Area Forecast Discussion
Issued by NWS Buffalo, NY

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135 FXUS61 KBUF 132100 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 500 PM EDT Sun Oct 13 2019 .SYNOPSIS... An upper level low will bring moisture and cooler air across our region tonight and Monday, resulting in narrow bands of lake effect rain to the northeast and then east of the Great Lakes. It will generally be quiet Monday night and Tuesday with high pressure nearby before a strong area of low pressure brings gusty winds, rain and possibly thunder mid-week. && .NEAR TERM /THROUGH MONDAY/... Surface high pressure continuing to slide off to our east this afternoon. Deep occluded low over Lake Superior with surface cold front arcing down through lower Michigan. The remainder of the afternoon into this evening will continue to feature mainly clear skies, before clouds start to work into our area early tonight. The deep low over the northern Great lakes will slowly rotate into Ontario tonight with the surface cold front starting to impinge on the area by around 06z. Moist cyclonic flow and a developing favorable over-water thermal regime with 850 mb temperatures dropping to near 0C will result in a band of lake effect rain, which will be enhanced along the incoming surface boundary. Uniform south-southwest flow through about 10kft will initially set up the band of lake effect rain off Lake Erie near Niagara county around midnight or so, then we will see the band becoming more organized as it slowly shifts to the south as the low level flow veers westerly behind the passage of the cold front. By Monday morning, the band of lake effect rain off Lake Erie will extend along the shoreline inland across the Buffalo southtowns into Wyoming county. The later arrival of colder air and surface front will delay the development of the lake induced rain to the northeast of Lake Ontario, but should be getting underway by early Monday morning. The area is expected to remain firmly under the influence of mid level low pressure and attendant moist cyclonic flow right through the day Monday, as the low is expected to move very slowly to the northeast only reaching the vicinity of James Bay by Monday afternoon. 850 mb temperatures continuing to cool to near -2C will maintain favorable over-lake instability although incoming drier air and diurnal effects will gradually weaken the lake effect rain bands during the afternoon. Temperatures on Monday will be rather chilly only reach into the lower to mid 50s, with a few upper 40s across higher terrain. A brisk west wind will make these readings feel even cooler. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... Monday night and Tuesday surface high pressure will move east from the Ohio Valley to the Mid Atlantic. Subsidence and dry air extending north of the surface high will bring dry conditions to the majority of the area outside of lake effect areas. It will turn quite chilly away from the lake effect clouds, with lows in the mid to upper 30s away from the immediate lakeshores with some frost possible from the Niagara Frontier eastward across the Genesee Valley. Meanwhile lake effect clouds should prevent frost across most of the western Southern Tier and across Oswego County. Meanwhile, a westerly flow with 850mb temps around -2C will support a marginal lake effect setup, with lake induced equilibrium levels slowly falling from about 9K feet to 7K feet Monday night and early Tuesday morning. Off Lake Erie, expect a few scattered light showers or drizzle to persist Monday night across the western Southern Tier with light rainfall amounts. Off Lake Ontario, a few scattered showers across the Tug Hill in the evening will drift a little farther south into Oswego County overnight. A weak band of rain showers will then remain across Oswego County through early Tuesday morning before rapidly moving out into the lake and dissipating as boundary layer flow turns southerly late Tuesday morning. Rainfall amounts should be fairly light in this band, up to a tenth of an inch or so given the marginal synoptic scale moisture and relatively shallow inversion heights. Once the lake effect rain ends southeast of Lake Ontario, the rest of Tuesday will be dry with a good deal of sunshine filtering through a modest increase in cirrus level clouds. Temperatures will be close to average, with highs around 60 at lower elevations across Western NY, with mid 50s higher terrain and North Country. Late tuesday night and Wednesday our attention turns to the most significant system of the week. A sharp mid level trough will move east across the Great Lakes, with an associated deep surface low moving across lower Michigan Tuesday night before reaching Georgian Bay Wednesday. A trailing cold front will sweep east across the area Wednesday. 12Z model guidance has trended just a few hours slower, which will keep the majority of Tuesday night dry with showers arriving towards daybreak Wednesday across Western NY. The majority of the rain will fall in a 2-4 hour window just ahead of the cold front Wednesday. Strong DPVA ahead of the mid level trough, increasingly diffluent mid/upper level flow, and strong moisture transport/convergence in the low levels supported by a 50+ knot low level jet will produce widespread showers, a few of which could be briefly heavy. Model guidance suggests a solid 0.50-0.75" of rain with this front. Instability is limited, but the very strong forcing may be enough to support a broken band of low topped thunderstorms along the cold front. If these materialize, they may pose a risk of locally strong wind gusts given the very strong flow aloft. The track of the moderately deep surface low to our north and west fits the pattern recognition for strong post-frontal winds in our area. Low level lapse rates will steepen in the cold advection regime behind the cold front, and southwest winds will channel favorably down Lake Erie. Winds aloft behind the cold front are not terribly strong however, in the 40-45 knot range a few thousand feet off the deck. This may support wind advisory gusts in the typical locations along the Lake Erie shore and extending northeast across the Niagara Frontier to near Rochester. There will be a brief break in the rain following the cold front. Later Wednesday afternoon and Wednesday night deeper wrap around moisture will arrive as the strong mid level closed low crosses the eastern Great Lakes and heads into New England. The wrap around moisture and forcing from the mid level trough will produce a few scattered showers Wednesday night. More importantly, deepening cold air will support growing lake induced instability. Flow may be sheared initially, but should align better from the WNW later Wednesday night as lake induced equilibrium levels rise to 15-20K feet. This will support a robust lake response east and southeast of the lakes, with rain showers becoming widespread. Deep moisture and lift extending up through the graupel growth zone may support some thunder as well. && .LONG TERM /THURSDAY THROUGH SUNDAY/... The upper level pattern will prove to be quite interesting during this period. While a robust but progressive shortwave trough moving through the Lower Great Lakes will support the most widespread lake effect precipitation of the young cool weather season...a persistent 150 to as high as 175kt East Asian jet screaming across the open north Pacific will set the stage for more Indian summer weather. As for the day to day details... A stacked storm system centered over New England for much of Thursday will produce a deep cyclonic flow of chilly air over the Lower Great Lakes. This will continue to support a fairly strong lake response...with lake to cloud base delta t values averaging 15 deg c. Fortunately...H85 temps of zero to -2c will not be low enough to support any snow...but the resulting lake driven convection could include some heavier rain showers. Given the height of the -10c isotherm (most likely region for graupel) and depth of the corresponding mixed phase region...the heavier showers could be electrified. Will add some lightning to these areas...which will be mainly focused southeast of Lake Erie and especially southeast of Lake Ontario. This whole scenario is about six hours delayed from earlier forecasts... but aligns well with lower sheared environment in deepening west to northwest flow. Otherwise...it will be a poor day to be out and about as a gusty northwest wind and fairly widespread lake driven rain showers within the ongoing cold advection will prevent many areas from climbing out of the 40s. Surface ridging will start to cross the Lower Great Lakes Thursday night. This will lower the limiting subsidence inversion to under 5k ft while the bulk of the synoptic moisture will be stripped away. come scarce. Leftover rain showers southeast of both lakes will taper off as a result (esp off Lk Erie) with temperatures generally dropping into the upper 30s and lower 40s. Ridging at all levels will cross our forecast area Friday and Friday night. While there may still be a few nuisance lake showers east of Lake Ontario Friday morning...this scenario will promote fair dry weather. It will remain on the chilly side of normal though...as the most efficient warm advection should become established over our region until Friday night. Speaking of which...overnight mins Friday night will likely take place by midnight with slowly rising mercury readings through the pre-dawn hours of Saturday morning. Earlier guidance packages suggested that a weakening Pacific based cool front would pass through our region on Saturday. The freshest guidance is even less impressed with this boundary as it is now forecast to essentially washout across southern Ontario before it even gets here. This will leave a southwest flow of milder air over the Lower Great Lakes. H85 temps climbing into the upper single digits c should easily be able to support afternoon temps of at lest the low to mid 60s f...so Saturday should be a fairly nice day to get out and enjoy the foliage. An even nicer day is being advertised on Sunday...as a burgeoning sub tropical ridge over the Southeast coast will help to pump our H5 hgts to near 580dm...levels more typical of late summer. H85 temps may get into the mid teens by late Sunday. If this were to verify... a large swath of our forecast area would experience max temps of 70 or better. The warmth will very likely continue beyond this period into the start of the new work week. The anomalously strong East Asian jet mentioned earlier will ultimately be responsible for this warmth... as they often lead to troughiness over the Inter-mountain region which teleconnect to burgeoning ridges in the East. These features also effectively cut off any intrusions of cold air from the Canadian Archipelago. That being said...the pattern will remain progressive so the troughiness (and associated cooling) over the nations mid section will make its way across the Great Lakes for the middle of the week. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... Unlimited VFR flight conditions across the area through at least 06z tonight as surface high pressure slides to the Atlantic coast. Southwesterly surface winds gusting to near 20 knots at KBUF and KIAG on the northwest side of the high. An upper level low to the west will spiral moisture and cooler temperatures eastward tonight, that will likely bring lake effect rain, with the rain forming on a surface trough that will mark the onset of cooler temperatures. This will bring MVFR flight conditions at times Sunday night to KIAG and KBUF for the second half of the night. The core of the Lake Erie band may remain just to the north of KJHW Sunday night. A later arrival of moisture and cooler air over the eastern end of Lake Ontario will likely keep KART VFR through Sunday night. Outlook... Monday...A chance of lake effect showers and MVFR CIGS east and northeast of the lakes, otherwise VFR. Tuesday...Mainly VFR. Wednesday...Showers likely with areas of MVFR. Gusty Winds. Thursday...A chance of lake effect showers and MVFR CIGS east of the lakes, otherwise VFR. && .MARINE... An upper level low will slowly rotate northeastward through tonight across southern Canada, and eventually towards James Bay by Monday afternoon. Southwest winds on Lake Erie will freshen tonight and tomorrow as a surface trough crosses. Higher winds and waves are offshore and across Canadian waters this afternoon. Winds and waves will increase along the New York Lake Erie shoreline tonight and Monday. A Small Craft Advisory is in effect on Lake Erie through Monday evening. On Lake Ontario winds and waves will increase and Small Craft Advisories are likely Monday as the trough crosses. Colder air coming in aloft will bring the potential for waterspouts on both Lake Erie and Lake Ontario late tonight and Monday. Surface high pressure will push towards the Lakes Tuesday, with winds and waves falling below SCA thresholds by late Monday night on Lake Ontario. Winds and waves will be light Tuesday with the surface high nearby before increasing once again as a deeper and colder storm system passes through the Eastern Great Lakes midweek. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 11 PM EDT Monday for LEZ040-041. && $$ SYNOPSIS...Thomas/TMA NEAR TERM...TMA SHORT TERM...Hitchcock LONG TERM...RSH AVIATION...Thomas/TMA MARINE...HSK/Thomas/TMA

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