Area Forecast Discussion

KEY MESSAGES

- Heavy Rain Potential Continues Tonight into Sunday morning

- Largely Dry for the Upcoming Work Week

- Near to Slightly Below Normal Temperatures Next 7 Day

DISCUSSION

Issued at 328 PM EDT Sat Sep 19 2026

- Heavy Rain Potential Continues Tonight into Sunday morning

We will be maintaining the Flood Watch as is with this forecast update. As expected, the heaviest rain that has already fallen has occurred across the 5 counties that are in the watch. Ground truth reports show that the heaviest rain has been across Allegan County with a number of reports in the 2-3 inch range. Additional rain is expected tonight, so the Watch continues. Given the saturated ground additional rainfall will go directly into runoff.

The setup largely remains the same with a diffuse surface boundary to our south and waves of low pressure working eastward towards the Great Lakes. PWAT values are up around 2.00 inches which are high even for mid summer. High resolution models show the low level jet aimed at our far southern CWA towards I-94. This should be the focus area for heavy rain tonight based on the moisture transport vectors centered in that area as well. So, the Flood Watch area stands the best chance to see flooding/heavy rain.

the first wave of precipitation will work in form the west after 500pm with more substantial rain after dark and especially overnight. The rain moves southward on Sunday as high pressure begins to slide in from the north.

- Largely Dry for the Upcoming Work Week

We will largely be dry this upcoming week as high pressure will be situated across the Great Lakes region. Aloft however there is an upper low meandering through the region, so it not inconceivable that we see some scattered showers that will be diurnally driven in the afternoon and evening. Deep moisture is not present though given the surface high.

- Near to Slightly Below Normal Temperatures Next 7 Day

It will feel like fall this week with most days seeing high temperatures in the 60s. Normal highs for today in Grand Rapids today are in the lower 70s which cool to the upper 60s by next weekend.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 136 PM EDT Sat Sep 19 2026

Low clouds and occasional drizzle to continue for the next 4-6 hours before more widespread precipitation begins to move in. IFR and LIFR conditions will be common through the taf period. Some thunder possible...especially KAZO/KBTL/KLAN/KJXN with KGRR and KMKG less likely to see sustained thunderstorms. Some improvement in conditions possible very late in the TAF period...but not confident enough now to introduce it except for KMKG.

MARINE

Issued at 328 PM EDT Sat Sep 19 2026

The general surface pattern of high pressure located to our north over Canada/northern Great Lakes and weak low pressure off to our south will remain in place the rest of the weekend and into early next week. This will bring about easterly/off shore winds. For the most part, waves are generally expected to be 2 feet or less. There is an indication however that waves may push into the 3 to 5 foot range Sunday into Monday, especially from Whitehall north up the shoreline. At this point, holding off on any headlines.

GRR WATCHES / WARNINGS / ADVISORIES

MI...Flood Watch through Sunday morning for MIZ064-065-071>073. MARINE...None.