textproduct: Grand Rapids

KEY MESSAGES

- Showers with isolated storms this evening into early Sunday

- Watching the upper low position for Monday and Tuesday

- Another period of rain chances mid week

DISCUSSION

Issued at 200 PM EDT Fri Jul 31 2026

- Showers with isolated storms this evening into early Sunday

Upper trough close to closing off near the MN/IA border this afternoon remains poised to bring a period of rain beginning this evening, and continuing potentially into early Sunday.

The better rain axis begins just west of the Chicago/Milwaukee areas early this afternoon. This will take some time and evolve as it moves toward the area. The system overall is a slow mover as it closes off aloft. In addition, we have a fair amount of dry air aloft that will eat away at the leading edge of the precipitation shield.

In addition, the nose of the 850 mb low level jet is driving a lot of this initial rain. The way the upper low is moving SE, the convergence ahead of the low level jet is not impressive over our area tonight as the better convergence moves south of the area. We expect rain amounts to be on the lighter side through most of tonight, but high probabilities moving through the night.

Then on Saturday, we transition from the forcing via the low level jet, to more the deformation zone of the upper low and resulting mid level fgen Saturday morning and early afternoon. This actually looks to be the best potential for rain for most of the area during this entire event.

The potential for thunder is rather low, but non-zero for tonight and Saturday morning. The better chance actually looks to be once the mid level deformation likely moves out, and we see the rain scatter out a bit, and some heating take place. The cold pool aloft combined with the diurnal warming will produce enough instability to pop some showers and isolated storms tomorrow afternoon and early evening. Some of these could be locally heavy with Precipitable Water values quite a bit elevated to around 2.0 inches. We are not expecting event totals to cause any hydrology issues. We could be looking at some local flood advisories with prolonged heavy downpours over any one location.

The upper low remains close enough, with the occluded front lifting northward to SE LOwer then on Sunday. Much of the area should end up dry on Sunday with a dry flow coming in from the NNW to NNE. The SE corner of the forecast area is likely to keep some rain chances in most of Sunday. One thing we have to watch for as is typical with upper lows, is the exact movement of it. The models don't typically nail down the exact track with slight strength differences and short waves helping to complicate progs.

- Watching the upper low position for Monday and Tuesday

The best thought right now for Monday and Tuesday is that we should see drier conditions return to all of the area with seasonable temperatures. We see the large upper ridge over the Western U.S. be pushed toward the area by Monday and linger through Tuesday.

The caveat to this is dependent on the upper low being pushed out also. There is a chance that the upper low could be delayed in moving out. This could happen with the large ridge over the Atlantic holding up the progression of the low, and/or the upper low could remain closed and want to hold over the area a bit longer. We will ride the drier forecast for now, but this will have to be monitored.

- Another period of rain chances mid week

Also dependent on the upper low moving out, will be the next system that will be trying to move toward the area around mid-week next week. We see a stronger long wave trough that initially pushes the ridge toward the area. Then a piece of that trough continues east, and tries to flatten the ridge a bit. If it does not get blocked from coming in, it looks to affect the area late Tuesday into early Thursday. This pattern should keep the area from being affected strongly by any big heat ridge for now.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 132 PM EDT Fri Jul 31 2026

VFR conditions will continue into Saturday morning when rain and lowering ceilings move in with MVFR conditions expected to prevail after 12Z. Light and variable winds through the evening then going easterly on Saturday with gusts over 15 knots at times.

MARINE

Issued at 200 PM EDT Fri Jul 31 2026

We are looking at marine headlines (Beach Hazards and Small Craft Advisories) likely being needed for the Sunday time frame.

We are starting off the weekend with favorable conditions today, as the water temperature has warmed back up after an upwelling event earlier this week along with warm and dry conditions. This will deteriorate as rain moves in this evening, and flow becomes offshore with the approach of the system. This will push the warmer water back offshore.

The offshore winds will then increase by Sunday and turn from the North. This will build the waves into the hazardous category. This event looks to last into Monday morning before winds, and eventually waves come down significantly.

GRR WATCHES/WARNINGS/ADVISORIES

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