Area forecast discussion
National Weather Service New York New York
751 PM EDT Wednesday may 22 2013
Synopsis...
a stalled front will remain in the vicinity into Thursday. A cold
front will then slowly approach from the west Thursday...then move
into western portions of the tri-state Thursday night. A wave of
low pressure develops along this slow moving cold front
Friday...remains just east of the region Saturday...and then
tracks north along the New England coast on Sunday. High pressure
over the Great Lakes builds southeast across the area Monday into
Tuesday. A warm front will then approach from the southwest by middle
week.
&&
Near term /until 6 am Thursday morning/...
most of the showers and thunderstorms north of the County Warning Area are
beginning to dissipate with loss of diurnal heating. Would not
expect mush in the way of convective activity...mainly for the
northern third of the County Warning Area...for the rest of the early evening
hours.
However...broken line of showers and thunderstorms slowly trying
to organize over central PA. With relatively light upper level
flow...these storms will take some time approaching western
portions of the County Warning Area...and if they do make it here...it will not be
until late tonight with latest hrrr indicating scattered activity after
08z. Will continue to carry slight chance...as marine layer should
continue to inhibit convective activity from forming.
With marine layer intact - would expect low cloud deck to re-
establish itself across the area overnight. Could see patchy fog
as well - possibly locally dense near the Atlantic coast.
For lows used a blend of 50 percent mav guidance with 25 percent
met guidance and 25 percent NAM 2-meter temperatures. Forecasting
lows 10-15 degrees above normal.
&&
Short term /6 am Thursday morning through Thursday night/...
mixing associated with passing 700-500 hpa shortwave Thursday
morning should erode the marine inversion - but still will be
left with quite a bit of middle to high clouds with moist SW flow
aloft.
Pre-frontal trough moving into the lower Hudson Valley/NE New Jersey
Thursday afternoon should serve as trigger for scattered-numerous rain showers
with embedded thunderstorms and rain. Likely probability of precipitation mainly from NYC-interior SW CT
zones on west and chance probability of precipitation east of that line. Some suggestion from
NAM/GFS that eastern areas will remain dry Thursday...but for now
too much low-middle level moisture and increasing low level jet to
forecast that at this time.
With 30-35 knots bulk shear...1000-1500 j/kg of cape and bulk
Richardson numbers 15-30 have the potential for isolated severe
storms Thursday afternoon across NE New Jersey/lower Hudson Valley and
maybe NYC and SW CT zones. Main threat is gusty winds and large
hail. Also need to watch for low level helicity with S surface flow
and SW flow at 850 hpa.
For highs Thursday used a blend of mixing down from 975 hpa near
the coast and 950 hpa inland...with NAM 2-meter temperatures and a
blend of mav and met guidance. Forecasting values around normal
east to a few degrees above normal west.
Deep SW flow aloft...becomes diffluent at 500 hpa after midnight.
Have the potential for heavy rainfall as a result. Refer to the
hydrology section for details. Severe threat could linger into the
evening across western zones as well.
For lows Thursday night used a blend of mav/met guidance with
values forecast around 10 degrees above normal.
&&
Long term /Friday through Wednesday/...
models have trended considerably slower and deeper with the
approaching upper trough over the middle section of the country. There
is very good agreement with the 12z GFS and European model (ecmwf) on taking a closed
upper low from the Middle Atlantic States on Friday NE to over New England
on sun. The NAM and ggem are trending in that direction...but are
more progressive beyond 00z Sat. Preference at this time is to go
with the slower GFS/European model (ecmwf) solution based on model trends and the run
to run continuity being exhibited over the last several model cycles.
As for sensible weather...this results in a wet...cool weekend with
the potential for another 1 to 2 inches of rainfall in the Friday-Sat
time frame. Since this is a big adjustment from the previous
forecast...have ramped up rain chances Friday into Sat...but these may
be underdone...especially for Sat where there is a trend in the
forecast to dry things out Sat into sun. Latest European model (ecmwf) keeps
conditions wet into sun with a gusty northwest flow on the backside. So
this is the point in the forecast where conditions may continue to
deteriorate with subsequent model runs.
Once again...while the forecast has aggressively taken a downward
note for the Holiday weekend...rain chances may be on the increase
Sat into sun based on latest trends in the model guidance.
In addition...some of the rainfall on Friday...or at least the first
half of the day may be convective with localized heavy rainfall with
any embedded thunderstorms. Thereafter...the airmass stabilizes in
the low-levels with Post-frontal rain/showers...primarily driven by
frontogenetic forcing on the backside of the low. Wind gusts Sat
into sun may be up to 35 miles per hour...but this is the potential...with the
forecasts significantly lower at this time.
As for temperatures...daytime highs with the cloud cover and rain will be 5
to 10 degrees below normal. Stayed below guidance. Overnight lows
will be close to seasonable. A gradual warm-up to near seasonable
levels is then forecast Mon-Wed.
&&
Aviation /00z Thursday through Monday/...
a stationary frontal boundary will remain north of the terminals
through the forecast period. A low pressure system and cold front
approach slowly from the west during the day Thursday.
MVFR ceilings and fog develop late this evening and overnight for
the New York City terminals and west. To the east IFR ceilings and
fog will be developing...with LIFR at times after 07z. MVFR
conditions during Thursday with showers developing after 17z.
Isolated thunderstorms will be possible also.
Wind will be generally from the south 10 knots or less through late
tonight...then south to southwest 10 to 15 knots late tonight into
Thursday.
New York metropolitan enhanced aviation weather support...
Detailed information...including hourly taf wind component forecasts can
be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)
Kjfk fcster comments: amendments late this evening for MVFR
ceilings and fog developing. Amendments for timing of showers and
thunderstorms Thursday. Some thunderstorms may produce gusty
winds.
Klga fcster comments: amendments late this evening for MVFR
ceilings and fog developing. Amendments for timing of showers and
thunderstorms Thursday. Some thunderstorms may produce gusty winds.
Kewr fcster comments: no unscheduled amendments tonight. Amendments
for timing of showers and thunderstorms Thursday. Some thunderstorms
may produce gusty winds.
Kteb fcster comments: no unscheduled amendments tonight. MVFR
ceilings and fog possible after 09z. Amendments for timing of
showers and thunderstorms Thursday. Some thunderstorms may produce
gusty winds.
Khpn fcster comments: amendments late this evening for MVFR
ceilings and fog developing...with IFR at times. Amendments for
timing of showers and thunderstorms Thursday. Some thunderstorms may
produce gusty winds.
Kisp fcster comments: amendments this evening for IFR ceilings and
fog. Amendments Thursday for slowly improving conditions. Showers
late afternoon Thursday.
Outlook for 00z Friday through Monday...
Thursday night-Friday...numerous rain showers...isolated thunderstorms possible.
MVFR to IFR in showers...fog and stratus.
Saturday...rain showers likely with MVFR or Lower. North winds 25-30g35kt.
Sunday...most likely VFR with northwest winds 20-25kt. Potential for gusts
up to 40kt.
Monday...VFR. Northwest winds 15-20g25kt.
&&
Marine...
went ahead and expanded the dense fog advisory to include all
waters as web-cams near Li sound...mainly eastern Li sound...
indicated lowering visibility. So far...dense fog advisory will expire
at 6 am Thursday...but this may have to be extended through the
middle-morning hours.
Seas are running 1-2 feet below wavewatch forecast - so for now have
taken 1 feet off of wavewatch through Thursday night. Still expect
seas to come up to Small Craft Advisory levels tonight and continue through
Thursday night. Winds also increase late tonight and remain up
into Thursday night. Increasing low level jet through Thursday
night increases potential for Small Craft Advisory level gusts over the coastal
ocean waters - so have kept headline as Small Craft Advisory vice converting to an
Small Craft Advisory for hazardous seas.
Marine inversion appears will limit mixing - so while could see
occasional gusts to 25 knots over the remainder of the waters from
late tonight into Thursday night - do not have confidence to issue
Small Craft Advisory at this time for the non-ocean zones.
There is a good potential for Small Craft Advisory conditions to continue through the
upcoming weekend as low pressure forms over the waters on Friday and
lifts slowly to the north and east. Small Craft Advisory conditions are becoming
increasingly likely...with the potential for gale conditions Sat
into sun. Winds and seas begin to subside late sun into Monday with
high pressure building in from the Great Lakes region.
&&
Hydrology...
there is the potential for around 3/4 to 1 inch basin average quantitative precipitation forecast
Thursday and Thursday night with locally higher amounts.
Do not expect any widespread flood threat Thursday from any
rain showers/thunderstorms and rain but could see some minor flooding under any stronger
convection - especially if there is any training.
The heaviest rainfall in this time frame will be late Thursday
night - with localized rainfall rates of 1-1.5 inches/hour possible
noting precipitable waters of 1.5-1/75 inches in this time
frame. If these rates are realized...especially if the storms
producing them pass over areas receiving locally heavy rainfall
Thursday...there is the potential for localized flash flooding.
The threat for localized heavy rainfall will continue into the first
half of Friday with embedded convection. Thereafter...a stratiform rain
and/or showers develops on the backside of developing low pressure.
An additional 1 to 2 inches of rainfall is possible Friday into Sat.
This may exacerbate any ongoing flooding. Rain may linger even into
sun based on latest model trends.
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 website.
&&
Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...dense fog advisory until 6 am EDT Thursday for anz330-335-338-
340-345-350-353-355.
Small Craft Advisory until 6 am EDT Friday for anz350-353-355.
&&
$$
Synopsis...maloit/dw
near term...maloit/mps
short term...maloit
long term...dw
aviation...met
marine...maloit/dw
hydrology...maloit/dw
