505 FXUS63 KGRR 091849 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 249 PM EDT Tue Jun 9 2026 .KEY MESSAGES... - Rounds of strong to severe storms possible through Thursday night - Very warm and humid through Thursday night - Showers/storms Saturday night with cooler air to follow && .DISCUSSION... Issued at 249 PM EDT Tue Jun 9 2026 - Rounds of strong to severe storms possible through Thursday night The batch of showers that moved through earlier and caused some isolated damage have moved well east of the area this afternoon. In their wake, a few spotty showers so far have popped up away from Lake Michigan where 1000 J/kg of MU CAPE has developed with diurnal heating taking place. The SW winds are keeping areas downwind of Lake Michigan quite a bit more stable, especially with fog and stratus over the lake. As mentioned in the previous discussion, the deep layer shear this afternoon is quite light, under 20 knots, so there should not be anything organized. We should see a lull in the activity after any pop ups this afternoon/early evening, until potentially late Wednesday afternoon/evening. We have no good synoptic feature (i.e. MCV, low level jet) to bring anything organized over the area tonight. We will warm up significantly Wednesday afternoon, leading to MU CAPEs of 2-4k J/kg over the area, highest to the southwest. We could see something pop up along a lake boundary Wednesday afternoon, but the main focus is on a MCV and low level jet coming in mid-evening Wednesday evening. The strong instability will be enough to help the MCV light up with convection. It will initially be strong to severe to our west with plenty of mid-level dry air leading to DCAPEs of around 1500 J/kg. This is more than sufficient to cause strong outflows out of the storms. Some of the stronger winds could reach parts of the area before it weakens with a lack of shear after it loses its fuel. That might not be the end of the excitement for Wednesday night, as we have a chance of another cluster of storms forming and affecting the area. This comes as a larger scale low level jet ramps up ahead of the larger wave NW of the area. As is always the case with convection, subsequent rounds of convection timing and location are dictated by outflows and such. We will say that multiple sets of data are in fairly good general agreement with potentially two rounds of convection, leading to slightly higher confidence. We will likely see another lull in the activity from late Wednesday night through most of Thursday. We will likely see some better short wave ridging affecting the area behind the Wed night wave, and another stronger wave Thu evening/night. The wave coming through Thu evening will have another stronger low level jet to fire convection, as the main cold front follows closely. We should still have plenty instability leftover from the daylight hours Thu with MU CAPEs over 3000. The low level jet will just feed additional instability over the area as we start to lose diurnal instability. The concerning part of this will be the strong shear that will accompany this round. Deep layer shear should be over 40 knots, and low level shear with the low level jet will be quite strong in the 30s. SRHs could be above 300 m2/s2 with enough low level shear, and the nicely curved hodographs verify this. That is quite a ways off yet with multiple rounds of convection possible. However the dynamics have the potential for a very active Thursday evening/night. - Very warm and humid through Thursday night We will be holding off on any heat headlines for Wednesday and Thursday this afternoon, but they still remain possible for southern areas especially. We are looking at highs in the mid 80s to around 90F. Given dew points expected to be in the lower 70s, we would see heat indices of mid to upper 90s down south, and slightly lower up north. Right now, there is just not enough confidence to pull the trigger, so will let later shifts re-evaluate. - Showers/storms Saturday night with cooler air to follow We will see things quiet down significantly on Friday in the wake of the front with much cooler temps (maxing out around 80F) and dew points falling into the 50s. We will see some lingering moisture in the morning with the upper wave overhead. That should move out in the afternoon. We will see the new upper low complex over Western Ontario sit there and rotate for a bit. The next feature of note from it to affect the area will be a short wave that has been consistent to drop down Saturday night. This will be enough to bring another cold front to cool things down even more with a flow from the NNW. It will be behind this front that we will see temps max out in the 70s early next week. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 145 PM EDT Tue Jun 9 2026 A warm/muggy/soupy airmass will remain entrenched over West Michigan through the TAF period. This will set the stage for isolated showers/storms through roughly 21Z this afternoon... particular at AZO/BTL/JXN, where subtle low level convergence appears maximized. After a brief period of VFR weather at most TAF sites later this afternoon into early evening, expect low clouds and fog /borderline MVFR-IFR conditions/ to redevelop after 04-05Z at all TAF sites. Visibilities/ceilings may crash lower than current TAFs depict, and this will need to be monitored. Aside from MKG near the Lake Michigan shoreline where fog and low clouds may persist, expect VFR conditions to return 13-14Z Wednesday - albeit with some light haze. Winds through the TAF period will remain generally light from the west/southwest... 10 kt or less. && .MARINE... Issued at 249 PM EDT Tue Jun 9 2026 && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Dense Fog Advisory until 11 AM EDT Wednesday for LMZ844>849. && $$ DISCUSSION...NJJ AVIATION...Smith MARINE...NJJ

NWS GRR Office Area Forecast Discussion