Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181150 AFDOKX Area Forecast Discussion National Weather Service New York NY 750 AM EDT Mon Jun 18 2018 .SYNOPSIS... A trough of low pressure builds in to western portions of the Tri-State today, followed by a cold front crossing the area tonight. Weak high pressure then builds in Tuesday and Tuesday night before giving way to another cold front pushing through the area Wednesday and Wednesday night. High pressure then builds over the area through Thursday night then slides offshore Friday and Friday night. Another frontal system impacts the area this weekend. && .NEAR TERM /THROUGH TONIGHT/... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. WNW flow sets up aloft by this afternoon as the deep layered ridge axis sinks to the SE. It should be dry this morning due to subsidence from the departing ridge. A weak 700-500 hPa shortwave trough moves into western areas this afternoon, as a pre- frontal trough sets up over the Lower Hudson Valley and NE NJ as well. The pre- frontal trough will enhance low level convergence to the W and N of NYC with the shortwave serving as a trigger to act on CAPEs progged in this area of at least 1500 J/kg and around 30-35 kt of 0-6 km Bulk Shear. Bulk Richardson numbers are fairly high (generally greater than 70) so they do not support super cells and but favor the possibility of multi- cellular convection out ahead of the cold front. The NAM has been fairly consistent in indicating this potential over NE NJ/Lower Hudson Valley late this afternoon/early this evening over the past two nights. The latest Convection Allowing Models (CAMs) are supporting this idea as well, but a few hours faster. The GFS is a bit slower than both the NAM and CAMs. Based on this, agree with SPC in assessing a marginal risk for Severe Thunderstorms over the Lower Hudson Valley, but would think that the threat goes a bit farther S into NE NJ than they indicate. Any severe storms over the Hudson Valley could maintain themselves as they track into interior portions of S CT Winchell, so there is a marginal severe threat there as well. If there is any severe weather this afternoon/early evening in the threat area, it will be due to damaging wind gusts. After this first round of convection, there should be a lull, then there should be another round late tonight ahead of the cold front. There is some question as to how well this convection holds together as it moves into our marine dominated airmass, so have capped pops at chance. However, precipitable waters increase to around 2" this afternoon and remain high until the cold front moves through. As a result, there is the threat for locally heavy rainfall with both rounds of convection. Refer to the hydrology section of the AFD for details. With the CMC-Global being alone in wanting to linger precipitation into Tuesday, have opted for the faster timing of a non-CMC-Global blend with the cold frontal precipitation. Highs today should be around 10-15 degrees above normal. With Interior areas and most of NYC reaching the upper 80s to lower 90s and some pockets of mid 90s passable in NE NJ and the Lower Hudson Valley. It is this area that there is a high likelihood of heat indices reaching 100 degrees this afternoon. As a result, have continued the heat advisory from 15Z to 00Z for NE NJ and the Lower Hudson Valley. Elsewhere heat indices should top out in the 90s over the interior and most of NYC and in the 80s near the immediate coast. Lows tonight will run around 10 degrees above normal. There is a high risk of rip currents at Atlantic Beaches mainly this afternoon and evening. && .SHORT TERM /TUESDAY/... NW flow at all levels will dry and clear things out fairly rapidly. Highs on Tuesday should be around 5 to 10 degrees above normal. It likely will be warmer at coastal areas on Tuesday than today, due to the lack of a seabreeze on Tuesday due to the NW flow. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... NW flow aloft continues Tuesday night and with no shortwaves progged to move through the area, it should remain dry with minimal cloud cover. The flow flattens on Wednesday as a northern stream closed low builds into Quebec. As it does so, a shortwave rotating around the base of this trough moves towards the area in the afternoon. This could bring some spotty showers to mainly western zones Wednesday afternoon. The axis of this cutoff low then crosses the area Wednesday night, brining more widespread showers to the entire area. In addition with showalter indices progged to go to the 0 to 4 range, have added a slight chance of thunder to the forecast as well. PRecipitable waters return to around 1.75 to 2 by late Wednesday, so locally heavy rainfall could again be possible. See the hydrology section of the AFD for details. NW flow then returns to the region on the backside of the trough Thursday and Thursday night. With relatively dry low levels, both of these periods should remain dry. Deep layered ridging builds in Friday and Friday night, with associated subsidence keeping things dry. A mean trough builds into the NE for the upcoming weekend with unsettled weather the likely outcome - so should see a few rounds of showers and possibly some rumbles of thunder as well mainly from Saturday afternoon through Sunday. Temperatures Wednesday-Sunday should generally be within a few degrees of either side of normal. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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High pressure to the south will give way to an approaching cold front tonight. Watching low stratus just SE of KJFK and also along the south shore of Long Island that has brought IFR cigs to KISP. Think lower cigs should stay SE of KJFK, but may impact KISP through the morning, with cigs improving to MVFR by 14Z. Widely scattered tstms with brief MVFR/IFR vsby and gusty winds are possible with a pre-frontal trough late today and early this evening, most likely from about 20Z-22Z at KSWF, 21Z-23Z at KHPN/KBDR, 22Z-01Z at the NYC metro terminals, and 00Z-02Z at KISP. Since the expected coverage is scattered at most and not guaranteed to have direct terminal impacts, have continued to mention via VCTS rather than PROB30/TEMPO. This could change with later issuances as confidence in timing and coverage increase. An additional round of showers/tstms with the front itself late tonight as it passes through. S-SW flow will increase today, with sustained winds 10-15 kt and gusts around 20 kt this afternoon and early evening. Sea breezes at KJFK/KLGA/KISP could be stronger, with sustained winds at or just over 15 kt and gusts approaching 25 kt. ,,,NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/ KJFK TAF Comments: Low stratus over the ocean just remain just SE of the terminal radius. The afternoon KJFK haze potential forecast is YELLOW, which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: The afternoon KLGA haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KEWR TAF Comments: The afternoon KEWR haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KTEB TAF Comments: No unscheduled amendments expected. KHPN TAF Comments: No unscheduled amendments. KISP TAF Comments: Unscheduled amendments possible to deal with morning low clouds and associated IFR/MVFR conds. .OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY... .Tuesday...Sight chance of an early morning shower with MVFR vsby, otherwise VFR. NW winds (right of 310 magnetic) 15G20KT. .Tuesday night-Wednesday...VFR. .Wednesday night...Chance of showers and possibly a tstm, with MVFR or lower conds, as low pressure passes to the south. .Thursday-Friday...VFR.
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&& .MARINE... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. SW flow increasing to 15-20 kt late today, with near shore gusts up to 25 kt late this afternoon and early this evening, warrants issuance of SCA for the ocean waters and the Long Island south shore bays. The SCA will continue through the night for the ocean E of Fire Island Inlet, and into early Tue morning E of Moriches Inlet, as those winds builds max seas up to 5 ft during that time. A wave of low pressure passing S of Long Island Wed night has some potential to produce SCA conditions on the ocean waters. ECMWF weaker with this wave as opposed to the stronger GFS, so have capped winds and seas under SCA thresholds for now. && .HYDROLOGY... On average a few tenths of an inch of rain should fall over the area this afternoon and tonight. However, given the expected abundant low level moisture, there is the potential for locally heavy rainfall with any given storm. As a result, there is the potential for minor flooding, especially for an area experiencing repeated storms producing locally heavy rainfall. No significant, widespread hydrologic impacts area expected from Tuesday and Tuesday night. Locally heavy rainfall is again possible Wednesday afternoon and night, with minor flooding possible yet again. There is still some uncertainty on how much the average rainfall will be from this system, so the possibility of localized flash flooding cannot be 100% ruled out at this time. No significant widespread hydrologic impacts are expected Thursday and Friday. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NYZ067>071. High Rip Current Risk through this evening for NYZ075-080-081- 178-179. NJ...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NJZ002-004-006-103>108. MARINE...Small Craft Advisory from 3 PM this afternoon to 9 PM EDT this evening for ANZ345-355. Small Craft Advisory from 3 PM this afternoon to 9 AM EDT Tuesday for ANZ350. Small Craft Advisory from 3 PM this afternoon to 6 AM EDT Tuesday for ANZ353. && $$ SYNOPSIS...Maloit NEAR TERM...Maloit SHORT TERM...Maloit LONG TERM...Maloit AVIATION...Goodman MARINE...Goodman HYDROLOGY...Maloit EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.