Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 172354 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 654 PM EST Fri Nov 17 2017 .SYNOPSIS... High pressure shifting across our region will continue to provide a brief return of fair weather into tonight. Saturday, a strong storm system will track across the region with a round of widespread rain and gusty winds. This will be followed Sunday by colder temperatures and accumulating lake snows southeast of the lakes. && .NEAR TERM /THROUGH SATURDAY/...
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High pressure will slide to our east while the an area of low pressure begins to strengthen while tracking to near Saint Louis. A warm front ahead of this storm will shift into the Ohio Valley. Much of our area can expect fair/dry weather to prevail for most of the overnight although under widespread mid and high cloud cover ahead of this system. Late tonight, moisture transport and lift brought on by a low level jet oriented with the warm front will bring rain into far western New York between 4am and 6am. Expect temps to lower this evening before southerly flow yields steadily rising temps for the balance of the night. Across far western New York, this will result in evening lows in the lower to mid 30s giving way to readings in the upper 30s to lower 40s by daybreak, while further east evening lows in the 20s will give way to temps in the 30s by the start of Saturday morning. Expect that surface temps will be above freezing for nearly all locations before the rain arrives late tonight into early Saturday morning. There is just a slight/low chance that across the interior North Country, away from Lake Ontario, temps may still be at or just below freezing when the leading edge of the rain arrives. This has led to a chance of freezing rain possible for an hour or two. Confidence remains below 50% however do to slight differences in model timing for the onset of rain. An hour faster would lead to a higher probability for some limited freezing rain, while an hour slower would yield just plain rain. Saturday, Model consensus tracks the feature surface low across Illinois/Indiana to near or just north of Lake Erie while deepening to the vicinity of 990mb. Strengthening southerly flow ahead of this will promote rising surface temperatures and widespread rain spreading from western into central New York. 850mb temps increasing to between +3C (north country) and +8C (western SoTier) would normally support high temps pushing into the 60s but with widespread rain, expect that evaporational cooling will only support a high of low 50s in WNY and mid 40s in the North Country. PWATs of between 0.75 and 1 inch is a slight positive anomaly for this time of year with model consensus QPF yielding a healthy 0.75-1 inch for WNY with 0.25 to 0.5 inch across CNY through 7pm Saturday. Rainfall will probably come in several waves, with the first arriving in the AM, possibly followed be a break for a few or several hours. Heavier periods of rain will arrive later Saturday afternoon in the western Southern Tier where the low level jet strengthens ahead of an approaching cold front. Winds will not be gusty through the day as warm advection keeps the higher winds aloft from mixing down.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... Winter headlines may be needed during this period, as a transition to accumulating lake snows takes place southeast of both lakes. Deepening surface low pressure is expected to track just to the north of the region Saturday night, which will swing a powerful cold front through the area. Deepening cold air behind the cold front will set the stage for some mixed lake effect precipitation east of both lakes. There could even be a coating of wet snow along the Boston Hills and Chautauqua ridge and Tug Hill region. Winds will ramp up within the cold air advection pattern, especially Sunday. Momentum transfer profiles suggesting 45 to 55 mph wind gusts at best, with the highest wind gust potential confined to the immediate shorelines of Lake Erie and Lake Ontario. A cold cyclonic flow of air will continue across the lower Great Lakes Sunday into Monday. This will set the stage for lake effect snows southeast of the lakes in a northwest flow regime. Over-lake instability certainly looks outstanding with profiles suggesting moderate to extreme instability developing with lake induced CAPES over 500 J/KG and inversion heights very respectable. However, the synoptic moisture fields are far from outstanding with omega displaced below favorable dendritic growth zone combined with less than ideal shear profiles all would suggest this lake effect event likely be a plowable, but not significant snowfall from the southern Tug Hill over to east of Rochester off Lake Ontario and the Chautauqua ridge and Boston Hills off Lake Erie. Lake effect snows will begin to diminish off of both lakes Monday in response to a ridge of high pressure quickly building in across the lower Great Lakes, which will effectively limit synoptic moisture and lower the capping inversion. As the ridge builds in, the steering flow will slowly pivot the weakening snow bands northward toward Buffalo and into the Tug Hill before ending by Monday evening. && .LONG TERM /TUESDAY THROUGH FRIDAY/... A shortwave trough will dip across the Eastern Great Lakes region this period, with several additional shortwaves maintaining a deeper long wave trough over the region through the holiday. Sunshine Tuesday will fade through the day as a cold front nears the region...with the cold front bringing a mix of rain and snow Tuesday night, changing to all snow later Tuesday night and Wednesday as deeper colder air (-10C/850 hPa) builds over the eastern Great Lakes. This colder air will generate lake instability with details of how much moisture and wind direction to still be resolved relating to lake effect snow potential for Wednesday-Thursday. Another frontal boundary will likely dip southward from Canada Friday...maintain chances for snow, especially across Lake Ontario and points eastward which at this time will be closer to the frontal boundary. Temperatures Tuesday will be above normal...but expect at or below normal temperatures the remainder of the forecast period. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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An elongated ridge of high pressure will slide off to our east while the an area of low pressure tracks toward Chicago and continues organize. Expect VFR conditions to continue for much of the night under widespread mid and high cloud cover. Winds aloft increase overnight out ahead of the approaching low, LLWS is expected WNY TAFs (KBUF/KIAG/KJHW/KROC) 8-12z. Rain is expected to reach far western New York (KBUF/KIAG/KJHW) by 9-10z with lowering cigs to MVFR/IFR by 12z Saturday. There may be several waves of rain, with a few or several hours of dry weather in between, but overall CIGS will continue to show a slow lowering trend. MVFR to IFR cigs will linger through the day Saturday with widespread rain, steadiest and heaviest toward the Southern Tier by late afternoon. Outlook... Saturday night...Rain changing to snow...and becoming windy. Sunday-Monday...Lake effect SN, IFR SE of lakes, otherwise VFR/MVFR. Tuesday...Mainly VFR. Wednesday...Rain and snow showers with a chance of MVFR/IFR.
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&& .MARINE... High pressure over Lake Ontario will continue a short period of sub- advisory-level conditions this afternoon into tonight. As we move on into the weekend, a strengthening storm system will track northeast across the Great Lakes. This may bring a period of gale force winds to Lakes Erie and Ontario Saturday night and Sunday behind a cold front with gale watches in effect. && .TIDES/COASTAL FLOODING... Developing very strong onshore winds will build significant wave action from late Saturday night into Sunday night along the Lake Ontario shoreline. The combination of already higher lake levels and continued wave action will result in increased shoreline erosion, especially where the lakeshore is already unstable from erosion earlier in the year. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lakeshore Flood Watch from late Saturday night through late Sunday night for NYZ001>007. MARINE...Gale Watch from Saturday evening through Sunday afternoon for LEZ040-041. Gale Watch from Saturday evening through Sunday afternoon for LOZ042>045-062>065. && $$ SYNOPSIS...SMITH NEAR TERM...SMITH/ZAFF SHORT TERM...TMA LONG TERM...THOMAS AVIATION...SMITH/ZAFF MARINE...SMITH TIDES/COASTAL FLOODING...TMA

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