Area Forecast Discussion
Issued by NWS Upton, NY

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442 FXUS61 KOKX 201709 AFDOKX Area Forecast Discussion National Weather Service New York NY Issued by National Weather Service Boston/Norton MA 109 PM EDT Tue Apr 20 2021 .SYNOPSIS... High pressure settles to the south today as a cold front approaches from the west. Low pressure develops along this front tonight which then strengthens on Wednesday as the system moves across the region. The low then moves over the Canadian Maritimes Thursday as high pressure builds to the south and west. The high will then be in control into the first part of the weekend. Another frontal system potentially impacts the area on Sunday. && .NEAR TERM /THROUGH TONIGHT/... 950AM Update: No major changes to the near term forecast. The latest visible shows any minor fog has burned off and wispy high cirrus clouds have moved in from the west. Temperatures are also warming up nicely into the the mid and upper 50s. We remain on track to reach the low and middle 70s away from the coast. Forecast remains on track. See previous discussion below. ------------------------------------------------------------- Patchy fog across eastern Long Island and interior southwest CT and interior Lower Hudson Valley should quickly diminish shortly after sunrise. An upper ridge axis moves offshore today as high pressure builds to the south and west. A cold front will also approach from the north and west. It is possible that this boundary reaches the interior Lower Hudson Valley this afternoon as a strong northern stream shortwave traverses across southeast Canada. The frontal boundary should have no impact to sensible weather as any lift resides well north of the area. There will be a gusty southwest flow ahead of this front, with gusts 20-25 mph. Otherwise, it will be warm, dry and mostly sunny today. High temperatures are above most guidance and closer to the 50th percentile of the NBM. Have also made adjustments upward a few degrees in the typical warmer urban NE NJ and NYC metro away from the influence of the sea breeze. Highs away from the coast should be in the lower 70s with middle 70s possible in the warmer spots. Across Long Island and coastal Connecticut, highs will be a bit cooler in the middle and upper 60s. A much stronger shortwave digs across the Great Lakes and midwest tonight, amplifying the flow over the eastern states. The amplifying flow and frontal boundary may be enough to develop an isolated shower across the interior this evening or tonight. The frontal boundary should begin to lift to the north overnight. This is due to the flow amplifying aloft as the shortwave trough approaches. Low pressure will also develop along the front across the Middle Atlantic. Otherwise, it should remain dry with increasing clouds towards morning. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... The low pressure wave will lift across Southern New England on Wednesday, dragging the cold front across the region. Strong dynamics with the middle and upper level shortwave, divergence aloft, and convergence along the front will provide deep layered lift. The most organized forcing looks to lie along and just ahead of the frontal boundary. While a few showers cannot be ruled out in the morning, the bulk of the convection will move across the region in the afternoon and evening. The higher resolution models continue to signal the development of a line of showers and embedded thunderstorms quickly moving across the area from west to east early to mid afternoon along and west of the Hudson River, and mid to late afternoon east of the Hudson River. The line should be moving offshore in the early evening. Have followed closely to the simulated reflectivity fields for general PoP timing as the guidance seems to have a relatively good handle the line. The major differences lie in the exact timing. The amount of destabilization is also a bit uncertain, but model soundings indicate about 500 J/kg of SBCAPE from around the NYC metro on north and west coinciding with about 35-50 kt of low level flow. SPC continues to highlight a marginal risk of severe thunderstorms with the main threat from isolated damaging wind gusts. Surface based instability drops off to near zero across much of southern Connecticut and central and eastern Long Island due to a stronger maritime low level inversion. However, have mentioned chance of thunder here as well due to the strong dynamics and elevated instability. This should however prevent any severe storms further east as the line encounters the more stable low level air. There are no flooding concerns with the line as it will be moving fairly quickly across a given area. Southerly winds may gusts 20 to 30 mph ahead of the front outside of the line of showers and embedded thunderstorms. Strong cold and dry advection takes places behind the cold front Wednesday evening and Wednesday night. Winds will shift to the W and NW and could gust 25 to 35 mph at night with the strong cold advection. Highs during the day on Wednesday should be in the 60s. If clouds are not as extensive early in the day, the locations away from the coast could warm a few degrees higher than currently forecast. Temperatures crash behind the front and should drop into the lower to middle 30s by early Thursday morning. The growing season does begin across the interior zones on April 21 and temperatures may hit the freezing mark early Thursday. The strong winds will prevent any frost development. Gusty winds continue on Thursday as the low pressure strengthens while moving over the Canadian Maritimes. High pressure also builds to our south and west, creating a strong pressure gradient over the region. W-NW wind gusts 25 to 35 mph are likely, and could reach 40 mph near the coast. There is a low chance for a few gusts up to 45 mph, especially given the deep mixed layer indicated by forecast soundings. Highs on Thursday will be well below normal in the upper 40s inland to the lower 50s near the coast. Winds weaken some Thursday night, but should still remain gusty enough to preclude frost again. Lows will be in the middle to upper 30s for most locations. && .LONG TERM /THURSDAY THROUGH MONDAY/... High pressure will build to the south and west through Friday and then off the Mid Atlantic coast Saturday. A progressive, yet amplifying upper trough over the Mississippi Valley on Saturday will move across the area on Sunday. Global models are in good agreement with a strong frontal wave developing over the Carolinas Saturday and passing near or just south of Long Island on Sunday. This would bring rain to the region Saturday night into Sunday. High pressure will then follow early next week. Temperatures will rebound to normal or even slightly higher through Saturday. Sunday could be cooler depending on how much interaction there is with the northern branch. Generally, stayed close to the NBM, but leaned bit lower for Sunday. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Mainly VFR conditions are expected through the TAF period. Gusty winds diminish around 22z-23z this evening, then become light for the overnight period. Ceilings should remain VFR. VFR conditions continue for the first half of Wednesday. A cold front will move across the region providing showers and isolated thunder showers as well between 19z and 21z Wednesday, ceilings may briefly drop to MVFR/IFR. Ahead of the front S winds will be breezy, sustained 10 to 15 knots and gusts to 25 knots. Shortly after the frontal passage wind will become WNW with gusts to 35 knots. Ceilings rebound to VFR conditions overnight into Thursday morning. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... Chance of low clouds and patchy fog tonight. .OUTLOOK FOR 0Z THURSDAY THROUGH SUNDAY.... .Thursday...VFR. WNW gusts 25-30kt. .Friday...VFR. WNW gusts 20-25kt. .Saturday...Mainly VFR, chance of MVFR in rain at night. .Sunday... MVFR/IFR possible with rain likely. Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 && .MARINE... High pressure settles south of the waters today. S-SW flow increases into the afternoon and gusts could reach around 20 kt. Otherwise, sub-SCA conditions continue through tonight. S flow increases ahead of a strong cold front on Wednesday, with SCA conditions likely on all waters in the afternoon. The cold front moves across the waters by evening. Gales are possible on the ocean behind the front and may continue into Thursday. Have issued an SCA on all waters Wednesday afternoon and have issued a gale watch Wednesday night into Thursday on the ocean. The SCA on the non ocean waters continues Wednesday night and will likely need to be extended into Thursday. Lingering SCA conditions likely on Friday in a gradually diminishing west flow, especially on the ocean. All areas will briefly fall below SCA criteria on Saturday before a coastal low impacts the area late saturday night into Sunday. && .HYDROLOGY... No hydrologic impacts are expected through the week. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from noon Wednesday to 6 AM EDT Thursday for ANZ331-332-335-338-340-345. Gale Watch from Wednesday evening through Thursday afternoon for ANZ350-353-355. Small Craft Advisory from noon to 6 PM EDT Wednesday for ANZ350-353-355. && $$ Gaucher

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