943 FXUS63 KDTX 242301 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 601 PM EST Tue Nov 24 2020 .AVIATION... Widespread precipitation will continue to lift across the southeast MI airspace late this evening. Intervals of higher intensity bursts will allow ongoing rainfall to occasionally/briefly mix with snow from FNT southward into the Detroit corridor over the next couple of hours. This will maintain a window for mainly MVFR level restrictions across this corridor during this time. MBS will tend to hold within an all snow precipitation type for several more hours, before gradually warming from south to north favors a transition to rain overnight as precipitation diminishes. Pockets of light rain possible overnight all areas, but with a tendency for low cloud to vacate as conditions temporarily settle into VFR. Secondary surge of deeper low level moisture arrives by mid-late morning, favoring an aggressive reduction in ceiling heights and visibility during this time. Increasing potential will exist for LIFR conditions to emerge on Wednesday. Winds generally from the south-southeast aob 10 kts through Wednesday. For DTW...window for snow to mix in with rain ending as heavier precipitation lifts to the north and temperatures hold well above freezing. Lower cloud lingers through the remainder of the evening, with some improvement likely overnight. Lowering cloud bases again w/ some vsby restrictions expected just beyond 12z Wednesday. .DTW THRESHOLD PROBABILITIES... * High for ceiling at or below 5000 feet through this evening. Low overnight, then high again after 12z Wednesday. * Low for visibility at or below 1/2SM Wednesday. && .PREV DISCUSSION... Issued at 318 PM EST Tue Nov 24 2020 DISCUSSION... Warm advection arm lifting through southeast Michigan this afternoon, but bulk of jet forcing jet displaced just to the west of the CWA. Precipitation has begun to punch through the dry low levels, and there is still enough low level wet bulbing anticipated to support a little light snow as temperatures lower with the onset of precip (but not reaching the freezing mark, except perhaps north of M-46). Fortunately, the latest RAP/HRRR and indicating a convincing northward shift to the warm front, north of the CWA by Midnight, with the influence over the mid level dry slot taking hold overnight. Surface temperatures above freezing and high DGZ (above 500 MB) should help limit snow accumulations with riming taking place due to the warm mid levels. Will continue to highlight mainly just 1-2 inches across Tri-Cities region and far northern tip of the Thumb (with half an inch or less most everywhere else). Local probabilistic guidance for snow accumulation in Midland/Bay is trending down. Despite this, would not rule out 3 inches in the far northern reaches of the Counties, something similar to the 12Z WRF-NMM. Storm system currently exiting the Four Corners region, sending a pretty good surge of moisture into southern Lower Michigan on Wednesday, as PW Values increase to around 1 inch. However, this large upper level low looks to be unraveling/weakening just a bit, as the max height fall center tracks through the northern Ohio Valley during the day, and tough call on where and how long the mid level deformation axis will reside, as bulk of models quickly lift the 700 trowal north by 00z Thursday. Thus, rainfall amounts should be manageable around half an inch for most locations. The exception may be north of M-46 where enhanced low level FGEN could support upwards of an inch. Split upper level flow once again Thursday-Friday, with good agreement with another closed 500 MB low over the Four Corners region, with a progressive/moisture starved northern stream shortwave trough/cold front sliding through the Great Lakes region. Unimpressive post frontal amount of cold air for late November standards, as 850 mb temps only progged to drop into the mid negative single numbers early Saturday morning, per 12z Euro. After what looks like a quiet weekend, potential winter storm setting up for early next week, as strong storm system comes out of the Gulf of Alaska, with what looks to be eventual phasing with the Four Corners energy. There looks to be unanimous consent, it is just when and where phasing occurs (eastern Plains vs Appalachians) leading to longwave trough encompassing the eastern half/third of North America. Need-less-to-say, 12z EURO is very aggressive with the impact to southeast Michigan. The 00z Euro ensemble members (~50 percent) were also fairly convincing with significant amount of measurable QPF centered around 00z DEC 1. Still, we are talking Days 6-7 and will remain conservative with the standard/climo 30 pop for now. MARINE... A warm front lifts northeast across Lake Huron this afternoon and evening with southeast surface wind increasing to around 15 to 20 kt with gusts to 25 kt over Lake Huron. Waves build across the southern and central basins tonight with Small Craft Advisories going into effect for the Lake Huron nearshore zones from Port Austin to Port Sanilac. Rain/snow fills in over the next few hours with a transition to all rain tonight into Wednesday morning. The next round of rain moves in on Wednesday afternoon with a low pressure system that tracks across the southern Great Lakes. This system will be weakening, so not expecting a strong wind response as it moves out on Thursday. Dry conditions with generally westerly flow then follow for the late week with the next cold front moving in on Friday night. HYDROLOGY... Any snowfall around this evening tapers off to light rain/drizzle before temporarily ending tonight. Widespread rain moves through tomorrow and tapers off tomorrow evening/night. Average rainfall is expected to be around half an inch, but totals of 1 inch or slightly greater look possible along and north of M-46. Even so, with these higher rainfall amounts spread over a relatively long period, flood concerns should be limited to poor drainage areas, with just nuisance flooding if any. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory until 4 AM EST Wednesday for LHZ441-442. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....MR DISCUSSION...sf MARINE.......TF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.