Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 170619 AFDOKX Area Forecast Discussion National Weather Service New York NY 119 AM EST Wed Jan 17 2018 .SYNOPSIS... Low pressure develops along the Mid Atlantic coast tonight and then passes near or just east of Long Island on Wednesday before moving up the coast into the Canadian Maritimes Wednesday night. High pressure will then build to the south through Friday and move into the western Atlantic this weekend. A cold front then passes through Monday night into Tuesday morning. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... No significant changes were made to the forecast with this update except to delay precip timing a bit from NYC on east. It looks like precip will blossom after 06-08z as the upper trough dynamics interact with the developing secondary low. No changes were made to the winter weather headlines. Light snow continues to fall across NW Orange County. Starting to see reflectivity increase as better dynamics begin to move into this area. Steadier precipitation will continue to overspread from the west through the night and then blossom across the rest of the area towards day break. Have taken an initial look at the 00z NAM12, 00z 3-KM NAM and they generally support the current forecast. QPF may be a bit lower than previous runs, but overall looks close. The latest HRRR also is in general agreement with the ongoing forecast. The biggest challenge continues to lie with the northward extent of the warmer air and how far the rain/snow line works. Despite temperatures currently running a bit cooler than previously forecast in the NYC metro area, a surge of warmer air at the surface to just above 925 mb is anticipated. This is due to a prolonged period of S-SE winds ahead of the developing low. The transition of energy from upper trough/weakening primary low is to the secondary low is slow such that an inverted trough is expected to extend back into the Hudson Valley of New York. This should allow the rain snow line to make it about 10-20 miles north and west of I-95 corridor in New Jersey to near or just south of a line from HPN to DXR. Temperatures will remain nearly steady overnight and even slowly rise. Lows will range from the upper 20s in the interior to the mid 30s along the coast. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Low pressure near Long Island in the morning lifts northeast during the day and up into the Canadian Maritimes by Wednesday night. Precipitation shuts down across most of the area by late morning/early afternoon and perhaps ends as period of snow at the coast. Even if the changeover to snow occurs a bit faster than indicated in the city/at the coast, limited duration of precipitation on the backside of the low will limit any accumulation. Highs will top out in the mid to upper 30s with NW winds developing on the backside of the storm. Gust up to 20 mph develop late in the day and possibly linger into first half of the night. Cold air will follow for Wednesday night with lows in the teens inland and around 20 at the coast. This is slightly below normal. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Surface high pressure will build to our south on Thursday and Friday. Meanwhile, an upper trough shifts through with some shortwave energy Thursday night into Friday. Moisture looks insufficient for any PCPN, so dry weather is expected. Highs a few degrees below normal for Thursday, returning to near normal on Friday. Ridging aloft will then keep the weekend dry with warming temperatures. Low pressure enters the Great Lakes Region Sunday night, eventually tracking through Quebec on Tuesday. Some warm advection PCPN may reach some of the northern zones Sunday night into Monday morning, which could be in the form of a wintry mix. A cold front otherwise approaches with increasing chances of rain during the afternoon and night. Some timing differences still exist among the global models with the cold front passage, so have capped PoPs at chance through Tuesday morning. Rain chances otherwise diminish Tuesday afternoon with dry weather likely returning Tuesday night. Temperatures Sunday through Tuesday will remain above normal. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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A developing coastal low with move north towards the region this morning, tracking just southeast of Long Island early on today, and then into the Canadian Maritimes this evening. Conditions expected to lower to IFR early this morning as precipitation develops across region. Expect all snow at KSWF with LIFR conds, which may be moderate at times between 07z and 13z. Between 5 and 7 inches of snow expected. Rain expected to develop for NYC/NJ metro terminals and KBDR after midnight, likely mixing with snow towards daybreak, and then changing to all snow after 11-13z. IFR conditions with a quick coating to 2 inches of slushy snow likely for NYC terminals, with 1 to 3 inches for KEWR/KTEB/KBDR during the morning push. Low potential for these amounts to be about one inch higher, with LIFR conds. KHPN likely to have a mix of rain/snow early this morning, before changing to all snow with LIFR conds towards daybreak, with 2 to 4 inches of snow likely. Low potential for this amount to be about one inch higher. All rain expected for KISP/KGON. Precip taper off from W to E Wed morning into early afternoon, with conditions improving to VFR. E/NE winds for coastal terminals less than 10 kt overnight, becoming N/NNW for all terminals towards daybreak. Winds become WNW with gusts 20 to 25 kt Wed afternoon continuing into Wed eve push, likely averaging just right of 310 magnetic. .OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY... .Late Tonight-Thursday Night...VFR. WNW winds G20-25KT on Thursday. .Friday...VFR. W-SW winds G20KT possible. .Saturday-Sunday...VFR.
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&& .MARINE... SCA in effect for the ocean waters as seas remain 4-5 ft. Ocean seas increase a bit more tonight. Flow returns to a NW direction and begins to gust late on Wednesday. SCA conditions continue on the ocean for Thursday through Friday morning, then sub-advisory conditions are expected for a brief period Friday afternoon and night. Winds and seas then pick up with marginal advisory conditions on the ocean during Saturday and Saturday night. A weaker pressure gradient then returns relatively tranquil conditions for Sunday. && .HYDROLOGY... No significant hydrologic impacts are expected. && .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...
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CT...Winter Weather Advisory until 1 PM EST this afternoon for CTZ005>008. NY...Winter Weather Advisory until noon EST today for NYZ069-070. Winter Storm Warning until noon EST today for NYZ067-068. NJ...Winter Weather Advisory until noon EST today for NJZ002-004- 103>105-107. MARINE...Small Craft Advisory until 6 AM EST Thursday for ANZ350-353- 355.
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&& $$ SYNOPSIS...JC/DW NEAR TERM...DS/DW SHORT TERM...DS/DW LONG TERM...JC AVIATION...JE/NV MARINE...JC/DW HYDROLOGY...JC/DW EQUIPMENT...

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