textproduct: Grand Rapids

KEY MESSAGES

- Rain chances remain through Wednesday night for southern areas

- Drier weather Thursday and Friday

- Stronger system with heavy rain potential Saturday

DISCUSSION

Issued at 240 PM EDT Tue Sep 15 2026

- Rain chances remain through Wednesday night for southern areas

Most areas saw at least one round of at least showers with scattered storms at some point today. The main area of rain earlier was the remnants of a 60 knot low level jet that moved over the area very early this morning. Another secondary weaker low level jet of 35 knots is supporting the showers exiting the SE corner of the area. The remainder of the rain is dissipating as we see the wave and low level jet forcing moving out, and weak short wave ridging building in.

Most areas will see little to no additional rain tonight. The exception to this will be areas across the far southern portion of the area overnight. The sfc front is sinking south, and another low level jet will intersect it. This will even be a bit weaker, but just enough forcing given the deep moisture in place. MU CAPEs are forecast to increase to a few hundred J/kg with the arrival of the low level jet. This instability will be elevated, so the potential of severe weather is quite limited.

Another low level jet will clip the far southern portion of the area again Wednesday night, bring additional shower/storm chances. There was a fair amount of disagreement with rain placement Wednesday night. A better consensus has developed, with the nose of the low level jet likely along I-94, and bringing rain mostly south of I-96. Once again, instability will be elevated being further removed from the sfc front to our south. Some localized heavy rain will be the main threat.

- Cooler and drier weather Thursday and Friday

Once the low level jet Wednesday night passes, the front will be driven further south away from the area. In addition, we will be seeing a stronger system start to become organized well west of the area. This will temporarily stop the weak impulses coming through, and just allowing some ridging to reside for a couple of days. The lack of rain and breaks in the clouds will allow for some sun to warm max temps up a couple of degrees compared to the cooler weather under the clouds and rain. Temperatures will be quite seasonable with highs well into the 70s, and lows in the 50s.

- Stronger system with heavy rain potential Saturday

The better organized system will start affecting the area late Friday with a strengthening flow ahead of it from the SW. The atmosphere should saturate sufficiently late Friday night to allow rain to begin to reach the ground.

The best chance of rain will come centered on Saturday as the low level jet axis noses over the area in a weakening state. The warm sector of this system stays south of the area as the low moves through the heart of the area. The vast majority of the instability will stay south of the state border. There may be a chance of some thunder across the far southern counties.

The most likely highest impact with this system will be heavy rain potential. The vast amount of moisture that will be associated with this system and the strength and slow speed, will all for some heavy rain amounts to be possible. WPC has our area placed under a Slight risk for Saturday, which we agree with strongly at this time.

Things become quite uncertain for Sunday and beyond. We will see the pattern reload with an upper low to our west, bringing a deep SW flow over the area. This will eject short wave troughs at times, and interact with higher moisture. The question is where does the main axis set up. It is too far to pin down those details at this time, so we will continue to monitor the trends.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 759 PM EDT Tue Sep 15 2026

It's presently MVFR cigs in central Michigan at RQB and MOP, but conditions will improve there tonight and deteriorate in southern Michigan. Developing rain showers in southern Michigan may become scattered thunderstorms soon and persist for much of the night, given the instability present within the cloud layer at 5,000 feet. AZO, BTL, and JXN will be most affected by the chance of thunderstorms. Showers may occasionally be present near GRR and LAN also. Later tonight into Wed morning, MVFR to IFR cigs are likely to develop over AZO, BTL, and JXN, and probably LAN also. GRR may be very close to the edge of the MVFR cloud bank too.

MARINE

Issued at 240 PM EDT Tue Sep 15 2026

The Gales from earlier have diminished, and are quickly diminishing more this afternoon with the passage of the front. The gradient behind it is not significant, so winds will continue to drop. Waves will take a bit longer to drop below 4 ft, but should at all areas by later this evening.

The next couple of days look much quieter with a much weaker gradient expected with ridging nearby. The next period of potential headlines will be starting on Friday and lingering into Saturday with a strong system expected to approach and move through the area.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement until 11 PM EDT this evening for MIZ037- 043-050-056. MARINE...Small Craft Advisory until 11 PM EDT this evening for LMZ846>849.