Area Forecast Discussion
Issued by NWS Upton, NY

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599 FXUS61 KOKX 191559 AFDOKX Area Forecast Discussion National Weather Service New York NY 1059 AM EST Thu Jan 19 2017 .SYNOPSIS... Weak high pressure will be in control through Friday morning. An upper level disturbance will approach from the south on Friday, and weaken as it moves across Friday night. High pressure will then briefly return on Saturday. Deepening low pressure moving across the southern states on Sunday will reach the southern Mid Atlantic region by Monday morning, while high pressure builds southeast into the Canadian Maritimes. The low will intensify into a significant coastal storm as it moves up the coast toward the area Monday through Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Northern stream shortwave passing near the region this morning will provide mostly cloudy skies in some places. Clouds will begin to clear through late this morning as NW downslope flow dries out the lower levels of the atmosphere behind the shortwave. Mostly sunny skies are forecast thereafter with temperatures rising to around 10 degrees above normal. Readings range from the upper 40s inland to the low 50s in NYC/NJ metro and Long Island. It would not be out of the question for readings to be a bit higher based on the anomalously mild pattern we are currently seeing across the country. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Middle and upper level ridging builds overhead tonight with surface high pressure in control at the surface. Some hints at returning stratus deck overnight on the 00Z NAM12. However, this appears aggressive and will go with a mostly clear forecast. Time heights from the 4-km nam and GFS show some increase in moisture around 2kft, but not enough to warrant a broken or overcast deck of stratus. Lows will range from the upper 20s inland to the lower and middle 30s near the coast and NYC metro. Southern branch shortwave energy across the midwest will eject eastward and shear out as it approaches on Friday. The ridge axis moves overhead Friday and weakens in response to the approaching energy. Frontal boundary associated with this system likely stays to the south, but with the energy approaching clouds increase from south to north through the day. Much of the daytime on Friday will be dry with pops increasing to likely in the late afternoon and early evening for mainly the NYC metro and NE NJ tapering to chance into the Hudson Valley and western Long Island. There is good agreement among the 00z GFS, GEFS, ECMWF, CMC, NAM, RGEM, and SREF in an average of a tenth of an inch of liquid between 21z Fri and 00z Sat where likely pops are forecast. High temperatures on Friday continue about 5 degrees above normal in the lower and middle 40s. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Likely PoP in the forecast for Friday night for NYC metro, the lower Hudson Valley, and western Long Island as a weakening frontal system moves across. With the upper level support plowing into a longer wave ridge and shearing out, chances for rain appear lower across most of southern CT and eastern Long Island. Another trailing shortwave may produce a few sprinkles or showers Saturday afternoon, with the bulk of the day being dry and on the mild side, with highs 50-55. Attention focuses thereafter on a storm forecast to take shape as Pacific upper jet energy crashing onshore the California coast later this week consolidates over the southern states this weekend, then intensifies over the Mid Atlantic region as the upper level system closes off and becomes negatively tilted, and as it picks up significant moisture aloft from a tropical connection to the Caribbean and Eastern pacific and interacts with a vertically stacked high moving into the Canadian Maritimes. For us this spells potential for multiple impacts including strong winds, heavy rain and coastal flooding, with likelihood of occurrence in that general order. EPS probabilities for wind gusts over 50 kt have been as high as 60-80 percent for the immediate coastline for two successive cycles, and the extended 00Z GFS/ECMWF MOS guidance predicts sustained winds 25-30 kt along the coast and in the higher interior elevations. Most of the rain should fall over a fairly long period of time, but there is potential for a period of heavy rain and some rumbles of thunder late day Monday into Monday evening as the low moves up the coast, with low level moisture convergence becoming maximized via a 60-70 kt easterly LLJ and lessening static stability, with TT indices approaching 50 and Showalter indices dropping to about 1C. These impacts could last into Tuesday if the storm slows down more than model fcst, which is quite possible as it closes off aloft. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... High pressure builds in from the west through the TAF period. Mainly VFR conditions are expected today into much of tonight. Also another exception will be Friday when there will be another chance of MVFR/IFR before and with the rain. There is though some concern for MVFR cigs developing this afternoon across the area, but confidence of occurrence is low at this time. Winds will be generally NW near 10 kt, then drop off again tonight to a more northerly direction at near 5 kts or less. 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: Winds could be a few kts higher than forecast this afternoon. Low chance of MVFR cigs this afternoon/evening. KLGA TAF Comments: Winds could be a few kts higher than forecast this afternoon. Low chance of MVFR cigs this afternoon/evening. KEWR TAF Comments: Winds could be a few kts higher than forecast this afternoon. Low chance of MVFR cigs this afternoon/evening. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Winds could be a few kts higher than forecast this afternoon. KHPN TAF Comments: Winds could be a few kts higher than forecast this afternoon. Low chance of MVFR cigs this afternoon/evening. KISP TAF Comments: Winds could be a few kts higher than forecast this afternoon. Low chance of MVFR cigs this afternoon/evening. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... .Friday-Friday night...MVFR or lower in -RA, mainly late Friday afternoon through Friday evening. .Saturday-Saturday night...Mainly VFR. .Sunday-Sunday night...MVFR or lower in -RA, mainly late Sunday afternoon through Sunday night. Moderate rain develops at night. NE gusts 20-25 kt by end of Sunday afternoon. NE gusts 30-40 kt Sunday night. .Monday...Chance of IFR with moderate to heavy rain and strong E-NE winds. NE gusts 35-45 kt. && .MARINE... SCA for Hazardous Seas remains in effect on the ocean waters today. Easterly swell from an offshore low should help keep seas above 5 ft through the day, before subsiding this evening. If the trend is slower than currently forecast, the SCA may need to be extended into a portion of tonight, mainly east. Then winds and seas should be below SCA levels on all waters through Sunday morning. An intensifying storm moving up the coast early next week will likely bring easterly gales to all waters from Sunday night into Monday night, Storm force wind gusts may be possible on the ocean and easternmost Long Island Sound. && .HYDROLOGY... No significant precipitation is expected through Saturday night. Significant rainfall of 1.5 to 3 inches, with locally higher amounts over 4 inches, is likely with a coastal storm early next week. Highest rainfall amounts currently expected across Long Island and coastal CT. This should be enough to cause at least minor areal flooding. Current 24-hour FFG of 4 inches for the Yantic River in eastern CT suggests small stream flooding may be likely, and minor flooding of some larger rivers is not totally out of the question, should the higher rainfall amounts materialize. && .TIDES/COASTAL FLOODING... A coastal storm may cause minor to locally moderate coastal flooding if its highest surge coincides with the morning high tide cycle either Mon or Tue, which is the higher of the two daily high tide cycles. Surge needed to cause minor coastal flooding is about 1.5-2.5 ft on the Long Island South Shore back bays, and 2.5-3.0 ft elsewhere. Surge needed to cause moderate coastal flooding is about 2.5-3.0 ft on the Long Island South Shore back bays, and 3-4 ft elsewhere. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 6 PM EST this evening for ANZ350-353-355. && $$ SYNOPSIS...Goodman/DS NEAR TERM...BC/Goodman/DS SHORT TERM...DS LONG TERM...Goodman AVIATION...JM MARINE...Goodman/DS HYDROLOGY...Goodman/DS TIDES/COASTAL FLOODING...

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