textproduct: Grand Rapids

KEY MESSAGES

- Small chances for showers and storms today

- Additional shower and storm chances Wednesday through Friday

- Above normal temperatures through the 7 day forecast

DISCUSSION

Issued at 354 AM EDT Tue Sep 1 2026

- Small chances for showers and storms today

Light southwest flow is in place this morning along with dew points around 70F. Upstream a cold front is situated from the U.P. southwest across Wisconsin and into Iowa. We remain in the warm sector today with building instability. MUCAPE values even at this early hour range from 2,000 j/kg in Southwest Lower Michigan to around 4,000 j/kg in Iowa. The front remains upstream today and only slowly sags into the area tonight while losing definition. Aloft, it is difficult to pick out much of any shortwave activity upstream early this morning and model data moving through the day shows little energy aloft either. The bottom line is a threat for some isolated showers and storms is certainly there today/tonight, but there is little to truly pinpoint timing or areas. Confidence in morphology of storms today is low as is the threat for storms at all. Would not be surprised to see some isolated activity during the heat of the day today, but have kept the forecast dry. We do have some small pops around 20 percent this evening based on a consensus of short term models and blends. SPC has the area in a marginal risk today, which is related to an increase in wind fields at 850mb and 500mb after 00z. Again, we will need a kicker/lifting mechanism and at this point that component is nebulous.

Have held off on any heat headline today as index values are marginal only in the far south. We could see heat index values approach 100 from AZO over to JXN this afternoon, but most areas should hold in the 90s for maximum apparent temperatures today.

- Additional shower and storm chances Wednesday through Friday

The surface front will remain in the area on Wednesday which may provide a focus for showers and thunderstorms. Multiple shortwave's are forecast to be moving through the generally zonal flow aloft on Wednesday as well. Strong instability will remain in place on Wednesday making for better chances for showers and storms. SPC has some of our far eastern areas towards the U.S. 27/127 corridor in a Slight risk for severe weather. Cannot rule this out given strong winds aloft remaining in place.

Additional shower and thunderstorm activity is expected on Thursday and Friday as well before high pressure builds in for the weekend. That said, quite a few ensemble members of both the GFS and the ECMWF indicate precipitation potential into the weekend as well. Suffice it to say, forecast confidence in precipitation in the coming days is not high owing to transient weaker shortwaves aloft and a weak surface pattern most days.

- Above normal temperatures through the 7 day forecast

We are expecting above normal temperatures through much of the period with the warmest days being today and Wednesday. A slow cooling trend is noted into early next week. It will take until next Monday before we see temperatures approaching normals for this time of year.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 135 PM EDT Tue Sep 1 2026

Radar shows a band of showers/storms moving ESE across southern Lake MI and far southwest Lower MI. This precipitation is close enough to AZO and BTL to include in the TAFs.

There is some concern for strong storms developing mid lake near MKG around midnight and moving ESE across LAN/JXN during the overnight hours. A few models show this, but not all. We included a prob30 for this potential except at AZO/BTL which should be far enough south to preclude mention.

Given high dewpoints and residual moisture from recent rains, some fog/haze is possible Wednesday morning.

MARINE

Issued at 354 AM EDT Tue Sep 1 2026

As forecast, waves subsided below advisory levels yesterday evening. Sub advisory conditions are now expected the next couple of days at least. The pressure gradient will be fairly slack it appears as a weak boundary sags into the area today and remains near through the end of the work week. Without a low of some depth and/or a building high winds will remain on the lighter side. Waves look to be 2 feet or less the next few days. The caveat however as always is thunderstorms. We are expecting at least some periodic thunderstorm activity through Friday which will bring a local uptick in wave action as the storms and associated localized wind move through.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...None.