Rapid City, MI 49676 Weather

Key messages

- Some lake induced clouds/showers tonight/Friday.

- Sunday rain chances? Small but not zero:

- Better rain threat beyond Monday.

Discussion

Issued at 256 PM EDT Thu Oct 29 2026

Pattern Synopsis/Forecast: Well-defined split flow pattern across western Canada is leaving the CONUS under the influence of the quasi- zonal southern branch of that split. Persistent upper low along the Pacific Northwest coast south of a strong short wave ridge (nearly +3 sigma 500mb height anomaly) across Alaska/Yukon Territory (a combined strongly negative PNA/EPO teleconnection). Remnants of an old upper low northeast of Hawaii are approaching southern California and the Baja Peninsula. Closer to home a pair of short wave troughs are tracking across northern Ontario/northwest Quebec: and a pair of weak PV anomalies over the Dakotas. Drier air is advecting into the upper Lakes from the Midwest..displacing a narrow axis of around an inch and a quarter of precipitable water. This is accompanied by low/mid level cold air advection: with sub- zero 850mb temperatures spreading into western Lake Superior. Surface cold front crossing the Great Lakes today: secondary cold front much farther north across northern Ontario and extending west into the Prairie Provinces.

Split flow will consolidated right across the upper Lakes to end the week; northern branch short wave trough will cross the Lake Superior basin Friday while southern branch flow remains dominant. More amplified troughing along the west coast will try and push heights up across the region for the weekend. Remnant short wave trough heading into Mexico today will eventually drift across the central/southern Plains Saturday and into the southeastern U.S. Sunday. West coast troughing will eventually make its way into the nation's midsection for the first part of next week: but that means short wave ridging/higher heights across the Great Lakes. Short wave trough may eventually try and make a run toward the region for mid to late week.

High pressure over the northern Plains builds into Michigan/ Wisconsin by Friday morning. Secondary cold front over northern Ontario will slip south tonight: pushed along by above mentioned northern branch short wave trough. Looks like it will push through Upper Michigan overnight before dissipating Friday. Surface high will propagate through the Great Lakes Saturday and into New England and the mid Atlantic Sunday. This sets up southerly return flow into the Midwest and Great Lakes to start next week. Inland propagating western trough looks to eventually spin up a lee cyclone over the central High Plains Monday: and because of the slow movement of the trough there may be several iterations of cyclogenesis/frontal waves through midweek along the north-south oriented baroclinic zone.

Primary Forecast Concerns:

Some lake induced clouds/showers tonight/Friday: Thick Sc deck lies across Lake Superior and much of Upper Michigan at mid afternoon: replete with gravity wave ripples. Persistent west-northwest fetch tonight will be longest into eastern Upper and extending into northern Lake Huron: longer fetch leading to a deeper CBL (inversion height around 800mb off Lake Superior). Much shallower CBL the farther south you go down Lake Michigan with a much shorter fetch/loss of effective fetch. Most showers should be confined to eastern Upper.

Sunday rain chances? Small but not zero:: For the weekend will need to watch short wave remnants moving into the Plains. Deep moisture getting pulled north ahead of this "system": some of this looks to get into Michigan Saturday night/Sunday though consensus PoPs are minimal through Sunday. Saturday at least looks dry: we'll see how things trend for Sunday.

Better rain threat beyond Monday: Rain chances should increase heading into Tuesday as more substantial system associated with slow moving western trough expected to bring stronger thermal/moisture advection into the Great Lakes. Rain chances will continue through the midweek period.

Aviation

Issued at 632 PM EDT Thu Oct 29 2026

Still looking at some MVFR producing lake clouds impacting KCIU and KPLN tonight, with just some more scattered and higher based clouds at the other locations. Clouds scatter out heading through Friday. Northwest winds will continue, at times gusty.

Watches, warnings and advisories

MI: None. MARINE: Small Craft Advisory until noon EDT Friday for LHZ346>348. Small Craft Advisory until 5 PM EDT Friday for LSZ321-322.