Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 081057 AFDOKX Area Forecast Discussion National Weather Service New York NY 657 AM EDT Sat May 8 2021 .SYNOPSIS... Weak low pressure southwest of the region will eventually move farther southeast today into tonight, eventually moving well out into the Atlantic. A warm front approaches on Sunday and a low develops along it. The low moves across early Monday. High pressure will then begin to build in to the west of the region for the rest of Monday. This high pressure will then build into the region for the middle of the week. Another storm system approaches for late in the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Forecast mainly on track with just some slight adjustments to temperatures and dewpoints as well as cloud coverage to better match observed trends. Weak low pressure southwest of the region will very slowly move east, getting to just south of Western Long Island by the start of the evening. POPs for showers will maintain a consistent gradient in that higher POPs will be towards and north and west of NYC with lower POPs farther east across Southeast Connecticut and Eastern Long Island. Mainly dry conditions are expected for Eastern Long Island and Southeast Connecticut. Some mesoscale models depict some discrete cells forming that look to be localized heavier showers or even some isolated thunderstorms late this morning and this afternoon. The higher instability will be positioned to the southwest of the region which varies from under 50 J/kg according to GFS to near a few hundred J/kg according to NAM. There could be a rumble of thunder with shower activity this afternoon for parts of Northeast NJ and the Lower Hudson Valley but probabilities for this are less than 15 percent so opted to leave out of forecast for time being. Abundant clouds and an easterly flow through much of the day along with vertical mixing up to near 900mb will limit high temperatures. Highs will be slightly warmer farther east (upper 50s) and slightly cooler farther west (mostly mid 50s) within the forecast region.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/...
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For tonight, the weak wave of low pressure travels farther southeast and farther away from Long Island. The low will continue to weaken as well. The main pressure gradient will be between a stronger low pressure area moving from Nova Scotia towards Newfoundland and high pressure in the Mid-Atlantic. This high will build into the area but the local region will remain on the northwest periphery of it. A NW flow will develop across the local region. However, the winds will remain light without much cold air advection. Although lows will be lower than the previous night with more efficient radiational cooling. MAV/MET blend used and lows will range from the upper 30s in rural and inland locations to upper 40s within NYC. Drier conditions are expected and clouds will gradually decrease as cyclonic flow decreases with strong upper level low moving from Nova Scotia towards Newfoundland. The mid level pattern exhibits more of a zonal pattern with rising heights across the local region. For Sunday, the local region will remain on the northwest periphery of the high pressure centered in the Western Atlantic around and to the east of the 30N/70W mark. The high will slide farther east and farther away Sunday afternoon, giving way to an approaching warm front. Isentropic lift and warm air advection in the low levels will allow for the development of overrunning stratiform rain from Sunday afternoon into Sunday evening as the warm front moves closer to the region. A low will develop along the warm front as well. Not expecting much of any instability, so left out mention of any embedded thunder. A sunny start to the day Sunday will transition to mostly cloudy during the afternoon with some initial rain making its way into western parts of the region, including Northeast NJ, Lower Hudson Valley, NYC, Western Long Island and SW Connecticut. SW flow in the low levels will help with warm air advection, so a mild day is expected, warmer than the previous day by around 5 to 7 degrees. Sunday`s forecast high temperatures are mainly in the 60 to 64 degree range. This will still be below seasonal normals however by about 3 to 5 degrees. By early Sunday evening, the rain is expected to have spread into the remainder of the forecast region. Rain is expected to prevail Sunday night. The low along the warm front moves across early Monday. The low and front will move east of the region thereafter, allowing for high pressure to begin building in to the west of the region. Rain will taper off Monday from NW to SE early in the day. Chances of rain in the morning to early afternoon will be followed by mainly dry conditions thereafter. Lows Sunday night are only expected to drop into mid 40s to lower 50s. These will be close to normal lows for this time of year. Highs forecast on Monday are in the low to mid 60s, a slightly warmer trend than previous forecast as the models seem to have trended faster with the front and low pressure progress, moving out of the region faster than previously forecast.
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&& .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Much of the long term will be dominated by high pressure with mostly clear skies for the middle of the week. Low pressure to the northeast of the area pushes a weak cold front through on Tuesday with high pressure building in from the west. This will result in a relatively tight pressure gradient and allow for breezy NW winds through much of the day Tuesday and Wednesday. It`s not until the low pressure moves away and high pressure build overhead by Wednesday afternoon that winds begin to weaken. Though it will be breezy, precipitation is not expected. High pressure continues to dominate the area Thursday allowing for clear and dry conditions. models then diverge on a solution toward the end of the week. The GFS develops an area of low pressure over the area that looks to linger for a few day while the ECMWF and CMC keep high pressure over much of the area through the end of the week and into at least the beginning of the weekend. Have PoPs for night and through the day on Friday to account for the uncertainty in the forecast. Temperatures will generally be around average with highs each day this week in the 60s. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... High pressure offshore will eventually give way to an approaching area of weak low pressure coming from the south and west through early this morning. VFR conditions may continue through TAF period. There is a chance for MVFR conditions (mainly with visibility) after 12Z today as showers from the approaching low move through the terminals. Therefore, included PROB30 for this chance. There is a low chance of a heavier shower with embedded thunder mainly for the westernmost terminals by early afternoon but probability and confidence is low enough to not include it in the TAFs. Generally light E wind turn back to the SE Saturday morning. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... Amendments may be needed for the timing of showers for the western terminals. .OUTLOOK FOR 06Z SATURDAY THROUGH WEDNESDAY... .Saturday evening...VFR, with MVFR possible at times with rain showers early. .Sunday...Mainly VFR. W-SW wind gusts 15-20 kt, mainly during the day. MVFR to IFR possible at night with rain becoming likely. .Monday...MVFR to IFR possible with chances of rain. .Tuesday...Mainly VFR. NW wind gusts 20-25 kt .Wednesday...VFR. NW wind gusts to around 20 kt. Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 && .MARINE... Conditions remain well below SCA criteria on the waters through tonight. For Sunday through Monday, mainly the ocean could get to SCA level wind gusts with SCA level seas late Sunday night into Monday. With frequency of SCA gusts on Sunday only expected to be occasional, no SCA issued at this time. SCA conditions are likely for the ocean waters midweek for elevated seas on Tuesday and gusty winds on Wednesday. Sheltered waters look to have marginal SCA conditions on Wednesday for gusty winds but all waters look to drop below small craft conditions by Wednesday night as high pressure moves overhead. Conditions remain sub-SCA Thursday and into early Friday. && .HYDROLOGY... No hydrologic impacts are expected through the short and long term forecast period. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JM/MW NEAR TERM...JM SHORT TERM...JM LONG TERM...MW AVIATION...MW MARINE...JM/MW HYDROLOGY...JM/MW

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