146 FXUS63 KDTX 302055 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 355 PM EST Fri Dec 30 2022 .DISCUSSION... Compact mid-upper geopotential height gradient with corresponding strong +170 knot upper level jet and midlevel frontal zone is parked over Southeast Michigan this afternoon. Well organized near surface anticyclonic flow trajectories in advance of the front has very moisture rich air streaming into Michigan with PWATS around 1.00 inch which is NAEFS 90th percentile and at the maximum moving average for Dec 30th. Beginning this evening, jet dynamics will notably increase as both more anticyclonic curvature and a coupled upper level jet structure approach Southeast Michigan. The increase in ageostrophy will result in increased midlevel frontogenesis and a wave of low pressure riding along the front tonight. System relative flow and plan view of isentropic surfaces shows two separate steeper frontal slope structure that focuses lift. The northern slope is just north of I 69 associated with the 299-303 Ke surfaces and will likely establish the northern edge of the QPF (invof the Tri Cities and western Thumb). The southern slope is along the 309-313 Ke surfaces which hangs up near the Detroit and St Clair Rivers and Lake St Clair. There is much disparity amongst QPF amounts, but throwing out the typical high outliers gives some confidence on QPF amounts tonight of 0.5 to 0.75 inch possible for the southeastern 1/4th of the cwa, lesser amounts north and west. Hand edited PoPs across the board for tonight to get a greater coverage of categoricals. A weak midlevel low circulation at 775-650mb will push through the forecast area between 12-15Z Saturday. Did carry high PoPs through the morning hours, but models are fairly adamant in no active isentropic lift during that time period. Temperatures are expected to drop over the southern forecast area during the day. Very quiet weather is expected for New Years Eve evening. A very progressive pattern will be in place as the next upper level jet packet will push into Southeast Michigan already by Sunday morning. Strong anticyclonic curvature to jetlet aloft is shown to correspond to strengthening absolute vorticity elements within an amplifying longer wavelength PV reservoir. Models are trending more bullish on the prospects of light precipitation Sunday morning tied to increase in warm air advection and isentropic ascent. Questions exist on the integrity of the lift as a survey of forecast soundings show very little omega, in a region that is void of any great upper level jet forcing. The same models are showing a depth to the moisture that is quite surprising which brings uncertainty to the quality of the setup. The other item that will be monitored are the surface temperatures expected Sunday morning as they will like be below freezing. So any light overrunning of moisture may present some problems. Not having a tremendous amount of confidence the atmosphere will be that deeply saturated, so included a chance of light snow or light freezing drizzle Sunday morning. Models continue to advertise a deep Pacific trough system closing off over the Midwest and western Great Lakes early next week. Orientation of the upper level jet features suggests there is a good probability in a strong negatively tilted low as it impacts Southeast Michigan. Early indications are this will be a moisture rich system that will have the cwa firmly situated within the warm sector. && .MARINE... A weakening cold front progresses eastward across Lake Huron this afternoon before stalling near southern Ontario and Lake Erie tonight. Cold advection will be weak and southwest winds will become light and disorganized tonight before organizing out of the north/northwest at 10 kt or below on Saturday. A low pressure system then lifts out of the Ohio Valley, tracking along the front into the eastern Great Lakes by late Saturday. This system will bring a swath of light to moderate rain to Lake Erie, Lake St. Clair, and southern Lake Huron. A disorganized pressure field fills in for Sunday into Monday with winds generally 10 to 15 kt. The next low pressure system then lifts into the Midwest on Tuesday, bringing a warm front and widespread rain to the region. && .HYDROLOGY... A frontal zone is expected to remain stalled out over Southeast Michigan through tonight. A weak area of low pressure is expected to ride along this boundary bringing widespread rain to the area. A tight gradient of rainfall is anticipated, but rainfall of 0.5 to 0.75 inch will be possible through midday Saturday. && .PREV DISCUSSION... Issued at 119 PM EST Fri Dec 30 2022 AVIATION... Steady moisture flux under south-southwest flow continues to bring in a stream of showers and low stratus from DTW to FNT. Low MVFR to IFR ceilings currently observed across the airspace will steadily lower to IFR through the afternoon as persistent rainfall saturates the sub-cloud layer. Still some uncertainty as to how quickly this saturation process occurs and the role that surrounding drier air may play. TAFs thus reflect the general trend for lowering cigs/vis through the evening. A cold front approaching from the west this afternoon shifts winds to westerly and eventually northwesterly overnight, while focusing moisture primarily between PTK and DTW as it stalls over Lake Erie. Development of a subtle inversion aloft and diminishing SW flow lends to LIFR cigs with potential for visibility restrictions given such moist near-surface conditions. Ceilings and visibilities begin to improve mid-morning Saturday as the front releases further east. For DTW... approaching frontal boundary stalls over Lake Erie this evening, with winds veering NW by tonight. Stratus lowers through the evening, although timing will be largely dependent on shower intensity overhead. Still a good signal in guidance for cloud bases to reach LIFR by early Saturday morning, with IFR visibility restrictions given the moist near-surface conditions. DTW THRESHOLD PROBABILITIES... * High for ceiling 5000 ft or less today and Saturday. * High for precipitation as all rain today and tonight. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...CB MARINE.......TF HYDROLOGY....CB AVIATION.....MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.