Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1059 PM EDT Friday Apr 17 2015
a weak trough of low pressure will move through this evening. A
cold front will approach on Saturday and pass through by evening.
High pressure builds briefly across the area on Sunday and then
gives way to an approaching frontal system from the southwest on
Monday. A frontal wave passes just south and east of the area Monday
night...followed by a cold frontal passage 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 am Saturday morning/...
at 01z...the trough of low pressure was about halfway through the
forecast area. It will continue to track southeast through the remainder
of the evening...with any lingering showers coming to an end.
Skies will clear skies overnight with a light northwest flow. Lowered
lows a few degrees in the normally cooler spots due to light
winds and clear skies allowing for good radiational cooling
conds...but still generally expected to range from the middle 50s in
the NYC metropolitan area to upper 40s inland and across eastern Long
Short term /6 am Saturday morning through Saturday night/...
Sat looks to be the warmest day of the year thus far...with
mostly sunny skies...deep mixing with 800 mb temperatures +8 to +10c...and
downslope westerly flow...leading to highs well into the 70s even
along the coast...and upper 70s west of NYC. Gusty winds will
likely begin by late morning. A potent northern stream shortwave diving
across upstate New York and New England in the afternoon will drive a
cold front through during the evening. This front will be
accompanied by a band of high-based stratocu and a noticeable
increase in wind...with gusts 25-35 miles per hour.
Long term /Sunday through Friday/...
ridging both aloft and at the surface translates west to east across the
area on sun. To the west...an amplifying full latitude trough will
lift north and east across the Great Lakes and into the NE Monday into
Tuesday. Global models in particular...the 12z GFS and European model (ecmwf)...are in
relatively good agreement with small timing differences...but larger
differences exist with quantitative precipitation forecast.
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. A frontal wave is forecast to pass
just south of the area Monday night...in essence keeping the area just
north of the warm front. The cold front follows Tuesday morning. Strong
warm air advection on Monday with a 50-60 knots southeast low level jet will produce moderate to
occasionally heavy rain for much of the day. Instability aloft could
also result in some elevated thunder Monday night. Rainfall amounts of
1 to 2 inches are forecast...with the highest amounts from NYC and
points north and west. The southeast flow will enhance orographic lift.
Gust 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 coming
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 /03z Saturday through Wednesday/...
a weak front exits Li and CT overnight...allowing high pressure to
build in from the west on Sat.
Some patchy fog has developed ahead of the front...impacting kgon.
This will dissipate after the frontal passage. Otherwise...VFR through the taf
Winds shift to the northwest tonight behind the front...then back to the
west or SW Sat morning. Winds will gust 20-25 knots on Sat...with higher
gusts possible. Sea breeze development possible on Sat. Best
chances for sea breezes are with kjfk...kisp...and kbdr.
Outlook for 00z Sunday through Wednesday...
Sat night...VFR with decreasing winds.
Sun...VFR. Surface wind light NE becoming southeast 10kt in the afternoon.
Monday...MVFR becoming IFR. Increasing east-southeast surface wind. G30-35kt in afternoon.
Tuesday...MVFR becoming VFR. G20-25kt.
Wednesday...VFR becoming sub VFR by the afternoon.
S-SW flow 10-15 knots ahead of an approaching weak cold front
building ocean seas generally to 3 to 4 feet on the eastern ocean
waters this afternoon and evening.
Near shore Small Craft Advisory conds may be possible on all waters Sat afternoon
and early evening with the approach and passage of a cold front.
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 into Wednesday.
dry weather...minimum relative humidity 20-30 percent...and winds gusting to
25-35 miles per hour will lead to elevated potential for fire growth/spread
Sat 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 Fire Weather Watch is in effect from 12 PM to 8 PM
given expected weather conditions and after feedback from fire
weather officials reporting dry fuel 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 2 inches...with the highest amounts
from NYC and points north and west. Localized higher amounts will be
possible in the hills north and west.
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
the kokx WSR-88D is out of service. Technicians are working on the
problem. Estimated time of repair is currently unknown.
CT...Fire Weather Watch from Saturday afternoon through Saturday
evening for ctz005>012.
New York...Fire Weather Watch from Saturday afternoon through Saturday
evening for nyz067>075-078>081-176>179.
New Jersey...Fire Weather Watch from Saturday afternoon through Saturday
evening for njz002-004-006-103>108.