Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 170810 AFDOKX Area Forecast Discussion National Weather Service New York NY 410 AM EDT Fri Aug 17 2018 .SYNOPSIS... A frontal system will approach today and pass offshore on Saturday. A wave of low pressure is forecast to develop on the cold front, slowly passing south and east of Long Island Sunday into Monday. A warm front approaches on Tuesday, lifting through Tuesday night or Wednesday morning, followed by another cold front Wednesday night. High pressure then builds in for Thursday. && .NEAR TERM /THROUGH TONIGHT/... Two hazards in the near term: heat and svr wx. Temps today in the 80s to near 90, and dewpoints will increase as the flow backs to the s by 16z. The airmass is warm so not much modification from the ocean is expected. The heat idx may approach 100 in the normal NJ hot spots, as well as srn portions of the city, with otherwise 90s across the region. Some upr 90s even across most of Long Island due to the enhanced humidity. No changes made to the heat advy, as only a few spots, which are in the advy, reached the 2-day 95 degree criteria yesterday. A complex svr threat today, as the increasing moisture will pump sbcape abv 2000, and for some spots abv 3000 in the mid aftn early eve window. Aftn and eve progs have llvl winds veering to perpendicular at h7. 0-1km ehi about 3 in the high cape areas. 0-6km shear increasing thru 00z. This setup seems to yield a damaging wind and isold tor threat. There is the potential that this does not pan out, particularly if some of the the global modeling is correct, and convection is initiated earlier in the day not allowing cape to build sufficiently. However, the NAM seems to be verifying this mrng, and has been performing well with tstms recently, lending confidence to the svr threat which is reflected in the official fcst, hwo and ehwo. Mesoscale trends can now be followed thru the day to fine tune the fcst. The tstms should weaken aft midnight, but may not completely dissipate like in the early summer. The upr forcing will be displaced from the activity however, not getting here until Sat. This may help to serve as a limiting factor for late ngt svr. There is a moderate rip current risk at the ocean today. && .SHORT TERM /SATURDAY/... The cold front will slowly pass thru the cwa on Sat. At this point it looks like there might be too much convective debris and there might also be a battle with compensation subsidence, thus limiting the svr threat. There will however be some upr support along with the front, and little to no cin, so at least some sct shwrs and tstms are fcst. Warm and humid with heat indices in the lower 90s. There is the potential for the 2-day heat advy criteria to be met across portions of LI, but right now the amount of clearing needed is too uncertain to produce the required fcst confidence. The NBM was followed for temps. There is a moderate rip risk at the ocean. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... It appears that an unsettled pattern will dominate much of the long term period. A shortwave trough approaches from the Ohio Valley Sat night. Meanwhile, a weak cold front associated with low pres over Nova Scotia will drop through the area becoming nearly stationary somewhere in the Mid Atlantic region on Sun. A wave of low pres will develop along the frontal boundary and slowly pass to the S and E of Long Island into Mon. There is some uncertainty with how far south the front gets and how much the upper trough sharpens as it approaches. This will ultimately determine where the low tracks. Nevertheless, have raised pops a bit through Sun night since most guidance indicates pcpn. NAM begins to diverge with its upper pattern by Sun night so it was discounted. As the wave moves out to sea on Mon, ridging briefly builds in providing dry conds with near seasonable temps, although it will remain humid. Onshore winds return Mon night as a warm front approaches from the S, pushing dewpoints back into the 70s and thus increasing humidity levels further. Much of Tue may remain dry with perhaps an isolated shower/tstm N and W of NYC with chances increasing further Tue night and Wed as the front lifts through. We`ll remain warm sectored on Wed as a cold front approaches from the west, progged to move through Wed night. Sct showers/tstms should increase in coverage during the aftn and continue until the front moves through. High pressure returns for Thu. Temps start out below normal on Sun due to rain and clouds, near normal Mon and behind the front Thu, and above normal Tue and Wed. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... A cold front will slowly approach from the west today. Winds continue to gradually diminish overnight, then strengthen from the S-SW later today. Afternoon seabreezes expected today and should even reach KEWR/KTEB after 18Z. Could see a few showers and maybe a stray tstm near KEWR/KTEB between 18Z-21Z, with the main push of activity with the approaching front arriving between 22z-00z for the NYC terminals. Timing should be slightly later east of NYC. Showers and thunderstorms expected Friday night, with MVFR/IFR conditions in storms. Winds become SW late. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: KJFK TAF Comments: Occasional wind speeds may be higher than forecast. Amendments likely late for timing of SHRA/TSRA. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Amendments likely late for timing of SHRA/TSRA. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Timing of seabreeze may be off by +/- 1 hour. Amendments likely for timing of SHRA/TSRA this afternoon/evening. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Amendments likely for timing of SHRA/TSRA this afternoon/evening. KHPN TAF Comments: Amendments likely for timing of SHRA/TSRA this afternoon/evening. KISP TAF Comments: Occasional wind speeds may be higher than forecast. Amendments likely late for timing of SHRA/TSRA. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .Sat...MVFR or lower conds at times in any showers/tstms. W flow becoming NE Sat eve. .Sun...Chance of MVFR cigs in the morning. .Mon...VFR. .Tue...Chance of MVFR cigs. && .MARINE... An enhanced sly jet is expected to develop this aftn and eve, bringing the wrn ocean and wrn bays near sca lvls. Elsewhere, winds and seas are expected to remain blw criteria, however, strong tstms in the aftn and overnight could produce hazardous winds and torrential rain reducing vis. Additional tstms can be expected Sat. Marginal SCA winds/seas are possible on the ocean waters Sun into Sun night resulting from a moderate NE flow. Otherwise, sub-advsy conds are expected through the period. && .HYDROLOGY... Heavy tstms this aftn and tngt could result in minor urban flooding. There is also an isold flash flood threat where the strongest activity concentrates. There is the potential for between 1/2 and 1 inch of rainfall associated with a wave of low pressure passing south of Long Island Sun/Sun night. No hydrologic impacts are expected from this. Additional showers/tstms are expected Tue and Wed associated with a frontal system. These will have the potential to produce heavy rain, especially on Wed. && .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 6 PM EDT this evening for NYZ071>075- 176>179. NJ...Heat Advisory until 6 PM EDT this evening for NJZ006-104- 106>108. MARINE...Small Craft Advisory from 2 PM this afternoon to 1 AM EDT Saturday for ANZ345-353-355. && $$ SYNOPSIS...JMC/24 NEAR TERM...JMC SHORT TERM...JMC LONG TERM...24 AVIATION...BC MARINE...JMC/24 HYDROLOGY...JMC/24 EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.