textproduct: Grand Rapids

KEY MESSAGES

- Scattered showers and storms today

- Strong to severe storms possible Wednesday and Thursday

- Turning cooler for Friday through Monday

DISCUSSION

Issued at 407 AM EDT Tue Jun 9 2026

- Scattered showers and storms today

Scattered convection continues to occur even at this hour (3am) due to a slight increase in the low level jet and weak instability that remains in place. We are not expecting anything widespread through daybreak but showers and a few storms will continue to percolate given the hi-res models showing a 25-35 knot LLJ through daybreak.

The focus will then turn to the afternoon and evening as the low level jet redevelops across the southern half of the forecast area (I-96 southward). The low level jet will be a focus for convection across the southern CWA, while a mid level shortwave trough will bring an increase in storms for the eastern half of the forecast area. So, much of the area will see showers and storms this afternoon and evening, once the morning low clouds lift. Deep layer shear is not strong today so not expecting organized severe weather. SPC has us in general thunder and that matches out thinking.

- Strong to severe storms possible Wednesday and Thursday

Strong to severe storms will be possible both Wednesday and Thursday. The Storm Prediction Center has the area in a Slight Risk on Wednesday and an Enhanced Risk on Thursday.

A warm front will lift through the area on Wednesday which will provide a focus for convection. The LLJ ramps up to 35 to 45 knots at least with some models showing a convectively enhanced jet of over 50 knots. A couple rounds of storms appear possible during the afternoon/evening and into the overnight. We are most likely looking at a linear system moving our direction from WI/IL with wind being the primary threat. Deep layer shear is not all that strong Wednesday afternoon/evening, but upper level diffluence will aid the maintenance of the storms. MUCAPE values will likely reach the 2,000 to 3,000 j/kg range.

Thursday the parameter space is even better which is why the SPC has us in a Enhanced Risk for severe weather. MUCAPE values will increase to 3,000+ j/kg with deep layer shear increasing to better than 40 knots in the evening. Given the CAPE/shear balance and values all hazards are in play. The cold front looks to be the primary forcing mechanism and it moves through the area Thursday night.

PWAT values in the 1.75 to 2.00+ range will make heavy rain and localized flooding a threat with all storms this week. The highest moisture content will be Thursday into Thursday night when torrential downpours are possible.

- Turning cooler for Friday through Monday

We turn cooler behind Thursday nights cold front. Friday and Saturday, temperatures may remain near normal. By Sunday and Monday however we will likely be slightly below normal. Highs on Monday will likely hold in the middle 70s.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 749 AM EDT Tue Jun 9 2026

A batch of mainly just showers are moving through the terminals this morning. These will hang around for at least a couple of hours, then gradually move out to the east. There will be some lower ceilings and visibilities in the IFR category to the north, closer to the wave of low pressure moving by. Southern areas should be mainly MVFR. Conditions will improve slowly this afternoon with visibilities improving quicker. KMKG will hold on to lower conditions longer with fog and stratus coming in off of Lake Michigan.

We are expecting a few showers and storms to pop up this afternoon, mainly for the southern and eastern terminals. Have used a PROB30 to account for this chance. Clouds will partially clear out, before fog and low clouds redevelop overnight. IFR is likely, especially at KMKG.

MARINE

Issued at 407 AM EDT Tue Jun 9 2026

Winds and waves look to remain below advisory levels today, tonight and through Wednesday morning. It is during the afternoon on Wednesday when winds and waves begin to ramp up. By Wednesday evening Small Craft Advisories and Beach Hazard Statements will likely be needed. The increase in winds will be due to a tightening pressure gradient between a Plains trough and a high of the middle Atlantic coast. Waves will reach the 4 foot threshold in the evening and through the overnight from Holland northward.

There is the potential for dense marine fog today given very moist air moving over colder lake waters. Holding off on a Marine Dense Fog Advisory at this point, but we will be monitoring webcams.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Dense Fog Advisory until noon EDT today for LMZ847>849.