Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 010053 AFDOKX Area Forecast Discussion National Weather Service New York NY 753 PM EST Wed Nov 30 2016 .SYNOPSIS...
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A frontal system will move across the area tonight, followed by high pressure on Thursday. A series of weak troughs will pass through from Friday into Saturday. High pressure will briefly build in from Saturday night into Sunday. Then a low pressure system may impact the area Sunday night into Monday.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Warm front was just entering the coastal waters south of Long Island as of 00Z, and with the aid of a strong southerly LLJ and the associated developing surface low moving across northern PA/central NY later tonight, the front should lift through a good portion of the area, with temps rising into the lower 60s throughout mainly after midnight, possibly mid 60s in NE NJ. Heavier showers in advance of the warm front attm across SE PA, north central NJ, and south of Long Island should move across this evening, then precip should taper off to spotty light rain or drizzle before the cold front sweeps through late tonight, accompanied by a narrow line of low-topped convection that is currently located over western PA. Cannot rule out a stray rumble of thunder this evening via elevated instability head of the warm front. As the cold front moves through later tonight, the narrow convective line should move through. Its instability while weak will likely be sfc- rooted, so stronger cells could produce strong wind gusts via downward momentum transfer of SW H7-9 winds between 40-50 kt. There could be a period of locally dense fog just before warm fropa later tonight, possibly persisting right along the coast thereafter until cold fropa as very moist air with sfc dewpoints near 60 moves northward across colder ocean waters with SST in the mid 50s.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
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Dry weather returns this time frame as upper low remains well to the north, and two surface lows will be located well to the north as well. Secondary low, that initially moves nearby as triple point low near the coast intensifies as it tracks toward the Canadian Maritimes. Fairly tight pressure gradient remains in place behind this system as high pressure builds well to the west. CAA is noted, but downslope flow and a lag in the cold air allows for above normal readings during the day per MOS and model blend. Winds persist Thursday night, which should preclude radiational cooling from occurring.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Forecast models in good agreement to end the week and start the weekend, with troughing over the region as a closed low north of the region lifts into southern Ontario/Quebec. Expect generally dry...cool...and breezy conditions Friday 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 nw of NYC) Fri afternoon through Sat. Conditions remain generally quiet with seasonable conditions heading into Sunday as high pressure builds over the region. There are significant differences in models Sunday night and Monday with the 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. 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. As a result, this portion of the forecast will remain unchanged and with low chance POPs in the forecast. Dry weather is expected on Tuesday, with another low chance for rain on Wednesday as another weak low approaches. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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A warm front moves through late this evening, followed by a cold front overnight. Mainly IFR conditions are occurring with some local variations from that category down to LIFR and up to VFR. The IFR and lower conditions should prevail though with intermittent rain and fog. There will be some potential for showers and isolated thunderstorms ahead of the cold front going into the overnight period. Uncertainty though with timing and location of any thunderstorms. Eventually, conditions improve to VFR by Thursday morning and continue at VFR through the rest of the TAF period. Winds will still be mainly E-ESE this evening ahead of the warm front, and then shift after the frontal passage to S-SW late this evening. With that, gusts will become more frequent as well with winds overall increasing slightly. Winds further increase after a cold frontal passage, with winds shifting to a west wind. Wind gusts continue through much of the TAF period, mainly near 20-25 kt. Low level wind shear generally between 03Z and 08Z will make for occasionally higher gusts than forecast. Winds at 2kft will be near 50kt out of the SW for the low level wind shear. 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 categorical changes could be 2-3 hours off from forecast. Wind shifts may also vary 1-2 hours from forecast. KLGA TAF Comments: Timing of categorical changes could be 2-3 hours off from forecast. Wind shifts may also vary 1-2 hours from forecast. KEWR TAF Comments: Timing of categorical changes could be 2-3 hours off from forecast. Wind shifts may also vary 1-2 hours from forecast. KTEB TAF Comments: Timing of categorical changes could be 2-3 hours off from forecast. Wind shifts may also vary 1-2 hours from forecast. KHPN TAF Comments: Timing of categorical changes could be 2-3 hours off from forecast. Wind shifts may also vary 1-2 hours from forecast. KISP TAF Comments: Timing of categorical changes could be 2-3 hours off from forecast. Wind shifts may also vary 1-2 hours from forecast. An isolated thunderstorm possible 04-08Z. .OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY... .Thursday night...VFR. West winds diminish late. .Friday...VFR. West gusts around 20 KT. .Saturday...VFR. NW gusts around 20 KT. .Sunday...VFR. .Monday...VFR...possibly lower at times depending on the track of low pressure to the south.
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&& .MARINE...
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Easterly winds have increased ahead of an approaching warm front, with a few gusts up to 35 kt possible across far eastern sections early this evening. After warm fropa expect S-SW winds to increase to 15-25 kt with gusts 25-30 kt on all waters except NY Harbor, so SCA remains in effect for all except the Harbor through tonight. Patchy to areas of fog will likely form into this evening just ahead of the warm front High dew point air advecting northward over mid 50 degree water should allow this fog to form. Extent of the fog remains in question however, and winds may hinder this development. Winds will shift around to the west late tonight as a cold front moves through. Expect these westerly winds to increase, and SCA conditions are anticipated across all waters Thursday afternoon through Thursday night. Winds over the ocean waters remain elevated per WaveWatch and NWPS. SCA conditions for sea and wind gusts will remain likely on the ocean waters through Saturday in a tight gradient between Canadian Maritimes low and Central/Southern US high. On the non- ocean waters, marginal sca gusts possible during this period...particularly on Long Island Sound. With high pressure building back into the region Sat Night into Sun...a return to sub-SCA conditions would be expected. The sub- SCA conditions are expected into early next week.
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&& .HYDROLOGY...
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Rainfall of about 1/4 to 1/2 inch had already taken place as of 00Z, with lighter amounts across far eastern sections. Another 1/2 to 3/4 inch expected tonight, with the highest amounts from NYC north/west, with event total rainfall of 1-1.5 inches there, and from 1/2 to 3/4 inch across eastern Long Island and SE CT. 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 from Thu through Sunday. Potential for significant precip returns Sunday night into Monday, with low predictability in the details at this point.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 6 AM Thursday to 6 AM EST Friday for ANZ338-345. Small Craft Advisory until 6 AM EST Friday for ANZ330-335-340- 350-353-355. && $$ SYNOPSIS...BC/PW NEAR TERM...PW SHORT TERM...PW LONG TERM...BC AVIATION...JM MARINE...BC/PW HYDROLOGY...BC/PW

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