Area Forecast Discussion
Issued by NWS Upton, NY

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658 FXUS61 KOKX 281154 AFDOKX Area Forecast Discussion National Weather Service New York NY 754 AM EDT THU JUL 28 2016 .SYNOPSIS... Weak high pressure slides offshore today. A wave of low pressure approaches and passes nearby Friday. High pressure briefly builds into the region for Saturday. Unsettled weather returns Sunday and Sunday night with the passage of another low pressure system. Drier weather is expected for the first half of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The region will lie between a closed low over Northern Quebec and Southeastern US ridging today...with zonal upper flow gradually backing to the SW ahead of a broad trough digging east of the Mississippi River. Hot and humid conditions today...with highs in the lower to mid 90s across the interior. Heat indices across NYC metro/NE NJ amd Lower Hudson valley will likely run in the mid to upper 90s. A few spots across NE NJ could flirt with 100 degrees in the afternoon as sea breeze works inland and increases dewpoints...but appears to be sparse. Southerly flow along the coast will promote early sea breeze development and should cap temps in the mid to upper 80s along south coasts. Stratus advecting in off the ocean this morning...expected to overspread LI and SE CT through daybreak. Patchy fog possible along south coastal areas. Expect stratus to mix out fairly quickly after daybreak with strong heating. Weak shortwave energy moving through aloft and ample moisture could spark an isolated shower/tstm along the sea breeze boundary late morning into afternoon. Limited instability...potentially capped at mid-levels...should keep any tstm development pulsey and sub-severe. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Models in good agreement with a southern wave over the Lower Mississippi River Valley getting picked up by a digging Upper Mississippi River Valley/Great Lakes trough today...and then sliding ne towards the area Friday. At the surface...developing low pressure along a stalled frontal boundary over the Tennessee River Valley tonight...track ne towards the region Friday morning. Models are converging on a track in the vicinity of the region on Friday...but still subtle differences in terms of timing and track will present a significant mesoscale forecast challenge. Synoptic lift...interacting with deep gulf moisture of 2 to 3 stds above normal...instability feed from the south...and focus for convergence along the warm front/coastal front ahead of the approaching low will provide the ingredients for heavy rainfall during the late tonight through into Friday afternoon period. To the north of the track of the 850 hpa low...models indicating a moderate to heavy frontogenetic rain band with a little if any convection. Operational and ensemble depicting potential for 1 to 3 inches within this swath over a 6 hr period. Along and just on the cool side of the warm front back to the triple pt...potential exists for not only elevated convection...but surface based. This would pose both a flash flood threat and lesser severe threat. Threat for flash flooding from training convection as steering flow closely parallels warm front. The GFS/NAM initialized SBU WRF is depicting swaths of 7 to 10 inches along this boundary due to training convection...but location is quite varied. This is a concerning signal, and cant be ignored based on the available instability and moisture. The limited severe threat appears to be for weak tornadoes based on strong veering wind profile...low lcls...low-level cape...and sufficient low-level shear/helicity in se inflow. Unfortunately the exact mesoscale setup will likely only become clear as the event nears tonight into early Friday morning. So where exactly these threats line up is still quite uncertain. Would like to let dayshift evaluate some of the ensemble cams before issuing a flash flood watch. Will continue to address the flash flood and convection threat in HWO. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... 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. 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. The only timeframe that looks to have organized pcpn is late Saturday night into Sunday night. Currently looks to be an overrunning event with a wave of low pres tracking along an old frontal boundary to the south of Long Island. However...there are some indications that the low track could be further north so this will need to be monitored. Upper support is not impressive though...with only a 40kt jet streak and weak vorts so not anticipating a high impact event. Otherwise...pcpn moves out Friday evening with dry weather on Saturday with high pressure moving across. There`s also the potential for isolated showers/tstms during the first half of next week...mainly N and W of NYC during the aftn hours. Temps will be near normal levels through the period with highs in the 80s and lows generally in the 60s to lower 70s. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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Winds will become southerly at most terminals today and increase to around or just over 10 kt near the coast in the afternoon with sea breeze enhancement. Exceptions to the rule will be KLGA, which could have an ENE morning sound breeze, and KEWR/KTEB, where SE sea breezes close to 10 kt expected mid to late afternoon. Low clouds/fog impacting KISP should burn off quickly with daytime heating. Cannot totally rule out an isold shower or tstm this afternoon, mainly near sea breeze boundaries on Long Island. KISP could experience brief vicinity impact. Showers with approaching low pressure could bring IFR vsby to some of the NYC metro terminals by daybreak Fri, and MVFR to most other terminals. ...NY Metro Enhanced Aviation Weather Support... Detailed information including hourly TAF wind component fcsts can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: G20kt possible 20Z-23Z. KLGA TAF Comments: Brief G15-18kt possible 21Z-23Z. KEWR TAF Comments: Brief G15-18kt possible 20Z-22Z. The afternoon KEWR haze potential forecast is green, which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Brief G15-18kt possible 20Z-22Z. KHPN TAF Comments: No unscheduled AMD. KISP TAF Comments: Unscheduled AMD possible to fine tune timing of return to VFR conds this morning. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... .Friday...IFR likely in showers/tstms. Rain heavy at times. Tstms could produce strong winds in the morning and early afternoon NYC metro terminals and KISP. .Friday night...Becoming VFR. .Saturday...VFR. .Saturday Night into Sunday night...Chance of showers/tstms with MVFR or lower conds. .Monday...Mainly VFR.
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&& .MARINE... Sub sca conds expected today as weak high pressure slides offshore. 20 kt gusts possible in NY bight and adjacent nearshore waters late today. Marginal se sca gusts possible on ocean waters if low pressure tracks north of the waters late tonight/Fri morning. Marginal N/NE gusts possible on ocean waters if low tracks to the south. In addition...seas may build to marginal sca levels Friday afternoon into Fri Night as southerly swells work in. Marginal SCA conds may be met Fri night as the low departs but should fall back below by morning. Sub-advsy conds are then expected through the rest of the forecast period. && .HYDROLOGY... There is potential for significant rainfall of 1-3 inches, with locally several inches of rain from late tonight into Friday afternoon with a low tracking near the area. Potential exists for flash flooding from training convection along a warm front, dropping several inches of rain in a short period of time. Farther north of the warm front, rain would be mainly stratiform and result in mainly minor urban and poor drainage flooding. Unfortunately the exact location of these scenarios may not become clear until the event nears tonight, so continue to monitor the latest NWS forecasts for updates on this flooding threat. The next chance for organized rainfall is Sunday. Although exact amounts are unclear at this time, they should be less than an inch. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Dense Fog Advisory until noon EDT today for ANZ330-340-345. Dense Fog Advisory until 9 PM EDT this evening for ANZ350-353- 355.
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&& $$ SYNOPSIS...24/NV NEAR TERM...NV SHORT TERM...NV LONG TERM...24 AVIATION...Goodman MARINE...24/NV HYDROLOGY...24/NV

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