FXUS63 KGRR 191259 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 859 AM EDT Thu Jun 19 2025 .KEY MESSAGES... - Showers moving out today with the upper trough - Convective chance small but not zero tonight/Friday night - Building weekend heat && .DISCUSSION... Issued at 340 AM EDT Thu Jun 19 2025 - Showers moving out today with the upper trough Radar shows the back edge of the rain shield associated with the surface low moving across Lake MI attm. The GFS and ECMWF are consistent in moving the low into Ontario and Quebec later today. The showers will end once the upper trough axis (currently over the MS Valley) moves through this afternoon. Latest IR loop shows clearing skies over western Wisconsin and we should share in that by this afternoon. Thus, showers this morning followed by skies becoming mostly sunny this afternoon. Today will be the last day with highs in the 70s for a while. - Convective chance small but not zero tonight/Friday night A building ridge will develop over the Plains later today and that will drift east to the MS Valley tomorrow. Short waves riding the ridge are expected to combine with an increasing LLJ during the late evening and fire convection over the upper MS Valley tonight and Friday night. The NAMNest moves this convection southeast along the thickness contours and over Wisconsin late tonight and into the northern cwa Friday morning. The HRRR does something similar but fires convection a bit quicker and moves it over the northern cwa by midnight while simultaneously firing an MCS over MN and moving it south across northern IL by Friday morning. That seems a bit too far south given the CAPE gradient and convective firing location farther north over MN. For now, we'll retain the 30-40 PoPs across the northern cwa. A stronger wave develops in the strong warm advection regime over MN Friday night and uses the nocturnal LLJ as fuel to push it east. I think the GFS is too far north and like the HREF solution better that moves in a bit farther south near the CAPE gradient. The NAMNest develops a bowing MCS and moves it ESE across northern Wisconsin to northwest Lower by Saturday morning and clips the northern cwa. This evolution will need to be watched. For now we are going with 40-50 PoPs over the northern cwa late Friday night. - Building weekend heat The building upper ridge will drift toward Michigan this weekend. H8 temps are progd to rise from 12c to near 24c by Saturday and Sunday. This will send temperatures well into the 90s. When combined with dewpoints in the lower 70s, apparent temperatures climb into the lower 100s: a heat advisory appears inevitable Friday through Sunday, but it looks we may just miss extreme heat warning criteria, but it will be close. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 728 AM EDT Thu Jun 19 2025 Light showers continue to decrease in coverage and are all but over at MKG. Widespread IFR ceilings will gradually lift throughout the day as drier air works in from the west and all terminals should be VFR by this afternoon. && .MARINE... Issued at 859 AM EDT Thu Jun 19 2025 Agree with the overnight shift's assessment that conditions on the lake will be dangerous for a time. Have gone ahead and issued a Beach Hazards Statement as well after IWX reached out and coordinated this morning. So, we now have a Small Craft Advisory and Beach Hazard Statement in effect from Grand Haven to the south. The time was extended through 200pm based on HRRR winds and HRRR driven wave modeling. The South Haven pier observation site has been gusting to 30 knots and the Cook Nuclear buoy just south of our marine area has peaked at 5 feet this morning. South Haven webcam is quite rough on the north side of the north pier. Period of stronger winds and larger waves are associated with an area of low pressure pulling away from the region to the east. Winds and waves should settle down this afternoon. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Beach Hazards Statement until 2 PM EDT this afternoon for MIZ056- 064-071. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for LMZ844>846. && $$ DISCUSSION...04 AVIATION...04 MARINE...Duke