Scattered to Numerous Severe Storms Possible Wednesday
Updated: Jun 9, 2020
Severe thunderstorms capable of Large Hail, Damaging winds, and even a couple of tornadoes will be possible Wednesday. The highest threat is across roughly the eastern two/thirds of lower Michigan in the enhanced risk (level 3 out of 5) area. As of Tuesday evening, here is the latest categorical outlook from the Storm Prediction Center.
Although severe weather is possible across all of lower Michigan, the highest risk is highlighted in orange on the map above. The time frame to be most concerned about severe storms is between 12pm and 10pm as the storms move from west to east across the area. Large hail, Damaging winds, and even a couple of tornadoes will be possible with this setup.
Showers and Thunderstorms will likely develop between US-131 and US-127 between noon and 2pm. From here they will become scattered to numerous in coverage with all severe modes possible. The storms will gradually move east throughout the afternoon and evening and finally exit Michigan east of Detroit and Port Huron by 10pm. It is important to stay weather aware and have multiple ways to receive severe weather warnings tomorrow afternoon. Stay tuned to my social media pages for frequent updates. Below is a detailed discussion on the 'why' behind the forecast.
All severe weather modes will be possible Wednesday. There are many ingredients that are favorable for the development of severe weather. By tomorrow morning, the remnants from Tropical Storm Cristobal will have moved north of the Great Lakes and another area of Low Pressure will be ejecting out of the Central Plains. This low is producing a risk of severe weather this evening across portions of Kansas and Nebraska. This risk will shift to Michigan and Ohio by tomorrow afternoon.
As the upper-level trough shifts from the Plains to the Great Lakes between tonight and tomorrow, it will become negatively tilted, which means the trough will be angled from northwest to southeast. This is important because not all troughs set up like this and interestingly, many troughs of this nature east of the Rockies support a risk for severe weather, especially this time of year. A negatively tilted trough indicates the Low pressure is mature, instability is increasing, and vertical wind shear is abundant. Right there, we have 2 of the 4 ingredients needed for severe weather: instability, and shear. What's left? Lift and Moisture. Well, we have those also. A cold front will act as lift tomorrow afternoon and dew points will be in the 70s, which indicates high humidity and plenty of moisture. Everything is on the table to support severe weather, but now, what types of severe are possible and what risks may support or inhibit storm development?
Let's begin by dissecting the thermodynamics and kinematics individually and then determine which severe modes will be possible and what the risk is. First, we'll discuss instability. A warm front is moving north through mid-Michigan this evening, which will advect a warm and humid air-mass into the area overnight. This means lows tonight will stay in the 70s and gusty south winds will increase moisture and instability overnight. CAPE, a measure of instability, should already be favorable Wednesday morning, with values near 1,000 j/kg. These values should increase to over 2,000 j/kg by early afternoon. Any sunshine will enhance CAPE values tomorrow morning, but either way, there will already be sufficient instability in place to support thunderstorm development. The higher the CAPE becomes, the stronger the thunderstorm updrafts can become and the more intense the storms may become. Any sunshine tomorrow morning will help to enhance the instability in place.
Next is shear, which also looks plentiful. Computer models are indicating 25-35+ knot wind shear in place tomorrow afternoon, which is enough to support organized severe storms and possibly even some rotation. With this in mind, we look at Storm Relative Helicity, which is coming in at 100-150 meters squared/second squared. Ideal values to support potential tornadic rotation are 150+ meters squared/second squared, but it's still high enough to monitor and be concerned about. Additionally, LCL heights, (cloud base heights above the ground) are coming in at <1,000 meters, which is a very low cloud base, and may aid in rotation development. Overall, the vertical wind shear is unidirectional with height, which suggests straight line damaging winds are more likely, but still can't rule out the risk of a tornado with this setup.
The last two are lift and moisture. A cold front will come through late afternoon/early evening, which is right at peak heating of the day. There is also plenty of moisture with dew points rising above 70, making it feel oppressively humid. So, again, we see that all the factors are favorable for the development of severe weather during the afternoon and evening, with a risk for Damaging winds, and a few tornadoes. Perhaps the one factor that is lacking a bit is the lapse rate, which is not particularly high, but still notable. As a result, the Large Hail threat is not as high as it could be, but is certainly still a threat. After all, the more intense the updrafts are, the larger the hailstones can grow inside the cloud before falling to the ground. Moderate instability will cause strong updrafts.
In the end, this is a favorable setup for severe weather as far as the ingredients and timing are concerned. Perhaps a couple factors that may limit severe potential would be not seeing much sunshine tomorrow morning as well as storm initiation location and timing, but overall, this is a severe threat that could produce damage and cause power outages.. Severe weather setups are not a guarantee, but should be taken seriously. Have multiple ways to receive warnings tomorrow and take action to protect yourself should storms reach their potential and produce damage across the area tomorrow.