Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 241151 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 651 AM EST Fri Feb 24 2017 .SYNOPSIS... Unseasonable warmth will continue through Saturday morning. Through this morning, a warm front will bring widespread showers and some scattered thunder. A strong cold front will cross the region Saturday, and may be accompanied by thunderstorms with gusty winds, followed by windy conditions Saturday afternoon and evening. A quick shot of colder air Sunday may bring some lake effect snows east of the lakes. && .NEAR TERM /THROUGH TONIGHT/... A large low pressure system tracking through the central CONUS toward the Great Lakes today will force a surface warm front northward across the region today and tonight. This front sank southward through the region last evening rather uneventfully, but is now being reinvigorated by increasing moisture advection and frontogensis ahead of this very dynamic low pressure system. Numerous to widespread showers with some rumbles of thunder are already spreading northeastward across western NY early this morning. This trend will continue through mid-day as the warm front lifts northward and nose of the best moisture advection surge northward well into Canada by this afternoon. Thus rain will taper off from by mid-morning in the southern Tier to early afternoon in the North Country. PW values in the top 99th percentile for this time of year will produce some locally heavy rainfall. Elevated instability over the surface warm front boundary will also allow for continued rumbles of thunder embedded with the heavier showers. As precipitation tapers off, expect some clearing to make it into the Southern Tier, to near the NYS Thruway by this afternoon, as this area become established in the warm sector ahead of the approaching low. The surface warm frontal boundary is expected to get hung up on, and enhance, the developing lake breeze circulation south of Lake Ontario. This will create a very impressive temperature gradient between the NYS Thruway and the south Lake Ontario shoreline, as well as a large forecast high temperature bust potential for Niagara Falls east to Rochester. Locations on the cool side of the front will easily be in the 40s-50s, while locations on the warm side of the front will be in the 60s-low 70s. It should be fascinating to watch the temperature gradient across the lake shore counties south of Lake Ontario. Would expect a given location in those counties could see some interesting temperatures swings during the day if the front wavers back and forth as the lake breeze strengthens in the afternoon. Locations south of the NYS Thruway should become solidly established in the warm sector, with even sunshine breaking out in the afternoon. High temperatures will likely soar in these locations, with downslope southerly winds, and an airmass near all time record warmth for the month of February. GFS and EC forecast 925 mb temperatures range from +15 to +17C by 00Z; per the SPC sounding climatology at KBUF (back to 1948) the warmest 925mb temperatures ever recorded in February was +16.6C. With this in mind, locations south of the Thruway could easily challenge their all-time warmest February high temperatures. The warmest ever recorded at KBUF in February was 71 degrees on 02/26/2000, the current forecast for today has 69 degrees at KBUF, but would not be surprised to see us make a run at the record. HOWEVER, the main potential for failure to reach the record at KBUF will be if the warm frontal boundary becomes hung up several miles farther south, taking longer for us to get into the warm sector. The warmest readings in the forecast area will be in the Genesee Valley and northern Finger Lakes as is typical with southerly downslope winds, but high temperatures will likely easily top out in the mid 70s, with a forecast high of 75 degrees in Dansville. The North Country will be very slow to warm up today, as the warm frontal boundary gets hung up southern Lake Ontario for much of the day. However by this evening, with a weakening lake breeze and large synoptic push ahead of the approaching low pressure system, the boundary will lift northward well into Canada tonight. Expect locations in along the Saint Lawrence Valley to be locked into the cool side of the front with a northeast wind all day today. This will keep cloud cover and some patchy fog in place, along with high temperatures struggling to get out of the 30s to low 40s. Then overnight tonight, temperatures will rise well into the 50s as the front moves northward. Thus temperatures in much of Jefferson county will rise all night, peaking in the mid to upper 50s by Saturday morning. Tonight, expect an extremely mild and fair weather night across the region, with temperatures remaining in the 60s (about 40 degrees above normal low temperatures for this time of year!) across western NY and the mid to upper 50s in the North Country. We will be solidly in the warm sector ahead of the approaching low pressure system, so dont expect any precipitation for much of the overnight period. Toward daybreak Saturday the cold front will approach western NY, complete with strong showers and scattered thunderstorms capable of producing strong gusty winds, but more on that below. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... On Saturday a sharp mid level trough will move east across the Great Lakes, taking on a negative tilt with time. At the surface, a deepening surface low will track northeast across the central Great Lakes, reaching western Quebec by late in the day. A trailing surface cold front will cross the area from west to east during the morning and early afternoon. Large scale forcing will be strong, with strong DPVA ahead of the negatively tilted mid level trough and a coupled jet structure aloft providing strong divergence in the upper levels. Low level convergence will be strong along the advancing cold front, with moisture transport further enhanced by a 50 knot low level jet. PWAT values will exceed 1 inch just ahead of the front, which is 3 standard deviations above normal for late February. The high quality dynamics and moisture coming together will support a band of moderate to heavy rainfall along the advancing front, which will last for a few hours at any given location. There will be some instability available along the front as well, with Lifted Index of around -1C and modest SBCAPE of up to 200J/kg. This will support a chance of a few scattered thunderstorms along the cold front, embedded within a band of heavy showers. The band of heavy showers and scattered storms will likely produce gusty winds as they move east across the area, along with heavy downpours. If a focused line of frontally forced convection is able to develop spotty damaging winds cannot be ruled out, and SPC has maintained a marginal risk for a portion of the area. Behind the cold front, a secondary period of stronger winds will develop as strong cold advection develops from late morning through the afternoon and evening. The track of the surface low is very favorable climatologically, to the north and west of the area. The low is not particularly deep to support a true high wind event however. Strong pressure rises and implied subsidence behind the cold front will support downward transfer of stronger winds aloft. Subsidence and mixing of winds from aloft will be further enhanced by a decent tropopause fold, with the 1.5 PVU surface decending to around 600mb. Model guidance is still not in very good agreement with respect to how much wind will be available aloft to mix down. The GFS remains 5- 10 knots stronger than the NAM with mean wind in the 2-5 thousand foot layer. If the GFS verifies, gusts would likely approach warning criteria northeast of Lake Erie, while the NAM would suggest a low end advisory. Given the model differences, we will take a middle ground between the NAM and GFS and go with a solid wind advisory for the Niagara Frontier and Chautauqua County from late Saturday morning through Saturday evening. If the stronger guidance ends up verifying, an upgrade to a high wind warning may be required for portions of the advisory area, but there is not enough confidence to go that route yet. Further complicating the situation, the thawed and muddy ground conditions may facilitate more tree damage than normal for the expected wind gust speeds. Saturday night and Sunday the deep low will exit to the northeast across Quebec. A period of wrap around moisture and ascent with the passage of the mid level trough will produce a few scattered snow showers Saturday night. The airmass will also become cold enough to support a modest lake response east of the lakes, with lake induced equilibrium levels rising to around 8K feet briefly. East of Lake Erie expect lake effect snow showers to peak from late evening through the early overnight Saturday night across the western Southern Tier and portions of southern Erie and western Wyoming counties, with snow showers then weakening by Sunday morning and ending by Sunday afternoon. Expect total amounts of 2-3 inches across the higher terrain east of Lake Erie. East of Lake Ontario, expect snow showers to peak later Saturday night and Sunday morning across the Tug Hill and portions of Oswego County, with lake effect then weakening in the afternoon. Expect total accumulations of 2-5 inches east of Lake Ontario, with the higher amounts restricted to the Tug Hill Plateau. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... The main feature to contend during this period will be yet another Colorado Low cutting across the Great Lakes around the middle of next week. The overall pattern during this time frame will be quite transitory...as a broad low amplitude trough over the country will give way to a progressive longwave trough that will start over the western states. Significant cutter storms typically mark the change in the overlying pattern...and this time period will feature such a storm. The details... Sunday night and Monday, a weak mid level trough and associated surface low will track from the northern Great Lakes east across Quebec, with a trailing weak trough brushing by the Lower Great Lakes. The combination of weak synoptic scale forcing and very limited lake enhancement may produce a few snow showers east and northeast of the lakes Sunday night and Monday morning, with any leftover precip changing mainly to a few rain showers by Monday afternoon as the boundary layer warms. Significant cyclogenesis will begin across the central High Plains late Monday and Monday night. For what its worth...the operational ECMWF again looks to be most realistic with this whole storm...so have leaned more heavily with this guidance package. The newly formed storm system will track across the Plains to near Chicago on Tuesday...while its associated far reaching warm frontal boundary will approach our region. This could lead to some light rain or snow for our region...which will transition to all rain and increase in coverage and intensity Tuesday night and Wednesday as the parent low is forecast through the Lower Great Lakes. In the wake of this system...there will be the risk for gusty winds Wednesday night and Thursday...although guidance is not quite as impressive looking with it than it was in earlier runs. There is also markedly more spread in the various ensemble solutions. Following this storm system, model guidance continues to support a return to winter for Thursday through the following weekend with temperatures returning to at or below normal, and a series of clipper systems bringing several opportunities for snow and lake effect snow. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... Expect widespread mainly MVFR CIGs this morning as a warm front pushes northward through the region, producing widespread showers and scattered thunderstorms. Some of the heavier showers will produce localized IFR vsby, although this won`t be widespread. The warm front is expected to stall near the south Lake Ontario shoreline today. Locations south of this will see cloud cover scatter out and improve to VFR through the afternoon and evening. IAG/ROC will be very close to this boundary, and will see the most persistent MVFR conditions. KART will remain on the cool side of the boundary with persistent MVFR as well. Tonight conditions will lower to MVFR across the area with increasing moisture ahead of an approaching strong cold front boundary for Saturday morning. Outlook... Saturday...Periods SHRA with MVFR and local IFR, then windy. Sunday...VFR but IFR to MVFR in lake effect snow SE of both lakes. Monday...VFR, possible MVFR...depending on low location with a chance of rain and snow showers. Tuesday...Chance of rain with MVFR/IFR possible. && .MARINE... A warm front will lift north across the eastern Great Lakes through today with rain showers and isolated thunderstorms but winds and waves are not expected to build until late Friday night and Saturday when a powerful cold front will cross the Lower Great Lakes from west to east. Strong, possibly gale force winds will be found in the wake of the front Saturday and Saturday night. && .HYDROLOGY... There is a potential for flooding across the Eastern Lake Ontario Region starting late Friday night and lasting into early next week. While the snow pack has largely melted across Western New York, a significant snow pack remains east of Lake Ontario, including the Black River basin. Snow water equivalent values are about 130% of normal, with this snow pack expected to become increasingly ripe through the end of the week due to the warm weather. On Saturday, a strong system will pass to our north with a prolonged period of warm (50+ degree) temperatures expected late Friday through Saturday until the passage of a cold front drops temperatures below freezing Saturday night. This will be combine with gusty winds and high dewpoints to rapidly melt a significant portion of the snow pack in place. This system will also bring a period of rain Saturday, with amounts expected to average around an inch. This may result in multiple issues east of Lake Ontario. First, the combination of snowmelt and rain may cause areal flooding on small, faster responding creeks and rivers starting late Saturday. Some ice jams are also possible. After this, runoff will cause the Black River and its tributaries that drain the Tug Hill Plateau and the western Adirondacks to respond Saturday night and Sunday and lasting into next week. MMEFS ensembles show a low probability for flooding at McKeever and Boonville, but chances may be higher than indicated if surface temperatures exceed the model consensus. The risk is greater for the Watertown forecast point, extending upstream to Lyons Falls with extensive snow pack contributing to the runoff for the entire basin. Flooding is also possible on the Salmon River and other rivers in northern Oswego County that drain the western slopes of the Tug Hill. With this in mind, a flood watch has been issued for Oswego, Jefferson, and Lewis counties from Friday night through Sunday. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Flood Watch from this evening through Sunday evening for NYZ006>008. Wind Advisory from 10 AM to 10 PM EST Saturday for NYZ001-002- 010>012-019-085. MARINE...None. && $$ SYNOPSIS...CHURCH NEAR TERM...CHURCH SHORT TERM...HITCHCOCK LONG TERM...HITCHCOCK/RSH AVIATION...CHURCH MARINE...CHURCH HYDROLOGY...APFFEL/HITCHCOCK

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