Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 400 PM EST Mon Nov 11 2019 Valid 00Z Tue Nov 12 2019 - 00Z Fri Nov 15 2019 ...Great Lakes... Days 1-3... ...Significant and widespread Lake Effect snow event in the favored N/NW snow belts on Day 1... Strong CAA behind a cold front and low pressure system moving into New England will create extremely favorable conditions for Lake Effect snow in the favorable N/NW snow belts. This includes the eastern U.P. of MI, western L.P of MI as well as eastern portions of the L.P. including near Saginaw Bay. Persistent N/NW unidirectional low-level flow and extremely cold 850mb temps falling to -20C will create steep lapse rates and deep inversions towards 10kft. SLR's may reach 25:1 in the cooling airmass, and the intense lift may be sufficient for convection as theta-e lapse rates fall to 0, evidence for at least conditional instability. CAMs continue to indicate the potential for mesovorticies in the strongly convergent environment which could further enhance snowfall. The only limiting factor is subtle wind shifts which could drift the bands W/E slightly, but where bands are most persistent, well over 12" of snow is likely, and probabilities for 18" are as high as 20% (mainly just tonight) across isolated shorelines in western MI. After a brief respite in MI on D2, renewed Lake Effect snowfall may again develop on D3 ahead of a clipper, but on SW flow this time. Temperatures will still be cold enough to produce the low-level deltaT required for instability and LES. WPC probabilities for 4 inches in the favorable S/SW snow belts have increased to moderately high for D2.5. ...Northeast... Day 1... Low pressure moving along a cold front currently over eastern OH will push northeast across the interior Northeast CONUS tonight, departing Maine Tuesday. The track of the surface low remains inland with the axis of heaviest snowfall northeast from Lake Erie to the Adirondacks/Green Mtns to far northern Maine. A swath of wintry mix including around a tenth inch of freezing rain is expected south of the snow over central upstate NY and north-central New England and much of Maine. The heaviest snow with moderate probabilities for a foot are confined to a narrow band collocated with jet exit region ascent and 850-600mb fgen pivoting northeast across the highest elevations of Adirondacks and into portions of northwest Vermont and far northern Maine. Lighter snows are expected on either side of this band due to WAA/ascent. Although the system is progressive, periods of heavy snow are possible, and WPC probabilities are high for an additional 6 inches after 00Z northeast from Lake Erie, Lake Ontario, to northern Maine. Further south and east into central New England and closer to the coast, strong WAA which will enhance snowfall north, will also produce a warm nose >0C to cause a mixture of snow/sleet/freezing rain. Where sfc temps remain below freezing, a period of freezing rain is likely, and WPC probabilities for 0.1" are above 40% for the southern Adirondacks and central parts of VT/NH/ME. Some wrap around Lake effect snows will continue Tuesday night of lakes Erie and Ontario in NW flow. ...Texas to Kentucky... Day 1... A katabatic cold front, supported by a positively tilted upper level trough, looks to advance fast enough to allow a light freezing rain potential across south Texas tonight into Tuesday before precip ends. Precip should end there before the column is cool enough to cause sleet or snow. There are generally low probabilities for a hundredth inch of ice inland from the TX coast for all south Texas except the lower Rio Grande Valley. Farther northeast the breadth of undercutting by cold air is more narrow, but there is a short window for light freezing rain potential tonight into Tuesday from northern LA/MS/AL and most of TN/KY. Jackson