Forecast Summary:
Several rounds of showers and thunderstorms will move through the region throughout the day today and into the overnight hours. These showers and storms will bring the risk for excessive rainfall, possibly leading to flooding and flash flooding, as well as a threat for severe weather later this evening.
Threat For Heavy Rainfall & Flooding, Flash Flooding:
While not discounting the latter discussed severe weather risk, the threat of heavy rainfall and flooding is the primary concern today. As aforementioned, several rounds of showers and thunderstorms will move through the area today. The first is moving onshore now near Grand Haven and Muskegon, as shown in the radar loop below.
Rain showers will continue through the day as demonstrated by this forecasted radar imagery from the NWS in Grand Rapids:
The risk for Excessive Rainfall is rather impressive/somewhat rare for lower Michigan. The Weather Prediction Center has placed parts of the area, along and north of a Muskegon to Mount Pleasant line, under a Slight Risk (level 2/4) risk for Excessive Rainfall and areas south of that under a Marginal Risk (level 1/4). A rare Moderate Risk (level 3/4) is also in place, very close to us, on the other side of the Lake.
What we start to worry about with scenarios like this when we have several rounds of showers and storms, is that areas that have already seen rainfall, and perhaps flooding, may continue to see heavy rainfall in an event/effect we call "training of storms" (when showers/storms move over the same area multiple times in quick succession with little to no time for the area to dry-out).
Because of this risk for the training of storms today, areas along and north of M-46 are also under a Flood Watch through early Sunday Morning to account for the threat of flooding across the area.
Growing Severe Weather Potential:
Aside from the heavy rainfall and flooding threat, there is also a risk for Severe Weather across the entire area today. The Storm Prediction Center has outlined a broad Slight Risk across much of the central part of Lower Michigan.
As we've discussed several times already, West Michigan will see several rounds of showers and storms. Any showers and storms we see this morning and into the early afternoon are not expected to have any kind of severe weather threat.
The threat of severe weather will come later this afternoon and evening and into the overnight hours, possibly with two separate rounds.
All severe weather hazards are in play. The area of most concern for an all-hazards threat (tornadoes, wind, and hail) will be this afternoon with any storms that form along the frontal boundary across the northern part of our coverage area (Muskegon, Montcalm, Lake, Mason, Ocenana, Mecosta, and Osceola Counties) where the SPC has outlined a 5-10% risk of tornadoes, a 15-30% risk of damaging winds, and a 5-15% risk of large hail. In these areas, especially east of US-131, it it definetly possible that we see a couple of tornadoes develop given the strong wind shear, very high SRH (Storm Relative Helicity - the ability for storms to spin/rotate) values, and just enough instability/CAPE (storm energy juice) for some low-topped (short) supercell storms to develop. Damaging winds, small to large hail, heavy rainfall, and flooding will, of course, be a hazard with any supercells that develop as well.
Other parts of the area, especially along and south of the I-96 corridor, will be faced with an all-hazards threat as well overnight and will see more instability due to less shower/storm activity throughout the day today. However, these areas will not see conditions that are as favorable for tornadoes, while certainly non-zero (2-5%), the threat here will not be as focused on tornadoes and more so on the threat of damaging winds, heavy rainfall, flooding, and perhaps some hail.
There is a lot of uncertainty with this forecast, as per usual here in Michigan, lack of certain ingredients needed to support severe weather and day-time rain showers across the area are going to significantly limit our forecast confidence and this event will likely be a now-casting type situation where we are forced to guess right up until storms form - or don't.
Stay tuned to our social media accounts for updates and alerts. We may need to activate Storm Chase Mode later this afternoon and evening.
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