Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 070340 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1040 PM EST Fri Dec 6 2019 .SYNOPSIS... Lake effect snow showers will develop southeast of Lake Ontario tonight. Less favorable conditions exist east of Lake Erie with only flurries expected across the Southern Tier overnight. High pressure will move across the region later Saturday, and off New England by Sunday with dry weather. The next system will bring briefly warmer weather and rain for early next week, followed a blast of much colder air, with potentially significant lake effect snow event mid week. && .NEAR TERM /THROUGH SATURDAY/... Regional radar and MRMS show snow showers from Georgian Bay and Lake Huron to the southern shore of Lake Ontario and inland across western NY late this evening. Observations and webcams show most of this snow as very light with visibility barely changing. The upstream connection to Georgian Bay and Lake Huron will continue into the overnight hours. Temperatures at 850mb will fall to -13C to -10C which will produce enough lake instability for a lake response. While snow showers and flurries have been of little impact, a more organized lake response should take form southeast of Lake Ontario overnight. There will be a 6-hr window, between 1AM-7AM where 1-3 inches are possible from Wayne to southern Oswego counties. There will be a weaker response SE of Lake Erie with less fetch and minimal upstream connection and therefore negligible lake effect snow over the typical higher terrain. Elsewhere, expect only a few flurries or just some decreasing clouds this evening. Some areas may see a period (or several periods) with clear skies. On Saturday, any remaining lake effect ESE of Lake Ontario should come to an end by or around midday, with partly or mostly sunny skies elsewhere as surface high pressure builds over the region behind the departing upper level trough. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... Saturday night, a 1033 surface high gradually drifts east across New York State, then off the coast near Long Island/Massachusetts by Sunday morning. In its wake, a warm front will cross the region overnight and return southerly flow strengthens. This will initiate warm advective processes across the Lower Lakes in advance of the next system, especially on the day Sunday. Otherwise, look for dry conditions to be maintained with increasing high clouds. Lows will be found in the teens east of Lake Ontario, while elsewhere temperatures will be mainly in the low 20s. Surface high pressure off the coast of Long Island/Massachusetts will head further out to sea Sunday. While this occurs, the trough and cold front will approach the Lower Lakes from the northwest. Still expecting a mainly dry day as our region will still be in between the two features. Also, southwesterly flow will continue to pick up with warm advective processes in full swing, so expecting a fairly breezy day. High temperatures will climb into the low to mid 40s west of the Genesee Valley and upper 30s to near 40F elsewhere. Well, it was nice while it lasted with the dry weather coming to and end. Sunday night, the cold front inches closer to Western NY and then slows its progression. Meanwhile, a potent shortwave trough over Montana will be in the process of tracking east into the upper Mid-west. Additionally, moisture off the Gulf of Mexico and Atlantic will be in the process of surging northward. Lift from a 45-50 knot LLJ together with a coupled upper level jet will lead to increasing chances for showers overnight. While most location will see precipitation in the liquid form, there might be some snow east of Lake Ontario. This is where deeper colder air mass will reside initially at the start of the precipitation. There, a few tenths of an inch of snow will be possible before the transition over to rain. With warm advection processes in play, temperatures won`t likely change all that much overnight. Lows will occur early and bottom out in the 30s to low 40s, with the coldest readings found east of Lake Ontario. Complex storm system arrives Monday with rain then turning MUCH colder Tuesday with the potential for significant lake snows. More on that in the long term. Shortwave trough over the upper Midwest tracks east and into the upper Great Lakes on Monday. The surface low over Oklahoma then heads towards the Great Lakes arriving across Michigan by Monday evening. Meanwhile, another low develops along the Mid-Atlantic, as previously mentioned Atlantic moisture surges north up along the northeast coast. This is where the best forcing will occur and higher precipitation amounts will be found. While we won`t see the heaviest of the precipitation (all liquid during this period), a good 0.30-0.50 inch will be likely across area basins. With a much milder air mass in place and H850T in the neighborhood of +4/+5C, look for highs to peak in the upper 40s to low 50s. Low pressure will be found just to our west Monday evening and will track northeast off into Quebec Canada overnight. While this occurs, it will send a strong cold front into and then across the Lower Lakes on Tuesday. Look for synoptic precipitation to diminish from west to east behind the front. With the cold frontal passage, cold air advection will quickly ramp up with H850T plummeting to -11/- 12C. Otherwise, initially temperatures won`t change all that much until the frontal passage just before day break across Western NY. So, there will be a wide disparity in terms of low temperatures. Across Western NY lows will likely be found in the mid to upper 30s, with 40s likely elsewhere ahead of the front. && .LONG TERM /TUESDAY THROUGH FRIDAY/... ...SIGNIFICANT LAKE EFFECT SNOW EVENT CONTINUES TO LOOK POSSIBLE BY MID WEEK... An Arctic cold front will plow across the region on Tuesday. As such, cold air will rapidly pour into the area in the wake of the front causing the lingering rain showers from Tuesday morning to abruptly transition over to snow showers as we head into Tuesday afternoon. Winds shifting to westerly at 850 MB for Tuesday night and Wednesday will advect cold air into the region, causing the 850 MB temps to drop to around -15C for Tuesday night into early Wednesday, before a reinforcing shot of even colder air moves across the Lower Great Lakes Wednesday into Wednesday night, with 850 MB temps possibly bottoming out as low as -20C. In addition, multiple parameters remain in place for a potentially significant lake effect snow event mid week, including good over-lake instability, available moisture and positioning of upper and lower level features suggesting for a strong lake response off both Lake Erie and Lake Ontario beginning Tuesday night continuing into most of the day on Wednesday. As per usual, there is some uncertainty regarding the exact positioning of the lake effect bands, however the lower resolution models are suggesting winds to be generally westerly/west-southwesterly for most of this time period. Winds will veer a bit to west-northwest for a time Wednesday night, causing lake snows to shift more east- southeast of the lakes into Thursday morning. High pressure will pass just south of the region later Thursday into Friday, with lowering precipitation chances as we progress toward the end of the period. Winds will begin their gradual shift from west-northwesterly Thursday morning, to more southwesterly by late in the day Thursday as high pressure moves southeast of the area. Although this will signal the beginning of the warm advection process, it will be a slow one. Temps aloft will still be plenty cold enough to support a lake response, though will be quite muted when compared to the previous as shear and drier air (lowering cap) come into play as well. Will most likely see the typical south to north `sweep` of the lake bands as winds slowly back from west- northwest to southwest Thursday into Thursday evening. Any lingering snow showers northeast of the lakes Thursday night will become even more sparse by Friday as progressively warmer air continues to push in aloft. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Light snow showers and high-end MVFR/low-end VFR cigs will move into western NY tonight. Upstream moisture and cold air advection will lead to lake effect snow southeast of Lake Ontario overnight and into Saturday morning. This should stay between KROC and KART and not severely impact the terminals. The snow bands may clip KROC late tonight but confidence is low at the time. This snowband will diminish Saturday morning. On Saturday a surface high will advance towards the Eastern Great Lakes, with VFR flight conditions and light winds. Outlook... Saturday afternoon...VFR. Sunday...VFR. MVFR in Rain Sunday night with LLWS possible. Monday...Areas of MVFR in rain. Tuesday...MVFR with rain showers ending from west to east. Snow showers possible late. Wednesday...IFR within lake effect snow east of the Lakes. && .MARINE... Northwest flow will continue to increase across Lake Ontario tonight. Small Craft Advisories are in effect for Lake Erie and western Lake Ontario. By the time winds and waves increase further east across Lake Ontario, conditions will drop across Lake Erie overnight. Winds and waves will persist through Saturday across Lake Ontario. A short period of lighter winds are expected later Saturday and Saturday night, but southwest winds will then spread across the region on Sunday. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 1 AM EST Saturday for LEZ040-041. Small Craft Advisory until 4 PM EST Saturday for LOZ043-044. Small Craft Advisory until 10 AM EST Saturday for LOZ042. && $$ SYNOPSIS...HSK/Zaff NEAR TERM...HSK/Zaff SHORT TERM...AR LONG TERM...EAJ/JM AVIATION...HSK/Thomas MARINE...HSK/Zaff

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