Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 301749 AFDOKX Area Forecast Discussion National Weather Service New York NY 1249 PM EST Wed Nov 30 2016 .SYNOPSIS... A frontal system will impact the region this afternoon into tonight. High pressure returns for Thursday. A series of weak cold troughs will pass through the region late week into the beginning of the weekend. High pressure briefly builds in Saturday Night into Sunday...then a low pressure system may impact the area Sunday night into Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Steady rain moves in, possibly heavy at times per meso model simulated reflectivity. This activity ahead of low level warm frontal boundary providing lift, and approaching upper level support. A rumble of thunder is possible later on within any heavier convection. Temperatures should remain nearly steady or rise a degree or two this afternoon. Highs well into the 50s, with near 60 in the New York metro area. These highs may be a degree or 2 too low if the warm front lifts north of the area earlier than is forecast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Influx of warm air and higher dewpoints will allow for isolated thunderstorms, especially if temperatures today are a bit warmer than forecast. MUCAPE of just under 1000 J/kg noted in the 06Z 12km NAM over and just south of Long Island, generally from 8 pm through 11 pm tonight. This coincides with strong lift in association with the front. With strong forcing/shear...weak instability...and good convergence along the cold front...will have to monitor for organized squall line development late today across Central/Eastern Pa and if so its eastward progression this evening. This potential is depicted by several high res models...with different levels of weakening as it races ahead of shortwave energy in a weakly unstable environment towards the coast this evening. If any organized convection can develop and maintain itself into the region...potential for isolated strong/severe wind gusts exists. Precipitable water values of greater than 1.50" expected move into the area at this time as well. Exact area of axis of heavy rain still somewhat uncertain, as the better forcing and a line of convection was noted in the 00Z NAM over inland areas. Current thinking is that areas inland (Lower Hudson Valley, Northeast New Jersey, and inland Connecticut) will see the higher rainfall amounts with enhancement in precipitation due to orography. Given drought conditions, widespread flooding still looks unlikely. However, given the recent heavy rains yesterday, some of the flashier streams in New Jersey may approach bankfull. Again, do not think this will be widespread, and issuances of Flood Advisories may cover these later today, with a low chance of seeing warnings issued for those areas. Main problem will be minor urban and poor drainage flooding. Rain tapers off late tonight, and dry conditions return for Thursday, with continued above normal temperatures. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Models in decent agreement with mean troughing over the region late week into the start of the weekend...as the deep closed low over the Upper Mississippi River Valley lifts ne into southern Ontario/Quebec through Friday. Generally dry conditions...seasonably cool...and a bit breezy conditions expected Thu Night thru Sat in persistent deep WNW flow. A couple of weak shortwaves/surface troughs moving through the region may trigger some isolated sprinkles (and or flurries across nw hills) Fri Aft through Sat. Generally tranquil and seasonable conditions heading into Sunday as upper flow flattens or becomes slight ridged...with high pressure building over the region. Thereafter...significant divergence in models handling of the late weekend/early next week eastward evolution of a deep Western US trough. The main difference is whether the base of the trough closing off into Northern Mexico this weekend...travels with the parent northern stream shortwave or gets left behind. The implication being...a phased eastward moving trough would bring potential for a southern low and significant precip tracking up the east coast for Sun Night into early next week. Meanwhile...the latter detached scenario would just bring another weak trough through the region with perhaps some light precip. Either scenario is in play...with SBU ensemble sensitivity pointing at interplay of western Pacific and northern Pacific shortwave energy over the next 48-60 hrs playing a key role in downstream evolution of this trough for the late week/weekend. Based on the complex interaction...may continue to see flip-flop of operation models and considerable spread in ensembles for this time frame for the next few days. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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A warm front moves through early this evening, followed by a cold front late tonight. Flight category forecast will vary widely among all area terminals. Conditions deteriorate through the afternoon with rain/showers and drizzle impacting all terminals with mostly IFR expected. Isolated thunder possible right ahead and along the cold front overnight after 04z. Light and variable winds become easterly near 10 kt shifting SE- SW behind warm front early this evening. Gusts 20-25 KT tonight. Stronger gusts possible in any thunderstorm overnight. Low level wind shear likely for JFK/LGA and points east starting this evening. 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: Deteriorating conditions to IFR likely. Wind gusts forecast may be off by 1 or 2 hours. KLGA TAF Comments: Deteriorating conditions to IFR likely. Wind gusts forecast may be off by 1 or 2 hours. KEWR TAF Comments: Deteriorating conditions to IFR likely. Wind gusts forecast may be off by 1 or 2 hours. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Wind gusts forecast may be off by 1 or 2 hours. KHPN TAF Comments: Tempo 1/2 SM vsbys might not occur. Deteriorating conditions to IFR likely. Wind gusts forecast may be off by 1 or 2 hours. KISP TAF Comments: Deteriorating conditions to IFR likely. Wind gusts forecast may be off by 1 or 2 hours. .OUTLOOK FOR 18Z THURSDAY THROUGH MONDAY... .Thursday...VFR. West gusts 20-25 KT. .Friday...VFR. West gusts around 20 KT. .Saturday...VFR. NW gusts 20-25 KT. .Sunday...VFR. .Monday...VFR...possibly lower depending on the track of low pressure to the south.
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&& .MARINE... Cancelled the marine dense fog advisory earlier based on latest observations. Will need to monitor fog later on with the approach of the warm front as high dew point air advects northward over the middle 50s water. East winds increase this afternoon, even across non ocean waters. Seas build as a result. A few gusts to 25 kt are possible across Long Island Sound late for a brief time. SCA conditions expected over the ocean waters through Thursday with winds and seas remaining above SCA criteria as a frontal system impacts the area today and high pressure builds in on Thursday. SCA conditions for sea and wind gusts likely on the ocean waters midweek through Saturday in a tight gradient between Canadian Maritimes low and Central/Southern US high. On the nearshore waters, marginal sca gusts possible during this period...particularly on LI sound with ideal wsw fetch. With high pressure modeled to build towards the area Sat NIght into Sun...a return to sub-sca conditions would be expected. && .HYDROLOGY... Another 0.75-1.5 inches of QPF expected this afternoon into tonight, with localized 2+ inch swaths with any training heavy showers/convection. The main threat is urban and poor drainage flooding, with a low prob of flash flash flooding with any training convection. In addition, quick responding streams, such as the Rahway at Springfield and the Hohokus Brook, could approach or just barely exceed bank full. The overall flood potential is not widespread enough to warrant a flood watch. No significant precipitation expected Midweek through Sunday. Potential for significant precip returns Sunday night into Monday...but low predictability at this point. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ350-353- 355. && $$ SYNOPSIS...JP/NV NEAR TERM...JP/PW SHORT TERM...JP LONG TERM...NV AVIATION...IRD MARINE...JP/NV/PW HYDROLOGY...JP/NV

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