Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 180542 CCA AFDOKX Area Forecast Discussion...CORRECTED National Weather Service New York NY 142 AM EDT Fri Aug 18 2017 .SYNOPSIS... A warm front will approach tonight and move north through Friday morning. A cold front approaches Friday, moving across the region late Friday night. A frontal system will slowly pass offshore on Saturday. High pressure will then build in through the beginning of next week, followed by a midweek cold frontal passage. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Main showers still located where higher sfc Theta-E is situated across central PA and farther north into Western Central NY State. This environment along with the showers approaches closer to the region towards daybreak. As showers enter, heavy downpours will be possible due to high precipitable waters of approximately 2 inches that will be moving in which goes with the higher Theta-E. An area of low pressure will track east across the northern Great Lakes tonight. A warm front associated with the system is expected lift north through the local area overnight and into Friday morning. Showers and possible thunderstorms will spread across the area overnight and into Friday morning. Temperatures tonight will be in the upper 60s to lower 70s.
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As a warm front moves north a strong southerly flow will usher in behind, bringing an influx of moisture across the area. Latest HRRR indicates some heavier shower activity in the 11-15Z timeframe Friday. This would certainly be possible as precipitable waters are forecast to increase to between 2 and 2.3 inches. Dewpoints will rise back into the 70s across the region along with instability resulting in thunderstorms and heavy rain to develop. There may be a break in the precipitation for a brief time once the warm front lifts north, and until the cold front nears later in the day. Storms will weaken and move into Long Island and southern Connecticut by Friday night. Temperatures on Friday will be in the upper 70s to lower 80s with lows in the upper 60s to lower 70s. There is a moderate risk of rip currents at NYC and Nassau County ocean beaches.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... The frontal boundary/sfc trof will slowly slide offshore on Sat. Trends will need to be monitored for a slowing of this feature, as the main upr trof which will force it ewd is still progged to be over OH at 18Z Sat. The slower the boundary exits, the slower shwrs and especially clouds will exit. Based on the 12Z data, areas along and w of the Hudson dry, with the rest of the area low chances for pcpn. Dry weather Sat ngt thru Mon ngt with high pres progged to move in. 12Z GFS timeheights indicate sunny skies on Mon with perhaps some fair wx cu, particularly along the sea breeze front. Chances for shwrs and tstms Tue thru Wed ahead of a cold frontal passage. Best chances are Wed closest to the front attm, so as the event draws closer pops may be eliminated for Tue. A blend of the guidance and 2m data was used for temps thru the period. The numbers will generally be abv average until the fropa next week. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... A warm front approaches from the southwest tonight. A cold front will approach from late Friday. Stratus deck that developed along the south shore of Long Island near KJFK has now spread to KISP and the other city terminals. Uncertainly remains as to whether it remains through the night, however keeping an optimistic forecast. Otherwise...VFR with deteriorating conditions around daybreak. Friday will be very unsettled with the threat of showers and scattered thunderstorms in the morning and then again with the approaching cold front late in the afternoon. There is uncertainty with improving conds in the warm sector after the warm front passes in the morning, may be too optimistic in the NYC metro. Gusty winds and MVFR/IFR are possible with any heavier shower or thunderstorm. Light southerly winds overnight before increasing again 10 to 15 kt Friday. Gusts to 25 kt possible Friday afternoon across much the region but especially along the coast. Higher gusts possible with any thunderstorm. .OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY... .Saturday night...MVFR or lower flight cat possible in showers/tstms with gusty winds possible during the evening. Fog/stratus with MVFR or lower conds may linger through the overnight. .Sunday and Monday...VFR. light NW wind becoming SW by Late Sunday and Monday. .Tuesday...Iso shra/tstms possible with MVFR or lower conds...otherwise VFR. && .MARINE... A warm front approaches tonight and moves across the area waters Friday morning. Southerly winds will increase ahead of an approaching cold front Friday, resulting in 15 to 20 kt winds. Seas may briefly build close to 5 feet Friday afternoon and into Friday evening. Will hold off on a SCA for Friday afternoon and evening given low confidence in widespread SCA conditions developing. There may be some lingering 5 ft seas on the ocean Sat as a front passes e of the waters, but all areas are fcst to be blw sca lvls by Sat ngt. Winds and seas are then progged to remain blw sca lvls on all waters thru next Wed. && .HYDROLOGY... Heavy rainfall is possible by morning as a warm front moves northward through the region. Another round of heavy showers and thunderstorms will be possible by evening with the cold frontal passage. Rainfall accumulations are expected to be around a half an inch to an inch, with locally higher amounts possible in thunderstorms. At this time it remains difficult to pinpoint where heavier showers and thunderstorms will develop. No significant hydrologic impacts are expected, but some minor urban flooding is possible. Impacts from potential showers and thunderstorms Tuesday into Wednesday are uncertain at this point, however at least minor nuisance flooding will remain a possibility. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JMC/Fig NEAR TERM...MD/Fig SHORT TERM...Fig LONG TERM...JMC AVIATION...CB MARINE...JMC/Fig HYDROLOGY...JMC/MD/Fig is the U.S. government's official web portal to all federal, state and local government web resources and services.