Area Forecast Discussion
Issued by NWS Buffalo, NY

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563 FXUS61 KBUF 230014 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 714 PM EST Sun Jan 22 2017 .SYNOPSIS... Warm and moist conditions will remain through the night with above normal temperatures, and areas of fog or drizzle. Then low pressure developing across the Southeastern states will move to the mid-Atlantic on Monday and then into Southern New England on Tuesday. This will bring rain and wet snow into our region with potentially significant snow accumulations in some areas. && .NEAR TERM /THROUGH MONDAY/... For the remainder of the night the low stratus and fog will remain the issue through the night. Northeast flow will continue through the night, this between an area of high pressure over eastern Canada, and two storm systems...one off the Atlantic coastline, and a second system over the southern Tennessee Valley. This northeast flow is a bit stronger than previous nights. The northeast flow will continue to advect cool, moist air over the warm lakes that will generate low stratus and fog along the southern Lake Ontario shoreline. The stronger flow has carried this fog inland to the NYS Thruway, with the fog expanding across the hills and valleys of the Genesee Valley. Additional fog is also forming along the immediate Lake Erie shoreline, with this fog reaching Route 5 and the NYS Thruway as well. Expect the fog to continue through the night, and into tomorrow morning. Low pressure from the Southeast will creep closer to our region, with a chance of showers across the Southern Tier late tonight. A consensus of 12Z guidance is slower than previous runs, so timing has been delayed to account for this. There still remains high confidence in precipitation with synoptic scale lift from a deep moist easterly mid-level flow and divergence aloft. By late Monday afternoon even slower model guidance has precipitation to the south shores of Lake Ontario, with steady precipitation expected across the Southern Tier and Upper Genesee Valley expected during this time. Thermal profiles will start off too warm for snow, but will cool with dynamic cooling as the system taps into slightly cooler air from the ENE. Even though model guidance is in generally good agreement, thermal profiles are so close that even a small error in forecast soundings will be the difference between rain and snow. Based on model consensus, preciopitaiton is expected to change over to snow first across the upper Genesee basin and Finger Lakes region, with modest accumulations of a 1 to 3 inches possible by sunset Monday. Elsewhere, expect mainly wet rain, with perhaps some wet flakes mixing in through late Monday afternoon. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... The main focus through the short term period remains on the strong and complex storm system moving up the east coast in the Monday night through Tuesday time frame. High pressure positioned off to our north and approaching milder air ahead of the approaching surface low from the DelMarVa will set up a complex thermal profile across western and north central New York. Precipiation associated with the approaching low will have already reached at least southern portions of the area Monday evening, with higher elevations already have transitioned over to all snow. This transition over to snow should take place for all areas as heavier precipitation makes it way into the region. Latest ensembles showing a high likelihood of more than an inch of liquid equivalent over much of western and north central New York Monday night into Tuesday. Later Monday night and into Tuesday, NAM and GFS forecast soundings showing a warm layer, mainly between 800mb and 700 mb arriving on a strengthening easterly flow, as strong as 75 knots in some of the guidance. This will result in a period of sleet mixing in at times. Better confidence has been gained this cycle, not only with a period of heavy precipitation, but with thermal profiles as well. Therefore, will issue a winter storm watch for the Genesee Valley eastward. The placement of the heaviest snow totals within the watch area still remains quite uncertain, but current thinking is there will be a swath of 5 to 10+ inches over the higher elevations from Allegany/Wyoming counties through the Bristol Hills, then up through the Tug Hill. On Wednesday morning, a narrow ridge axis will extend up the Eastern Seaboard while low pressure tracks across the Central Great Lakes Region. A warm front associated with this low will likely bring some precipitation which may start off as rain or wet snow but trend to all rain as temperatures warm. This will be followed by an ill- defined cold front and surface trough which will move across the region Wednesday night and bring more rain, which will mix with wet snow overnight as weak cold advection begins. Outside of the showers, Wednesday should be a breezy day with highs in the upper 30s to lower 40s. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Welcome to the coldest time of the year...or at least in climatological terms...what SHOULD be the coldest time of the year. In the days leading up to this period...it has felt anything but wintry though...as a split flow over the country has been dominated by a Pacific maritime airmass. This rather warm regime will come to an end during this time frame as a temporary block in the mid level progressive flow will become established. A closed low will stall in the vicinity of the Labrador Sea while a fragile ridge will take shape along the west coast of the continent. A more robust ridge would normally exhibit signs of being able to withstand the battering of Pacific based shortwaves...but guidance is suggesting that it could be more susceptible to breaking down. This would limit the depth and strength of the northwest flow out of the Canadian Archipelago...thereby limiting the impact/ intensity of any cold air intrusion. That being said...the ensembles are in good agreement that enough cold air will be siphoned southward from Hudson Bay to finally push our mercury to at least normal levels for the weekend (end of this forecast period). There are some signs that the cold air could intensify as we push into the following week...but this is certainly not anything that the ensembles agree upon. The airmass during this period will gradually become cold enough to support a lake response...but with lake temps in the mid 30s over Lake Erie...we will need H85 temps to lower to at least -10c. As is nearly always the case at this point in winter...the Lake Ontario sfc temps are several degrees higher than those of Erie`s. Currently...they are generally in the low to mid 40s (as per GLERL)...so use the water temp at ROC with caution. Single point readings can often be misleading. The colder air that will lead to accumulating lake snows will gradually work its across the Lower Great Lakes in the wake of a very moist cold frontal passage on Thursday. The front is expected to generate fairly widespread rain and wet snow showers...especially during the second half of the day. Have raised pops to categorical to cover this fropa. As the cold air deepens Thursday night...some upslope will help to produce some wet snow showers over parts of the Southern Tier while true lake effect snow is likely to become established southeast of Lake Ontario. The passage of a shortwave within the chilly cyclonic flow on Friday should then promote scattered snow showers over the entire forecast area...but accumulating snows should be focused east of both lakes where mesoscale processes will dominate. Temps Friday will peak within a couple degrees from freezing. The cyclonic flow will continue to generate flurries and light snow showers over the region both Saturday and Sunday...with more persistent lake snows persisting in the snow belts east of both lakes. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Northeast flow at 00Z will continue to maintain IFR and lower flight conditions across KROC, KIAG and KBUF for the next 6 to 12 hours, before slowly improving with subtle increase in daytime mixing tomorrow. There may also be some areas of fog developing across the Southern Tier tonight, that may impact the KJHW terminal with IFR flight conditions late tonight. Monday a storm system will bring a period of rain to the region. Expect rain to reach the Southern Tier around daybreak, KIAG, KBUF, KROC just after noontime, and KART around the close of the TAF period. Though conditions may improve to MVFR/VFR briefly before the rain, within the rain, expect a deterioration back to IFR and MVFR flight conditions. Winds will generally remain from the northeast-east through the TAF cycle. Outlook... Monday night...Areas of MVFR/IFR with rain changing to wet snow. Tuesday...Areas of MVFR/IFR with wet snow mixed with rain. Wednesday and Thursday...VFR/MVFR with a chance of rain and snow. Friday...VFR/MVFR with a chance of snow showers. && .MARINE... Easterly winds will increase across Lake Ontario and Erie through tonight as we get caught between high pressure over Quebec and a deepening low pressure system moving into the Mid Atlantic. Small craft advisories have been issued for the western half of Lake Ontario as the east- northeasterly winds strengthen to 20 to 25 knots. Winds and waves will remain elevated until the low pressure system passes on Tuesday. Lake Erie remains less of a concern as wave action will directed away from the eastern end of the lake. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Winter Storm Watch from Monday evening through Tuesday afternoon for NYZ003>008. Winter Storm Watch from Monday afternoon through Tuesday afternoon for NYZ012>014-021. MARINE...Small Craft Advisory until 1 PM EST Tuesday for LOZ042-043. && $$ SYNOPSIS...APFFEL/THOMAS NEAR TERM...APFFEL/THOMAS SHORT TERM...TMA LONG TERM...RSH AVIATION...THOMAS MARINE...APFFEL

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