Area Forecast Discussion
Issued by NWS Buffalo, NY

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188 FXUS61 KBUF 190243 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 943 PM EST Mon Feb 18 2019 .SYNOPSIS... Scattered weak lake effect showers southeast of Lake Ontario will end early Tuesday as strong surface high pressure moves east across the state. The next system will approach the region by late Wednesday and bring a wintry mix to the region Wednesday night followed by a period of rain. This system may briefly end as snow on Thursday before another area of surface high pressure moves in for the end of the week. && .NEAR TERM /THROUGH TUESDAY/... Mesoscale processes will continue overnight south and southeast of Lake Ontario. The airmass above 4000` will quickly dry out. Lapse rates below this will be steep enough to support lake effect processes though, mainly from Wayne to Oswego County, although portions of Orleans and Monroe counties may see some scattered snow showers. Most of this will be light and hard to detect via KTYX or KBUF 88Ds, but we`ll have good coverage from GOES16 with no upper level cloud cover. Accumulations, if any, should be an inch or less. The remainder of the region should see slowly decreasing cloud cover but with upslope flow may hinder the ability to complete clear out with some flurries possible. Temperatures east of Lake Ontario however may plummet with fresh snow cover, light winds and clear skies, with overnight lows near (or lower) than 10F below zero. The remainder of the region should see temperatures mostly in the single digits or into the teens where cloud cover lingers the longest. Strong surface high pressure will then move east into the region for Tuesday. Localized lake effect right along southern Lake Ontario shoreline early Tuesday will try to keep going even under a strong cap near between about 3500-4000`, but eventually this will be pushed ENE and probably offshore, ending altogether in the afternoon. The remainder of the area should see variable clouds to mostly or sunny skies east of Lake Ontario. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... High pressure will be anchored directly overhead Tuesday evening and gradually begins an eastward ooze toward New England by Wednesday morning. This will allow for return flow from the south on the west side of the high to start to draw warmer air northward toward the CWA by Wednesday morning. As this occurs, the mid-level ridge axis will shift east of the area on Wednesday morning, and allow the area to start to be susceptible to mid-level moisture streaming in from the southwest ahead of the next sprawling upper low in the mid- latitude flow. The mid-level vort maxima will shift toward the Great Lakes rapidly on Wednesday, largely phasing into the anomalously strong upper jet streak that has become semi-resident in the northeastern U.S. The right entrance region of this feature will be anchored somewhere near the area, so with an upward catapult in layer moisture, upper divergence, and differential thermal advection, precipitation should blossom across the area as the wave translates in. With warm advection well underway, particularly off the deck on model soundings, a short period of inefficient snow will be likely before a transition to sleet/freezing rain and eventually rain will be common across the area. Given a very high dendritic growth layer and warm advection processes, snow growth will be inefficient, so 1-2" would seem to be the maximum for snowfall potential before a changeover. The length of time for freezing precipitation will largely be modulated by how difficult mixing out of cold air in the lowest elevations will be. That said, the Lake Erie shoreline and Buffalo area summarily have the shortest window for icing. Drier conditions return for a spell behind this system, as mid-level ridging returns to the area. && .LONG TERM /FRIDAY THROUGH MONDAY/... High pressure will move from west to east and across the area on Friday, which will provide dry weather which will last well into Saturday. Highs on Friday will range from the mid 30s to around 40 with lingering cloud cover eventually giving way to a partial clearing by Friday night. Saturday looks to be quite a nice day with warmer conditions and temperatures climbing into the 40s. The warmest areas will be the lake plains due to a developing southerly downslope flow when the surface high exits to our east. Cloud cover will increase from southwest to northeast with the approach of the next system, but any showers should hold off until late in the day or Saturday night. Things get much more active for the latter half of the weekend and into next week. A closed 500 mb low is forecast to move across mid-western states Saturday night, with the majority of model guidance then tracking a strong corresponding surface low across the Great Lakes region in the Sunday timeframe. Model agreement provides confidence in the general pattern even if there remains uncertainty in the exact strength, timing, and track. Latest model runs suggest the most likely track is across the central Great Lakes and then across southern Ontario province Sunday night. This would potentially bring strong to damaging winds behind the cold or occluded front with this system. A more westward track or weaker system would lower this risk, but given the latest consensus the wind potential is a least worth a mention in the HWO. This track would also bring rain and warm temperatures to most of the region, with upper 40s and lower 50s likely south of Lake Ontario. It`s a closer call across the North Country which will be closer to the track of the low. Depending on the track, precipitation may be mixed with snow there. The bulk of the precipitation will be Saturday night and Sunday, with model consensus suggesting a half inch to an inch of QPF with this system. Colder air will build into the region Sunday night, with lingering rain showers changing over to snow. By Monday, it may be cold enough aloft to support a limited lake response east of Lake Ontario which will be enhanced by upsloping in a a strong westerly flow behind the system. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Surface high pressure will move into the region by Tuesday but with continued localized lake effect SE of Lake Ontario. Therefore expect MVFR in most areas to gradually improve to VFR with mainly a stratocu deck in weak upslope flow. Outlook... Tuesday and Tuesday night...improvement to VFR areawide. Wednesday...Deterioration to MVFR/IFR with light mixed precipitation becoming likely overnight. Thursday...VFR/MVFR with a chance of snow and rain showers. Friday and Saturday...VFR. && .MARINE... Surface high pressure will build into the region for Tuesday with light winds lasting through Tuesday night. Advisory level winds will return by Thursday following the passage of another surface low and its trailing cold front. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...Zaff NEAR TERM...TMA/Zaff SHORT TERM...Fries LONG TERM...Apffel AVIATION...Zaff MARINE...Zaff

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