Area Forecast Discussion
Issued by NWS Upton, NY

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397 FXUS61 KOKX 231423 AFDOKX Area Forecast Discussion National Weather Service New York NY 1023 AM EDT Fri Jun 23 2017 .SYNOPSIS... A warm front will be well north of the region today. A cold front approaches tonight and moves across the area Saturday. A series of frontal boundaries will move across the Tri-State area Sunday through Tuesday. A large area of high pressure builds in thereafter. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Adjusted POPs for showers late this morning into start of the afternoon to be more confined with the higher coverage towards NYC and to the north and west. This is consistent with the mesoscale models forecast of reflectivity in the same time window. To the east, expecting mainly dry conditions to continue. Temperatures were adjusted slightly higher to better match observed trends this morning. Otherwise, no other remarkable changes made to the forecast database. The region will be between Bermuda ridging and deepening northern stream longwave trough across the north Central US today...with one distinct southern stream shortwave riding northeast this morning and then several weaker vorts riding northeast later today. At the surface...a warm front washes out/pushes north of the region this morning...with likely pre- frontal trough development in the lee of the appalachians this afternoon. Deep southwest flow with sub-tropical connection will result in an increasingly moist and humid airmass working into the region today. The initial shortwave rides north through the region this morning into early afternoon. LLJ forcing weakens as this activity works towards the region...but a marginally unstable and moist airmass in place should support scattered shower and isolated thunderstorm activity to work northeast through the region. Overall appears to be a marginal instability with moderate shear situation...which presents only a low probability of an isolated strong to severe storm. In the wake of this shortwave...potential for partial clearing and additional destabilization late this afternoon/early evening across NYC metro and points N&W. Although moderate instability/uni- directional shear levels could exists during this time...appears to be lack of a distinct focus or trigger for convection until the evening. In fact...subsidence and weak mid-level capping may limit convective activity across the region until late. Based on instability/shear environment there is a threat for isolated strong to severe storms during this time...conditional on sufficient heating and development along any differential heating boundaries or elevation. Otherwise...considerable cloudiness and convective debris today will keep temps in the lower to mid 80s for most of the region. If enough breaks in the clouds materialize...temps could rise into the upper 80s across NYC metro and points N&W. There is a moderate risk of rip current development today, due to building southerly winds waves and a 2 ft long period SE swell. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Northern stream longwave trough continues to deepen into the Upper Mississippi River Valley and Great lakes through the period...with the shortwave remnants of Cindy shearing northeast towards the region late tonight into Saturday morning. At the surface...a cold front over the Great Lakes will slide east towards the region tonight...with the remnant circulation of Cindy riding NE towards the region along the front. Leading edge of southern stream shortwave energy and pre- frontal trough approach the region this evening. Will have to watch for convection developing over Central/Eastern PA this afternoon...and whether line segments can translate east in the moderate mid- level flow into the Lower Hudson Valley/NE NJ before instability begins to wane. A conditional low threat for severe winds gusts exists mainly NW & W of NYC if this activity survives. The parade of shortwaves late evening into the overnight and tropical airmass will keep a threat for iso convection with heavy downpours overnight. Coastal stratus/fog development possible with high dewpoint airmass advecting across E LI/SE CT late today/this evening. Main concern during this period will be approach of cold front and remnant low of Cindy late tonight/Saturday morning. Environment presents a threat for flash flooding along and just to the south of the path of this low...with PWATS in excess of 2+ inches and Corfidi vectors indicating potential for slow moving or back building convective elements. Also can`t rule out an isolated severe wind/tornado threat if any MCS type activity develops in a weak instability but high shear/helicity and low- LCL environment. 745am Update...06z guidance is indicating that this feature may track to the south of the region. If 12z guidance continues with this theme...the above mentioned severe/flash flood threat may end up south of the region. Drying conditions in the wake of the cold front and Cindy circulation Saturday afternoon...with highs in the mid to upper 80s. A high risk of rip current is likely Saturday with building southerly swells and wind waves. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... NWP is in agreement that a broad upper level trough will remain east of the Rockies into early next week. The H5 flow then flattens from west to east as a cutoff low pres system moves through the western Canadian provinces...eventually consolidating with a vortex over northern Quebec. This will sharpen the trough with its axis passing through Tue night followed by weak ridging for the remainder of the forecast period. In terms of sensible weather...not a whole lot to talk about. A few cool frontal boundaries will pass through the local area...the first Sunday aftn/eve with just a chance of isold showers. Mid level warming will keep instability in check so no tstms in the forecast. The second boundary approaches on Monday and is very slow to move through the area. It may become hung up...before pushing east Tue night. Despite a decent shortwave and being in the RRQ of a 120+ kt upper jet...moisture looks very meager...thus have kept the forecast dry. Moisture is still limited on Tue...but there could be enough for isold showers/tstms in the aftn. Dry and seasonable weather then returns for the remainder of the forecast period. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... A warm front moves well north of the region today establishing a moist SW flow. Mainly VFR. Areas of MVFR are possible later today with cigs around 2500 ft and SHRA moving through for the late morning and early afternoon. There is also some potential for eastern terminals to briefly go to MVFR in the late afternoon due to low stratus. For now the tafs indicate VFR because coverage is in question and too uncertain at this time. More widespread sub VFR conditions are expected late in the TAF period. There will be a chance of isold-sct shwrs thru the day (Friday), with the best potential for thunderstorms after 19Z, particularly in areas along and west of the Hudson River. The sea breeze may attempt to back winds closer to the south again after 16Z today for eastern terminals. A chance at perhaps scattered thunderstorm coverage towards the evening push for the city 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 may be needed to address scattered showers and for any isolated thunderstorms that may develop. Winds may become more southerly after 16z. KLGA TAF Comments: Amendments may be needed to address scattered showers and for any isolated thunderstorms that may develop. KEWR TAF Comments: Amendments may be needed to address scattered showers and for any isolated thunderstorms that may develop. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Amendments may be needed to address scattered showers and for any isolated thunderstorms that may develop. KHPN TAF Comments: Amendments may be needed to address scattered showers and for any isolated thunderstorms that may develop. KISP TAF Comments: Winds may become more southerly after 16z. Amendments may be needed to address possible low clouds / ceilings that may develop after 18z. .OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY... .Saturday...MVFR or lower possible in shra/tsra. .Saturday night-Sunday Night...VFR. NW winds...becoming W/SW. .Monday-Tuesday...VFR. A chance of afternoon shra/tsra each day. && .MARINE... Southerly winds increase to marginal SCA on the ocean this afternoon...and likely continue into tonight. Occasional gusts to 25 kt possible on nearshore waters this afternoon. Ocean seas likely building to SCA levels this afternoon...and likely further build to 4 to 7 ft tonight. Winds subside and Saturday...but southerly swells are expected to keep ocean seas at 4 to 7 ft on Sat. The other hazards for mariners will be rounds of showers/thunderstorms this today into Saturday morning, and potential for dense fog development on the ocean waters and eastern LI nearshore waters this afternoon and continuing into tonight. Seas begin to subside Sat night...but could take until Sun morning to drop below SCA levels east of Moriches Inlet. A weak pressure field is then expected to prevail through Tue...keeping conds at sub- advsy levels. && .HYDROLOGY... Localized minor urban and poor drainage flooding is possible with showers and thunderstorm activity this afternoon into the first half of tonight. There is a threat for flash flooding late tonight through Saturday morning from a likely complex of showers and thunderstorm associated with a frontal wave (remnants of Cindy) moving through the areas. Uncertainty exists on the exact track of this wave...which could be from the Northern Mid- Atlantic to Southern New England. 745am Update...06z guidance is indicating that this feature may track to the south of the region. If 12z guidance continues with this theme...the above mentioned flash flood threat may end up south of the region. Otherwise, no other hydrologic concerns. && .TIDES/COASTAL FLOODING... Astronomical tides are running very high, especially during the evening high tide cycles today and Saturday. Less than 1 ft of surge is needed during these evening high tide cycles for minor flooding, and in some cases less then 1/2 ft. The expected S/SW flow is not favorable for surge, but a background anomaly will likely be enough for minor coastal flooding of the most vulnerable coastal locales along the south shore bays of Western Long Island, along Jamaica Bay, and along western Long Island Sound during this time. && .EQUIPMENT... KOKX weather radar is scheduled for maintenance starting today June 23rd for a period of 3 days. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 2 AM EDT Sunday for ANZ350-353-355. && $$ SYNOPSIS...24/NV NEAR TERM...JM/NV SHORT TERM...NV LONG TERM...24 AVIATION...JE/MET MARINE...24/NV HYDROLOGY...24/NV TIDES/COASTAL FLOODING... EQUIPMENT...

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