Area Forecast Discussion
Issued by NWS Upton, NY

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817 FXUS61 KOKX 241840 AFDOKX Area Forecast Discussion National Weather Service New York NY 140 PM EST Sat Feb 24 2018 .SYNOPSIS... A warm front approaches the region into tonight. A frontal system will affect the region with a low along the warm front moving across on Sunday. High pressure builds from the Midwest Sunday night and remains in control through the middle of next week. A low pressure system may approach for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Adjusted POPs near term using extrapolation from Doppler Radar and HRRR model reflectivity. An upper level jet from Baja California extends northeast through the Great Lakes for today. The heights at 250mb and 500mb remain nearly the same across the local region. At the surface, high pressure is moving farther away from the local region as the center of the high builds more into Southeast Canada. A developing low will be gathering energy and deepening as the low center moves into Missouri and Illinois with its associated warm front approaching the local region. Some weak lift already enabling some light rain to move into the region. Expecting rain to remain light without much forcing and with a relatively weak pressure gradient. The rain may become more periodic or intermittent in frequency across the coastal sections. The temperatures have already reached their maximum across much of the region, mostly low to mid 50s. Expecting temperatures to stay in the upper 40s to low 50s for the rest of the afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... The upper level jet strengthens, extending into Northern New England and the Canadian Maritimes tonight. The heights at 250mb slightly increase tonight across the local region. The 500mb heights remain nearly constant as a mid level ridge axis SE-NW orientation moves across the area. A strong shortwave pivots across the Great Lakes with increasing positive vorticity advection in the local region late tonight into Sunday. In addition, the upper level pattern shows diffluence in the jet levels for early Sunday and this conveys divergence. This increases the vertical forcing. At the surface, winds become more east to southeast and strengthen as the warm front continues to approach. The parent low to this front will be deepening as it heads into the Western Great Lakes, increasing the pressure gradient. The easterly flow will increase precipitable waters to between 1.1 to 1.4 inches, which will be above the 90th percentile for February 25th according to OKX sounding climatology. This increases the moisture content available for the forcing. For Sunday, the jet core moves closer to the region, with the right front quad moving near the area by the end of the day. As previously mentioned, the diffluence and divergence aloft will be there for Sunday morning into the early afternoon. At the surface, a low forms along the warm front with signals for triple point low. The rain continues tonight and increases in intensity late tonight through Sunday morning, when much of the rainfall is expected. Rain could become heavy at times and enhanced near higher terrain with orographic lift. Raw 2 meter temperatures from NAM and GFS were weighed more heavily in the forecast tonight and Sunday without much diurnal temperature range. Lows tonight upper 30s to lower 40s and highs Sunday mostly near 40-45. The core and jet streak maximum passes northwest of the region Sunday night. The heights at 250mb remain nearly steady Sunday and then slightly decrease late afternoon into the evening with a more rapid height fall late Sunday night. The heights at 500mb follow similarly with a slight decrease Sunday into Sunday evening followed by a greater decrease late Sunday night. Confluence occurs aloft Sunday night and the surface low moves east of the area Sunday night, giving way to high pressure building in from the Tennessee Valley. There will be a return to dry conditions and a more spatial spread of lows that will still be above normal. && .LONG TERM /MONDAY THROUGH SATURDAY/... The CONUS pattern of troughing in the west and ridging east of the Rockies looks to continue into next week. The upper pattern then appears to transition mid to late week next week as a closed low pres system moves onshore in California early, continues into the Plains mid week, and then possibly to the east coast by late week. Uncertainty abounds in the evolution of this upper energy as the week progresses. In terms of sensible weather, dry weather returns Sun night as low pres departs and high pres builds from the Midwest. The high will remain in control through the middle of next week, resulting in a continuation of above normal temperatures. Rain chances will begin to increase Thu as a WAA pattern ensues, although due to the aforementioned uncertainty in the upper pattern, precip could very well hold off until Thu night. Predictability is low on p- type this far out, but lack of cold air supply would favor liquid vs frozen at this point. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... A warm front approaches late tonight into Sunday. VFR for the rest of the afternoon, bcmg MVFR this evening, then IFR late tonight thru at least Sunday morning before improving conditions. -Shra/-ra through the period. N winds mostly under 10 kt shift NE this evening, then increase from the E and become gusty late tonight and Sunday morning. .OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY... .Sunday PM...-shra/dz with IFR improving to MVFR. .Sunday night and Monday morning...Chance of rain with IFR conds in the evening mainly KBDR/KISP/KGON. Otherwise bcmg VFR with areas of fog with IFR/LIFR conds possible overnight into the morning. .Monday afternoon through Wednesday...VFR. .Thursday...CHC sub-vfr in rain. CHC E winds G25kt. && .MARINE... Marine forecast remains on track. Sub-SCA conditions are expected through this evening with weak high pressure moving across the region. Easterly winds will increase late tonight into Sunday morning, with widespread SCA conditions expected. Potential for a period of marginal gale gusts during this time on the ocean, with seas building to 6 to 10 ft. Winds subside Sun Night with high pressure building in, but SCA ocean seas will likely take till Monday to subside. Sub SCA conds thereafter with high pressure building from the west. && .HYDROLOGY... Rainfall late today through Sunday is expected to produce around 1 to 1 1/2 inches of rain, much of it on Sunday. There could be some locally higher amounts, especially in any areas of orographic lift. With saturated grounds, minor poor drainage flooding is possible on Sunday. && .TIDES/COASTAL FLOODING... Easterly SCA winds will likely result in 1 to 1 1/2 ft surge and 3 to 4 ft waves into Western LI Sound, which may result in some localized minor flood/wave splashover in vulnerable areas with Sunday morning high tide. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 1 AM to 6 PM EST Sunday for ANZ330- 335-338-340-345. Gale Watch from 1 AM EST Sunday through Sunday afternoon for ANZ350-353. Small Craft Advisory from 1 AM Sunday to 7 AM EST Monday for ANZ355. && $$ SYNOPSIS...JM/NV NEAR TERM...JM SHORT TERM...JM LONG TERM...24 AVIATION...JC MARINE...JM/NV HYDROLOGY...NV TIDES/COASTAL FLOODING...NV EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.