Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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048 FXUS63 KDTX 170758 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 358 AM EDT Wed Jul 17 2024 .KEY MESSAGES... * An upper level disturbance crosses through Lower Michigan today providing scattered showers and perhaps a rumble of thunder or two. * High pressure then brings cooler, drier, and less humid conditions to the region through the end of the workweek. * Temperatures moderate over the weekend as high pressure departs, followed by an approaching boundary Sunday which offers low-end precipitation chances. && .DISCUSSION... Observations sampling the post-frontal airmass show a slow improvement in dewpoints this morning while gradient winds prepare to reorganize out of the northwest. A positively tilted mid-upper level longwave trough axis extending from southern Hudson Bay to the Upper Mississippi Valley is expected to pivot across the Great Lakes with time today. While weak and disorganized ascent may trigger some very isolated morning shower activity, height falls become more prominent across Southeast Michigan after 12Z as an arc of CVA descends on the region triggering an increase in precipitating rain showers. Primary limiting factor relates to the lack of substantive ThetaE advection as dry air dominates the mid-levels complicating saturation depths. Nevertheless, surface-H5 shear of 45+ knots combined with SBCAPE values up to 300 J/kg should suffice in scattered showers with perhaps a few late afternoon rumbles of thunder. Consensus QPF offers medium confidence with peak coverage during the midday hours, particularly across The Thumb and vicinity areas. Temperature-wise, the lagged elevated portion of the frontal zone has further southeastward progress to cover before H8 temps drop from the lower teens to upper single digits (C). This supports highs in the lower 80s for Metro Detroit and down toward the MI/OH border while readings will be a bit cooler, in the upper 70s across the northern half of the forecast area. More pronounced differential temperature advection eventually sweeps through Lower Michigan overnight. Skies are expected to trend toward clear late tonight as isentropic downglide steepens, augmenting cold advection processes. This yields a cooler start to Thursday with overnight lows dipping to sub-60F readings, the first dose of 50s since the start of the month. A massive synoptic ridge will encompass the entirety of western CONUS, from the Pacific Coast to the Mississippi River Thursday while a surface reflection of high pressure maximizes near 1025 mb over MN/IA. Cooler Canadian air filters in across the region along anticyclonic flow trajectories offering a mainly dry and climatologically cool forecast. One caveat attributed to a weak inverted trough/convergence axis situates along the central waterways Thursday afternoon. This may provide just enough forcing to allow a few sprinkles to develop along the eastern edge of The Thumb. No precipitation mention was made in the NDFD depiction of the outgoing forecast. Elsewhere, dry conditions prevail with a gentle northerly breeze. Diurnal temperatures maximize in the mid 70s with lows well into the 50s Thursday night. Drier pattern persists Friday and throughout much of the weekend as Lower Michigan situates within a split-flow configuration. Higher energy systems relegated to the opposite ends of the continent with a stalled, yet broad upper low over Quebec and an approaching Pacific low near The Cascades. Surface high eventually drifts into the Ohio Valley Saturday lending a return-flow setup which leads to temperatures moderating to near-normal through Sunday. Gradual daily increases in dewpoints present slightly more humid conditions into the start of next week as a cold front descends on southern Lower. The boundary likely stalls/washes out, bisecting the CWA and presenting the first opportunity for precipitation. && .MARINE... Cold front is now well to our east over central Lake Erie, leaving the Great Lakes under light northwest flow. The trailing upper trough axis maintains a low chance for shower or thunderstorm development this afternoon. Will need to monitor late tonight- Thursday morning as flow veers slightly more northerly, offering a brief window for nearshore waves to approach 5 feet. Otherwise, Canadian high pressure builds in for the rest of the week and this weekend affording dry and benign marine conditions. && .PREV DISCUSSION... Issued at 1148 PM EDT Tue Jul 16 2024 AVIATION... The loss in diurnal instability has finally allowed lingering convection to subside. Subtle post frontal low level dry air advection and a light north-northwest gradient will be a major limiting factor for fog and/or low cloud development overnight. An upper level trough will move across Se Mi late Wednesday afternoon. This will be the next chance for scattered convection. For DTW/D21 Convection...An upper level trough will bring a chance for scattered thunderstorms late Wednesday afternoon. At this time, the better chances are expected across the northern portion of the metro airspace. DTW THRESHOLD PROBABILITIES... * Low in thunderstorms Wednesday afternoon. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...KGK MARINE.......MV AVIATION.....SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.