Area Forecast Discussion
Issued by NWS Upton, NY

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267 FXUS61 KOKX 181822 AFDOKX Area Forecast Discussion National Weather Service New York NY 222 PM 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/... Forecast mainly on track. Montgomery NY reached heat advisory criteria with heat index of 103 degrees at 2PM. Temperatures and dewpoints on track. Pushed up timing of slight chance of showers and thunderstorms for interior parts of Lower Hudson Valley late this afternoon, limited coverage to start with capping aloft to overcome. WNW flow sets up aloft by this afternoon as the deep layered ridge axis sinks to the SE. 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 /15Z MONDAY THROUGH FRIDAY/... A cold front will approach this evening, and cross tonight. High pressure builds in from the north tonight. Widely scattered tstms with brief MVFR/IFR vsby and gusty winds are likely ahead of a pre-frontal trough late this afternoon into early this evening. 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. An additional round of showers, with low prob of a thunderstorm, with the front itself late tonight as it passes through. Potential for a brief period of SCT MVFR/IFR stratus at KISP or KGON this evening. Gusty S-SW flow of 10-15 kt with gusts 20 kt this afternoon and early evening. Sea breezes at KJFK/KLGA/KISP will be stronger, with sustained winds 15-20 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:/www.weather.gov/zny/n90 KJFK TAF Comments: Sparse convection potential this evening, btwn 22z and 01z. S winds 15-20ktG25kt through around 01z. KLGA TAF Comments: Sparse convection potential this evening, btwn 22z and 01z. S winds 15-20ktG25kt through around 01z. KEWR TAF Comments: Sparse convection potential this evening, btwn 22z and 01z. SW winds 15-20ktG25kt through around 00z. KTEB TAF Comments: Sparse convection potential this evening, btwn 22z and 01z. SW winds around 15ktG20-25kt through around 23z. KHPN TAF Comments: Sparse convection potential this evening, btwn 21z and 01z. KISP TAF Comments: Sparse convection potential this evening, btwn 21z and 01z. S winds 15-20ktG25kt through around 00z. .OUTLOOK FOR 18Z 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...Showers likely, possibly a tstm, with MVFR or lower conds, as low pressure passes to the south. .Thursday-Friday...VFR. .Saturday...A chance of showers, possibly a thunderstorm, late Sat into Sat Night. && .MARINE... Ocean wind gusts to 20 kt occurring with seas building to 2 to 3 ft this afternoon. This will further trend up for the remainder of the day. 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 until 8 PM EDT this evening for NYZ067>071. High Rip Current Risk until 9 PM EDT this evening for NYZ075- 080-081-178-179. NJ...Heat Advisory until 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...JM/Maloit SHORT TERM...Maloit LONG TERM...Maloit AVIATION...Goodman/NV MARINE...Goodman HYDROLOGY...Maloit EQUIPMENT...

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