Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 250614 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 214 AM EDT Sun Jun 25 2017 .SYNOPSIS...
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Temperatures will continue to run cooler than average into early next week, as an upper level trough moves across the region. The cooler temperatures will be accompanied by showers at times, as a series of upper level disturbances cross the area. The trough will move east by Wednesday, with warmer temperatures expected by mid- week.
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&& .NEAR TERM /THROUGH TODAY/...
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Expect dry conditions with mainly clear skies through the rest of the pre-dawn hours. The cooler temperatures aloft, combined with diminished cloud cover will translate to cooler overnight readings than we have seen of late, with lows dipping into the upper 50s along the lake plains, with mid 50s across the higher elevations inland. A broad mid-level longwave trough extends from the Northern Plains across the Great Lakes and into the Northeast region this morning. Water vapor imagery showing an embedded vigorous vorticity max over Lake Michigan that is expected to cross western and central New York later today. Synoptic scale lift from this shortwave and low-level forcing from a surface trough and 30+ knot low level jet will contribute to scattered mainly diurnal showers and isolated thunderstorms. The most widespread coverage will be during the afternoon corresponding to peak heating and closer to the passage of the surface trough. Gusty southwest winds 25-30kts downwind of the lakes should provide a lake shadow to keep shower/storm coverage mainly inland. Temperatures will top out a few degrees below normal due to the influence of the longwave trough and associated pool of cool air aloft. Highs are forecast to top out within a few degrees of 70. Dewpoints only around 50 will yield very comfortable humidity levels.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... Through the course of this period a long wave trough will pass across the Great Lakes region, reaching its greatest depth Monday night as a strong shortwave passes through. Within this trough temperatures at 850 hPa will bottom out around +5 to +6C, and at 500 hPa temperatures of -20C within this trough will be around 4SD below normal for this time of year centered across the Ohio Valley. Sunday night a swath of deeper moisture will settle southward across Lake Ontario and later Lake Ontario. As temperatures at 925/850 hPa drop to around +10/+6C lake instability will increase over a +22C (Lake Erie) and +19C (Lake Ontario) lake surface. While rain showers will be possible across the lake plains, greatest chances will be across the higher terrain of SW NYS and the Tug Hill to SE of Lake Ontario region where orographic uplift on a west to northwesterly wind in addition to lake induced CAPE values of 1500 to 2000 J/KG should generate rare late June lake enhanced precipitation. Any lake enhanced rain will become more scattered during the late morning hours during increased daytime mixing. The approach of an upper level shortwave later Monday will again increase the coverage area of showers and thunderstorms over the region. The deep 500 hPa trough and its associated cool pool will encourage some thunderstorm development, and with low freezing levels and WBZ heights around 6- 8K feet some graupel or small hail will be possible. However the skinny CAPE profiles suggest that larger hail will be unlikely. Showers and thunderstorms will diminish Monday night with the passage of the shortwave within the base of the long wave trough. There may linger a few lake enhanced rain showers deeper into the night, especially across the North Country which will lie under the cooler air aloft. Tuesday we will remain within the influences of the upper level trough, through now behind the robust shortwave, and slowly rising heights aloft the rain shower coverage/intensity should be less than Monday. The still cool pool aloft will continue the chances for a few thunderstorms. By Tuesday night the upper level trough will be pushing away from our region with any linger rain showers largely ending by the late evening hours. A few lake effect rain showers may develop off Lake Ontario as low level convergence increases on a westerly flow. However we will also begin to warm a degree or two at 850 hPa, so lake instability will not be as great as previous nights. Temperatures will be well below normal Monday and Tuesday with both days only pushing mid to upper 60s for highs. Overnight lows will drop back into the upper 40s to mid 50s closer to the lakes. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... While humidity will increase to uncomfortable levels during this period...temperatures will not stray very far from normal. This will be due to an eastward displacement of the sub tropical ridge that during the summer typically supplies our region with very warm and sultry weather. The heart of this ridge will be centered well off the coast of the Carolinas between 60-70W longitude rather than 70-80W...so this will allow a very broad low amplitude trough to become established over the center of the country. The overall result will be to keep the true heat out of area...although we will have our fair share of humid conditions. Unfortunately...the position of the low amplitude trough to our west will also mean that the core of the sub tropical jet will undulate back and forth across the Great Lakes region. This will keep active weather over our forecast area...as several significant waves/sfc lows will track east along a frontal boundary that will essentially mimic the position of the overlying jet. Given the time of year... this will enhance/focus diurnally enhanced convection. As for the day to day details... Wednesday should be the `nicest` weather day of the period...as a shortwave ridge will work its way across the Lower Great Lakes. While there could be some disorganized lake effect rain showers east of Lake Ontario to start the day...any lake effect will quickly be broken apart by strong diurnal mixing. Otherwise...we can expect at least partial sunshine with a comfortable afternoon as temperatures in the 70s will be accompanied by relatively low humidity. Conditions will start to deteriorate Wednesday night as a warm front will extend east across our region from the Upper Great Lakes. While the strongest isentropic lift along and head of this boundary should be to our north and west...there will be the potential for some late night showers and storms. While the warm front will push north of our region during the day Thursday...we will become firmly entrenched within the more unstable warm sector of the parent system. This will allow any boundaries to touch off some showers and thunderstorms...which appears to be a favored solution by many of the ensembles. Will thus raise pops to likely. Otherwise it will be a warmer and more humid day with temperatures climbing into the lower 80s for the bulk of western New York...while readings will be in the 70s east of Lake Ontario and across the higher elevations. The increased humidity will be more noticeable as dew points will be some 10 deg higher...reaching into the low to mid 60s. As low pressure moves east and weakens across the st Lawrence Valley Thursday night...its trailing cold front will settle south and essentially stall over our forecast area. This will keep unsettled conditions in place with fairly frequent showers and thunderstorms expected into the start of the weekend. In fact...with dew points forecast to climb into the upper 60s for most areas on Friday... storms will likely contain heavier than normal downpours resulting in an elevated risk for flash flooding. Stay tuned. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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Expect mainly dry VFR conditions overnight. These will largely last through today with showers and a few thunderstorms expected to develop during the afternoon hours. Lower VIS is possible in any passing scattered to numerous showers/isolated storm. Tonight, a much cooler airmass will move over western and central New York. This will promote some lake effect showers east of the lakes with lake effect clouds also developing and lowering to MVFR east of the lakes. MVFR is most possible at KJHW. Outlook... Monday through Tuesday...Mainly VFR with scattered to numerous showers and thunderstorms...mainly in the afternoons. Wednesday...Mainly VFR. Thursday...VFR/MVFR with a chance of showers and thunderstorms.
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&& .MARINE...
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Southwesterly winds will increase again today. Waves will rise higher particularly on the eastern half of Lake Erie, as winds strengthen further as a strong upper level disturbance moves through. Small craft advisory conditions will develop on the eastern end of Lake Erie this afternoon and perhaps on the eastern end of Lake Ontario tonight. After a brief respite Monday morning, another passing upper level disturbance will likely bring another period of small craft advisory conditions to Lake Erie Monday night.
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&& .BUF WATCHES/WARNINGS/ADVISORIES...
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NY...Beach Hazards Statement from noon EDT today through this evening for NYZ010-019-085. MARINE...Small Craft Advisory from noon today to 2 AM EDT Monday for LEZ040-041. Small Craft Advisory from noon today to 8 PM EDT this evening for LEZ020.
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&& $$ SYNOPSIS...SMITH/TMA NEAR TERM...APFFEL/SMITH/TMA SHORT TERM...THOMAS LONG TERM...RSH AVIATION...SMITH MARINE...SMITH/TMA

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