Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 180249 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1049 PM EDT Mon Jun 17 2019 .SYNOPSIS... A frontal boundary will remain stalled just south of the area through Wednesday with a chance of a few showers and maybe a thunderstorm at times across the Southern Tier. Otherwise weak high pressure over southeast Ontario and Quebec will keep the rest of the area mainly dry with temperatures near average. Low pressure will then move through the eastern Great Lakes Thursday with another round of more widespread, possibly heavy, rainfall. && .NEAR TERM /THROUGH TUESDAY/... The loss of daytime instability has allowed for showers to end across our region this late evening. Minimal change expected in position of stalled out frontal boundary through Tuesday. Front is keeping higher dewpoints and PWATS over 1.5 inches more over central Ohio and Pennsylvania. Convectively enhanced shortwaves riding along the front along with building instability will result in clusters of showers and thunderstorms staying mainly to the south of the Southern Tier through Tuesday. Could see a few showers or isolated thunderstorm over especially the Southern Tier due to lift on northern fringe of any shortwaves and with just enough deeper moisture and instability. Better chance of showers would occur if any shortwaves and instability timed out with substantial clearing. Like last night, there could be some fog in the Southern Tier as well with slightly more moisture closer to the stalled out front. Temps tonight will fall into the mid to upper 50s while highs on Tuesday should reach the 70s across all of Western to Central NY and maybe even upper 70s if there is enough sunshine. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... ...Significant Rainfall Thursday into Thursday night... Generally quiescent conditions will continue as the main forcing for precipitation remains to the south of the area through mid-week. High pressure will slowly drift north of Lake Ontario and eventually off to the east. This will allow the front that will have been draped across the Ohio Valley to start to meander northward on Thursday. A fairly potent wave is set to run along this boundary on Thursday into Thursday night. This will be the main weather maker for the short term period. Model and ensemble solutions continue to come into better agreement for the Thursday/Thursday night system. Timing seems to have been worked out pretty well with an early morning start over western New York and a late Thursday night exit from the North Country. Further, the track of the low level circulation looks to run along or just north of the NY/PA border. This places the best low-level convergence smack across our CWA. When this is coupled with a back- building upper level jet streak over Ontario and Quebec, the stage looks to be set for a fairly prolonged period of lifting. Combining all of this with PWAT values taking a surge toward 1.6 inches and modest elevated instability, it certainly seems there will be a potential for heavy rainfall. This has been and will continue to be featured in the HWO. Additional model precipitation guidances continues to point at a threat for widespread 1.5 to 2 inch amounts, especially over the northern Finger Lakes and higher terrain of the North Country. Temperatures through the period will be largely modulated by precipitation. Because of this, diurnal spreads will be wider through Wednesday with daytime highs near normal and overnight lows a bit cooler than normal due to our position on the cool side of the boundary. Beyond then, copious rainfall will subdue our daytime highs. && .LONG TERM /FRIDAY THROUGH MONDAY/... After experiencing a drenching rain on Thursday...the first half of this particular forecast period will feature improved weather that will allow for some much needed drying. A large mid level circulation currently over the Gulf of Alaska will eject several strong impulses...one of which will dive across the Pacific Northwest and Intermountain Region on Friday. The impact of this will be to force the amplification of a progressive ridge over the Ohio Valley and Upper Great Lakes. This will promote clearing skies over our forecast area Friday and Friday night. The ridge will continue to sharpen over the Upper Great Lakes on Saturday...while high pressure centered over Hudson Bay will nose southward across our forecast area. While this will support fair dry weather across the bulk of the region...a tightening baroclinic zone stretching from Pennsylvania and Lake Erie to the Upper Great Lakes COULD be enough to allow for some late day showers over the far western counties. Will maintain slgt chc pops for now in this area as model continuity with this feature has not been reliable. The ridge axis will move across our area Saturday night and Sunday. This should enable the aforementioned baroclinic zone and associated sfc warm front to push across the Lower Great Lakes...thereby supporting at least the chance for some showers over the western counties. By Monday...the ridge is forecast to be well to our east. A broad trough will be found over the Upper Great Lakes during this time... with a Pacific based frontal system pushing across our region. Will use high chc pops for this scenario. In regards to temperatures...we can anticipate subtle warming during the course of this period. Mercury readings that will average a degree or two below normal to start will climb a bit above normal for Sunday and Monday. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... For the 00Z TAFS VFR flight conditions will be found across much of the region, with light winds within a weak pressure gradient pattern. The exception will be the Southern Tier where some river valley fog may expand up across the KJHW terminal later tonight. Also a few weakening showers this evening over the interior So. Tier will return to the same areas Tuesday. Outlook... Tuesday Night...Mainly VFR. Wednesday...Mainly VFR with isolated showers possible. Thursday...MVFR/IFR with periods of rain and isolated thunderstorms. Friday...MVFR. A chance of showers. Saturday...VFR. && .MARINE... A frontal zone will remain stalled from the Ohio Valley to Pennsylvania through Wednesday while weak high pressure settles across southeast Ontario and southern Quebec. This will keep a weak pressure gradient across the eastern Great Lakes, with light winds and flat wave action. Low pressure will track near the eastern Great Lakes on Thursday, but the exact track and strength of the low is uncertain. Winds and waves may approach Small Craft levels Thursday into Friday depending on the eventual strength of this system. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...JLA NEAR TERM...JLA/Thomas SHORT TERM...Fries/RSH LONG TERM...RSH AVIATION...Thomas MARINE...JLA

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