FXUS63 KGRR 241106 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 706 AM EDT Thu Apr 24 2025 .KEY MESSAGES... - Dry Today - Showers and Storms Friday - Dry Weekend With Shower/Storm Chances Tuesday && .DISCUSSION... Issued at 256 AM EDT Thu Apr 24 2025 - Dry Today Upper-level ridging across the area will keep conditions dry. A cold front across Wisconsin will drift south today, stalling this afternoon near I96. South of the front, strong mixing and dry air aloft will lead to RH values falling into the 20s, leading to elevated fire danger. RHs north of the front will be in the 30s to low 40s. One mitigating factor for fire weather concerns will be light winds. Weak gradient flow will keep winds at or below 10 mph today. Dry conditions likely persist much of Thursday Night as well. - Showers and Storms Friday Precipitation chances increase Friday as a mid-level shortwave drives a surface low across the state. A cold frontal boundary associated with this low will drop south across the area, with instability developing ahead of it. MUCAPE values ahead of the front will increase to 1000-2000 J/kg bringing a thunder risk in the afternoon and early evening. The best instability will be roughly south and east of a South Haven to Mount Pleasant line. The threat of severe weather is low, with insufficient deep layer shear (20-30 knots), but given ample instability only a modest increase in shear could support convective organization. - Dry Weekend With Shower/Storm Chances Tuesday Northerly flow behind the front will lead to a cooldown for the weekend, with advancing high pressure keeping conditions dry. Forecast moisture profiles show plenty of dry air so ample sunshine will be present. Southerly flow will increase Monday and Tuesday as a low pressure system advances into the region. Dewpoints climb into the 60s leading to a broad warm sector across lower Michigan. A mid-level wave will drive a cold front across the area Tuesday, though the timing of this front is still uncertain. Ahead of this front, the moist ambient airmass supports forecast MUCAPEs aoa 1500 J/kg. Combined with forecast deep layer shear values in excess of 50 knots, the environment could be favorable for severe thunderstorms. As expected at this range, mesoscale features remain uncertain. However given the favorable synoptic setup for severe weather, close evaluation of forecast trends will be needed in the coming days. && .AVIATION /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 706 AM EDT Thu Apr 24 2025 Showers and thunderstorms this morning are remaining well north of TAF sites. VFR conditions are expected under the high pressure system that will set up over the area today. Winds will be light and variable then become more easterly tonight with winds moving in off of Lake Huron. && .MARINE... Issued at 256 AM EDT Thu Apr 24 2025 No marine concerns are expected through mid-day Friday given weaker gradient flow. Increasing northerly flow Friday into Friday Night will make conditions hazardous to small craft likely. Isolated gusts to gales are possible, though it is unclear at this time whether we can mix deep enough to support that. Periods of thunderstorms are also likely, with locally higher winds and waves in any storms. Winds diminish late Saturday into Sunday as high pressure moves back into the Great Lakes. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Thomas AVIATION...RAH MARINE...Thomas