Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 071418 AFDOKX Area Forecast Discussion National Weather Service New York NY 918 AM EST Thu Dec 7 2017 .SYNOPSIS... High pressure builds through Friday. A series of weak low pressure waves pass south and east of the area Friday night into Saturday night. A cold front will then cross the region Sunday followed by another cold front and potential low pressure Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Forecast on track with just a few minor adjustments to reflect latest observations. Deep longwave trough extends from Canada all the way down to the southwest and southern plains states. Strong h2-3 HPA jet remains in place through today oriented SW to NE. At the surface, ridging builds in from the west, with a persistent westerly flow prevailing. Cooler, more seasonable air expected today, as temperatures peak in the middle to upper 40s, close to seasonal norms. Used a blend of the MAV/MET and earlier cool EC guidance. West winds may be gusty at times, especially this afternoon around 20 mph. Cirrus shield pushing east, with plenty of sunshine expected through much of the day. Additional cirrus moves in late, and this cirrus may be here for awhile.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Deep longwave trough makes eastward progress as strong upper jet remains oriented SW to NE over the area. Weak shortwave passes to the north early tonight, with additional CAA behind a sfc trough. As the main upper trough axis moves eastward, waves of low pressure develop and ride along a stalled cold front off the southeast coast by Friday. Heights lower with the closer approach to the trough through this period. Expect thickening cirrus tonight and Friday, warranting an increase in clouds, and mainly filtered sunshine Friday, if any sun is seen at all. At this time, it looks like any stratiform precip remains to our south through the day Friday as atmosphere remains rather dry in the lower and mid levels. Minimal pops maintained late in the day for southeast LI Friday. Temps remain seasonably cool tonight and Friday. Lows tonight look to range from the lower 20s inland to the lower 30s in NYC. Not too confident in amount of radiational cooling, which could be late at night since winds continue behind the sfc trough. On Friday, readings from the upper 30s to middle 40s expected, a bit cooler thanks to CAA and filtered sunshine. A mos blend followed, MET/MAV and EC guidance. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... An unsettled weather pattern will be the main story in the long term with an amplified upper level flow. Deep ridging will persist along the west coast which leads to mean upper troughing across the east. The first focus will be with several waves on a frontal boundary/baroclinic zone progged to be located offshore Friday night through Saturday night. There will also be two shortwaves within the mean troughing that have to be watched. One shortwave will be rounding the base of the trough along the Gulf Coast and Southeast into Saturday. A more potent shortwave will dive southward from the Great Lakes to the Tennessee and Ohio Valleys. The shortwave across the Gulf/Southeast is modeled to be elongated which is likely causing several waves to form on the offshore front. Once the second shortwave nears late Saturday, a more consolidated low pressure is progged to form east of the 40N/70W benchmark. These two shortwaves do not phase in time to get a significant impact from this low pressure. However, we will have to watch how much lift occurs from upper jet dynamics. The models in the past have shown a tendency to miss the impact of upper jet dynamics, well away from the low pressure. The models are indicating max winds in the jet close to 200 kt at 250 mb across northern New England. This could help push precip a bit further north and west, especially if the flow is more amplified than it is currently modeled. The 00z models have trended a bit east from previous cycles with their QPF fields and location of the developing low. In fact, the 00z CMC has gone away from its earlier solution and is now further east than the GFS, ECMWF and UKMET. Many GEFS members are almost completely dry during this time period as well, but there are a few that bring enough QPF for a light snowfall. Shifts in the models are likely to continue for the next several cycles, so have followed a consensus blend. Our new PoP forecast has tightened the gradient on the western edge and have kept high chance PoPs across eastern Long Island and southeast Connecticut, where there continues to be potential for a light accumulating snowfall. As mentioned above, it will not take much for a trend on the higher side and potentially further north and west. At the same time, trends further east with less amplification would mean little to no precipitation/snowfall. We should have a better idea of the likely outcome as better sampling of the upper level features occurs in the next day or so. The low quickly lifts to the north and east later Saturday night into Sunday as the upper trough axis slides across the region. High pressure briefly follows for Monday before the next amplification of the mean upper trough occurs Tuesday into Wednesday. The models continue to indicate low pressure development over or just offshore late Tuesday into Tuesday night. It is still too early at this time to get specific with precip type and amounts, but it does appear that there is another chance at snow with this system. Temps remain colder than normal throughout the long term, with highs struggling to reach 40 degrees this weekend. Temps may reach the lower and middle 40s early next week before potentially dropping into the 30s for highs on Wednesday. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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High pressure will be centered to our SW through tonight. A wave of low pressure will be passing along a stalled front well offshore on Friday. VFR conditions are expected. W winds increase to 10-15 kt with gusts 20 to 25 kt developing through this afternoon. Wind gusts gradually subside tonight, first for terminals outside of NYC. Westerly flow 5-10 kts is expected for Friday. 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: Timing of gusts start/end could vary 1-2 hours from TAF. Gusts could peak a few kts higher than gusts in TAF late this afternoon and early this evening. The afternoon KJFK haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KLGA TAF Comments: Timing of gusts start/end could vary 1-2 hours from TAF. Gusts could peak a few kts higher than gusts in TAF late this afternoon and early this evening. The afternoon KLGA haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KEWR TAF Comments: Timing of gusts start/end could vary 1-2 hours from TAF. Gusts could peak a few kts higher than gusts in TAF late this afternoon and early this evening. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Timing of gusts start/end could vary 1-2 hours from TAF. Gusts could peak a few kts higher than gusts in TAF late this afternoon and early this evening. KHPN TAF Comments: Timing of gusts start/end could vary 1-2 hours from TAF. Gusts could peak a few kts higher than gusts in TAF late this afternoon and early this evening. KISP TAF Comments: Timing of gusts start/end could vary 1-2 hours from TAF. Gusts could peak a few kts higher than gusts in TAF late this afternoon and early this evening. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... .FRI-SAT...Possible RASN and MVFR mainly for terminals east of NYC Fri afternoon into Fri night, higher chances for SN Sat into Sat night for all terminals with MVFR/IFR possible. .SUN...Mainly VFR, iso MVFR/-shsn east of city terminals during the day. NW gusts 20-25 kt during the day. .MON...VFR.
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&& .MARINE... Gusty winds early this morning should diminish somewhat briefly. However, a strengthening low level jet will result in an increase in westerly winds this afternoon and into tonight. In fact, a few gusts up to gale force is possible briefly early tonight. The winds then diminish late tonight and into Friday as the pressure gradient relaxes. As such, will extend SCA through tonight, and add western LI sound, NY Harbor and the south shore bays of LI mid afternoon through this evening. Seas build today and tonight before subsiding Friday. A weak pressure gradient will remain over the waters Friday night into Saturday as several frontal waves pass offshore. High pressure begins to build to the west Saturday night into Sunday, strengthening the pressure gradient over the waters. This should bring winds to SCA levels on all waters on Sunday, with SCA gusts possible on the ocean Sunday night into Monday as a cold front passes. Ocean seas will also build over 5 ft, and remain there Sunday morning through Monday night. && .HYDROLOGY... No hydrologic problems are expected through early next week. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. See our headline news on the web at: http:/weather.gov/nyc && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 2 PM this afternoon to 1 AM EST Friday for ANZ335-338-345. Small Craft Advisory until 6 AM EST Friday for ANZ330-340-350- 353-355. && $$ SYNOPSIS...DS/PW NEAR TERM...PW SHORT TERM...PW LONG TERM...DS AVIATION...JM/NV MARINE...DS/PW HYDROLOGY...DS/PW EQUIPMENT...

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