textproduct: Grand Rapids

KEY MESSAGES

- Cooler, drier, and less humid through Friday

- Next threat of rain on Saturday

- Heat and humidity returns next week with storm chances

DISCUSSION

Issued at 334 AM EDT Thu Jul 17 2025

- Cooler, drier, and less humid through Friday

Cold front is well evident on the radar and in the sfc observation network this morning. As of 07z, the front stretched from near Alma to Battle Creek with winds from the SW ahead of it and dew points in the 70s, to gusty winds from the WNW behind it with dew points falling quickly into the 60s.

A few remaining showers are in place over Central Lower Michigan on the backside of the sfc low that is supported by the MCV that moved through the region. There are a few sprinkles/very light showers along the front. All of the showers will come to an end as one more short wave moves through early this morning, and the sfc low and cold front push east of the area.

We will see quite a bit of cloud cover stick around through most of the day. Late this afternoon and evening is when we see clouds scatter out, and eventually become mostly clear overnight and last through Friday. Highs today with the clouds and cold air advection will only reach the 70s, and again on Friday with much more sunshine.

- Next threat of rain on Saturday

Our next chance for rain after the lingering showers this morning will come centered around the Saturday time frame.

There is an upper trough over the desert SW that will eject some short wave energy into the main jet and then approach the area. This wave is expected to stay just south of the forecast area. At the same time, the shear zone of the upper jet will be just to our north. This wave will support a cold front that will be pushed southeast through the area. Initially it looks like we will see the two areas of rain split north and south of the area. As the front drops down, that will help to bring rain to areas in between the two waves.

As far as thunder potential is concerned, the models are showing instability building to as low as -5C Lifted Indices with a sfc based parcel, and similar values for 925 mb and 850 mb based parcels. The best instability will be as you head further south, especially south of I-96. CAPEs are forecast to be over 2000 J/kg and effective shear values are forecast to increase to 35 to 40 knots. Those parameters are definitely something to monitor.

- Heat and humidity returns next week with storm chances

We will see any rain chances clear out by Sunday and likely stay away through Monday. In the wake of the sfc low, upper waves, and cold front, we will see a fairly expansive Canadian Sfc ridge build over the area. Plenty of subsidence to squash anything that tries to build.

Once the high moves out by late Monday, we will be looking at heat trying to build back over the area from the SW. As the heat dome builds this way, we will likely see the axis of more active short waves and resultant MCS' pass through the area Tuesday into Wednesday. This type of pattern is very difficult to try to nail down any details, especially this far out. We will see the potential for one or more rounds of storms potentially moving through as early as Monday night and then being possible right through Wednesday. It will be dry most of the time with building heat and humidity right on the verge of moving over the area.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 147 AM EDT Thu Jul 17 2025

All thunderstorm activity from last evening has pushed well east of the terminals, and is done for this event. We have a cold front pushing through the terminals at this early hour, which has a few sprinkles and is shifting the winds from SSW to WNW, and increasing the gusts. Behind this front, lower clouds are moving in. These lower clouds will drop into the IFR category about an hour or two after the front passage.

The IFR will persist in the morning before the clouds start to lift with diurnal heating and drier air moving in. We will see conditions steadily improve during the day and into the evening. VFR conditions will eventually return later in the day, and then clouds will scatter out toward sunset.

Winds will become gusty this morning from the WNW up to around 30 knots. Winds will then diminish steadily late in the afternoon to early evening.

MARINE

Issued at 334 AM EDT Thu Jul 17 2025

Our well advertised wind/wave event is well underway already this morning. In fact, some of the initial gusts immediately behind the frontal passage were touching Gales briefly. Those isolated Gale gusts have disappeared, and we are seeing solid SCA and Beach Hazards conditions at all of the coastal observations. The winds and waves will continue through a good chunk of the day, before diminishing this afternoon and evening.

Once this current event ends late today, we are looking at a fairly quiet period for a few days with winds below 20 knots. We continue to mention that the strong north flow going offshore will facilitate a decent upwelling event where water temps could drop 20F fairly quickly.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through late tonight for MIZ037-043-050- 056-064-071. MARINE...Small Craft Advisory until 2 AM EDT Friday for LMZ844>849.