616 FXUS63 KGRR 111051 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 651 AM EDT Thu Jun 11 2026 .KEY MESSAGES... - Severe weather likely this evening - Turning cooler behind a Sunday cold front && .DISCUSSION... Issued at 414 AM EDT Thu Jun 11 2026 - Severe weather likely this evening A complex scenario today in regard to severe weather as the morphology of the event is not certain off to our west during the day. That said, what pushes into Southwest Lower Michigan this evening could be significant including threats of all hazards, damaging winds, large hail, tornadoes and torrential rain. A sharp shortwave trough is plowing east from the Northern Rockies into the Plains states tonight with convection already developing in Nebraska (more on this in a bit). Strong mid and upper level winds are inferred from both satellite and radar imagery as clouds/echoes are shearing downstream rapidly. The upper wave moves eastward today across the Plains which will pull a surface low northward into Wisconsin by evening. The Nebraska convection this morning is a critical piece to this event as it rolls eastward with the advancing upper trough and strong winds fields. The question is does the convection survive all morning and push across Lake Michigan during the mid afternoon hours. We will follow the HREF for guidance on this. The HREF weakens the initial convection as it moves towards or out over Lake Michigan this afternoon. This will allow the main surge to move in this evening out ahead of the main upper wave. If the first round of convection survives and spreads into Lower Michigan this afternoon that could modulate our event for the evening. We do not think that is going to happen. We expect the second round of storms to surge into the Lake Michigan shoreline around 8pm. The neighborhood probabilities in the HREF are much higher with the second round leading to our confidence in how this event will likely play out. The parameter space is rather high end this evening with MUCAPE values increasing to 3,000 to 4,000 j/kg in the GFS as surface dew points surge back into the lower 70s F. Shear values reach 40-60 knots in the 0-6km layer with the bulk of that shear occurring in the lowest kilometer or two. HRRR hodographs this evening are looped and large in the lowest 2-3 kilometers. HRRR Sig Tornado Parameter values reach 4-9 this evening which is why the SPC has placed a CIG1 conditional intensity for our entire area meaning tornadoes may reach the EF2 level. If storms are able to remain discrete or develop nearby a supercellular tornado threat is possible given the CAPE/Shear balance. 850mb wind speeds will be on the order of 40-50+ knots aiding the low level shear. We expect discrete cells to grow upscale quickly into a linear system with damaging winds likely. The highest tornado threat looks to be across Western Lower Michigan, but given the dynamics in place this evening cannot rule anywhere out of the tornado threat. Strong damaging winds are also possible given the magnitude of the low level jet in place. A CIG1 for wind is also in place across the entire area meaning winds to 75 mph are possible. The entire CWA is in an Enhanced risk by the SPC which does not happen too often. Given the threats today...it is a day where it will pay to be weather wise. Pay attention to possible watches this evening and subsequent warnings. PWAT values will surge into the 2.0 to 2.25 range this evening making torrential rain likely. 1-2 inch per hour rates will certainly be possible. Rainfall in the heaviest swaths this evening could quickly reach the 1-3 inch range. Be aware that short term flooding is very possible this evening especially for urban areas and along small streams. Drainage systems will quickly be overwhelmed by the high rainfall rates. - Turning cooler behind a Sunday cold front Another cold front is expected to move through the Great Lakes Saturday night and Sunday. Another round of showers and storms will accompany the front. We expect to turn cooler behind this front with highs cooling back into the upper 60s to lower 70s. Focus is clearly on the high end weather that is likely this evening. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 650 AM EDT Thu Jun 11 2026 Overall the thinking has not changed in how today is expected to progress. We have some diminishing areas of rain and some localized lower ceilings associated with that. The rain should taper off in the next couple hours...or through 14z. Ceiling should lift as well with mainly VFR conditions prevailing by late morning. VFR weather is then expected to prevail through the afternoon. The main item of note with this 12z set of TAFs is we are expecting severe thunderstorms to move through the TAF sites between 00z and roughly 05z. At this point have prevailing thunder during that time frame but have held off on high end wind gusts given how far out in time it still is. Storms this evening will contain low ceilings and visibilities to IFR and lower, torrential rainfall and the potential for winds gusts over 45 knots. && .MARINE... Issued at 414 AM EDT Thu Jun 11 2026 Have opted to issue a Beach Hazards Statement and Small Craft Advisory from this evening through the morning hours of Friday (through noon). The low level jet increase tonight as well as the storms themselves should stir up the lake quite a bit. We are in agreement with the WaveWatch3 which is indicating solid 3-6 footers up and down the shoreline. While it is still early season and the bulk of the waves will occur overnight it is prudent to warn mariners of the increasing wave field and swimmers especially for Friday morning. Conditions should tone down Friday night into Saturday on the Big Lake. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement from this evening through Friday morning for MIZ037-043-050-056-064-071. MARINE...Small Craft Advisory from 8 PM this evening to noon EDT Friday for LMZ844>849. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion