314 FXUS63 KDTX 300717 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 317 AM EDT Fri Oct 30 2020 .DISCUSSION... Upper level trough tracking across the Great Lakes Region this morning, with surface high pressure becoming established over the Central Great Lakes this afternoon. Thus, any lake effect activity coming off of Lake Huron this morning will push offshore toward noon as sfc-low level winds become northwest. 850 MB temps certainly cold enough to support snow showers, as they drop into the high negative single numbers, but cloud depths do not look to extend much above 850 MB, and thus ice nuclei could be missing. The next shot of cold air arriving on Sunday actually looks to present a much greater chance of snow showers for most of us. Even as winds become northwest this morning, low level lapse rates look to be steep enough to generate some modest cape, and would not rule out an isolated rain/snow shower for western areas as well. Mostly cloudy skies and 850 MB temps near -8 C suggests maxes mostly in the lower 40s today. With clear skies tonight and winds becoming calm, guidance temps in the 20s to around 30 degrees for the urban heat island of Detroit appear reasonable. Sunshine tomorrow will allow temps to rebound a good 20+ degrees as warm advection pattern ramps up through the day ahead of our next storm system. Latest water vapor imagery shows strong upper level low/wave along the British Columbia Coastline which will be swinging through for the second half of the weekend. Additional energy dropping south on the backside from the Yukon will provide a good cold infusion, with 850 MB temps forecasted to drop off toward -10 C on Sunday. The cold cyclonic flow with pronounced surface troughing suggests high scattered-numerous lake enhanced activity as 700 MB cold pool of -20 C tracks through. 00z NAM/Euro advertising 850 MB winds of 50 knots by early Sunday evening, which should translate to gusty west- northwest winds of 30-40 MPH at the surface, which has support with our local probabilistic guidance. Pretty good surface based capes progged intersecting the DGZ, and light accumulations (dusting to <1") on grassy surfaces appears likely, as NAM indicates freezing levels right near the ground. Right now, based on the Sunday afternoon timing, a well defined I-94 corridor band should struggle to get organized with the diurnal instability/convective rolls. Aggressive height rises/subsidence and subsequent 850 MB warming will quickly shut off any activity Sunday evening/night. 500 MB height rises look to continue right into Wednesday, supporting much above normal temperatures in the warm advection regime with the jet stream displaced north of the Conus. 850 MB temps progged to reach into the mid teens by Wednesday. Fog/low clouds always a concern in November, which can short circuit maxes, as MEX guidance and euro mos ensemble box plots suggesting highs 60+ degrees right through the end of the work week. && .MARINE... Northeast winds of 15 to 25 knots will shift to the northwest this morning and decrease as high pressure builds into the Central Great Lakes. Light and variable winds tonight will be short lived, as strong storm system tracks through over the Weekend. South-southwest gales on the front end with the warm air advection is possible Saturday night, but higher confidence in west-northwest post frontal gales over Lake huron late Sunday into Sunday night, with cold airmass also conducive for snow squalls. Have issued a Gale watch just for the open waters of Lake Huron for now, but nearshore waters will likely have to be added for the cold advection late Sunday/Sunday evening. A warm advection westerly regime will then take hold early next week as upper level ridge builds in, and winds are expected to be moderate and hold predominately under 25 knots. && .PREV DISCUSSION... Issued at 1203 AM EDT Fri Oct 30 2020 AVIATION... Cold air advection in the 1.2 and 3.5 kft agl layer and lake-origin moisture ducted below midlevel inversion resulted in numerous to widespread light rain/drizzle for areas mainly north of I 96 early this evening. Secondary cold air advection is expected in the 3.5 to 6.5 kft agl layer which will then deep the lapse rates conducive for precipitation from 6-12Z. Low confidence exists on coverage of light precipitation late tonight as radar trends have not been very impressive. Cloud is expected to persist throughout the late morning with rising cig heights. For DTW...It has been difficult for drizzle activity to move southeastward into the lower elevation areas near the Rivers. Low confidence exists on light rain/drizzle activity. DTW THRESHOLD PROBABILITIES... * High in ceilings below 5000 feet this morning. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Lakeshore Flood Advisory until 10 AM EDT this morning for MIZ049- 055-063. Lake Huron...Gale Watch from Saturday evening through late Sunday night for LHZ361>363-462>464. Small Craft Advisory until 10 AM EDT this morning for LHZ421- 441>443. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...SF MARINE.......SF AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.