Area Forecast Discussion
Issued by NWS Upton, NY

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446 FXUS61 KOKX 281427 AFDOKX Area Forecast Discussion National Weather Service New York NY 927 AM EST Tue Feb 28 2017 .SYNOPSIS... A warm front approaches from the south today, then lifts to the north tonight, followed by a strong cold front which approaches the area Wednesday, then crosses the Tri-State Wednesday night. Strengthening low pressure in the Canadian Maritimes Thursday will be followed by an Alberta Clipper moving across the local region Friday. The clipper system moves quickly offshore Friday night with high pressure approaching from the west. This traverses the region Saturday night and then off the southeastern U.S. Sunday. Meanwhile for Sunday and into early next week, low pressure will approach the region from southeastern Canada. && .NEAR TERM /THROUGH TONIGHT/...
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Updated mainly for the cloud cover across Connecticut and Long Island this morning in association of a short wave moving through south of the area. This was producing showers and isolated thunderstorms over the ocean waters. Weak ridging aloft slides across the area today behind the shortwave, another weak shortwave moves through the weak ridge this afternoon. This along with very weak lift will result in a slight chance of light rain. A passing 700-500 hPa shortwave tonight coupled with persistent moist SW flow aloft and a surface warm front lifting to the N in response to a 60 kt 950 hPa jet passing just S of Long Island overnight - should produce a more widespread rainfall tonight, becoming more spotty after midnight as the low level jet exits to the east. In addition have the potential for areas of fog tonight, possibly becoming dense in areas after midnight.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... The GFS remains a fast outlier with the 700-500 hPa northern stream trough and associated sfc-850 hPa cold front Wednesday/Wednesday night, so a non-GFS blend was generally followed during this time frame. Appears there could be a lull in the precipitation Wednesday morning, then pops increase to likely to categorical across western zones in response to a pre-frontal trough acting on moist low level flow. With Showalter Indices below zero for most if not all the day, have chance of thunder west and slight chance thunder east (higher chance of thunder west due to more surface instability). Still looking at around 500-1000 J/KG of CAPE progged across NYC/NE NJ/Lower Hudson Valley/SW CT and 60-70 kt of Bulk Shear. Flow is fairly unidirectional - so would expect convective line segments to be main mode. With a 70 kt 950 hPa Jet forecast to track S of Long Island enhancing forcing, have the potential for Strong to Severe Thunderstorms where surface based - basically from New Haven County/NYC on west. SPC has most of NE NJ and Western Portions of the Lower Hudson Valley + Staten Island in a Slight Risk of Severe Thunderstorms with areas to the east in a marginal risk. If there is any severe weather, the threat will be primarily from damaging wind gusts where the storms are surface based. The timing for any severe threat would be late afternoon and early evening - right now, due to uncertainty only have gusty winds with thunder in the forecast from New Haven County/NYC on east during this time frame. Wednesday should be very warm, with potential for record highs with warm surge ahead of cold front. Depending on how fast things cool off behind cold front, there could be some maximum minimums set for the day as well (temperature at 1159pm might be low for the day - especially out west). See the climate section of the AFD for details. && .LONG TERM /THURSDAY THROUGH MONDAY/... The upper level jet will be situated south of the region Thursday through Saturday along with there being a deep upper level trough within the Northeast. The trough will begin to lift Saturday night with ridging thereafter going into Monday. The upper level jet will not be as strong and will be moving across the region and eventually north of it early next week. A much colder airmass will be on the way Thursday eventually entering the region Thursday night and prevailing through Saturday night. Colder than normal temperatures can be expected with cold air advection from a gusty NW flow Thursday into Thursday evening. An Alberta Clipper will be arriving Friday, providing a chance of snow across the region with a conspicuous wet bulb cooling scenario. Despite the highs being in the upper 30s to near 40 for locations towards the coast, the falling snow aloft will cool the column down to below freezing after a short time. Forecast POPs could go up with subsequent forecasts as most GEFS members were showing precipitation across the region on Friday. The liquid equivalent amounts were mostly less than a quarter of an inch and with temperatures being above freezing initially, not much in accumulation is expected at this time, keeping snow generally less than two inches. Conditions dry out Friday night into Saturday with another blast of cold air delivered on another round of gusty NW flow with an area of high pressure building to the west of the region. The flow aloft becomes more progressive with ridging aloft and the airmass will moderate Sunday into Monday. The winds decrease Saturday night along with continued dry conditions as the ridge of high pressure moves across. The high moves off the Southeast coast Sunday and further shifts south Monday. Temperatures will return to being above normal. Concerning precipitation Sunday into Monday, a low pressure area approaching from the north and west will bring mainly rain, although north of NYC there could be some snow as well depending on the timing of the precipitation. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... VFR conditions early this morning as high pressure builds farther offshore and a warm front approaches from the SW. Have updated TAFS to reflect prevailing VFR conditions for the late morning and afternoon. Some periodic MVFR conditions cannot be ruled out by the early afternoon, but confidence was not high enough to put in TAFS. Winds start off light and gradually pick up through the day, but generally less than 10KT. A strong SW low-level jet approaches late Tuesday night with low-level wind shear likely at the coastal terminals with 40-50KT winds at 2000 ft. The greatest uncertainty is with how quickly cigs lower, eventually to widespread IFR/LIFR Tuesday evening. Timing could change and will continue to monitor latest trends. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Timing of IFR conditions low confidence and may be off by up 2 hrs. KLGA TAF Comments: Timing of IFR conditions low confidence and may be off by 2 hrs. Winds may shift to SE +/- 1 hour of forecast. KEWR TAF Comments: Timing of IFR conditions low confidence and may be off by 2 hrs. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Timing of IFR conditions low confidence and may be off by 2 hrs. KHPN TAF Comments: Timing of IFR conditions low confidence and may be off by 2 hrs. Winds may shift to SE +/- 1 hour of forecast. KISP TAF Comments: Timing of IFR conditions low confidence and may be off by 2 hrs. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... Wednesday morning...Areas of fog, then rain. MVFR/IFR and possibly lower. LLWS possible with SW winds 45-55 kt at 2kft early. SW winds G15-20KT possible Wednesday morning. .Wednesday afternoon-Wednesday night...Showers and a chance of thunderstorms. MVFR or lower possible. SW winds G20-30KT. Winds become westerly late Wednesday night. .Thursday...VFR. W-NW winds G25-35KT. .Friday...MVFR/IFR possible with a chance of light snow. NW winds G20-25KT. .Saturday...VFR. NW G20-25KT. && .MARINE...
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A shortwave passing over the ocean waters this morning was producing showers and isolated thunderstorms. Updated the probabilities and weather for this. Otherwise the wind and the seas forecast remains on track. A weak pressure gradient force will keep winds well under small craft advisory levels through this afternoon. Areas of fog, quite possibly dense, likely will form on the waters tonight. Winds increase late tonight as the pressure gradient tightens, building seas to SCA levels on southern portions of the coastal ocean waters. Winds Wednesday/Wednesday night are a bit tricky. While soundings show limited if any potential for strong winds (60-70kt) at around 2000 ft to mix down, there is some potential that sustained winds over the coastal ocean waters could reach gale levels. For now it appears the most likely outcome is Small Craft Conditions on all waters, with a small (less than 50 percent) chance of gales. As a result, have an issued an SCA for the coastal ocean waters from 3am tonight-6am Thursday and for the remainder of the coastal ocean waters from 6am Wednesday-6am Thursday. The ocean seas will stay at minimal SCA levels for much of the long term period from Thursday through Saturday. The highest of the ocean seas will be Thursday from leftover swell, with forecast ocean seas of 8 to 11 ft. Also on Thursday, Central and Eastern Long Island Sound will build seas to 5 ft from a more gusty westerly fetch developing. Gales will be possible for all waters, but more probable for the ocean Thursday. Those winds will decrease Thursday night initially to SCA levels for the ocean and then below that by overnight Thursday night. Non-ocean waters will have sub SCA winds Thursday night. Another round of gales possible for the ocean Friday through Saturday with SCA winds for non-ocean waters. Winds then subside below SCA levels Saturday night.
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&& .HYDROLOGY... Rainfall from this afternoon through Wednesday night should run from 1/2 to 3/4 of inch, with locally higher amounts possible. While the possibility is low, stronger convection could cause isolated minor flooding of poor drainage/urban areas. No hydrologic impacts expected from any precipitation late this week through Monday. Release from spring snow melt is occurring down the Connecticut and Housatonic Rivers. && .CLIMATE... Record highs for Wednesday March 1 Location.......Record High/Year Set.....Forecast High Newark..................75/1972...............73 Bridgeport..............59/1972...............63 Central Park............73/1972...............71 LaGuardia...............68/1972...............70 J F Kennedy.............58/2004*..............66 Islip...................60/2004...............64 * = and in previous years Record high minimum temperatures for Wednesday March 1 Location....Record High Min/Year Set.....Lowest Temperature during 24 hour day Newark..................43/1976...............54 Bridgeport..............41/1976...............49 Central Park............45/2004...............54 LaGuardia...............44/2004...............55 J F Kennedy.............42/1974*..............51 Islip...................39/2016...............50 * = and in previous years && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 6 AM Wednesday to 6 AM EST Thursday for ANZ330-335-338-340-345. Small Craft Advisory from 3 AM Wednesday to 6 AM EST Thursday for ANZ350-353-355. && $$ SYNOPSIS...Maloit/JM NEAR TERM...Maloit/MET SHORT TERM...Maloit LONG TERM...JM AVIATION...JE/DW MARINE...Maloit/JM/MET HYDROLOGY...Maloit/JM CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.