644 FXUS61 KCLE 171130 AFDCLE Area Forecast Discussion National Weather Service Cleveland OH 630 AM EST Tue Dec 17 2019 .SYNOPSIS... Low pressure will move northeast through the Ohio Valley this morning. An Alberta Clipper storm system will move southeast through central Ontario, Canada tonight. The Clipper will force an Arctic cold front through the local area Wednesday morning. High pressure will build east across the area Thursday and slow in forward motion through the end of the week. A warm front will lift northeast across the area late Saturday. && .NEAR TERM /THROUGH WEDNESDAY/... Some banding is taking place along the northern fringe in what appears to be the best area of forcing to the northwest of the low track. Snow will continue along the northern tier counties with a mix of snow/sleet/freezing rain to the southeast. Precipitation will all transition over to snow before ending today. Only minor adjustments to temperatures and removed mention of freezing rain out of southern Ashtabula county since it should remain all snow there. Very limited freezing rain is expected over northwest Pennsylvania. Previous Discussion... A wintry forecast is in store for the forecast area during this period. An upper level low pressure system will dive southeast across the Great Lakes region through Wednesday. This will cause surface low pressure to move northeast through the Ohio Valley this morning and allow a slow moving surface high pressure to build east toward the area through the period. The low pressure system continues to push warm air into the region in the mid levels causing mixed precipitation to occur. Temperatures at the surface away from the lake shore are in the lower 30s at this time resulting in some freezing rain in the winter weather advisory area. Otherwise, snow is falling across the rest of the area. As the low pressure system moves east of the area, colder air will follow behind the system and change all of the precipitation over to snow before ending by this afternoon. As the upper level low pressure system moves southeast across the area, a fast moving Alberta Clipper storm system will move southeast across central Ontario, Canada. The low will force an Arctic Cold front southeast across the area Wednesday morning. Significantly colder air will move into the region behind the front and will cause surface temperatures to drop through the 20s into the teens by evening. Wind chill values will drop into the single digits most areas with some areas of values just below zero. Some light snow shower activity will occur with the Arctic Cold front tomorrow morning but expecting fair weather otherwise across much of the forecast area by afternoon. The big story with this package is the possibility for lake effect snow to develop in the northeast snow belt. Latest model soundings and short term guidance suggests an area of convergence will develop late tonight and continue into Wednesday along the lake shore of northeast Ohio and northwest Pennsylvania setting up a band of lake effect snow in this area. Instability will increase to moderate over the primary snow belt area as temperatures fall through the day Wednesday into Wednesday night. Inversion heights hover around 7000 feet and should be adequate depth for the lake snow band to develop. The snow band will persist through this forecast period and begin to shift a bit inland by Wednesday evening. Therefore, expecting snow accumulations between 6 and 10 inches with locally higher amounts in the snow bands across the eastern half of Lake, the northern half of Ashtabula, and all of Erie county in Pennsylvania. Issued a winter storm watch for lake effect for the above mentioned counties starting at 06z tonight through 12z Thursday morning. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... Arctic air will continue to spill over the eastern Great Lakes Wednesday evening with surface temperatures falling through the teens and wind chills down into the single digits to around zero. 850 temperatures will be hovering around -17C to -20C through Wednesday evening before temperatures aloft begin to moderate later Wednesday night as the core of the Arctic air moves eastward. The lake effect snow machine will continue for the primary Snowbelt areas through Wednesday night with gradual decrease in organization and intensity as the night goes on. High pressure moving across the Ohio Valley will nose up into central Ohio with lighter winds by Thursday morning and clearer skies. Temperatures will be coldest across central and western Ohio with overnight low temperatures down into the single digits potentially. The lake effect snow showers will wrap up by Thursday morning. Southerly winds return on Thursday and the slow moderation in temperatures will begin. There will be slow clearing from southwest to northeast across northern Ohio into NW Pennyslvania. Most areas will not crack the freezing mark Thursday afternoon. Upper level heights will rise Friday and temperatures will climb to seasonable average levels in the upper 30s to around 40 degrees. && .LONG TERM /SATURDAY THROUGH MONDAY/... The weekend is looking relatively quiet and decent weather for late December standards. The region will be in a fast moving westerly flow but the systems riding through the upper level flow look like they will stay just north of our area with minimum weather impacts to our area. Southwesterly winds will bring relatively milder weather Saturday through Monday with high temperatures slightly above average in the 40s. There will be passing high cloudiness along with periods of sunshine this weekend. And looking even further into the Christmas holiday for the middle of next week, the weather pattern looks to remain on the quiet side for our area. Our chances of having a White Christmas locally are looking very slim to none at this time. && .AVIATION /12Z Tuesday THROUGH Saturday/... Light snow will continue across the northern portions of the forecast area with a mix of sleet/snow/freezing rain across the southeast this morning. All precipitation will transition over to all snow before ending later this morning. Low pressure will move northeast through the Ohio Valley region this morning. Ceilings and visibilities will continue in the IFR/LIFR range with the advancing low pressure system. A gradual return back to VFR pushing into the area from west to east during the day today. Winds will be 10 to 20 knots across the area as well with the low pressure system. .OUTLOOK...Non-VFR possible with lake effect snow in the snowbelt through Thursday. && .MARINE... Low pressure will be moving from the Ohio Valley this morning to the New England coastal region late today. Northerly to northwesterly winds and waves will increase through the morning. There will be a brief time window where the winds and waves will decrease this afternoon into the early evening before a stronger Arctic cold front moves across the lake tonight. To make it more simple, we have extended the ongoing Small Craft Advisory through Wednesday night and added the western basin nearshore water to a SCA starting tonight through Wednesday night. Strong gusty northwest winds will follow the passage of the cold front tonight through Wednesday evening with gusts up to 30 knots. Waves will increase up to 4 to 9 feet potentially along the lakeshore waters. High pressure builds back in on Thursday with better marine conditions expected through Saturday across the region. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...Winter Storm Watch from late tonight through Thursday morning for OHZ012-014-089. Winter Weather Advisory until 1 PM EST this afternoon for OHZ020>023-027>033-036>038-047. PA...Winter Storm Watch from late tonight through Thursday morning for PAZ001-002. Winter Weather Advisory until 1 PM EST this afternoon for PAZ001>003. MARINE...Small Craft Advisory until 7 AM EST Thursday for LEZ147>149. Small Craft Advisory from 1 AM Wednesday to 1 AM EST Thursday for LEZ142-143. Small Craft Advisory until 1 AM EST Thursday for LEZ144>146. && $$ SYNOPSIS...Lombardy NEAR TERM...Lombardy SHORT TERM...Griffin LONG TERM...Griffin AVIATION...Lombardy MARINE...Griffin