Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 151341 AFDOKX Area Forecast Discussion National Weather Service New York NY 941 AM EDT Thu Mar 15 2018 .SYNOPSIS... A few surface troughs moves across the area through Friday as low pressure spins over the Canadian Maritimes and high pressure builds to the west. A cold front moves through the region late Saturday, followed by high pressure building down from southern Canada Sunday into early next week. A complex low pressure system then affects the region Monday Night into Wednesday Night. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Clouds will begin to decrease this morning as the region becomes situated within negative vorticity advection. This will be short-lived as another 500 mb shortwave dives south and eastward within anomalous upper trough this afternoon. Clouds will increase from west to east as the shortwave approaches this afternoon into the early evening, especially across the western half of the area. There may be just enough lift and moisture for isolated-scattered rain or snow showers this afternoon as the vort energy associated with the shortwave nears our western zones. Gusty westerly winds will continue today with temperatures a few degrees warmer than Wednesday in the lower 40s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Shortwave axis moves offshore tonight with any lingering rain or snow showers diminishing with loss of daytime heating. A reinforcing shot of cold and dry air advects southward with deep northwest flow on the backside of the upper trough. The positioning of the upper trough does not appear to change too much through Friday with only a slight shift eastwards towards the North Atlantic. Much drier air will be in place on Friday with dew points falling into the teens. Despite this dry low level air, weak shortwaves embedded within the northwest flow should be enough to develop a scattered to broken deck of clouds in the afternoon. Do not anticipate any precipitation with such low dew points at the surface and no appreciable lift. Highs on Friday will be around ten degrees below normal in the upper 30s to lower 40s. Strong pressure gradient between building high pressure to our west and low pressure across the Canadian Maritimes supports gusty NW winds 25 to 30 mph in the afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Models in general agreement with the large scale CONUS omega blocking pattern mid week, gradually breaking down heading into the weekend. The stubborn SE Canadian upper low of this week will gradually weaken and lift towards Greenland this weekend, replaced by a quick moving but intense polar low. Meanwhile a closed upper low currently over the PAC gradually gets caught up in the southern stream and rolls its way across the country this weekend. This energy will eventually facilitate phasing between the northern and southern stream into the Eastern US early to mid next week. There is good model agreement in resultant deep Eastern US troughing development by mid week, but quite a bit of model spread in the timing, intensity and track of the closed upper low anchoring this trough. SBU CSTAR ensemble sensitivity analysis is keying in on the evolution of the NW US closed upper low, but more so the downstream effects of a strong closed, cutoff low developing south of the Aleutians and dominating the eastern PAC this weekend. It appears that shortwave energy (wavepacket) emanating from this Aleutian/E Pac low is the forcing for N/S stream phasing and development of a coastal low during the Mon Night into Wed Night time frame. Significant model spread in this time period is lending to a low confidence forecast on the timing, track and intensity of coastal low pressure/s Monday night into Wednesday Night. The signal has been consistent for a period or periods of precip with a complex low pressure system during Mon Night into Wed Night, but details on precip type and amounts, strength and duration of winds, and other sensible hazards is low at this time. Monitor subsequent forecasts through the weekend as the energies and interactions above become better resolved by NWP. Before then a relatively tranquil, fair and below seasonable temp pattern for the region Friday Night into Monday in between streams of a split upper flow. A strong polar low swings through Northern England this weekend, sending a polar front through the region late Saturday. Meanwhile, appears shortwave energy that pivots around the base of the Western US closed low today, will remain riding along the southern stream. This will have a quick moving southern low tracking well south of the region this weekend. Will have to watch for any interaction between these streams to ride this low further north, but unlikely at this point. Primary uncertainty during this time period is magnitude of polar air that sinks south into the region Saturday Night into Sunday, as there is model spread on this. Temps could be a few degrees cooler than forecast if the polar low sinks a bit further south. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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Strong low pressure continues to churn in the Canadian Maritimes. A trough will swing across the region this evening. Gusty westerly flow will then continue through much of today, with gusts near 20kt. Winds do go just south of west into today, especially for KEWR and KTEB. Gusts and winds then subside into the early evening with approaching trough / disturbance. Another round of scattered rain/snow showers swings through for very late in the day for the NYC terminals. Winds may gust behind these showers towards 03-05z Friday, then winds will increase overall into Friday morning with tightening pressure gradient on WNW flow. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Timing of gusts subsiding late in afternoon may be off by 1-2 hours. 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 subsiding late in afternoon may be off by 1-2 hours. 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 subsiding late in afternoon may be off by 1-2 hours. 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 subsiding late in afternoon may be off by 1-2 hours. KHPN TAF Comments: Timing of gusts subsiding late in afternoon may be off by 1-2 hours. KISP TAF Comments: Timing of gusts subsiding late in afternoon and evening may be off by 1-2 hours. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... .Fri...VFR with NW gusts 25-30KT. .Sat...VFR with NW gusts around 20-25KT early. .Sun...VFR. .Mon...VFR becoming MVFR or lower in snow / wintry mix overnight.
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&& .MARINE... Gales continue on all waters this morning. Winds are beginning to weaken on LI Sound and Bays and the NY Harbor, but have elected to keep the gale warning in place through 15z as boundary layer winds still support gales. Waves on LI sound this morning have been running 5 to 6 ft in a strong westerly flow. These waves will gradually subside through the afternoon as winds weaken somewhat. Small craft advisory winds are then expected on all waters through this evening. Winds will likely weaken below SCA levels tonight on LI Sound, LI Bays, and NY Harbor. With a strong pressure gradient in place, SCA gusts are likely on Friday. A few gale gusts are possible on the ocean waters on Friday, but it appears marginal at this time. Ocean seas will remain elevated above 5 ft through Friday. SCA conditions likely on all waters Friday Night into Saturday with cyclonic flow around Canadian maritimes low pressure and high building to the SW of the region. Although not seen in the model wind fields, there is potential for this to continue into Saturday Night behind a polar front with shot of caa. Winds then weaken Sunday into early next week as high pressure builds into the waters. && .HYDROLOGY... No significant hydrologic impacts are anticipated through Monday. There is the potential for a period or periods of moderate to heavy precipitation from late Monday night into Wednesday Night. At this time, predictability on any hydrologic impacts is low. && .TIDES/COASTAL FLOODING... There is the potential for a prolonged period of E-NE flow from Monday Night into Wednesday Night. Tidal departures of generally only 1 to 1 1/2 ft are needed for minor flooding for many locations during this time, and 2 to 3 ft for moderate. Depending on the exact track/strength of a coastal low or lows during this time frame, there is the potential for at least minor coastal impacts, but predictability on any details is low at timeframe. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Gale Warning until 11 AM EDT this morning for ANZ330-335-338- 340-345-350-353-355. && $$ SYNOPSIS...DS/NV NEAR TERM...DS SHORT TERM...DS LONG TERM...NV AVIATION...BC/JE MARINE...DS/NV HYDROLOGY...DS/NV TIDES/COASTAL FLOODING... EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.