Area forecast discussion
National Weather Service New York New York
1032 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/...
line of showers and thunderstorms over eastern PA beginning to
break up as they track northeast. Additional showers and
thunderstorms are firing up over northern Virginia and Maryland...and they are
tracking northeast as well. The bulk of the activity should stay
north of the region...but hrrr guidance continues to indicate
convective activity moving into the local area prior to daybreak
Thursday. Most of the activity should scatter out before it
reaches the County Warning Area...and the marine layer over the region should help
to temper any storm as well.
Otherwise...low clouds/fog will continue to establish itself over
the area. Fog may be locally dense near the coast.
Lows tonight generally in the middle to upper 60s...and in the lower
60s near the coast. These temperatures are about 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 /03z 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.
An area of showers moving into eastern Pennsylvania will weaken
overnight with scattered showers possible in the NYC vicinity
around 08z.
MVFR ceilings and visibilities in fog possible after 07z although
confidence in this occurring especially at the NYC terminals in
diminishing. IFR ceilings and MVFR visibilities in fog possible at
the terminals east of New York City...ceilings may become LIFR after
09z.
MVFR conditions likely 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.
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...
dense fog advisory remains up for all waters through 6am due to
fog restricting visibility to less than 1 nm. This advection may have to be
extended through the middle-morning hours.
Seas coming up to Small Craft Advisory levels and will 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
