Area forecast discussion
National Weather Service New York New York
400 PM EDT Tuesday may 21 2013
Synopsis...
a frontal boundary will remain just north of the region through
Wednesday as a cold front slowly approaches from the west. The
cold front will pass through the area early Friday. Canadian high
pressure builds in for the weekend and early next week.
&&
Near term /until 6 am Wednesday morning/...
advection fog/stratus remains along the South Shore of eastern Suffolk
County. Dense fog advisory there through 10 am...though this will
likely need expanding as the night progresses. Confidence on this
though is not that high at this time to warrant expansion.
Late this afternoon...with temperatures near 90 and abundant moisture...instability
is maximized. The lack of a trigger away from the front has kept
convection limited. Have lowered probability of precipitation for this evening and kept it
confined to the interior as a result. Even these probability of precipitation may be over
done. With the lack of more extensive convective initiation so far...have
dropped mention of convection this evening in the hazardous
weather outlook.
Warm and muggy overnight with blended MOS accepted.
&&
Short term /6 am Wednesday morning through Wednesday night/...
looks like a similar day on Wednesday as ridge slowly shifts
east. Morning fog and stratus will give way to at least partial
sunshine. Convection should be scattered at best with only marginal
instability in place...less than today. Highs in the middle
80s...except along the coast.
&&
Long term /Thursday through Tuesday/...
the upper trough over the middle section of the country translates
east through the end of the week and then offshore by the weekend.
Interaction with short wave energy in the northern branch of the
polar jet across eastern Canada will amplify the trough across the
Ohio Valley and Middle Atlantic States. This amplification results in
timing issues amongst the global models...with the operational 12z
GFS at the western end of the envelope. The European model (ecmwf) and ggem are the
quickest with swinging the front across the coast by Friday morning.
In fact...the GFS continues to become much slower than the all the
guidance Friday into Sat as the upper low closes off approaching the
Middle Atlantic States...taking on a negative tilt much closer to the
coast. This would result in a prolonged period of Post-frontal
rain into Sat. Preference at this time was to lean toward the
faster model consensus with precipitation shutting down Friday aft/eve.
Subsequent model trends will need to be closely monitored to see
if the frontal system slows down even further.
As for the sensible weather...cold front approaches from the west
Thursday...passing across the region Thursday night into Friday after. High precipitable water
values and moderate instability will lead to the development of
widespread showers and thunderstorms that works west to east during
this time. The isolated threat appears low at this time with the
low-level jet displaced east of the area and marginal deep layer
shear. Unidirectional wind profiles support some bowing line
segments. Wet-bulb zero values are warm supporting only small hail.
The main threat looks to be the potential for heavy rainfall...
especially if the upper flow backs further with the amplification of
the upper trough to the west. Average basis rainfall should be close
to an inch...with localized higher amounts.
A drier northwest flow set ups Friday night with strong cold advection. High
pressure builds across the Great Lakes and into the Middle Atlantic
States through early next week with temperatures several degrees
below seasonable levels.
&&
Aviation /19z Tuesday through Sunday/...
a nearly stationary front will remain north of the region through tonight.
Isolated-scattered thunderstorms expected this afternoon and evening...mainly north and west of the
city. There is the potential for any thunderstorms which form across northestern New Jersey
to slowly track east-southeast towards the city and weaken. There could be
some direct impacts especially kteb if this occurs.
Otherwise...VFR with southerly flow across the region.
IFR fog should return tonight. Any thunderstorms could alter the timing. Light
southerly flow...vrb at times...can be expected.
Conditions will be slower to improve on Wednesday. Think IFR most areas
until at least 14-17z. Potential for IFR or MVFR to remain in place
all day on the coasts with perhaps a few breaks.
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: fog may develop quicker than tafs indicate
this evening. Thunderstorms are expected to remain north of the terminal this evening
at this time.
Klga fcster comments: although thunderstorms are generally expected to
remain north of the terminal this evening...there is a low probability that a
weakening thunderstorm could impact the terminal.
Kewr fcster comments: there is a low probability of thunderstorms in vicinity of the
terminal this evening. Most activity is expected to remain north of the
Airport.
Kteb fcster comments: although most thunderstorms are expected to remain north
of the Airport...there is the potential for activity in vicinity of the Airport
this afternoon and evening.
Khpn fcster comments: although most thunderstorms are expected to remain north
of the Airport...there is the potential for activity in vicinity of the Airport
this afternoon and evening.
Kisp fcster comments: the fog may develop quicker than the tafs
indicate this evening.
Outlook for 18z Wednesday through Sunday...
Wednesday afternoon...MVFR or lower possible coast...VFR interior. Scattered rain showers
and thunderstorms possible.
Wednesday night...scattered rain showers and thunderstorms possible. IFR possible in fog and
stratus.
Thu-Fri...numerous rain showers and thunderstorms possible. IFR possible in fog and
stratus.
Sat...residual rain showers behind a cold front with MVFR. Becoming VFR
with northwest winds increasing to 20-30kt.
Sun...VFR with northwest winds 20-25kt.
&&
Marine...
dense fog across the eastern ocean waters...mainly near shore...and the
eastern Great South Bay. This advection fog is expected to expand
back west overnight.
South southwest sub Small Craft Advisory winds continue through Wednesday night.
Seas should slowly build Wednesday...but have undercut wavewatch
to prevent reaching Small Craft Advisory criteria until Wednesday night. Thinking
with strong inversion that wind forcing was overdone in the ww3
forecast.
A cold front will move across the area waters early Friday...with
high pressure building in at the surface on Sat. Winds could be
below Small Craft Advisory levels by Friday morning...with seas on the ocean
remaining above Small Craft Advisory criteria through much Saturday morning.
Undercut wavewatch during this time as it was slower bringing the
frontal system across the area. There is some uncertainty with the
seas due to the timing differences amongst the models.
&&
Hydrology...
scattered thunderstorms this afternoon this evening...mainly lower Hudson
Valley. Coverage is not expected to be large enough to present a
flood treat.
Scattered showers/thunderstorms Wednesday-Thursday will be capable of producing locally heavy
rainfall...with the best chances north/west of NYC. Total basin
average quantitative precipitation forecast for Wednesday-Thursday could be 1/4 to 1/2 inch...with locally higher
amts in thunderstorms.
Average basis rainfall should be close to an inch Thursday into
Friday...with localized higher amounts. Training of thunderstorms could
result in flash flooding.
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...dense fog advisory until 10 am EDT Wednesday for nyz081.
New Jersey...none.
Marine...dense fog advisory until 10 am EDT Wednesday for anz345-350-
353.
&&
$$
Synopsis...tongue
near term...tongue
short term...tongue
long term...dw
aviation...jmc
marine...tongue/dw
hydrology...tongue
