Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 190600 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 200 AM EDT Thu Jul 19 2018 .SYNOPSIS... High pressure will settle across our region through Thursday resulting in dry and comfortable weather. This high will then slide off the New England coast with a southerly return flow supporting increasing heat and humidity on Friday. Chances for showers and thunderstorms will then be on the increase for the weekend as a slow-moving low pressure system will approach the area. && .NEAR TERM /THROUGH TODAY/... Sprawling high pressure will move across the region with dry weather through Thursday. Aside from a few thin wispy patches of cirrus from time to time, mainly clear skies will prevail through the overnight. The combination of both a dry airmass and dry soil conditions will lead to a fairly wide diurnal temperature range by mid-July standards. Will hedge forecast lows a bit below guidance as good radiational cooling conditions will allow temperatures to fall into the lower to mid 50s along the immediate lakeshores and into the mid 40s across the interior valleys, with a few of the coolest spots possibly touching the lower 40s. This will also result in some fog developing in the typical river valley locations across the Southern Tier and east of Lake Ontario. Dry and pleasant conditions will continue for Thursday, with mainly sunny skies and just a light breeze through the afternoon. Will tack on about 5 degrees as 850mb temperatures warm to around +12C by Thursday afternoon. This will yield high temperatures on Thursday ranging from the mid 70s to lower 80s. && .SHORT TERM /TONIGHT THROUGH SUNDAY/... Thursday night high pressure will drift off the New England coast, with enough subsidence and dry air hanging back across our region to bring another clear night. Increasing southeast flow and warm advection will keep temperatures milder, with lows in the upper 50s to lower 60s on the lake plains, and low to mid 50s in some of the cooler Southern Tier valleys and east of Lake Ontario. Friday high pressure will remain off the New England coast. Meanwhile a cutoff upper level low and associated surface low will drift slowly towards the southern end of Lake Michigan. Deeper moisture and better forcing will remain west of the area through late Friday afternoon, keeping any shower chances away from our region. There will be some increase in mid level clouds across Western NY as moisture begins to spread into the area. 850mb temps rise to +15C to +16C in the southerly flow ahead of the next system. This will support highs in the upper 80s to lower 90s on the lake plains with an added boost from southeast downslope flow, and mid 80s farther inland. Friday night and Saturday the vertically stacked low to our west will spin in place across Indiana, keeping the bulk of the deeper moisture and better forcing west of our area across Ohio and far western PA. Some model guidance including the lastest 12Z NAM and GEM suggest a few scattered showers or a thunderstorm may clip far Western NY later Friday night and Saturday. If this does occur, coverage will remain very spotty. The rest of the area will remain dry with lingering subsidence and dry air from the departing high keeping moisture at bay. Lows will remain warm Friday night with ongoing southeasterly flow and some increase in clouds. Expect upper 60s on the lake plains and lower 60s across interior areas. Highs on Saturday will reach the mid to upper 80s on the lake plains, and upper 70s to lower 80s across higher terrain. Saturday night and Sunday the vertically stacked low to our west will make only very slow progress drifting to the southeast across the lower Ohio Valley. Meanwhile a separate low will move northward along the eastern seaboard, reaching New England on Sunday. Some of the deeper Atlantic moisture associated with this system may get captured by the Ohio Valley low, spreading deeper moisture into at least eastern portions of our area. The overall increase in moisture and weak forcing ahead of these two systems will bring a gradual increase in shower and thunderstorm chances from south to north across the area later Saturday night and Sunday. The increase in clouds and shower coverage will bring temperatures down some for Sunday, with highs in the upper 70s to lower 80s at lower elevations and mid 70s on the hills. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... The low pressure system over the Ohio Valley on Sunday will slowly drift southwest toward the lower Mississippi Valley and weaken to an open wave through Tuesday morning. An abundance of moisture will remain in place over the eastern third of the U.S., as this area of low pressure combined with an area of high pressure off the Atlantic coast provides a southerly flow along most of the east coast. Expected precipitable water values of 1.50" or greater during this time frame will be near or above values in the 90th percentile for these days. During this time a stationary boundary will also stall over the area and combined with the moisture over the region provide at least chance POPs for most of this time period. Depending on exactly where the best moisture axis establishes during this time period, some locally heavy showers or thunderstorms will be possible. Temperatures during this time period will generally range from the upper 70s to low 80s, with cloud cover and rain showers affecting some of the potential warming. Low temperatures during this time period will generally range from the upper 60s to around 70. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... High pressure will build across the region through Thursday with generally VFR conditions and mainly clear skies. The only exception to widespread VFR conditions could be across the river valleys of the Southern Tier and east of Lake Ontario where some fog and stratus may develop between 08 and 12z. This could impact sites such as KJHW and KELZ. Any leftover valley fog will lift out by mid-morning Thursday, leaving widespread VFR conditions area-wide through the end of the TAF period. Outlook... Thursday night and Friday...VFR. Saturday...Mainly VFR...with just a chance of showers and thunderstorms/attendant MVFR across far western New York. Sunday and Monday...VFR/MVFR with a chance of showers and thunderstorms. && .MARINE... High pressure over the Lower Great Lakes early this morning will drift to the coast by Thursday evening. The area of high pressure will become anchored along the New England coast Thursday night and Friday. This will result in continued light winds and negligible waves across the Lower Great Lakes. While this will translate into nice conditions for most recreational boating activities...winds may actually be too light today for ideal sailing. Looking ahead to the weekend...low pressure will make its way from the Upper Mississippi Valley to about Ohio by Saturday. This will promote deteriorating conditions with scattered showers and thunderstorms over Lake Erie and the western third of Lake Ontario with winds freshening from the southeast. Meanwhile fair weather should persist over the bulk of Lake Ontario. Unsettled weather is expected to become more widespread across all of the Lower Great Lakes for the second half of the weekend. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...JM/RSH NEAR TERM...JM/RSH SHORT TERM...Hitchcock LONG TERM...SW AVIATION...JM/RSH MARINE...RSH

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