Plaincast

What has changed

The evolution of MCS development tonight and how it will translate through the day today and later tonight will continue to be in flux.

Messages

Rounds of convection possible today and tonight, hinging on the initial systems this morning.

Cooler airmass and high pressure into the end of the week.

Discussion

KEY MESSAGE 1. All eyes this morning will be on the developing thunderstorm complexes currently in northern Minnesota and over eastern Lake Superior. Evolution has been slow thus far and IR imagery showing cloud top cooling is minimal at this point although growing in size over Whitefish Bay, and expect enhancement over the next few hours. Bulk shear vectors will take these developing complexes southeastward into the southern Great Lakes, where CAMs/rapid update models have had a hard time providing any consistency to their solutions on where MCSs will go and if/when they decay. As they move towards the Cleveland forecast area, plenty of elevated instability to work with, but atmospheric layer above the boundary layer needs some work in terms of humidity as it is pretty dry for the time being. Outside of the drier layer of air aloft, surface dewpoints in the mid 60s and usable mid level lapse rates exist. However, the timing of the MCS works against it for our area as it tracks southeastward towards dawn, and will likely suffer decay as cloud tops are forced to warm with minimal low level jet energy in place. That said, there is an expectation of a few lingering clusters of showers or showers with isolated thunder this morning from the Lake Superior MCS. Further west, the Minnesota system is one that high-resolution models and CAMs are suggesting will survive into the daytime, and could affect our forecast area later today. Ultimately, the forecast challenge here is that the rest of the day and into the overnight is likely going to rely on what happens with these initial systems, how long it takes or if the atmosphere needs to recover from them, if there are lingering wake MCVs, etc. Expect an evolving forecast, but know that the chances for convective activity will exist from this afternoon into the overnight hours.

KEY MESSAGE 2. A cold front will come through Tuesday morning with a wholesale airmass change with cooler and drier air in place. Additional upper trough axes will swing through the forecast area north to south, and the onshore flow coupled with this could generate showers with some lake enhancement as the 850mb temperatures drop into the lower teens. High pressure will then settle into the southern Great Lakes for the end of the week with temperatures in the mid 70s to lower 80s through Thursday.