Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 161144 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 644 AM EST Wed Jan 16 2019 .SYNOPSIS... A strong cold front will cross the region this morning and early afternoon, sending temperatures tumbling downward through the afternoon hours while also spreading areas of light snow through the evening hours. High pressure will then pass over the region later tonight...with a brief period of quiet weather through Thursday before another low pressure system brings a round of accumulating light snow Thursday night and Friday. A potentially significant winter storm this weekend will bring snow to the Eastern Great Lakes Saturday and Sunday to then be followed by bitterly cold wind chills Sunday night through Monday night. && .NEAR TERM /THROUGH TONIGHT/... This morning an area of low pressure is over western Quebec, well to the north of Lake Ontario. A cold front extends across southern Ontario Canada and just to the west of Lake Erie. This morning southwest winds remain gusty as the pressure gradient tightens over the region. Strongest winds are downwind of the lakes, with gusts up to 40 mph. Will maintain the winter weather advisory, primarily for freezing drizzle. After many reports of freezing drizzle this morning, the bulk of observations suggest that most of the precipitation is back to snow. However there are likely still areas of freezing drizzle. IR imagery displays cloud tops a degree or two cooler now than earlier this morning...a suggestion that ice nuclei are increasing in number, which would support this change back to all snow. Bufkit soundings suggest that the snow dentritic growth zone will increase some this morning, with cloud top temperatures perhaps cooling another degree or so. This will favor more snow than freezing drizzle, such that freezing drizzle may become all snow by midday. The cold front will cross the region today, between 9 am and 2 pm. This frontal passage will veer winds from southwest to northwest, disrupt the lake bands of precipitation off both lakes, and also begin a tumble to the temperatures by midday to the west, and early afternoon near the Finger Lakes. As a result lake snows will only amount to an inch or two on the higher terrain east of the Lakes...and high temperatures will only be a few degrees warmer than the daybreak readings. Tonight northwest winds will begin to diminish as surface high pressure nears the region and the pressure gradient relaxes. This surface high will also bring drier air into the low and mid levels...ending any lingering lake effect snows southeast of the lakes, and also allowing for a clearing trend to the skies. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... High pressure centered over the Adirondacks at the start of this period Thursday morning will drift east to the New England coast by sunset. While the ensuing backing of the winds aloft will start the warm advective process...the residual cold airmass in the low levels will keep the mercury from climbing out of the 20s (teens North Country) during the afternoon. Meanwhile...high and mid level clouds will gradually increase and thicken across the region...as a weakly organized southern stream storm system will approach from the Lower Ohio Valley. The moisture could deepen enough ahead of this system by late afternoon to support some light snow over the southwestern portion of the area (ie. Chautauqua, Catt counties). Otherwise fair dry weather can be expected across the region on Thursday. A flat southern stream shortwave will support a relatively weak surface storm that will track from the Upper Ohio Valley across our forecast area Thursday night. Will use a blend of the ECMWF and SREF mean for the track of the system. Either way you slice it though... our forecast area will be cold enough aloft for all of the associated pcpn to be in the form of snow. As we progress through the night...light to occasionally moderate snow will spread across the entire region. The main forcing for the snowfall will be a weakly coupled H25 jet...with a 110kt arctic jet over Quebec and a more impressive 140kt sub tropical jet over the Deep South. Liquid equivalent amounts will average well UNDER a quarter inch with generally weak/unimpressive synoptic lift...so am generally only expecting snowfall amounts to be in the range of one to two inches. Some of the higher terrain of the Srn Tier could pick up 2 to 4 inches due to orographics and somewhat better microphysics that will favor better snow growth due to aggregation. That being said...this snowfall will be FAR from crippling. We will have to wait for the next system during the weekend for that threat. The weak area of low pressure will move out of the region Friday morning before exiting the New England coast later in the afternoon. This will allow the steady synoptic snow to taper off and end as lake enhanced snow showers as the day progresses. Daytime snow accumulations in most areas should average under an inch...but areas southeast of Lake Ontario could experience slightly higher values. This will be better defined in later packages...but given that H85 temps will drop to -15c...some lake enhancement will be a good bet. A huge arctic high centered over the Canadian prairies will nose to the southeast across the Lower Great Lakes Friday night. This will keep a cold northerly flow in place over our forecast area so that there should be at least the chance for more lake induced snow showers for the counties lining the south shore of Lake Ontario. Accumulations from this activity will be insignificant though. && .LONG TERM /SATURDAY THROUGH TUESDAY/... ...Major Winter Storm Likely This Weekend... After several days of general lock step agreement...both within and between the operational GFS and ECMWF guidance packages...there has been some unexpected changes to the outlook for the upcoming winter storm. While the models are still in fairly strong agreement...they have both shifted their track for the cyclone further south by some 50 to 75 miles. This may not sound like much...but it would place the area of heaviest synoptic snow south of our region. That being said...there are still several days before the system will impact the region and the forecast track could shift back to the north... so we need to be very vigilant as we progress through the end of the work week. It would be foolish to let your guard down at this point. Breaking this event down piece by piece...the impetus for this potentially very impactful storm system can be traced to the open Pacific. An impressive and very well defined shortwave...seen in hemispheric WV imagery...was roughly 1000 miles west of San Francisco as of 06z.This troublesome bundle of energy will make its way to the California coast by Thursday morning. After crossing the intermountain region Thursday night...the increasingly robust shortwave will induce strong cyclogenesis over the southern Plains Friday afternoon and night. The deepening storm system will cross the Lower Mississippi Valley on Saturday...while high pressure centered to our north will give way to a burgeoning...far reaching warm frontal boundary and subsequent inverted sfc trough. This feature will extend across northern Virginia Saturday afternoon and night and serve as a guide for where the main cyclone will track. Again...this track will be 50 to 75 miles further south than earlier guidance packages were depicting. The subtle southward shift in the forecast track for the system is CLEARLY due to a later phasing of the system with the northern branch. Earlier runs had this phasing taking place late Saturday or Saturday evening...where now this is DELAYED by 8 to 12 hours. This delay is enough to keep the storm moving on a more easterly track rather than allowing it to turn to veer to the northeast. The result of this will be to place a more pronounced baroclinic zone over our region. While the main low level jet ahead of this storm is still going to be well south of our forecast area...H925-80 winds of 25 to 30mph will still impinge upon the sloping surface to initiate lift to start the snowfall early on Saturday. The light snow over the western counties will pick up in intensity while spreading to the east during the afternoon. At that time...the lift will be greatly assisted by a coupled H25 jet...and to some extent over the Southern Tier...some orographics. This will lead to deteriorating travel conditions in the afternoon...particularly over the Southern Tier. Solid consensus between the various medium range guidance packages then track the deepening sub 1000mb low across Virginia to roughly the Delmarva Peninsula by daybreak Sunday. While the main deformation zone with this storm should line up over Pennsylvania... deep lift over our region will still be provided Saturday night through both H925-70 frontogenetic forcing and strong H25 jet support. Since H85 temps over Lake Ontario will be in the vicinity of -12c...the counties that line its south shore will ALSO receive SIGNIFICANT lake effect enhancement as the steering flow will back from 060 to about 020. Unless the track of the storm moves further south...there will be the likelihood for a plowable snowfall throughout much of the region. On Sunday...the still strengthening winter storm will chug from New Jersey to the New England coast. The slow nature of the phasing process of the storm system seems to also be taking its toll on its forecast deepening and overall size. The sfc low...rather than bombing out as a circular cyclone...will be more elongated in its appearance. This may have an effect on the size and intensity of its deformation zone...which will be close to our forecast area. In any case...steady snow should continue across our forecast area on Sunday...with lake effect processes playing a big role for those counties lining its southern shore. H85 temps are still forecast to plummet to -24c by Sunday evening...so the character of the snow will become even `drier` and fluffier with snow to water ratios widening to at least 25:1. This will not be good news though...as strong northerly winds on the backside of the cyclone will result in CONSIDERABLE blowing and drifting throughout the day. Given the falling temperatures...wind chill values will likely become a concern as well with apparent temps possibly dropping to the minus teens (minus 20s for the North Country). The powerful winter storm will exit across the Canadian maritimes Sunday night and Monday...while a large arctic high will cross the Upper Great Lakes to the upper Mid West. A deep north to northwest flow between the impressive features will direct the coldest air of the season into our region...with H85 temps forecast to fall to around -24c. While the synoptic snow will have ended over our region...this brutally cold airmass will most certainly support more lake snow...particularly over the western counties. As we end the forecast period on Tuesday...a large area of high pressure move across our region. While this will encourage things to settle down a bit...although some leftover lake effect snow showers cannot be ruled out. In conclusion...though the upcoming storm system is still a few days out, VERY careful attention needs to be made to later forecasts. There will likely be significant winter weather impacts for the region including heavy snowfall, bitter wind chills and strong gusty winds creating blowing and drifting snow likely creating difficult if not impossible travel conditions in many areas. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... For the 12Z TAFS, MVFR ceilings are widespread across the region, with IFR for the higher terrain to the south. A cold front will pass across the TAF sites between 14Z and 19Z, with gusty southerly winds and scattered snow showers ahead of the front. Winds will veer to northwesterly this afternoon and evening...with gusts becoming less frequent as the pressure gradient relaxes. High pressure will spread drier air into the region for the second half of the TAF cycle, with an improvement to ceiling heights and a return to VFR flight through the night. Winds tomorrow night will be light. Outlook... Thursday...Mainly VFR. Thursday night and Friday morning...Widespread IFR in a period of light snow. Friday afternoon and night...VFR/MVFR with a chance of snow showers. Saturday..Deterioration to IFR with widespread snow developing. Saturday night and Sunday...Widespread IFR in heavy snow. && .MARINE... A cold front will cross the Lower Lakes today, with gusty southwest winds veering to northwest behind the front. This will maintain small craft advisory conditions on the Lakes, and also the Niagara River. We will add the Lower Niagara River into a SCA for a northerly component to the wind this afternoon and evening that may near 25 knots at the mouth of the Niagara River. Following the passage of this cold front, quieter conditions will return Wednesday night and Thursday as high pressure slides eastward across the region. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Winter Weather Advisory until 10 AM EST this morning for NYZ001>008-010>014-019>021-085. MARINE...Small Craft Advisory until 7 PM EST this evening for LEZ040- 041. Small Craft Advisory until 1 PM EST this afternoon for LEZ020. Small Craft Advisory from noon today to 7 PM EST this evening for LOZ030. Small Craft Advisory until 1 AM EST Thursday for LOZ043- 044. Small Craft Advisory until 10 PM EST this evening for LOZ042-045. && $$ SYNOPSIS...Thomas NEAR TERM...Thomas SHORT TERM...RSH LONG TERM...RSH AVIATION...Thomas MARINE...Thomas

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