Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 201937 AFDOKX Area Forecast Discussion National Weather Service New York NY 337 PM EDT Thu Jul 20 2017 .SYNOPSIS...
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A complex of showers and thunderstorms will approach the Tri-State Area this evening into early tonight. Dry conditions are expected for Friday in the wake of a cold front, however, hot and humid weather will continue. A warm front will approach late Saturday and lift north across the area into Sunday morning. Multiple waves of low pressure move through the area through early next week, followed by building high pressure for the mid to late week.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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The heat was on across the Tri-State Areas as of midday with the temperature reaching into the 90s at Central Park for the 9th time this year and tying June 13th for the hottest day of the year so far with the high up to 94 degrees as of writing. See the climate section below for more heat facts for 2017. The Heat Advisory remains in effect through this evening where it is out due to the combination of hot temperatures and high humidity values. Via mixing, dew points have since dropped across the area with a peak value of 77 degrees noted at JFK which is up there climatologically for this part of the world. The main issue tonight centers around the complex of showers and thunderstorms (in technical terms a MCS or mesoscale convective system) currently across the western parts of Upstate New York. All operational models have been keying on for several runs that this feature could impact our area this evening into tonight. The 12Z guidance has come in with better agreement, especially on the higher resolution models mainly the NAM 3km, the HRRR and the RAP which are in very good agreement even with timing. The somewhat detailed NAM 12Z or operational WRF-NAM and even the 12Z operational GFS which has been weaker with this complex on most runs, have hold this feature together as it heads towards the Lower Hudson Valley by this evening. As a result of this, I have boosted PoPs significantly area-wide, especially from The City on west and north. There are still some signs as this complex gets toward The City it may weaken as it moves into the maritime influenced air mass, but if this complex can come in initially more vigorous it may have better shot to maintain some thunderstorm activity all the way to Long Island. If not, then activity here on The Island may be more showers with no thunderstorms. Timing also has sped up arriving in the western CWFA by 6-8 PM and moving through The City around 9-11 PM and Long Island/southeast CT mainly between 10 PM and 2 AM. CAPE Values as well as LIs progged are much greater on the WRF- NAM than the GFS which is why the GFS remains weaker with this complex as it heads further east toward us. SPC has pushed a Slight Risk for severe thunderstorms into western Orange County for this evening. I went ahead and added gusty winds and heavy rain as hazards from the Hudson River on west where confidence in this is greatest. In summary: * A complex of thunderstorms will approach the area this evening from the west and move east, possibly weakening as it moves toward the immediate coast. * Some strong to severe thunderstorms are likely, with gusty winds over 50 mph possible along with hail. * Downpours producing rainfall rates in excess of one inch per hour may occur in any heavier thunderstorms that could result in poor drainage flooding, especially in more urbanized areas. * Those outdoors with plans this evening should watch the sky and be aware for any alerts. Travel may be impacted by low visibility, ponding of water/poor drainage flooding and gusty winds that blow any objects over or around especially during the evening commute. In the wake of activity, patchy fog may form in areas that get heavier rain briefly and temps cool to near the dewpoint. This is mostly likely in Orange County this evening for a bit. The actual "cold" front will lag a bit behind the convection. Based on progged Theta-E from the GFS (which sometimes is the best indicator of front locations in subtle temperature gradient situations) shows a packing of contours around 3 AM to 6 AM across the area, indicative of the front`s location. Dewpoints may drop a hair with the front`s passage. Lows tonight will still be in the upper 60s in the coolest spots well north and west of The City with readings in the mid to upper 70s in more urban areas. Some spots may actually set a calendar day low during any heavier convection this evening as rain cooled air drops toward the surface in convective downbursts. There is a low risk of rip current development through this evening.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
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West to northwest flow aloft sets up for Friday as the front drifts on south and stalls toward the Delmarva Peninsula. Drier air aloft should mix down a bit as the flow aloft remains offshore to 925 mb. However, this flow aloft is light (10 kts or less) that the seabreeze will likely return in the afternoon which would bring dewpoints at the surface back up. With the offshore, flow I have favored the warmer end of guidance and gone with the higher end of MOS. This will push temps to near 90 over well inland areas and into the low to mid 90s along the coast and in and around immediate NYC and urbanized areas in North Jersey. Thus the Heat Advisory was extended for most areas today except for Rockland, Westchester, western Bergen and southern Fairfield Counties which look to fall just short of criteria. Although moisture and some instability lingers I have kept the forecast dry as the presence of a lee-side surface pressure trough and seabreeze do not look to be enough to pop any lid to trigger convection tomorrow. Dry for Friday night with west/northwest flow aloft holding firm. Lows should be a little cooler, with readings in the low to mid 60s well north and west of The City to the mid 70s in NYC and Hudson County, NJ. I`m not enthused much for convection during the day on Saturday. Westerly flow aloft sets up and a surface stationary front is well to our south. Again, the only triggers will be the lee side surface pressure trough and the sea breeze. I left in a low end slight chance of a shower or thunderstorm along the sea breeze on Long Island and over interior areas where differential heating of the hilly terrain may set off something. Highs will be a bit cooler and many spots will only be in the 80s for a high. However, humidity will still be enough to make it a sticky Saturday. The warm front should start to lift back north Saturday night and return the potential for showers and thunderstorms from the south and west. Models show a spread in timing, so I broadbrushed in PoPs for this time frame. The better chance should be closer to sunrise on Sunday as a low-level jet of 40 kts+ moves from the Jersey Shore toward Long Island. With high PWAT values approaching 2 inches per the GFS, the threat for heavy rain will be there Saturday night along with gusty winds in any more potent convection. Lows will be a little warmer due to the increase in clouds and warm front lifting north.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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Much of the extended will be dominated by an unseasonably south latitude polar jet orientation, with multiple short waves moving through the Northeast in northwest flow, which is typically a pattern that offers very little predictability. Despite considerable uncertainty for the extended period, the pattern remains favorable for periods of heavy rainfall and thunderstorms as multiple Mesoscale Convective Systems move through the area in northwest flow. The greatest complexity with the forecast remains on where any frontal boundaries stall, which have impacts on temperature, wind, instability, cloud cover, etc, but most importantly on where exactly these systems will track. The forecast will need to be monitored over the next few days for any heavy rainfall/flooding and severe potential. By mid week, a brief respite in the active wet pattern may come as ridging builds aloft and confluent flow allows a surface high to strengthen. At least briefly, dew points and subsequently relative humidity values will finally fall to more comfortable thresholds. However, this may be short lived as the overall pattern still looks to be active.
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&& .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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Convective Complex Likely to Impact Terminals This Evening... A weak trough will be near or just west of the NYC terminals for the remainder of this afternoon, while a cold front approaches from the eastern Great Lakes. A convective complex developing over western NY state ahead of the cold front, will race quickly SE this afternoon into early this evening. There is some uncertainty as to how much of the complex stays together, but it seems likely that it will have an impact on most of the terminals, especially from NYC and points north and west. Strong gusty winds are possible with this activity. For the most part, outside of the convection, VFR conditions will prevail through Monday. W-SW flow this afternoon around 10 kt, with some occasional gusts up to 20 kt. Coastal terminals have the best chance for gusts this afternoon. Winds will become Northerly behind the complex this evening, then W-NW overnight into Friday morning. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Occasional gusts up to 20 kt this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KLGA TAF Comments: Winds may vary W-SW early this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KEWR TAF Comments: Winds may vary W-SW early this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KTEB TAF Comments: Winds may vary W-SW early this afternoon. Timing of showers and thunderstorms could be off by 1-2 hours this evening. KHPN TAF Comments: Timing of showers and thunderstorms could be off by 1-2 hours this evening. KISP TAF Comments: Timing of showers and thunderstorms could be off by 1-2 hours this evening. .OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY... .Friday Afternoon through Saturday...VFR. .Saturday Night-Tuesday...Episodes of showers and thunderstorms with MVFR or lower conditions possible.
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&& .MARINE...
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Although winds and seas are forecast to remain below SCA (Small Craft Advisory) levels of 25 kt and 5 ft from tonight through Saturday night, there is the potential for thunderstorms tonight and again Saturday night that could result in higher waves and winds. Marine Weather Statements and/or Special Marine Warnings are possible during this time. Depending on the exact track of the stalled front, southerly swells may begin to increase through the weekend into early next week, with a low probability for SCA conditions on the ocean by Monday. Conditions will gradually improve by mid to late week as winds decrease in building high pressure, allowing any lingering swells to slowly subside.
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&& .HYDROLOGY...
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There is a threat for a convective complex to track across the area this evening into early Friday morning. The main threat if this activity materializes would be minor urban flooding, with a low threat for flash flooding. A chance for flooding in periods of heavy rainfall and thunderstorms will continue late Saturday night into Sunday and Monday as a slow moving frontal system interacts with a moist and unstable airmass.
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&& .CLIMATE...
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Today marked the 9th day of 2017 the temperature has reached at least 90 degrees at Central Park. So far we have had two heat waves (at least 3 consecutive days of 90 degrees or greater) in 2017 at Central Park - from May 17th through May 19th and from June 11th through the 13th. The highest temp of 2017 at The Park has been 94 on June 13th and today, July 20th. Highest temps of 2017 for the other main climate stations in the area as of 3:10 PM EDT today: LaGuardia Airport: 101 on 6/13 JFK Airport: 94 on 6/13 and 7/20 Islip: 93 on 6/13 Newark: 99 on 6/13 Bridgeport: 94 on 6/13
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Heat Advisory until 6 PM EDT this evening for CTZ009. NY...Heat Advisory until 6 PM EDT Friday for NYZ072>075-078-080- 176>179. Heat Advisory until 6 PM EDT this evening for NYZ069>071. NJ...Heat Advisory until 6 PM EDT Friday for NJZ004-006-104>108. Heat Advisory until 6 PM EDT this evening for NJZ103. MARINE...None.
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&& $$ SYNOPSIS...MD/CS NEAR TERM...CS SHORT TERM...CS LONG TERM...MD AVIATION...DW MARINE...MD/CS HYDROLOGY...MD/CS CLIMATE...

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