Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 292227 AFDOKX Area Forecast Discussion National Weather Service New York NY 627 PM EDT SUN MAY 29 2016 .SYNOPSIS... High pressure over the western Atlantic gradually translates eastward tonight ahead of a frontal system working east from the Ohio Valley. A pre-frontal trough will work into the area by daybreak Monday and then dissipates across the area. A cold frontal passage will then follow late Monday night into Tuesday morning. High pressure then returns until a cold front slowly approaches at the end of the week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Fog bank along the south shore of LI expanded rapidly ahead of main bank well offshore this afternoon. This area will remain gradually overspread LI and the CT coast from south to north during the evening hours. Received a few reports of drizzle associated with the fog bank moving onshore...so have added this to the grids this eve. Also made some adjustments to sky/t/td to better reflect the stratus/fog extent next couple of hours as well as the drop in temps and increase in dewpoints as a result. Otherwise...high amplitude ridge over the western Atlantic finally weakens and translates east tonight in response to an upper trough lifting NE across the Great Lakes and into eastern Canada. This allows the westerlies along the northern tier of the country to expand eastward and allow for a more progressive flow. As this happens, tropical moisture rounding the western periphery of the ridge, as well as moisture associated with TD Bonnie over south Carolina. will get drawn northward ahead of an approaching cold front and pre-frontal trough. With the aforementioned upper trough lifting out to the NE, the RRQ of the upper jet will press east overnight along with a surface trough. Deep-layered moisture with PW values increasing to around 2 inches will interact with multiple lifting mechanisms for widespread showers to develop late tonight. Marginal instability will also allow for isolated thunderstorms. There is the potential for localized heavy rainfall with many locations seeing upwards of an inch by daybreak, especially from NYC points north and west. There is some uncertainty with the magnitude and location of convection along ahead of the approaching pre-frontal trough overnight. The GFS is most aggressive across the interior of the Lower Hudson Valley with the ECMWF to a lesser extent. The NAM WRF primarily focuses the strongest convection across the coastline. The GFS of late has grossly exaggerated the diurnal convection. How this translates forward with a synoptic scale system remains uncertain, but due to the tropical connection with this system have leaned toward the higher model QPF of the GFS. Overnight lows will remain mild in the 60s with dew points not far behind. This is above normal by about 10 degrees. There remains a moderate risk of rip current development at Atlantic facing beaches through this evening.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Deepest lift and moisture in the morning will be primarily from NYC and points east. In fact, model time height cross sections show drying in the low-levels but continued mid and upper level lift with the upper jet dynamics and mid level frontogenesis. Heaviest rain is forecast to end over all but eastern LI/SE by early afternoon, where it could linger a few more hours. Models have trended a bit slower the last couple of days with the evolution of this system. This is something to bear watching. Showers are forecast to linger through much of the afternoon. Localized flash flooding is a possibility during the morning/early afternoon hours with any embedded thunderstorm activity. Showers very well could linger into the nighttime hours, especially across LI/CT as some mid level energy associated with TD Bonnie shears NE into the Mid Atlantic Region. This will be watched closely with the potential for more significant rainfall. As for highs Mon, stayed on the cooler side of the MOS guidance with highs generally in the lower to mid 70s. Lows will remain mild in the lower to mid 60s. There is a moderate risk of rip current development at Atlantic facing beaches on Tuesday. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Models are in good agreement with the H5 pattern across north america through Wed...but then timing and amplitude differences with the next trough/cutoff low traversing southeast Canada during the second half of the week is impacting the progression of a cold front across the area. 12z EC still holding on to residual pcpn Tue morning therefore have maintained schc pops. Although tropical depression Bonnie will still be over coastal north Carolina...the focus for pcpn will have passed e with all pcpn remaining offshore. NHC`s 11am advsy tracks Bonnie to around 100 miles SW of the 40N 70W benchmark at 12z Friday. Due to its close proximity there could be a few showers Thu mainly across srn portions of the forecast area. As the front moves closer Thu night and Fri...showers and tstm chances will increase...although it now appears that additional moisture from Bonnie or its remnants will remain separate from the approaching frontal boundary. If the upper trough associated with this boundary speeds up however...this could change. This upper trough digs as it moves through the Midwest/Ohio valley leading to a slow progression of the sfc front across the area. While the forecast has pops from Thu Night through Sunday...think most of the activity will be diurnal. Temperatures will remain above normal levels Tue and Wed...with a return to near normal temps thereafter. && .AVIATION /22Z SUNDAY THROUGH FRIDAY/... VFR for most terminals with a few already getting affected by lowering clouds to IFR to below into this evening. This will spread west to other coastal and city terminals this evening. Rain showers will increase and become more intense into the overnight. There could be some improvement to MVFR for Monday PM for terminals away from the coast with otherwise IFR or below continuing. Rain showers...heavy at times continue through much of Monday. Any thunderstorms will be isolated. .OUTLOOK FOR 18Z Monday through Friday... .Monday Afternoon...MVFR away from the coast with IFR near the coast. Isolated showers/thunderstorms could produce locally heavy rainfall. .Monday Night...MVFR possible with a chance of showers. .Tuesday...Becoming VFR. .Tuesday Night-Wednesday night...VFR. E-NE winds g15-20kt Wednesday. .Thursday-Friday...Low chance of MVFR or lower in showers. E-NE winds g15-20kt Thursday. && .MARINE...
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Higher dew point air moving across the coastal waters tonight will result in areas of fog and drizzle that are forecast to expand north from the ocean waters to LI Sound and the adjacent harbors and bays. A persistent southerly flow will continue on the waters around the western periphery of the western Atlantic ridge. Seas will gradually build through Tuesday with the possibility of marginal SCA seas late Monday night into Tuesday. There is quite a bit of uncertainty on how much residual swell from Tropical Cyclone Bonnie will impact the coastal ocean waters early next week. Wind gusts could approach sca levels on the ocean on Thu. Otherwise sub-advsy conds are expected through the remainder of the forecast period.
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&& .HYDROLOGY... For tonight through Monday Evening...a widespread 1 to 1.5 inches of rain is forecast. Locally higher amounts are a good possibility. This rain could lead to minor urban and small stream flooding and there is chance for localized flash flooding as well. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Dense Fog Advisory until 6 AM EDT Monday for ANZ330-335-338- 340. Dense Fog Advisory until 6 AM EDT Monday for ANZ345-350-353- 355.
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