Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 190812 AFDOKX Area Forecast Discussion National Weather Service New York NY 412 AM EDT Thu Apr 19 2018 .SYNOPSIS...
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Low pressure tracks to south of Long Island this morning and will then move to the southeast of Cape Cod this afternoon. The deepening low then quickly exits into the Canadian Maritimes tonight through Friday. High pressure slowly builds in from the Great Lakes Friday night through Sunday night, then gradually slides offshore from Monday through Tuesday night. A coastal low approaches from the southeastern seaboard on Wednesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The main upper level jet will be south of the region. A persistent upper level low will remain in the Northeast. The mid levels convey a flattened mid level ridge moving east of the region with an approaching shortwave trough. At the surface, a low will be moving to south of Long Island this morning and then this low will be tracking to southeast of Cape Cod. Low level warm air advection has been occurring with some isentropic lift as well. This will be a setup for overrunning rain that will be main weather theme of the day. Going into this morning, higher terrain across the interior could have the precipitation as a rain/snow mix or even some snow. Little to no snow accumulation is expected, if anyplace gets any accumulation, it would be the higher terrain where temperatures will be slightly below freezing. Expecting a damp cool day as temperatures will not rise much from early morning values. Continuous rain expected on a light northerly flow to start but that flow will increase towards mid to late afternoon as pressure gradient becomes tighter between the low and strong high pressure still well out west into the Central Plains. Expecting cooler than normal temperature with the northerly flow and rain through the day. Used the cooler MET guidance for highs. Increased one degree along the coast for highs.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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The main upper level jet will remain south of the region through Friday. For Thursday night: Two more shortwaves pivot across the region in the mid levels. So despite the surface low moving farther away to the south of Nova Scotia, the region will remain in cyclonic flow aloft. The chances for precipitation while lower than earlier in the day, will be still be present mainly during the evening. Cold air advection on the backside could result in a light rain/snow mix across some parts of the interior, especially higher terrain. No snow accumulation is expected. Otherwise, the precipitation will end as rain. For overnight, more drying takes over with the persistent NW flow. With the abundant clouds, used a blend of guidance in terms of temperatures including the previous forecast. There will be some cold air advection but without ideal radiational cooling. Winds stay up so despite temperatures in the mid 30s for those parts of the region in the growing season, not expecting frost formation. For Friday: In the mid levels, the mid low will be moving east of the region, allowing for heights to build as ridging commences from well to the west. The same pressure gradient remains for Friday so that will mean more gusty NW flow. At the surface, the low will be moving near Newfoundland while the high will be moving into the Great Lakes and into the west of the Appalachians. NW flow continues so dry conditions will remain. Still expecting abundant clouds though, so will side with a blend for high temperatures including the previous forecast.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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NW flow aloft Friday night. With no shortwave embedded in the flow progged to impact the region, have continued with the dry forecast. Lows Friday night should be around 5-10 degrees below normal. A couple of northern stream 700-500 hPa shortwaves push through the area Saturday and Saturday night as the rotate around the base of a closed low over the Canadian Maritimes. With relative dry low levels and downsloping boundary layer flow, the shortwaves should pass through dry. Highs on Saturday and low Saturday night should be around 5-10 degrees below normal. Deep layered ridging then begins to builds in Sunday and continues to ridge over the area through Tuesday. Subsidence associated with the ridge should keep things dry and relatively (if not totally) cloud free during this time frame. Highs Sunday-Tuesday run a few degrees below normal and lows during this time frame run 5-10 degrees below normal. Noting that 1) the GFS has a known progressive bias in the long term and 2) that the upper level pattern features closed lows and fairly sharp ridges - both of which support a less progressive pattern - favor the slower lifting of the ridge axis to the NE and arrival of the next system in the ECMWF/CMC Global than the more progressive GFS handling of both features. The forecast Tuesday night-Wednesday is based on a blend of the ECMWF/CMC Global as a result. Tuesday night should be dry as the deep layered ridge axis lifts to the northeast. Most of Wednesday should probably be dry as well, but to keep things simple, given the inherent uncertainty this far out, have run chance pops the entire period for some warm advection induced rains. Lows Tuesday night should be near to slightly above normal and highs on Wednesday a few degrees below normal.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/... A wave of low pressure approaches overnight and passes south of Long Island Thursday morning, then strengthens as it continues out to sea during the afternoon. VFR overnight.There is some uncertainty in when conds drop to MVFR. Have conds dropping to IFR only at KHPN/KSWF/KISP/KBDR/KGON where confidence is a bit higher, although it is a possibility at remaining terminals for at least a couple of hours late morning/early aftn Thurs. Conds improve back to VFR late aftn from W to E. P-type could be an issue at KSWF. Soundings indicate a few hours of SN or RASN until mid levels dry out by around daybreak. NE winds 5-10kt overnight. As the low passes to the south and strengthens while departing, winds will back to the N then NW and increase to 10-20g20-30kt in the late aftn/eve. .OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY... Thursday night-Friday...VFR. NW winds G20-30KT, mainly Thu eve and after sunrise Fri. .Saturday-Monday...VFR. && .MARINE...
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Sub-SCA conditions will be in place today, but winds and seas will begin increasing. SCA thresholds are forecast to be met across the waters tonight through Friday morning with the ocean east of Moriches Inlet likely getting SCA conditions tonight through all of the day Friday. A relatively strong pressure gradient over the region Friday night, should allow for gusts to around 25 kt to persist over the coastal ocean zones and gusts to around 20 kt on the non-ocean zones. The pressure gradient begins to slacken on Saturday, with all waters falling to below Small Craft Advisory thresholds by Saturday morning. Winds Saturday-Monday night will be limited to 10 kt or less on the non-ocean waters. The coastal ocean zones will be similarly limited Saturday-Monday night, except for winds up to 15 kt are probable Saturday morning.
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&& .HYDROLOGY...
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Less than a half inch of rain expected through this evening with dry conditions for late tonight through Friday. No hydrologic impacts expected. It should be dry Friday night-Tuesday night, with light rain expected Wednesday. No significant hydrologic impacts are expected Friday night-Wednesday as a result.
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&& .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 6 PM this evening to noon EDT Friday for ANZ330-335-338-340-345-353-355. Small Craft Advisory from 6 PM this evening to 6 PM EDT Friday for ANZ350.
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&& $$ SYNOPSIS...Maloit/JM NEAR TERM...JM SHORT TERM...JM LONG TERM...Maloit AVIATION...JC MARINE...Maloit/JM HYDROLOGY...Maloit/JM EQUIPMENT...

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