Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 170227 AFDOKX Area Forecast Discussion National Weather Service New York NY 927 PM EST Sat Feb 16 2019 .SYNOPSIS... High pressure builds in through Sunday morning, then passes east Sunday afternoon. Weak low pressure will approach from the west Sunday night, then pass just south and east late Sunday night into Monday. High pressure will then return for Tuesday, followed by another low pressure system for mid week. High pressure builds back Friday into Saturday, with another low pressure system possible for the end of the weekend into early next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Forecast on track as high pressure will continue to build and nose in over the region tonight. A northern stream shortwave departs through the Canadian maritimes tonight, while a southern stream shortwave tracks east, well to the south. Cloud cover with both disturbances should remain well north and south of the region. With the the low level flow veering to the north, any moisture from the Great Lakes should shut off for NW zones. Therefore mainly clear skies should continue through the night and into Sunday morning. Diminishing winds will result in only a light northerly flow and clear skies, with far outlying areas decoupling completely. Therefore, with polar high influence and advection diminishing overall should see some spread with temperatures, with teens in outlying rural locations and mainly 20s in the more urban areas. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday morning should start off mainly clear, followed by increasing afternoon cloud cover as SW flow aloft gets better established. This will be in response to an upper level low across the high plains and Midwest. This will increase the warm advection in the upper levels in advance of the next storm system which is slated for late Sunday evening through Monday morning. Right now there is very good model agreement with the large scale features as ejecting upper level energy under the base the of the Midwest trough will get sheared due to the progressive nature of the southern branch. The model agreement is there with the surface reflection as well as weak low pressure will drive into the Central Appalachians towards WV, then a surface low is expected to develop along the Delaware, Maryland coast for Sunday night into Monday morning and eject quickly to the east-northeast. 12Z model QPF is not very impressive with this system with a general consensus of 0.1 to 0.3 inches, with a couple of outliers like the NAM showing a bit more QPF. The NAM warm tongue may be overdone, which is a typical bias of the model, but not totally discounting it. Based on the overall pattern and teleconnections the argument can be made that the low level cold air (cold air below 3kft) may not be that easy to erode and push out. There are hints of minor blocking, or a lack of overall progression over Eastern Canada with an upper level low near the 50 Lat 50 Lon position. The thinking now is that snow should begin close to 0z Mon for the city and western areas, with the snow starting a couple of hours late for the late evening perhaps across eastern and northeastern sections. Initially the profile should be cold enough for all snow at the onset, however the discrepancies are always in the details with NWP. The difficult aspect is to ascertain how much of an easterly flow will get established in the low levels, and for how long. There is not a whole lot of room for warm advection below freezing in the mid levels, therefore a change to a wintry mix is a high likelihood, with southwestern sections going over to light rain into early Monday morning. Another aspect that has discrepancies is a potential lack of moisture in the snow growth region for locations cold enough for mainly snow, especially as getting closer to 6 and 9z Mon. This could very well lead to a period of light freezing rain and drizzle for areas that remain below freezing at the surface. The likelihood for this will increase further north, and northeast across the region based on latest BUFKIT profiles, which is supported with closer proximity for northeast zones to the departing surface high pressure. With warm advection burst done into Monday morning anything that falls should be very light with lack of overall moisture depth. Where low level sub-freezing cold air holds light mixed precipitation and / or freezing drizzle may linger into the early afternoon. Overall it looks like a 1 to 2 inch type event at this time which is still enough to make for some hazardous travel, especially with the potential for freezing rain / freezing drizzle for Monday morning across at least portions of the region, and possibly down to parts of the Connecticut coast. High pressure will then build in later in the day with dry conditions returning into Monday night. && .LONG TERM /MONDAY THROUGH SATURDAY/... A confluence of weak mid-level northern and southern stream shortwave energy moves east across the region on Monday. At the surface, associated low pressure to the se of LI Monday morning will slide steadily offshore through the day. Deep moisture/lift axis slides offshore by morning, but a lingering surface trough, onshore flow and mid level lift will be enough to have lingering light precip through the day. With mid-level drying, ice nucleation is unlikely to occur aloft close to the city/coast, but could be marginally cold enough across interior for ice nucleation. Temps will likely hover near freezing Sun Night into early Monday morning for city and LI before warming above, with coastal CT and points just NW slowly warming above freezing through the mid to late morning, while interior and CT river valleys will likely struggle to get above freezing through the afternoon. So wintry precip Sunday Night, could briefly transition to freezing rain early Monday morning, before transition to mainly light rain/drizzle for city and LI. For coastal CT and just NW of NYC light freezing rain/sleet/snow likely change to light snow, rain and drizzle during the mid to late morning, but a mixture of light freezing rain/light snow still possible across interior into the afternoon. Although ice accumulation should be minimal, a trace of ice is possible away from south coast of LI and much of NYC/NJ metro to a few hundredths of an inch across interior, making for a treacherous morning commute across untreated surface for these areas. The late afternoon/evening commute could still be locally treacherous for untreated surface across the interior, with black ice even becoming an issue down to the coast in the late evening. Region then transitions into a confluent upper flow Tue into Wed, between upper ridging south of Bermuda and polar low sliding across central Quebec. At the surface, Canadian high pressure builds into the region Monday Night and overhead on Tuesday. Region comes more under the influence of the southern stream midweek, as early week SW US trough shears eastward towards the Great Lakes and New England, while SW troughing is reinforced once again. In the SW flow aloft, weak southern stream energy lifts up towards the region Tue Night into Wed, with associated southern low gradually approaching Wed and tracking near the region Thu. At this point, forcing with this system does not look to be too strong with another light precip event likely. Thermal profiles appear cold enough to start as all snow Wed/Wed eve, then gradually transitioning to wintry mix interior and all rain coast Wed Night into Thu morning, before gradually tapering off late Thu as mid- level shortwave passes. Thereafter, generally zonal PAC influenced upper low for late week into the weekend, lending to slightly above seasonable temps. Next chance of significant precip possible for late weekend into early next week as northern and southern stream show signs of interacting. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... High pressure builds across the terminals through Sunday morning, then offshore in the afternoon. Low pressure approaches Sunday evening. VFR through early Sunday evening. Conditions will lower to MVFR as a wintry mix develops after 00z Monday. Winds veer to the N tonight as they weaken below 10 kt. The winds at city terminals may not fall below 10 kt until after 06z. Winds continue to veer to the NE Sunday morning and then E to SE in the afternoon, remaining less than 10 kt. .OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... .Sunday night-Monday...IFR in wintry mix changing over to rain at the coast early Monday morning. .Tuesday...VFR. NW winds G20-25kt. .Wednesday...Snow possible with MVFR or lower conditions in the afternoon and evening, changing to a wintry mix at night. .Thursday...MVFR or lower in a wintry mix. && .MARINE... High pressure will build across the waters tonight through Sunday with sub SCA conditions through Sunday night. Low pressure passes to the south and east Sunday night. Marginal SCA conditions possible on the ocean waters Monday into Monday night, specifically for seas Monday, and more likely for SCA gusts Monday Night. Conditions fall below SCA Tuesday into Wednesday as high pressure builds in. The next chance for SCA conds will likely be Wed Night into Thu Night with next low pressure system moving over or south of the waters. && .HYDROLOGY... There are no hydrologic concerns through the middle of next week. && .TIDES/COASTAL FLOODING... A low pressure system tracking to the south of the region Sunday Night into Monday, and approaching full moon on the 19th, will bring potential for minor coastal flooding during the Monday morning high tide. At this point it appears to be a low-end event across the most vulnerable locales of the south shore bays of Queens and Nassau County, W LI sound, and a few spots in lower NY/NJ Harbor. 1 to 1 1/2 ft of surge, locally 2 ft, are need for for minor flood thresholds to be reached during Monday morning high tide. && .EQUIPMENT... NYC Central Park winds are out of service until further notice. Loss of data is due to a severed cable. Parts are on order. NYC NOAA Weather Radio Station KWO35 (162.55 MHz) will remain off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JE/NV NEAR TERM...JE/NV SHORT TERM...JE LONG TERM...NV AVIATION...DS MARINE...JE/NV HYDROLOGY...JE/NV TIDES/COASTAL FLOODING... EQUIPMENT...

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