Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 290641 AFDOKX Area Forecast Discussion National Weather Service New York NY 241 AM EDT Mon May 29 2017 .SYNOPSIS... A low pressure system approaches tonight and passes through during Monday into Monday evening. A weak cold front approaches from the west Tuesday, then crosses the area Tuesday night...followed by another on Wednesday. High pressure then builds to the south through Thursday night. Another cold front approaches on Friday then slowly crosses the area Friday night. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Light rain showers are making slow progress to the north and east as it tries to overcome the drier air in the mid levels. It has generally remained over Northeast New Jersey over the last few hours, with any widespread light precipitation becoming more scattered as it heads into the drier air. Tried to match up this slow progression with the POPs. Otherwise...a primary low pressure center slowly shifts eastward just north of the Great Lakes. An associated occluded front drifts towards us, and models are in general agreement that a secondary weak low pressure center forms along the front to our south before emerging off the Mid-Atlantic coast. Trends have been for a more defined secondary low, but there is still disagreement on the northern extent of its eventual track and associated lift. Between shortwave and isentropic lift, and synoptic lift from an approaching jet streak, thinking is that the likelihood of rainfall is still there by late tonight for the city and areas west of the Hudson. Patchy fog is expected as well with this being the 2nd night in a row with a SE flow. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/... The secondary low center remains to our south Monday morning as it shifts out of the picture in the afternoon. Meanwhile, the occluded front begins to move through the forecast area during Monday afternoon and exits to the east during the evening. Additional lift will still be present with jet streak dynamics and shortwave energy. Rain is therefore expected across the entire Tri-State area for the morning at least through the morning. For at least the city and west of the Hudson, much of the afternoon could be still be dry although breaks of sunshine will probably be limited. The threat of rain doesn`t exit east until around sunset, but any rainfall after mid- afternoon would probably be east of the city. Clouds and rain will limit high temps to only around 60. West of the Hudson is forecast to be mostly in the lower 60s, but even upper 60s can happen there if clouds break up more quickly than currently forecast. As for thunder, can`t rule any out with a few hundred J/KG of MUCAPE forecast, but this would be an isolated occurrence in during the morning/midday hours. Rain amounts are expected to average around a half of an inch. A weak high pressure ridge axis will stretch into the region during the nighttime hours. With low level moisture leftover from the rain and light to calm winds, expecting stratus and at least patchy fog during the overnight hours. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Global models remain in good agreement through Fri with an amplified H5 pattern across North America. Differences then emerge from Fri night through the weekend with the upper pattern...specifically how quickly the upper low over eastern Canada tracks ewd across the maritimes and nrn New England. Additionally...there are differences with the interaction of energy aloft associated with the next system that may impact the area next weekend. Tue through Fri...A closed upper level low over Ontario will slowly track ewd through the week due to a downstream omega block. A series of shortwaves and sfc fronts/troughs will move across the area during this time...bringing the chances for showers and tstms each day except Thu. Tue is expected to start out with fog and stratus with a light onshore flow. Some question on how thick and widespread the fog will be with the cloud cover...so have only included patchy fog in the morning for now. Soundings are indicating stratus or stratocu remains around for much of the day which makes high temps a challenge. Think there could be some breaks during the aftn...so leaned towards the higher temp guidance. A cold front approaching from the west will move across the area Tue night. There could be a few isold shra/tstms in western areas...especially late in the day. Chances for showers increase overnight as a weak wave of low pres develops along the boundary. Instability wanes with the loss of heating so have removed tstms after midnight. The next shortwave/weak cold front approaches on Wed and moves through Wed aftn/eve. Less available moisture...thus low chc pops with its passage. High pres builds to the S Thu with no discernible shortwaves moving around the low aloft. Thus...Thu/Thu night should be dry with mostly clear skies. As the low finally tracks through the Maritimes and nrn New England on Fri another cold front will move across the area. Sct aftn convection is a possibility...although instability appears weak attm. Front clears by Sat morning although this is where uncertainty aloft begins. Models currently agree that an approaching shortwave will impact the area Sat night into Sun...but they don`t agree on the details on timing on precip and strength of developing low over the Ohio Valley. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... A frontal system will approach late tonight into Monday, while weak surface high pressure remains in place and weak low pressure passes to the south this morning. With the surface high remaining in place and dry air still to be overcome especially NE of the NYC metro terminals, this will make for a very difficult forecast in terms of flight category. Rain over NJ and eastern PA has brought widespread IFR cigs to those areas, but do not think this will be the case in the NYC metro, with MVFR cigs developing after daybreak and remaining in that category at least through the morning. There is a chance that IFR cigs could develop late this afternoon or this evening as winds diminish and back a little more NE following passage of the weak low to the south. Removed earlier mention of thunder, as instability fueling storms over central PA should weaken and come to a halt just west of the area this morning. Worst case attm would be mention of VCTS at KEWR/KTEB/KSWF if any storms manage to make it a little farther east than expected. High confidence in winds through this morning, with G20KT at some coastal terminals, then lower confidence on direction this afternoon into this evening, which could range anywhere from NE to SE. .OUTLOOK FOR 06Z TUESDAY THROUGH FRIDAY... .Late Monday night...IFR in low clouds. KGON could remain MVFR. .Tuesday...IFR to start, improving to VFR by afternoon. Chance of afternoon/evening showers and possibly a tstm. IFR conditions possible at night. .Wednesday...Mainly VFR. Chance of afternoon/evening showers/tstms mainly NW of the NYC metro terminals. .Thursday...VFR. .Friday...Mainly VFR. Afternoon/evening showers/tstms possible. && .MARINE... Winds and seas increase during the late night hours of tonight in response to low pressure emerging off the Mid-Atlantic coast and passing to the south of the area waters. Have gone with a SCA on the ocean from midnight tonight through Monday afternoon. There could be a gust or two to 25 kt on the other waters late tonight into Monday night, but not worth expanding the SCA to these areas. Winds and seas then remain below advisory criteria Monday night as a high pressure ridge axis stretches in from the northeast. Sub-advsy conds continue through the remainder of the forecast period. If winds on Fri end up being a little stronger than forecast seas could build to 5 ft on the ocean waters. && .HYDROLOGY... No hydrologic impacts are expected with the rainfall late tonight into Monday. There is a slight chance of a thunderstorm during Monday morning/early afternoon, but only a low chance of minor urbanized flooding would occur with any thunderstorms. No significant widespread hydrologic impacts are then expected at this time from Monday night through at least Thursday night. && .TIDES/COASTAL FLOODING... Coastal Flood Advisories for Brooklyn, Queens, and Nassau as well as the Coastal flood Statements for SW Suffolk, and along the Kill Van Kull and Arthur Kill around Staten Island and adjacent portions of NJ have been cancelled as high tide for these areas has passed and water levels are now below minor coastal flooding levels. The Coastal Flood Statement remains in effect along the shores of Westchester/Fairfield western Long Island Sound as high tide continues through 3 am for these areas. Additional minor coastal flooding may occur with the high tide cycle Monday night...mainly for the southern bays of Nassau/NYC. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ350- 353-355. && $$ SYNOPSIS...JC/24 NEAR TERM...JP SHORT TERM...JC LONG TERM...24 AVIATION...Goodman MARINE...JC/24 HYDROLOGY...JC/24 TIDES/COASTAL FLOODING...

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