Area Forecast Discussion
Issued by NWS Upton, NY

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195 FXUS61 KOKX 290834 AFDOKX Area Forecast Discussion National Weather Service New York NY 434 AM EDT FRI JUL 29 2016 .SYNOPSIS...
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Low pressure over the Delmarva this morning passes to the south and east of Long Island through this afternoon. High pressure will then briefly build into the region tonight into the first half of Saturday, giving way to low pressure approaching from the Ohio Valley later in the day. This low will pass to the north as a few waves of low pressure pass along a frontal boundary to the south into early next week. High pressure then returns for the middle of the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Deep-layered lift with the approach of an upper jet and mid level short wave trough this morning will result in a strengthening frontogenetic band to the NW of surface low pressure over the Delmarva. Latest radar imagery shows band progressing across eastern PA and central MD with localized heavy rainfall reports across this area. Rainfall amounts up to 0.50 inches an hour were noted across eastern PA. Latest guidance has trended farther south with the low track and thus the axis of heaviest rain which pivots across the area this morning. There is good model clustering on keeping the heaviest rain to the south of Long Island. That being the case, coastal sections are still forecast to receive between 1 and 2 inches with localized higher amounts. The biggest change in the forecast is across the Lower Hudson Valley and interior southern CT, where less than an inch is expected on average. Thus,the flood watch has been trimmed back and remains in place for NE NJ, NYC Metro, LI, and coastal CT. Precipitable water values around 2 inches with upper air soundings typical of a tropical airmass. Narrow CAPES support slowly rising updrafts with mainly heavy showers and isolated thunderstorms. Due to the farther south low track, severe weather is unlikely. The heaviest rain will exit the area by late morning, perhaps lingering across eastern LI and SE CT into early afternoon. Thereafter, there will be a chance of scattered showers and possibly a thunderstorm, especially across the interior where there will be some clearing. Daytime highs will range from the upper 70s to lower 80s. It will remain very humid with dew points around 70 and little change in airmass on the backside of the low this afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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Weak ridging builds behind the shortwave tonight with surface high pressure building from the northwest. Lows will be near seasonable levels, but remaining muggy. Weak high pressure will remain over the region Saturday morning, resulting in a dry Saturday morning. Models have trended quicker with the next approaching shortwave, which may trigger scattered showers and thunderstorms as early as Saturday afternoon. Eastern LI and SE CT may be able to remain dry most of the day. Highs also will be near seasonable levels.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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Latest NWP guidance in fair agreement with the H5 pattern across North America consisting of strong high pressure over the southwest US...a Bermuda high over the western Atlantic and a mean trough extending from west of the Rockies to the east coast this weekend. Early next week the high out west expands back into the southern Plains sharpening the trough east of the Mississippi. The trough moves east of the area on Tue with upper level ridging building in for the middle of the week. Model trends over the past 24 hours have sped up the weekend system with pcpn moving in during the day Sat. The shortwave is lagging behind the RRQ of a 65kt upper jet...but could have decent warm rain processes with PW`s around 2 inches. However...the GFS looks suspicious aloft between 00z and 12z developing a coupled vort max/min in the mid levels thus enhancing pcpn total at the sfc. So...while there will likely be overrunning Sat night with a frontal boundary to our south...the best dynamics associated with the shortwave appear to pass to the N on Sun with the majority of the rainfall likely remaining to our N with areas N and W of NYC having the best chance to see pcpn. A few weak waves of low pres does develop along the boundary Sun and Sun night...but they look to pass too far S to have any real impact on the region. Have remained with chc pops for most of the area during this time except NW zones which will be closest to the upper jet and shortwave energy. There is also uncertainty with the location of the frontal boundary. EC is further N with it on Sun tracking the waves directly over the local area. Upper trough axis approaches Mon and moves through Mon night with sct showers/thunderstorms expected during this time. An isolated shower is possible on Tue although there may not be enough moisture and we could be capped as upper level ridging begins to build in. The remainder of the week looks dry with increasing heat and humidity.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Low pressure along the Mid Atlantic coast will pass to the south today. Associated bands of heavy showers with IFR vsby have already taken shape from just north of NYC into northern NJ, eastern PA, and northern MD. KTEB/KHPN have already experienced IFR and brief LIFR vsby with the heavier activity, and think most of this activity will remain there and at KEWR through about 10Z, then move eastward and impact all of the NYC metro terminals plus KHPN from about 10Z until at least 14Z, and KISP/KBDR from 11Z to at least 15Z. LIFR conditions at KGON attm should improve to IFR as rain arrives there by 12Z and continues until at least 16Z. Occasional rumbles of thunder not entirely out of the question. These showers could last a couple of hours longer than outlined above, then a slow improvement to VFR expected this afternoon. NE winds could gust between 15-20 at the coastal terminals this morning. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .Late Fri night into Sat morning...Light fog with MVFR vsby possible...then VFR late Sat morning. .Sat afternoon into Sunday...Chance of showers and possibly a tstm. MVFR or lower conditions possible. .Sunday night-Mon night...Chance of showers. MVFR conditions possible. .Tue...Mainly VFR. && .MARINE...
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Winds and seas are expected to remain below small craft advisory levels through Saturday. Low pressure is forecast to track south of the waters today with strengthening E/NE winds through this afternoon. Winds and seas are forecast to remain below SCA, but could gusts up to around 20 kt, especially on the ocean waters east of Moriches Inlet. Winds diminish tonight as high pressure builds across the waters. Sub-advsy conds are then expected through the rest of the forecast period.
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&& .HYDROLOGY...
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A flash flood watch is in effect for much of NE NJ, NYC Metro, LI, and coastal for the potential of 1 to 2 inches with locally higher amounts. The axis of heaviest rain at this time is expected across eastern sections of LI and SE CT. The next chance for organized rainfall Saturday into Sunday. Less than an inch is expected.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...Flash Flood Watch through this afternoon for CTZ009>012. NY...Flash Flood Watch through this afternoon for NYZ071>075- 078>081-176>179. NJ...Flash Flood Watch through this afternoon for NJZ004-006- 103>108. MARINE...None. && $$ SYNOPSIS...24/DW NEAR TERM...DW SHORT TERM...DW LONG TERM...24 AVIATION...Goodman MARINE...24/DW HYDROLOGY...24/DW

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