The NWS has been hinting at chances of frost coming towards the end of the week with nighttime temps in the upper 30s to low 40s. This would be outside the cities and more or less in the lower-lying areas. Grand Rapids is predicted to be around 43° while Otsego is predicted to be 39° Thursday night and 38° Friday night. Further north Big Rapids is showing 37 and 35 for the same nights. In my humble opinion the greatest chances of frost will be better north of US 10 for frost.
Keep in mind the NWS where I get some of my forecast data has been a bit off temp wise for the past week. Yesterday it was predicted to be near 75 however due to the smoke from the wild fires out west creating a haze temps were lower. Smokey skies may still be around today and tomorrow which may once again lower the predicted highs of the 70s today. We do have a southerly return flow of air moving in today which should help push temps warmer than yesterday. We have a slight chance of rain Wednesday evening which may bring a few sprinkles. Our next best chance of wide spread rain may not come until the 25th.
--Warmer with smoky skies today and Wednesday-- Southerly/return flow on back side of departing sfc high sends warmer temps into the region today and Wednesday before cold front arrives from the north late Wednesday. H8 temps push 18C although mixing won`t be that deep (more like 900 mb) so we`re looking at highs mainly in the 70s. Plus the persistent thick smoke aloft may help shave a few degrees off the highs. As far as the smoke aloft is concerned, experimental RAP/HRRR smoke guidance keeps it around through Wednesday, but the tail end of the 48 hour guidance suggests it may finally be pushed south and out of the area on Thursday. This happens as the upper trough digs farther south into the region and trajectories turn a bit more northerly. Interesting too in the experimental guidance is that the smoke layer appears to lower as the cold front drops south late Wednesday, even suggesting some potential for some low concentrations of near surface smoke for a time on Wednesday evening. --Chilly Thursday through Sunday, patchy frost-- Cold frontal passage looks a bit quicker in latest guidance and slips south through the region late Wednesday afternoon and Wednesday evening. Precip potential still looks low although can`t rule out a few light rain showers with the band of low clouds accompanying the front. Surface ridging is also quicker to build in behind the front, now implying a frost potential developing as early as Thursday night north of I-96. The surface ridge and associated cold/dry air mass hangs around through early Sunday, so the nighttime frost threat will exist on Friday and Saturday nights too. Best threat for widespread frost is north of I-96 on Friday night. --Dry pattern prevailing-- With dry air mass and surface ridging generally prevailing, the next 7 days will remain mostly dry other than the potential trace amounts with the Wednesday evening cold frontal passage. According to ECMWF ensemble data, our next decent chance of measurable rain is not until a week from Thursday.