FXUS63 KGRR 020749 CCA AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 347 AM EDT Wed Apr 2 2025 .KEY MESSAGES... - Wintry Mix Into The Morning - Conditional Severe Weather Threat Today - Rain Showers This Weekend && .DISCUSSION... Issued at 338 AM EDT Wed Apr 2 2025 - Wintry Mix Into The Morning After the initial band of warm air advection precipitation across the area, precipitation has been slow to fill in across West Michigan and upstream over Illinois. Dry easterly flow has helped limit precipitation so far. However, as the surface low moves into the Upper Great Lakes precipitation coverage should increase in the coming hours. While light snow and freezing rain is still expected through late morning across the current Winter Weather Advisory area, the maximum icing is now favored to be on the order of around 0.1-0.2" given lessened QPF. Will leave the current advisory in place given the continued risk for light freezing rain/snow. - Conditional Severe Weather Threat Today The forecast as far as severe weather potential today remains complicated by questions on the extent of atmospheric recovery. The first portion of the convective event is this morning as elevated instability makes its way into the forecast area. The primary concern with this portion of the event given training of heavier embedded cells. This may be enough for minor poor drainage and river flooding, especially if heavier cells repeatedly train over the same area. See the hydrology section for more details. Given ambient deep layer shear exceeding 50 knots, small hail is possible in any storms. The setup is favorable for gravity wave associated convection (GWAC) so a brief gust from an elevated storm is not off the table, however predicting these sort of events is challenging with any certainty before the event so confidence in gusts occuring is low. Attention then turns to the afternoon where a conditional risk of severe weather exists, depending on where atmospheric recovery can occur. What this will hinge on is whether morning convection can suppress the northward motion of the warm front this afternoon and evening. The ambient environment is very dynamic given 50 plus knots of deep layer shear and over 400 m2/s2 of 0-3km SRH. However, this can only be fully realized by the storm if sufficient instability exists for the storm to become surface based. What we know is a line of convection is expected to cross the CWA in the late afternoon and evening hours. The impacts of this line depends on the northward extent of the warm front and surface based instability. For areas that do not destabilize enough for surface based storms, convection will remain elevated with a lower severe weather threat, For areas that do see clouds and precipitation clear out later today and destabilize, the full effects of the very strong ambient winds will be felt by the storms with damaging winds, possibly excess of 70 mph, tornadoes, and large hail possible. The primary forecast challenge is where will destabilization occur? A perusal of 00z guidance still suggests where is not certain, and is dependent on outflow from morning convection and cloud cover. Consensus is near and south of I94 has the best chance to see surface based storms and the associated severe weather. However, some solutions such as the NAM suite do bring surface based storms and the best severe threat into the I96 corridor. It's important to note that while the ceiling of the event is elevated given the strong winds aloft, the questions of destabilization means who sees severe weather is uncertain and some or all of the area may not see severe storms today. Close monitoring of cloud cover trends, precipitation trends, and atmospheric recovery will be needed through the day to fine tune the exact threat area. - Rain Showers This Weekend Thursday and Friday remain dry across the area as ridging dominates the forecast. We then see a low pressure system cross the Ohio Valley Friday Night into Sunday with the rain shield reaching into lower Michigan. Widespread rainfall is likely, with areas near and south of I96 having a 30-50 percent chance of exceeding 1 inch of rainfall. It will be mild with highs in the 50s through Saturday falling into the 40s by Sunday. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 200 AM EDT Wed Apr 2 2025 A band on snow is currently moving through northern portions of the area impacting MOP, RBQ, LDM and north with accumulations around 1 to 2 inches over the next few hours. Rain and snow showers will then expand over the area early this morning with a window of freezing rain possible early this morning for MKG, GRR, and LAN. Freezing rain accumulations are more likely north of these sites. Any frozen precipitation transitions to rain this morning with some embedded thunderstorms. Ceilings will gradually drop to LIFR values with brief periods of LIFR possible. There is some uncertainty in the timing of thunderstorms throughout the day, but a lull is possible Wednesday afternoon before thunderstorms return in the evening. Low level wind shear will be present throughout the day initially from the southeast and then becoming southwesterly Wednesday evening as the warm front moves north of the area. Surface winds currently from the east gusting to around 25 knots will increase with gusts around 30-35 knots this morning before shifting to the southwest Wednesday evening. GRR Airport DSS Update: There is a slight time adjustment for the window of freezing rain that was provided earlier. The best window for any freezing rain will be between 5-8AM before warmer temperatures cause a transition to rain. Otherwise no other changes to the previous forecast. East to southeast winds gusting around 25 knots continue with gusts increasing to around 30 knots Wednesday morning. && .MARINE... Issued at 338 AM EDT Wed Apr 2 2025 The Gale Warning remains in effect through Wednesday Evening, with winds forecast to increase to gale force in the coming hours. However, waves with the gale force winds will be lower given the winds will be primarily offshore, with waves over 5 feet mainly several miles offshore and beyond. A Small Craft Advisory will be needed Wednesday Night into Thursday Morning after the Gale Warning, with gusts exceeding 25 knots expected and waves building in the nearshore as winds flip to westerly. High pressure then cases winds and waves to subside into Thursday afternoon. The other concern is for potential severe thunderstorms over the lake this afternoon and evening. A line of storms will develop behind the current showers and storms. Gusts in excess of 40 knots, hail, and waterspouts are possible with this line though it is not certain if this will occur. && .HYDROLOGY... Issued at 352 PM EDT Tue Apr 1 2025 Several rounds of showers and storms are expected to sweep across Lower Michigan between Wednesday morning and late Wednesday evening. We're expecting most locations to receive between 1 and 1.5 inches of rain during this time, though depending on how the clusters of thunderstorms evolve some locations could easily 2.5 inches or more. If thunderstorms move over the same areas repeatedly, we may overwhelm local drainages and result in some general flooding concerns as we go through the day Wednesday. As the rain that falls tomorrow starts making its way into our rivers, we'll be monitoring for possibility of overflowing some of the rivers. Currently, the Muskegon river is the only large river system in our area that is running higher than normal - mostly due to recent heavy rains and snowmelt in northern Lower Michigan. If rain totals tomorrow in this area start to surpass the expected 1 inch totals, we may be looking at pushing some of the lower river areas (Newaygo and Bridgeton) into the minor/nuisance flooding category. Meanwhile, most of the rivers in the Grand and Kalamazoo River watersheds are near or slightly below average for this time of year, so we've got a decent amount of space in these rivers to fill up. However, if rain totals across a large area start to pass the 2 inch mark, we may eventually start to see some minor flooding at a few spots around Lansing and downstream in Comstock Park. However, if rain totals stay in the 1 to 1.5 inch range in this area, we'll bring water levels up to bankfull but that will probably be about it. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until noon EDT today for MIZ037>040- 043>046-051-052. MARINE...Gale Warning until 11 PM EDT this evening for LMZ844>849. && $$ DISCUSSION...Thomas AVIATION...RAH MARINE...Thomas HYDROLOGY...AMD