We had a high temp of 80° in Otsego yesterday, the low was 62°. Today it will become a bit more uncomfortable with temps rising into the low to upper 80s. The warmest will be in Grand Rapids, Kalamazoo, and surrounding areas.
Heat and humidity will reach oppressive levels on Tuesday and Wednesday, where the combination will make it feel more like 95 to 103 degrees, even in the shade. Heat exhaustion is a concern, and hydration and frequent breaks are a must. Temperatures will tend to stay cooler near Lake Michigan beaches, where water temperatures are still only around 60 degrees, though waves and currents may result in a moderate risk for swimmers on Tuesday and Wednesday.
SPC Convective Outlook
Convection-allowing guidance continues produce a wide array of solutions in terms of timing and location of a potential MCS this morning into the afternoon. What is certain is that the environment will be favorable for widespread damaging wind gusts where an MCS ultimately develops. Low to mid-70s F dewpoints reside within the mid-Missouri Valley into the lower Ohio Valley already and steep mid-level lapse rates should move eastward over this low-level airmass tomorrow. 3000-4000 J/kg MLCAPE is probable near the surface boundary by afternoon. Deep layer shear will certainly favor storm organization. The question will be where and when intensification of convection will occur. Consideration was given to introducing a 30% severe wind probability/Enhanced area, but confidence remains too low. At least at present, portions of southeastern Wisconsin/northeastern Illinois into southern lower Michigan and adjacent Indiana/Ohio appear to have the greatest potential for greater damaging wind coverage. Some wind gusts could be significantly severe. Large hail will be possible and a couple of tornadoes could occur given the low-level shear near the boundary.
A Mesoscale Convective System (MCS) is a collection of thunderstorms that act as a system. An MCS can spread across an entire state and last more than 12 hours. On radar one of these monsters might appear as a solid line, a broken line, or a cluster of cells. This all-encompassing term can include any of the following storm types:
Mesoscale convective complex (MCC)—A particular type of MCS, an MCC is a large, circular, long-lived cluster of showers and thunderstorms identified by satellite. It often emerges out of other storm types during the late-night and early-morning hours. MCCs can cover an entire state.
Mesoscale convective vortex (MCV)—A low-pressure center within an MCS that pulls winds into a circling pattern, or vortex. With a core only 30 to 60 miles wide and 1 to 3 miles deep, an MCV is often overlooked in standard weather analyses. But an MCV can take on a life of its own, persisting for up to 12 hours after its parent MCS has dissipated. This orphaned MCV will sometimes then become the seed of the next thunderstorm outbreak. An MCV that moves into tropical waters, such as the Gulf of Mexico, can serve as the nucleus for a tropical storm or hurricane.
A derecho (pronounced similar to “deh-REY-cho” in English) is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of tornadoes, the damage typically is directed in one direction along a relatively straight swath. As a result, the term “straight-line wind damage” sometimes is used to describe derecho damage. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.
--Significant squall line remains possible late this pm-- The potential for a fairly strong squall line with some significant damaging winds remains a distinct possibility late this afternoon and/or this evening. The most likely area where significant impacts would be possible continues to be the southern half of the area, mainly along and south of I-96. That all said, there are still some details that continue to need to be sorted out with multiple small scale systems in play and their interaction with each other. The two main systems that will likely affect the scenario for Lower Michigan are two MCV`s. The first one is over Eastern SD, while the other is moving over Eastern NE as of 07z this morning. Our latest thinking is that we could see at least a couple distinct rounds of storms, and even maybe some training of storms that would cause some potential flooding. We believe that the MCV/wave in NE will be the one that makes it here first later this afternoon. The very warm and unstable air mass that is strengthening to our south will be slowly advancing toward the area. It seems that the arrival of this wave will help to bring an initial surge of elevated instability to the area on the edge of a low level jet later this afternoon. The synoptic models are all holding off the best forcing with the low level jet until later. This surge is likely to fire off some scattered showers/storms with the best instability still yet to come in. If the MCV can be strong enough, and tap enough of the extreme instability to the south, we could have a formidable line to deal with after about 20z or so. It seems then that the MCV over SD will move ENE into Central MN through early afternoon, before being redirected south as the upper ridge over the Plains amplifies, and we see a NW flow aloft develop. Most of the CAMs indicate that this will be coming down toward the after 00z or so, and potentially produce the stronger line of storms. This seems plausible as there will be more time for the instability to creep north, and for that MCV to interact with it. It will be interesting to see how this interaction actually takes place, and what the results will be on the severe potential. Aside from the mesoscale details, the potential remains quite high that wherever this line develops, damaging winds will be likely, with some being significant over 75 mph. This will be the result of mid level winds expected to increase to around 60 knots, and effective deep layer shear 70+ knots. The forcing of the wave, and cold pool that would develop would help to drive this and bring down the stronger winds aloft. Hail will be another threat as mid level lapse rates are well in the 7.0-8.0 C/km range, and the degree of CAPE available will help that cause also. Also, a tornado can not be ruled out, especially near the front where convection will be nearly sfc based, and where there is quite a bit of low level shear present. Any tornado that occurs would likely be embedded in the main line. Another facet to this is the potential of some flooding. The lines of storms themselves will be moving fast and are not the concern. The concern lies where training of storms could occur due to the interaction of the lines, and where they may pivot. Pwats are forecast to increase to over 2.00 inches, providing heavy downpours out of any of the storms. If training of storms occurs and these heavy downpours hold over one area too long, the rainfall amounts could add up quickly. --Hot and humid weather expected Tuesday-Wednesday-- We should see convection move out of the area easily by daybreak Tuesday. This is because the low level jet is forecast to be east of the area by then. Most of the area will not be quite in the warm sector yet, as the storms will hold it down a bit. The upper ridge building, and the shallow nature of the stable layer mixing out should send the warm front north of the area by mid-late afternoon. Clouds and some fog will be possible early with the front nearby. That will clear out then, and temps will make a run into the lower 90s. Combined with dew points in the 70s, heat indices should warm to around, or just over 100 degrees. We expect that a Heat Advisory will likely be needed. There is still a little more time to re- evaluate this, and we have been messaging it plenty already. This will continue through Wednesday. --Cooling off and mostly dry late in the week/next weekend-- The period of heat will come to an end with the passage of the cold front very late Wednesday night and early Thursday morning. This timing is not very conducive for diurnal heating and maximizing the the amount of instability. In addition, the best forcing aloft will be mainly north of our area, as that is where the short wave energy with the upper jet will be. A secondary cold front will then coming through toward daybreak on Friday. This will usher in the more noticeable change in air masses. With the passage of that front, we will see Canadian high pressure build down from the NW. The flow around the high will funnel cooler and drier air in from the NE initially, before the high moves overhead. This should keep the area cool and mostly dry next weekend.