215 FXUS63 KDTX 122050 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 350 PM EST Wed Feb 12 2020 .DISCUSSION... After a quiet day with a good amount of sunshine early, SE Michigan will receive a round of light snow this evening and overnight as a low pressure system lifts through the Ohio Valley. Forecast reasoning from previous discussions remains on track with little adjustments necessary as 12z guidance continues to hone in on an area-wide 1 to 2 inches tonight into Thursday morning with 2 to 3 inch accumulations limited to areas south of I-94. The upper wave will be shearing out as it races out ahead of the approaching longwave trough associated with a surge of arctic air, resulting in a relatively weak region of deformation forcing that will pass overhead in the 00z to 06z time frame. Isentropic ascent and fgen are maximized in the 725-650mb layer which falls just below the DGZ progged to reside around 15kft or 550-500mb. The final result will be modest snow-to-liquid ratios tonight of generally 12:1 or less, which, paired with QPF of a couple tenths of an inch, will be responsible for the light snow amounts. The bulk of the moisture advection will be caught in convection well south of the area. Onset of snow remains on target for around 7-8pm near the Ohio border, then spreads northward through the evening with snow starting in the Tri-Cities/Thumb around midnight or so. The aforementioned arctic front will advance across northern lower MI late tonight into Thursday morning. A brief lull in light snow is likely across the Metro area during the morning before the front and inbound height falls arrive. For the northern CWA, forcing from the front will coincide with forcing from the departing Ohio Valley low and lead to a consolidation in light snowfall during the mid- morning. More favorable thermal profiles along the front with some low-level instability intersecting the DGZ will lead to higher snow- to-liquid ratios Thursday and therefore fluffier snow. An additional 1 to 2 inches can be expected across SE Michigan with snow activity in more of a showery nature. With the strength of the cold advection and 25 kt northwest 850mb flow behind the front, a few marginal snow squalls can't be ruled out, especially south of M-59 where the instability will be maximized by the time the front moves through in the afternoon. This activity is not expected to be widespread. Afternoon gusts in the fresh cold advection will approach 20 mph and usher in wind chills in the single digits - actual temps falling to the teens by late afternoon. 850mb temps will dip below -20C by Friday morning, with fresh snow cover and some cloud clearing both contributing to temps cratering. Lows in the single digits and possibly below zero in the typical cool spots can be expected early Friday. The northwest flow will be diminishing by this point, but a slight breeze will persist and knock wind chills below zero. Highs Friday will struggle to reach the upper teens as the thermal trough tracks overhead. Some afternoon flurries will be possible as a shortwave drops into the longwave trough, but no accumulation is expected. The pattern remains progressive and return flow sets up Friday night, advecting in a more seasonable air mass by Saturday with temps improving to the lower 30s. A weak cold front brings the next chance of snow on Saturday night. Generally quiet weather is then likely for Sunday and Monday before the next potentially impactful system tracks into the Great Lakes for late Monday into Tuesday. Snow looks to be the primary ptype at this time, but depending on where the system warm sector develops, we could see a wintry mix or rain as well. && .MARINE... A low pressure system tracks northeastward through the Ohio Valley tonight bringing snow showers across the central Great Lakes region. Snow will linger through the day Thursday as an arctic front drops south across the lakes, setting up a cold north-northwest flow with some freezing spray likely in Lake Huron. This wind shift will bring the higher wave field south leading to hazardous boating conditions along the Thumb. A small craft advisory will go into effect Thursday morning through early Friday morning. Strong high pressure will overspread the region Friday reducing winds and waves. && .PREV DISCUSSION... Issued at 1220 PM EST Wed Feb 12 2020 AVIATION... A dry low level environment held firm by modest southerly flow will maintain VFR conditions through the remainder of the daylight period. Area of mainly light snowfall will expand northward into southeast Michigan after 00z. This will lead to low MVFR to IFR conditions in accumulating snow throughout the tonight period. While the northward expanse of this moisture may struggle to reach north of FNT, an arctic front arriving from the northwest will bring increasing potential for snow showers at MBS/FNT by Thursday morning. Periodic snow showers then expected areawide Thursday as this boundary eases across the region, augmented by increasing moisture flux off lake Michigan. Frontal passage will bring a wind shift to northwest, with gusts near 20 knots possible at times during the afternoon. For DTW...Period of light snow expected late this evening through the early morning hours. Onset of snowfall near 02z, with an accompanying rapid drop in ceiling heights during this time. Accumulation up to 2 inches tonight. Brief lull in activity possible mid-late morning Thu, before snow showers increase in coverage again Thu afternoon. DTW THRESHOLD PROBABILITIES... * High in ceilings below 5000 feet tonight and Thursday. * High for precipitation type as snow tonight and Thursday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Lakeshore Flood Advisory from 7 AM Thursday to 4 AM EST Friday for MIZ049-055-063. Lake Huron...Small Craft Advisory from 7 AM Thursday to 4 AM EST Friday for LHZ421-441>443. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...TF MARINE.......KDK AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.