Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
743 am EDT Sat Apr 18 2015
a cold front approaches today and moves across the area through
this evening. High pressure builds over the area Sunday and moves
offshore late in the day as a frontal systems approaches from the
southwest. A frontal wave passes over or right by the area Monday
night...followed by a cold frontal passage late at night into
Tuesday morning. A series of weak cold fronts or troughs will move
through during the midweek period followed by high pressure at the
end of the week.
Near term /until 6 PM this evening/...
forecast remains on track...the warmest day of the year on tap
with the combination of mostly sunny skies...deep mixing...850 mb
temperatures ranging from +8c to +10c...and downsloping westerly flow.
Highs today will range from the upper 70s to around 80 for NYC and
most areas along and west of the Hudson River...and in the middle 70s
for interior portions of southern CT and the rest of the lower
Hudson Valley. For Long Island...coastal CT...and coastal portions
of NYC...highs will top off in the low 70s.
A cold front approaches later in the day...allowing for winds to
shift from a SW flow to more of a westerly flow.
Short term /6 PM this evening through 6 PM Sunday/...
cold front moves across the region this evening. Winds may increase
to 15-20 miles per hour with 20-30 miles per hour with its passage...but winds diminish
as the evening progresses...and winds will shift to the north at
5-10 miles per hour by midnight tonight.
The front should come through dry...with the exception of some
middle-level clouds with its passage.
High pressure over eastern Canada will drop into the Gulf of Maine
with the center of the high just east of Cape Cod on Sunday. As a
result...winds will shift to the southeast...ushering a much
cooler and more seasonal airmass into the region. Highs on Sunday
will top off in the middle 50s to low 60s...except for Long Island
and coastal CT...where highs will only be in the low 50s.
Long term /Sunday night through Friday/...
an amplifying full latitude trough will lift north and east across
the Great Lakes and into the NE Sun night into Tuesday. This will
result in an approaching frontal system that will have both
Atlantic and Gulf moisture to work with. Precipitable water values will be on
the order of 2sd above normal. The 00z global models have sped up
the timing of this system by a little...but still some differences
regarding placement of higher rain amounts.
A frontal wave is forecast to pass over or nearby just the area
Monday night...in essence keeping the area nearby decent lift. Lift
will be enhanced...especially over the eastern half of the
County Warning Area...by frontogenetic forcing and a 50-60 knots southeast low level jet late Sun
night into early Monday morning. Thinking is that eastern zones will
probably end up with higher rain amounts in general. Instability
aloft could also result in some isolated elevated thunder Monday
night...which would add to the variability and some uncertainty
with the highest rain amounts for the tri state area. Rainfall
amounts of 1 to 1.5 inches are forecast...with the highest amounts
over Long Island and CT. Up to 2 inches locally is still possible.
The southeast flow probably enhances orographic lift...so forecast
amounts northwest of the city could be a little too low. So in
general...rain becomes likely late Sunday night for most
spots...with moderate to potentially briefly heavy rain Monday
morning. Middle levels dry out Monday afternoon...so light rainfall
or possibly even drizzle would be expected by late in the day.
Light rain remains likely Monday night as a weak low pressure wave
center moves through. Some fog development expected Monday night as
well with winds becoming lighter and plenty of moisture around.
Gusts up to 25 to 30 miles per hour will possible at the surface on Monday...but
temperature profiles will be inverted limiting any stronger winds from
Conditions dry out Tuesday into Wednesday with a series of weak fronts
and/or troughs moving across the region. These will reinforce a
seasonable airmass. High pressure then follows for the end of the
week. Upper air pattern will be dominated by a broad...flat trough
east of the MS River Valley.
Aviation /12z Saturday through Wednesday/...
high pressure for today with a cold front passing through this
VFR through the taf period. Light and variable winds becoming mostly
west...except SW sea breezes for kjfk/kisp/kbdr/kgon. Kjfk probably
shifts S late afternoon. Gusts 20-25 primarily in the afternoon and
evening hours. Winds shift northwest by midnight and become less gusty
Outlook for 12z Sunday through Wednesday...
sun...VFR. Surface wind light NE becoming southeast 10kt in the afternoon.
Sun night...rain/sub VFR/low level wind shear developing late. East g25-30kt late.
Monday...MVFR/IFR. Rain. Low level wind shear early. Increasing east-southeast surface wind. G30kt.
Tuesday...MVFR becoming VFR. West g25kt.
Wednesday...VFR. Chance sub VFR in the afternoon. SW g25kt.
a cold front approaches the waters later this afternoon and moves
across this evening. Generally sub-Small Craft Advisory conds...but a few nearshore
gusts to 25 knots are possible this afternoon.
High pressure builds east of the waters late sun after with an
approaching frontal system from the west. This will result in a
strengthening southeast flow Sun night into Monday with Small Craft Advisory conditions
likely across all waters. Seas will build to 7 to 10 feet on
Monday...then will be slow to subside Monday night into Tuesday. Sub-Small Craft Advisory
conditions are expected across the remaining waters late Monday night
dry weather...minimum relative humidity 20-30 percent...and winds gusting to
25-30 miles per hour will lead to elevated potential for fire growth/spread
this afternoon and early evening. Several wind shifts are expected
through the day...creating an additional hazard with any ongoing
fires. Initially northwest winds will shift to west- southwest
then southwest through the afternoon...before rapidly turning
northwest again around 6-7 PM with the approach/passage of another
cold front. Gusts may briefly strengthen after the cold frontal
passage. A red flag warning is in effect for the whole County Warning Area from 12
PM to 8 PM given expected weather conditions.
there is the potential for significant rainfall with
an approaching frontal system Monday into Monday night. Storm total
rainfall with this system will be from 1 to 1.5 inches...with the
highest amounts generally over Long Island and CT. Localized higher
amounts will be possible.
For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our web site.
a prolonged period of southeast flow late Sun night into Monday evening will
likely result in widespread minor coastal flooding. Astronomical
high tides will be running high following a new moon on Sat. In some
cases...departures of only half a foot above normal are needed.
Storm surge is likely to produce waters levels 1 to 1 1/2 feet above
CT...red flag warning from noon today to 8 PM EDT this evening for
New York...red flag warning from noon today to 8 PM EDT this evening for
New Jersey...red flag warning from noon today to 8 PM EDT this evening for