Area Forecast Discussion
Issued by NWS Upton, NY

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925 FXUS61 KOKX 250809 AFDOKX Area Forecast Discussion National Weather Service New York NY 409 AM EDT Fri May 25 2018 .SYNOPSIS...
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A back door cold front over southeast Connecticut and eastern Long Island will retreat to the northeast early this morning, as high pressure otherwise dominates into tonight. A low pressure trough will develop north and west of New York City on Saturday. Another back door cold front will pass through Saturday night into Sunday morning, becoming nearly stationary just to the south and west through Memorial Day. Another cold front will move through from the west on Tuesday, followed by building high pressure for the middle of next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Fog/low cloud bank remains in place over most of New London County and also along the CT River. As a result have extended the dense fog advy until 7 AM. As the back door front retreats and daytime heating ensues, the fog should burn off rapidly. A mostly sunny and very warm day still expected today, with highs 85-90 away from most south-facing shores, at or above the warmer of the GFS/NAM MOS guidance. Hybrid synoptic scale/sea breeze regime should lead to gusty conditions along the coast, and temps dropping through the mid to late afternoon, perhaps more quickly than fcst indicates.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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Mostly clear skies expected tonight, with some patchy ground fog possible mainly in the interior valleys. Lows tonight should be near 70 in NYC and in the 60s elsewhere. As flat upper ridging moves east, chances for tstms should increase through the afternoon on Sat. GFS way too quick to initiate storms, almost as soon as a sfc-based theta-e ridge develops, despite upper ridging and associated subsidence still overhead. Mid to late afternoon a more likely time frame for convection as PW quickly increases to near 1.5 inches. CAPE/shear values are only marginally supportive of severe wx-- more telling are microburst parameters indicating potential for pulse severe with the strongest cells mostly NW of NYC. Some cells could produce heavy rain, especially where repeat training can take place. This may become more likely toward evening and into Sat night as another back door cold front approaches and Corfidi vectors shorten.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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A shortwave trough moving across the Great lakes and into the Northeast from Saturday night through Sunday night will interact with a back door cold front dropping across the region. Thereafter, heights build across the eastern half of the country with a tropical low potentially impacting the Lower Mississippi and Tennessee Valleys. Global models are in very good agreement this cycle, in particular the GFS and ECMWF. The GGEM appears to be too aggressive with several frontal waves developing along the boundary to the south Sunday into Monday. There is the potential for localized heavy rainfall Saturday night into Sunday morning as a westerly upper flow and modest instability raises the concern for training along the cold front sagging south across the region. Severe weather seems unlikely due to a weakly sheared environment, however, mixed layer CAPE value around 1500 J/KG lend to the potential for pulse strong/severe in the evening. In addition, PW values overnight Saturday approach 2 inches. Cold front works south of the area early Sunday morning. However, post-frontal convection is likely to linger through the morning as a frontal wave passes to the south. Surface high pressure then noses in from the north through Sunday night. Weak warm advection still lends to a low chance of showers and perhaps drizzle/light rain Sunday night in an easterly flow. Outside of some scattered late day convection across the interior ahead of a weak cold front on Monday, the remainder of the period should be dry as high pressure builds to the north and offshore by midweek. Below normal temperatures for highs Sunday and Monday will return to well above normal levels Tuesday, with a slight downward tick Wednesday and Thursday as an onshore easterly flow reestablishes itself.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/...
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High pressure dominates through Friday. Other than lingering LIFR/IFR across SE CT at KGON, VFR conditions expected. S-SW winds will continue to diminish and become light and variable outside of city terminals. SW winds increase to 10-15 kt with gusts 20-25 kt into this afternoon. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .Late tonight...VFR. .Saturday...Mainly VFR. Showers and thunderstorms likely near the NYC metro terminals and to the N and W in the mid to late afternoon, with possible MVFR or lower flight cat and locally gusty winds. Higher chance of showers and thunderstorms at night. .Sunday-Monday...MVFR or lower at times with a chance of showers and thunderstorms. .Tuesday...Mainly VFR.
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&& .MARINE...
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Multiple SCA`s are in effect. First, a tightening pres gradient between low pres to the north and high pres over the western Atlantic should bring marginal SCA conds to the near shore western ocean waters and the Long Island south shore bays from mid afternoon until around sunset, with gusts up to 25 kt. Then for tonight, a strengthening sfc inversion will be developing over the waters, so despite increasing winds aloft mixing potential will be limited. A 15-20 kt sustained flow should bring ocean seas up to 5 ft out east tonight. Generally sub-SCA conditions expected thereafter in a weak flow regime, but could see a period of E flow gusting to 20 kt on the ocean waters Sunday into Sunday night.
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&& .HYDROLOGY...
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Localized heavy rainfall is possible Saturday night into Sunday morning as a cold front passes through. GEFS means approaching an inch across the area, but potential for locally 1 to 2 inches of rain. Minor urban and poor drainage flooding appears to be the main issue.
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&& .TIDES/COASTAL FLOODING... Water levels may reach minor flood thresholds along the south shore back bays of Nassau County and in western Long Island Sound with the Sunday afternoon/night high tide cycle. Forcing for increased water levels will be increasing E-NE flow as a front stalls to the south and strong high pressure sets up E of New England, along with increasing astronomical high tides with the full moon on Tue the 29th. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Dense Fog Advisory until 7 AM EDT this morning for CTZ007-008- 011-012. NY...None. NJ...None. MARINE...Small Craft Advisory from 2 PM this afternoon to 9 PM EDT this evening for ANZ345-353-355. Small Craft Advisory from 9 PM this evening to 6 AM EDT Saturday for ANZ350.
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&& $$ SYNOPSIS...Goodman/DW NEAR TERM...Goodman SHORT TERM...Goodman LONG TERM...DW AVIATION...JC MARINE...Goodman/DW HYDROLOGY...Goodman/DW TIDES/COASTAL FLOODING... EQUIPMENT...

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