Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 221051 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 651 AM EDT Fri Jun 22 2018 .SYNOPSIS... A storm system will slowly track across the Ohio Valley and the Eastern Great Lakes region this weekend, sending bands of rain showers and thunderstorms across the area later today and through out the weekend. There will be dry periods in between the bands of precipitation through the weekend. Some sunshine across northern areas today will bring forth afternoon highs near 80, before clouds limit high temperatures Saturday and Sunday to around 70 in a moderately humid airmass. && .NEAR TERM /THROUGH TONIGHT/... IR satellite imagery displays cirrus continuing to encroach upon WNY, with drier air associated with a Canadian airmass dissipating the cirrus as it reaches the Finger Lakes and Eastern Lake Ontario region. Surface analysis places an area of low pressure near IL/IN, while water vapor imagery displays a well defined shortwave centered near western IL. Regional radars display a leading band of rain showers across OH/PA and nearing SE Chautauqua county...with this activity very light as surface observations display just a few hundredths of an inch of rain measured at observing sites. For today the surface low will slowly track eastward, and begin to weaken this afternoon as the upper level low vertically stacks over the surface low. Drier air across central NYS/New England will erode the initial band of showers over OH/PA this morning. This drier air will also bring a mostly sunny day to the northern Finger Lakes and Eastern Lake Ontario region. As the saturation level lowers through the day across our western zones, and a belt of 20 to 25 knot low level winds and moisture convergence pushes into the So. Tier precipitation will become likely, with another wave of showers to reach our So. Tier around noontime. The slowing and weakening to the surface low coupled with drier air to the east will limit the eastward push to the precipitation. The precipitation will likely fall apart across the Niagara Frontier and Genesee Valley this afternoon. As the low to our west pushes slowly towards Ohio through the evening and overnight hours, additional bands of rain showers will push deeper into WNY through the remainder of the evening and overnight hours. There remains limited instability with this activity, with just a few hundred J/KG of elevated instability overnight. Will place isolated thunder into the grids, keeping generic showers the main qualifier. Rain showers chances will expand eastward across the Eastern Lake Ontario region late tonight. Here rainfall amounts will be light, less than a tenth of an inch. To the west an early start to the rain will allow a tenth or two of an inch of rain. North of the So. Tier sunshine will allow for highs in the upper 70s to around 80F. Thickening clouds across the So. Tier will hold temperatures to the lower 70s today. Tonight under cloudy skies lows will range from the upper 50s to lower 60s. Dewpoints will also be some 15 degrees or so warmer tonight, going from the lower 40s this morning to the upper 50s by late tonight. && .SHORT TERM /SATURDAY THROUGH MONDAY/... On Saturday a weakening upper level low and its surface reflection will track across the region. A diffluent flow aloft along with low level moisture and an associated warm front will be sufficient to generate fairly widespread showers. There will be limited instability south of Lake Ontario, with some embedded thunderstorms possible. Despite the high probabilities of rain, it should be noted that there will be breaks, with periods of dry weather between the areas of showers. Persistent cloud cover will limit warming with high temperatures in the upper 60s to lower 70s. Saturday night the surface low will slowly elongate across our area while steadily weakening into a remnant trough which will slide east across New England. Consequently large-scale forcing for ascent across our region will also become weak with showers scattered in nature. Cloudy skies will persist, with BUFKIT profiles showing lots low moisture and the possibility of fog as cloud decks lower across the Southern Tier. Radiational cooling will be limited with lows mainly in the lower 60s. On Sunday a larger upper level trough over Ontario and Quebec will steadily sharpen and push southeastward into our region, along with an attendant surface cold front. Increasing height falls and frontal convergence will interact with our still-moist airmass to produce the likelihood of another round of showers. Weak instability across the Southern Tier and interior portions of the Finger Lakes may result in some thunderstorms. With lots of cloud cover and 850mb temperatures of only around +10C across Lake Ontario, expect highs to be in the upper 60s to lower 70s. A few showers may linger Sunday night with the trough axis still across the region and an northerly flow promoting some upsloping south of the lakes. High pressure will then expand across the entire Great lakes region late Sunday night with showers ending from west to east. Model consensus suggests total rainfall amounts over the weekend to be around a half inch, with locally higher amounts to an inch possible. These would most likely be with thunderstorms across the Southern Tier. While the timing of the rain is not ideal in that it will be coming over the weekend, it will certainly still be very welcome from an agricultural standpoint. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... High pressure will ridge into the region on Monday, with increasing subsidence and drier air leading to clearing skies during the day. Temperatures will be comfortable with highs in the lower to mid 70s. High pressure will continue to move southeastward across the eastern Great Lakes Monday night and Tuesday. This will make for dry and seasonable weather during this time. The next system of concern will be a a mid-level trough that will traverse the Northern Plains and western Great Lakes mid-week. This will bring a return to warmer and more humid conditions as return flow around departing high moves off the Mid-Atlantic coast. A potential for showers and thunderstorms will increase Wednesday-Thursday and slightly normal temperatures are expected during this time. 00Z model consensus is a bit faster than previous guidance so raised PoPs slightly for Wednesday. While there still is considerable uncertainty in timing, most long range guidance shows a fairly strong winds aloft which could potentially support strong thunderstorms. Given timing uncertainty there is not enough forecast confidence to place this risk in the HWO yet. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... VFR flight conditions are found at the start of the 12Z TAFS, with just some cirrus passing across portions of WNY. A surface low, over the corn belt states this early morning, will slowly spiral eastward, with bands of rain showers inching closer to WNY. Expect some isolated to scattered shower activity to reach the western So. Tier, including the KJHW terminal through the day, with any activity light with VFR flight conditions. Will place a VCSH in the KJHW TAF as activity should not be widespread. As moisture lowers, ceilings will lower into the MVFR range across the higher terrain this evening...and will place this into the KJHW TAF. Tonight the surface low will track to Ohio, with bands of showers passing across WNY. Activity sparse during the early evening hours will likely pass across WNY in two waves, with one centered around midnight (VFR/MVFR), and a second around dawn Saturday morning (MVFR). Outlook... Saturday...MVFR...Showers likely with a chance of thunderstorms. Saturday night...MVFR/IFR with showers likely and chance of thunderstorms. Sunday...Mainly MVFR. A chance of showers and thunderstorms. Monday and Tuesday...VFR. && .MARINE... An east winds will increase on Lake Ontario today, but this wind direction will keep the bulk of the wave action over the open waters and Canadian waters, with waves 2-3 feet along the southern Lake Ontario shoreline. A low pressure system will track across the lower Great Lakes this weekend with some showers and thunderstorms possible. Wind speeds and waves are expected to remain below SCA conditions. Northerly winds will increase some late Sunday and into Monday following the passage of a cold front, through winds will remain weak enough to continue sub-SCA conditions on the lakes, with these sub-SCA conditions then continuing into the start of next week. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...Thomas NEAR TERM...Thomas SHORT TERM...Apffel/JJR LONG TERM...Apffel/HSK AVIATION...Thomas MARINE...Thomas

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