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000 
FXUS61 KOKX 232138
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
538 PM EDT Mon Oct 23 2017

.SYNOPSIS...
Strong high pressure continues to pull away from the New England
coast. A slow moving frontal system approaches late Monday night,
impacting the region Tuesday into early Wednesday with strong 
winds gusts and potentially heavy rain. The frontal system 
slowly moves east of the area Wednesday night with brief high 
pressure following through the end of the week. A cold front 
then merges with a developing coastal low Saturday night into 
Monday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
With upper level ridge passage clouds will dominate beginning
tonight. Complex frontal system over the Ohio and Tennessee 
valleys will draw closer tonight. With well established moist
southerly flow ahead of the front expect areas of patchy fog
along with drizzle in some locations. Lift is shallow and weak
overnight, except after 6z in far western zones when showers
begin to move in. 

Temperatures remain well above normal tonight due to clouds and
warm air advection. A model blend was used for temperatures.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
NWP guidance is in good agreement through Tue night.
A vigorous PAC shortwave will continue to dig the longwave 
trough and gets to the Gulf coast by Tuesday Night. The first
feature that will drive surface weather is a low level jet with
high PWs for this time of year. This will result in periods of 
rain, with embedded heavier showers and gusty winds. Some CAPE 
in model profiles suggest few rumbles of thunder on Tuesday.

The second feature which will drive any convective rain will be
the approaching frontal system for Tuesday night, with models 
indicating the best potential for widespread rainfall amounts 
above 2 inches to be east of New York City. With amplification 
of the longwave trough the frontal system is indicated by NWP 
models to slow and track very slowly across the region Tue night
in the longitudinally oriented steering flow. Trend with this 
update has been to continue to slow the system's progression 
through Tue night which would only serve to increase rainfall 
amounts for eastern sections.

The following potential hazards Tue/Tue night:

Heavy Rain: The slow movement of the front, deep lift, weak 
instability, and interaction with an increasingly moist and 
tropical airmass (+3 to 4 std) signal potential for multiple 
bands of heavy rain as weak waves lift north along the front. 
The higher resolution WRF based models continue to indicate the 
potential for a localized swath of 3-5 inches. This looks to be 
a credible threat based on synoptic pattern, but location/timing
is very much uncertain based on front and frontal wave timing 
and location. Would also like to see additional support of this 
in some other hi-res models. See hydrology section for 
associated flooding threat.

Strong Winds: A wind advisory is in effect for most of our CT 
zones, along with coastal zones in NY. A 45-55 kt 925 hpa LLJ 
moves overhead Tuesday into Tue night. The GFS BUFKIT soundings
indicating a 12 hr period of southerly winds gusts of 30 to 40 
mph, with potential for any low topped convective line/s ahead 
of the cold front being able to drag down localized 45-55 mph 
wind gusts to the surface. SPC has our area in a slight risk 
with damaging wind gusts the main threat. Not seeing the best 
low level lapse rates and 0-1 km shear, so not all that bullish 
on tornadic activity, with later shifts needing to further 
inspect.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
A slow moving upper trough will maintain significant moisture 
advection in broad, nearly unidirectional southerly flow into at
least the early portion of Wednesday. Primary update to the 
extended forecast was to slow the departure of the surface front
and associated precipitation, mainly across portions of 
Connecticut and Long Island. Ensemble forecasts still suggest 
some uncertainty with regards to end time of precipitation, 
though in general rates should taper off from west to east 
through the evening. Depending on how quickly rainfall ends, 
adequate mixing in the afternoon and evening with modest west- 
northwest flow may support a few gusts.

High pressure then builds through the remainder of the week with a 
return to more seasonable temperatures and humidity, though with 
some subtle moderation and warming to the air mass as the week 
progresses.

Meanwhile, a long wave upper trough will develop and slowly push 
eastward, allowing strong moisture advection again into Sunday. The 
increasing difluence aloft will aid in the development of a 
coastal low, which is then expected to merge with the frontal 
system, increasing chances of rain across the area. At the 
moment, the exact timing, accumulations and rates of any 
precipitation remain uncertain but the system will continue to 
be monitored.

&&

.AVIATION /22Z MONDAY THROUGH SATURDAY/...
A slow moving cold front will approach the region tonight but
not pass through the region until Tuesday night.   

MVFR returns this evening with patchy drizzle developing. 
Showers become more widespread from west to east after 06z with 
MVFR/IFR cigs.

With the approach of a low level jet, showers with embedded 
thunder are likely Tuesday. The rain will be heavy at times 
accompanied by strong wind gusts, especially near the coast. 
Compression and low level wind shear are likely, mainly SSW 
45-55kt@2kft for coastal terminals.

SE winds increasing near 15kt with gusts to 25kt possible this 
evening, especially near the coast (NYC and LI terminals). Wind 
increases tonight with gusts becoming more frequent around 25kt. 
Some gusts 30-40kt possible after 12z Tuesday, especially the NYC 
terminals.

     NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component forecasts, 
can be found at: http:/www.weather.gov/zny/n90

KJFK TAF Comments: Amendments for flight categories and wind 
are likely Tuesday.

KLGA TAF Comments: Amendments for flight categories and wind 
are likely Tuesday.

KEWR TAF Comments: Amendments for flight categories and wind 
are likely Tuesday.

KTEB TAF Comments: Amendments for flight categories and wind 
are likely Tuesday.

KHPN TAF Comments: Amendments for flight categories and wind 
are likely Tuesday.

KISP TAF Comments: Amendments for flight categories and wind 
are likely Tuesday.

.OUTLOOK FOR 18Z TUESDAY THROUGH SATURDAY...
.Tue...LLWS SSW 45-55kt@2kft for coastal terminals...shifting 
east after 20z. MVFR/IFR SHRA continues with low prob/sparse 
TSRA Tue afternoon.
.Tue night-Wed...IFR possibly continues in SHRA Tue night, low
prob/sparse TSRA early evening, improving to MVFR and possibly 
VFR by midday Wed.
.Wed night-Thu...VFR, with iso-sct MVFR in SHRA.
.Fri and Sat...VFR.

&&

.MARINE...
The pressure gradient will begin to tighten tonight as low 
pressure strengthens over the Great Lakes. The associated cold 
front passes through late Tuesday night.

SCA conds are expected to develop overnight with the potential 
for marginal gale force gusts Tue into Tue night on all waters. 
Gale watch remains in effect for this potential, although the 
higher winds may be more convectively correlated. As the cold 
front slowly moves east Wednesday into Wednesday, winds will 
gradually begin to subside in its wake, though lingering swell 
may maintain SCA- level seas at least into Friday night. Seas 
gradually subside into the weekend.

&&

.HYDROLOGY...
A widespread 2 to 3 inches of rain is likely Tuesday into 
Wednesday morning, with locally up to 4 inches. Concern is that
much of this rain could fall in a 6 hr period in slow moving 
and/or training bands of low topped convection/heavy rain, but 
the predictability on location of where this occurs is low. 

Despite antecedent dry conditions, these potential rainfall rates 
present an area wide potential for minor urban and poor 
drainage, with a localized threat for flash flooding. In 
addition, if the heavier rain amounts occur over Northeastern 
New Jersey and the Lower Hudson Valley, rapid rises in flashy 
small streams and minor flood impacts to adjacent areas would be
plausible. A flash flood watch may be needed as subsequent data
is evaluated.

Heavy rain threat diminishes Wednesday afternoon, with drying 
conditions expected Thursday night through Saturday.

The next chance for widespread rainfall across the area 
will be Sunday night, though the location and timing of any heavier 
amounts are uncertain at this time.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory from 8 AM Tuesday to 2 AM EDT Wednesday for 
     CTZ007>012.
NY...Wind Advisory from 8 AM Tuesday to 2 AM EDT Wednesday for 
     NYZ071>075-078>081-176>179.
NJ...None.
MARINE...Gale Watch from Tuesday morning through late Tuesday night for 
     ANZ330-335-338-340-345-350-353-355.
     Small Craft Advisory from 2 AM to 6 AM EDT Tuesday for ANZ330-
     335-338-340-345.
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ350-353-355.

&&

$$
SYNOPSIS...MD/JE/DW
NEAR TERM...JE
SHORT TERM...JE

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