Area Forecast Discussion
Issued by NWS Upton, NY

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780 FXUS61 KOKX 160117 AFDOKX Area Forecast Discussion National Weather Service New York NY 817 PM EST Sun Dec 15 2019 .SYNOPSIS... High pressure briefly builds over the region tonight, then drifts offshore Monday. A low pressure system approaches the region Monday and impacts the region Monday night and Tuesday before moving northeast to the Northern Atlantic Tuesday night into Wednesday. A polar front approaches Wednesday and moves across Wednesday night. Canadian high pressure moves in for Thursday through Friday night. The high lifts farther north of the area next weekend with possible close approach of offshore low pressure. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Just made some minor adjustments to hourly temperatures, dewpoints, and cloud coverage to better match observed trends. Forecast overall is on track. High pressure will build over the region tonight with dry conditions expected. Winds will gradually weaken, becoming light and variable west of NYC, and less than 10kt elsewhere from the west. This high will keep a warm front south of the area tonight. Lows will fall into the 20s and 30s. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday starts off with high pressure over the region, which will gradually shift to the east through the day. Meanwhile, a warm front will remain south of the area with precipitation gradually developing along the front. The 12z forecast guidance, along with some of the early 18z guidance shows that much of the precipitation will struggle to move into our area as it will struggle with the dry air from the departing high to the northeast. Thinking that if any precipitation falls during the day on Monday, it will be light and mainly in the form of flurries or light snow showers. By Monday evening, the high pressure moves far enough east to allow precipitation to push its way across the area from south to north. Even with the high nearby, signals of cold air damming will keeping cold air in place across the northern tier for much of Monday night. In terms of precipitation type, the precipitation should start off as snow everywhere with wet bulb cooling, then quickly transition to a rain/snow mix then to all rain by 06z Tuesday across NYC, Long Island and metro NJ. Elsewhere, a prolonged period of snow and a wintry mix can be expected, with snowfall totals ranging between 1-2 inches and ice accumulations up to 2 tenths of an inch. As a result, have issued a Winter Weather Advisory for much of our northern zones where the highest confidence is for the snow/ice combo. For now, have left coastal CT out of the advisory as confidence is not as high with ice accumulations and more rain may occur. The storm total ice forecast is showing any measurable ice accumulations to remain across the interior and this is where there is higher confidence of obtaining ice accretion. Stay tuned for any additional updates as changes to the forecast may be necessary depending on the timing of the precipitation and the rain/snow line. Temperatures on Monday will be in the 30s. Monday night, lows will be in the 20s and 30s, with lows occurring very early in the tonight period, and slowly warming through the night. && .LONG TERM /TUESDAY THROUGH SUNDAY/... First of all, the winter weather advisory will be ongoing for interior parts of the region with some additional snow and ice accumulations during Tuesday. All precipitation tapers off Tuesday evening. Second half of the storm event for Tuesday with the low center moving just south of the local area. 850mb freezing line will be north of the entire CWA during the day and then start to move farther southward with cold air advection on the backside of the low as it moves farther east of the area late afternoon into the evening. The second half of the storm event will feature a continuation of a wintry mix across the interior including some additional freezing rain while the coast will remain as plain rain as dewpoints are expected to be above freezing. At the end of the event late afternoon into early evening, there could be a brief window of a rain snow mix getting farther southward towards the coast, but only minor accumulations of less than an inch of snow expected and that is across the interior with no snow accumulation expected for the coast. Highs Tuesday will be from the lower 30s across the interior to the upper 30s to lower 40s along the coast. Conditions will become drier Tuesday night with weak high pressure from the southwest briefly building in. Clouds will decrease and NW winds will lighten. Lows Tuesday night are expected to be in the mid to upper 20s as winds will stay up enough to prevent ideal radiational cooling. A key part to the forecast is temperatures for these went with CONSRaw for temperatures Tuesday and transitioned from CONSRaw to a blend of CONSMOS and NAM12 for Tuesday night. For the rest of the long term, that high pressure area from the south and west will quickly way on Wednesday to an approaching polar front. This will be accompanied aloft by a very strong mid level shortwave as diagnosed from a strong positive vorticity max. This will bring some snow shower activity, slight to low end chance Wednesday into Wednesday night. Low confidence on timing and location of snow showers. Not expecting much if any snow accumulation. Much colder airmass moves in Wednesday night and lingers through Friday night. Temperatures are expected to be well below normal. NW flow will be gusty Wednesday night into Thursday night which will help advect in colder air. For next weekend, the high lifts farther northward. The airmass across the region will moderate. Models convey a vast array of solutions regarding low pressure offshore and its track. A lot of uncertainty in the local forecast in this timeframe. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... High pressure will briefly build over the region tonight, then drift offshore Monday. Low pressure will approach on Monday. W-NW winds should gradually diminish to under 10 kt overnight, then as the high passes east become light SW-S in the afternoon, then NE-E in the evening. Clouds should start to lower/thicken late tonight into Monday. Timing of precip and MVFR conds uncertain and could trend later than fcst. .OUTLOOK FOR 00Z TUESDAY THROUGH THURSDAY... .Monday night...IFR or lower likely. For the NYC metro and coastal terminals, wintry mix gradually changing to plain rain late, though EWR/KTEB/KBDR could see freezing rain linger into the early Tue morning push. KHPN/KSWF wintry mix, including freezing rain. .Tuesday...IFR or lower conds. Wintry mix, possibly changing back to all snow at KSWF before ending. Rain at NYC/NJ metro and coastal terminals, possibly changing to wintry mix before ending late. N winds G20kt in the afternoon. .Tuesday night...VFR. NW winds G20kt NYC metros/KISP mainly eve. .Wednesday...VFR. NW winds G25kt mainly afternoon. .Thursday and Friday...VFR. && .MARINE... Gales have subsided across most waters except for the ocean east of Fire Island Inlet. That gale warning remains until 10 PM tonight. Other gales were replaced with SCA. The SCA for the NY Harbor, Western Long Island Sound, South Shore Bays goes until midnight while the SCA for Eastern Long Island Bays and Eastern Long Island Sound as well as the ocean west of Fire Island Inlet goes until 6 AM Monday. Ocean seas will be a bit slower to respond with residual S/SE swells, but should fall below SCA from west to east through Monday morning. Sub-SCA conditions are expected for much of Monday and Monday night. SCA seas return on the ocean Tuesday with otherwise sub-SCA conditions all across the rest of the waters. Winds are below SCA criteria. SCA ocean seas remain through Thursday and then decrease to below SCA Thursday night and remain below SCA Friday into Friday night. For the wind gusts, SCA wind gusts expected Tuesday night across mainly the ocean waters. Wind gusts return to SCA levels on the ocean Wednesday afternoon and all waters have at least SCA level winds Wednesday night through Thursday with potential for gales on the eastern and ocean waters during this timeframe. SCA levels gusts forecast on the eastern and ocean waters Thursday night. Winds are mainly below SCA Friday into Friday night. && .HYDROLOGY... Remaining flooding concerns are for the larger stem rivers in CT with a combination of the recent rainfall and melting snow to the north. Another significant precipitation event is likely Monday through Tuesday, with liquid equivalent QPF of 0.5 to 1.00 inches possible. There is uncertainty in this amount given uncertainty in the track of the low and frontal positions. No significant widespread precipitation expected from Tuesday night onward through the rest of the forecast. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO35 (162.55 MHz) is still operating at reduced power. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory from 6 PM Monday to 6 PM EST Tuesday for CTZ005>008. NY...Winter Weather Advisory from 6 PM Monday to 6 PM EST Tuesday for NYZ067>070. NJ...Winter Weather Advisory from 6 PM Monday to 6 PM EST Tuesday for NJZ002-103. MARINE...Small Craft Advisory until midnight EST tonight for ANZ335-338- 345. Small Craft Advisory until 6 AM EST Monday for ANZ330-340-355. Gale Warning until 10 PM EST this evening for ANZ350-353. && $$ SYNOPSIS...BC/JM NEAR TERM...BC/JM SHORT TERM...BC/JM LONG TERM...JM AVIATION...Goodman MARINE...BC/JM HYDROLOGY...BC/JM EQUIPMENT...

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