Area Forecast Discussion
Issued by NWS Upton, NY

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586 FXUS61 KOKX 252143 AFDOKX Area Forecast Discussion National Weather Service New York NY 543 PM EDT Tue Oct 25 2016 .SYNOPSIS... High pressure slowly builds in from eastern Canada through Wednesday then moves east Wednesday night. High pressure then builds in to the southwest from Friday and Friday night. A frontal boundary then stalls nearby from Saturday into Monday, with waves of low pressure riding along it. High pressure then builds across the region through Tuesday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Upper trough lifts out of the northeast/eastern Canada this evening with building heights. At the surface, polar high pressure builds southeast from eastern Canada with gusty NW winds gradually diminishing . The coldest airmass thus far this fall will filter into the region with the interior dropping to around freezing, and coastal locations into the mid and upper 30s. The Pine Barrens region of Eastern LI will likely see some below freezing temperatures as well. This readings are nearly 10 degrees below normal. A freeze warning remains up across the interior. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... High pressure builds in briefly both aloft and at the surface with another day of gusty NW winds to start. Gusts will mainly be confined to the first half of the day and only up to 20 mph. Conditions will remain unseasonably cold with readings struggling to get to 50. Stayed just below MET/MAV MOS based on upstream readings. Models have trended slower with the southern branch Pacific storm system approaching from the Great Lakes Wednesday night. Clear skies and diminishing winds will allow for strong radiational cooling with many locations inland dropping to below freezing. Should a freeze not occur Wednesday morning to end the growing season, another freeze warning will likely be needed for portions of the forecast area. Mid and high level clouds increase overnight with gradually rising temperatures. Any precipitation is forecast to be just west of the Lower Hudson Valley/NE NJ by daybreak Thursday. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Northern stream ridging exits to the east on Thursday as a northern stream closed low moves across the eastern Great Lakes. How fast precipitation develops on Thursday will in large part be determined by how quickly the Northern Stream ridging exits and exactly how dry the low levels are Thursday morning. The ECMWF remains the most aggressive in bringing in precipitation. Looking at isentropic lift and saturation on the I-285 to I 300 surfaces on the ECMWF note flow is almost parallel to pressure contours over the CWA at 12z Thursday - so appears ECMWF is likely to fast in bringing in precipitation (it had this bias last winter also). As a result, limit slight chance pops at 12z Thursday to basically the NW 1/2 of Orange County - then gradually increase pops to categorical throughout by 21z Thursday. The question is how fast do the low levels warm N/W of NYC before the precipitation begins. High resolution models like the NAM typically handle low level cold air better than the GFS or ensembles, so weighed temperature forecast towards NAM 2-meter temperature and wet-bulb temperature once precipitation is forecast to have started. For now, it appears that if there is any precipitation over the Lower Hudson Valley and northern portions of NE NJ Thursday morning, a wintry mix of snow/sleet/rain/freezing rain is possible depending on elevation and timing. If confidence in occurrence of freezing rain occurs, would need to consider a winter weather and/or freezing rain advisory over at least portions of the Lower Hudson Valley for early Thursday morning. Any snow/sleet accumulation will be less than 1 inch, if any at all. Regardless all areas should be to plain rain by early Thursday afternoon, if not sooner. Isentropic lift increases significantly by afternoon, so have gone with moderate rain in the grids, though would not be surprised if locally heavy. The closed northern stream low tracks to the N Thursday night with its associated secondary surface low tracking near Long Island late Thursday night then to around Cape Cod by 12z Friday. Based on this have categorical pops for moderate rain Thursday evening, tapering off from w to e, with dry conditions expected over all but far NE New London county by 12z Friday. Showalter indices fall to the 0 to 1C range from around 2-8z from W to E so have a slight chance of thunder in the forecast as well Thursday night. Refer to the Hydrology section of the AFD for details on rainfall amounts and any potential impacts. Highs on Thursday were based on a blend of ECS/MET/MAV guidance, NAM 2-meter temperatures and a mix down from 950-875 hPa per BUFKIT soundings. Wet-bulbing will serve as the limiting factor on high temperatures - with Higher elevations well N/W of NYC struggling to reach the lower-mid 40s and the remainder of the area mainly in the upper 40s to lower 50s. Note if the developing secondary low tracks farther S than currently forecast and the low level flow remains more northerly - then highs might need to be undercut by 5-10 degrees depending on exact track of low and elevation. Lows Thursday night were based on a blend of MAV/MET/ECS guidance and NAM 2-meter temperatures and should run around normal in the immediate NYC metro and around 5 degrees above normal elsewhere. A relatively flat deep layered ridge builds in Friday- Saturday night, then slides to the east Sunday. Associated subsidence should keep things dry Friday-Friday night. A backdoor cold front pushes down from the north Saturday, and stalls out near by, but likely to the north through Sunday. Depending on exactly where the front stalls there could be a period of rain over the weekend. For now have kept pops to slight chance to low end chance - but this does not mean it will rain for all of/most of the weekend. On the whole there is a better chance for the weekend to remain dry than be wet, especially over NYC/Long Island/southern portions of NE NJ. A northern stream trough passes to the N Sunday night - with some question as to how far N it goes. The GFS keeps things dry while the ECMWF/CMC bring some rain to the region kept chance to slight chance pops in for Sunday night as result. With the GFS and ECMWF both showing deep layered ridging building in Monday/Monday night and sliding offshore Tuesday - went with a dry forecast at this time. For temperatures Friday-Tuesday: A blend of MAV/MET guidance, NAM 2-meter temperatures and a mix down from 875 hPa was used for highs on Friday, with values forecast to be around 5-10 degrees below normal. Lows Friday night were based on a blend of MEX/MEN/ECE/ECM/EKD/WPC guidance and should be near normal. The Superblend was used for temperatures Saturday-Tuesday, with near normal temperatures on Saturday then above normal temperatures Sunday, below normal temperatures Monday, and above normal temperatures on Tuesday. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/...
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High pressure slowly builds into the region through Wednesday. VFR through the TAF period. Winds around 310 true veer slightly towards 330 true overnight and Wednesday. Some gusts will likely linger through 00z, especially near the coasts, due to strong flow aloft. The magnitude of the winds will be decreased on Wednesday. ...NY Metro Enhanced Aviation Weather Support... Detailed information...including hourly TAF wind component fcsts can be found at: http:/ KJFK TAF Comments: Gusts may end or become more occasional an hour or 2 before 05Z. KLGA TAF Comments: Gusts may end or become more occasional an hour or 2 before 05Z. KEWR TAF Comments: Some variability in wind direction between 300 and 330 true is possible through 00Z. Gusts may end or become more occasional an hour or 2 before 06Z. KTEB TAF Comments: Gust frequency may decrease to occasional through 22Z. KHPN TAF Comments: Gust frequency may decrease to occasional through 22Z. KISP TAF Comments: Gusts may end or become more occasional an hour or 2 before 01Z. .OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY... .Rest of Wednesday...VFR with decreasing northwesterly winds. .Thursday...MVFR or lower possible in rain. Potential for a wintry mix across the interior before 15Z. Southerly winds. .Friday...VFR with strong northwest flow behind a cold front. Gusts to at least 25 kt are expected at this time. .Saturday and Sunday...VFR with southwest flow possible.
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&& .MARINE... SCA conditions will linger on the ocean waters through tonight and into early this evening for the remaining waters. Gusty NW winds are attributed to a tight pressure gradient between weakening low pressure over the Canadian Maritimes and high pressure building southeast from east central Canada. For Wednesday into Wednesday night, high pressure builds into the waters with sub-SCA conditions. Small Craft Advisory Conditions are likely on the coastal ocean waters and possible on the non-ocean waters from Thursday into Friday night. The pressure gradient relaxes sufficiently by the weekend to limit winds to 15 kt or less on Saturday and to 10 kt or less on Sunday. && .HYDROLOGY... Dry weather remains forecast through Wednesday night. From around 0.75 to 1.25 inches of rain is forecast Thursday and Thursday night, with locally higher amounts possible. The ponding of water in typical poor drainage areas cannot be ruled out as a result. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Freeze Warning from 2 AM to 9 AM EDT Wednesday for CTZ005>008. NY...Freeze Warning from 2 AM to 9 AM EDT Wednesday for NYZ068>070. NJ...Freeze Warning from 2 AM to 9 AM EDT Wednesday for NJZ002-004- 103-105-107. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ330- 335-338-340-345. Small Craft Advisory until 6 AM EDT Wednesday for ANZ350-353- 355. && $$ SYNOPSIS...Maloit/DW NEAR TERM...DW SHORT TERM...DW LONG TERM...Maloit AVIATION...JP MARINE...Maloit/DW HYDROLOGY...Maloit/DW is the U.S. government's official web portal to all federal, state and local government web resources and services.