northwest. Wind gusts should abate by around 00z, with wind speeds
falling to under 10kt. Winds continue to veer to the north then NE
tonight with speeds under 10 kt. Most terminals will become
light and variable for at least a few hours overnight.
Outlook for 12z Sunday through Wednesday...
Sunday afternoon-Monday....MVFR or lower possible. SW winds
g15-20kt possible Sunday afternoon. Low level wind shear possible Sunday night
mainly at southern terminals.
Monday night...IFR or lower conditions, low level wind shear and scattered
thunderstorms are possible.
Tuesday-Wednesday...VFR. SW-west-southwest winds g15-20kt possible
Tuesday. West-northwest winds g20-25kt possible Wednesday.
made minor changes this update to reflect the latest trends in
observations and guidance. The forecast appears on track.
A light to moderate pressure gradient over the region through Monday
will limit winds to 15 kt or less, with gusts of 20 kt or less. One
of those periods of 15g20kt winds this afternoon and evening will
bring seas on the coastal ocean waters east of Fire Island Inlet to
around 5 ft (mainly 10 or more miles from shore). There for have
issued an Small Craft Advisory for hazardous seas for the coastal ocean waters east
of Fire Island Inlet from noon today through midnight tonight.
The pressure gradient tightens Monday night, with 25-30kt gusts
possible. These winds will build ocean seas to 4-8 ft Monday night.
However, even with 40-50kt of winds at 950 hpa Monday night/early
Tuesday morning, will have to strong of a marine inversion for much
if any of that to mix down, so gales are not expected then.
Winds should be 15 kt or less Tuesday and Wednesday, with a light to
moderate pressure gradient over the waters. However, seas on the
coastal ocean waters should be slow to come down, and could remain
at or above 5 ft into Wednesday, especially over the southern
portions of the coastal ocean zones.
no hydrologic impacts are expected through Thursday.
A low pressure system approaching from the southwest may lead to
periods of heavy rain and the potential for hydrologic impacts late
next week into the weekend.
Marine...Small Craft Advisory for hazardous seas from noon today to
midnight EDT tonight for anz350-353.