154 FXUS63 KDTX 242313 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 713 PM EDT Sat Oct 24 2020 .AVIATION... High pressure ridge in place through the central Great Lakes and a static positioning to the upper level jet axis aloft leads to very little thermal advection locally through tonight. Nuisance boundary layer cloud trapped below midlevel inversion brings uncertainty with regards to persistence of cumulus/stratocumulus tonight. No active subsidence below 7000 ft agl also casts some doubt. Did keep a prevailing/TEMPO cloud through the evening hours based on observation trends. Additionally, lower troposphere trajectories will become more easterly with some lake moisture component later on. Expecting MVFR low VFR to eventually scatter out late tonight. Passing high cloud is expected to be overhead of Southeast Michigan with forcing taking place along the periphery of the upper level jet. .DTW THRESHOLD PROBABILITIES... * Medium for ceilings aob 5kft tonight. && .PREV DISCUSSION... Issued at 325 PM EDT Sat Oct 24 2020 DISCUSSION... Expect a varying degree of cloud cover across Se Mi tonight. There is a definite diurnal contribution to much of the cloud cover across Se Mi. While these will wane with the loss in daytime heating this evening, low level flow will veer to the east during the night as expansive high pressure extends across the northern lakes. Lake contribution will thus support at least some additional lower clouds into Se Mi. Mid/high level clouds will also drift int portions of the area from the west. In light of how cold the low level airmass is and with sfc dewpoints down into the low 30s, nighttime cooling will still support mins well down into the 30s despite some uncertainty in cloud trends. An upper jet max will be forced from the southern Rockies tonight into the central plains and Iowa late Sunday/Sunday night. Exit region jet dynamics will force some response along the deep layer frontal boundary across the Great Lakes. This upper jet support and increased mid level frontal forcing will then persist across Se Mi well into the day Monday. The NAM remains on the stronger side of the model suite with respect to the strength of the frontogenesis across Se Mi as well as a short wave impulse embedded within the flow. The result is a more bullish precip forecast across Se Mi Sun night and Monday. The remainder of the model suite remain much weaker with the larger scale forcing and have a more stable mid level profile across the southern lakes. Trends among ensemble members have also strongly favored a weaker solution. Thus pops across Se Mi will remain in the slight chance/low chance category Sun night and Monday. Ample cloud cover with the main sfc front well south will still ensure continuation of cool temperatures. Some phasing of upper jet energy late Mon/Mon night will lead to a strengthening of the deep layer frontal forcing across the Ohio valley. The northern edge of the elevated portion of the front may clip the southern portions of Se Mi Mon night, supporting a continuation of a chance of light rain. There is general agreement that a closed mid level circulation will develop within the base of the long wave trough over the southern Rockies and Texas Panhandle on Tuesday with a general weakening of the northern stream trough over the Great Lakes. The upper low is then forecast to meander across the southern US before getting reabsorbed into the northern stream over the eastern US during the end of the forecast period. Se Mi will remain north of the low level baroclinic zone, ensuring seasonally cool conditions through the end of the forecast period. MARINE... Northerly flow will persist across the eastern Lakes into tonight as high pressure continues to build into the region. Winds will go light and primarily easterly tonight into Sunday as the center of the high moves over northern Michigan. Next chance of precipitation will come Sunday night as a weak system lifts through the straits along a frontal boundary. High pressure building in behind this front will push it down through the eastern Lakes into Monday bringing chances of rain through the region. Winds behind the front will turn northwesterly Monday but gusts will remain in check as cold advection will be weak. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....CB DISCUSSION...SC MARINE.......DRK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.