What’s An MCS & T-Storm Chances

***Watch WISN 12 News at 5, 6, & 10 p.m. for the latest on thunderstorm chances!***

Thank you for stopping by the Weather Watch 12 blog!  Make sure to bookmark this page, each day we discuss the inside scoop on our weather conditions, and also give you a chance to ask the weather team questions!  In today’s blog we will highlight the upcoming rain chances and also discuss what a MCS is!

Let’s start off by discussing a weather term that you may hear a lot in the Spring and Summer months in our area.  The term is an MCS.  This stands for Mesoscale Convective System.

Here is the definition: Mesoscale Convective System(MCS). A complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms, and normally persists for several hours or more. MCSs may be round or linear in shape, and include systems such as tropical cyclones, squall lines, and Mesoscale Convective Complexes (MCCs) (among others).

These systems often appear as big blobs of rain on the radar, or sometimes can have a squal line or bow echo associated with them on the leading edge.  If one of these heads into our area, then biggest threat is often heavy rain, but another concern can be strong damaging winds.

One of these systems moved across the Midwest today.  While southeast Wisconsin only saw clouds, rain-heavy at times- slide across parts of Iowa and Minnesota.  Below is how the cloud shield looked around Noon Thursday, the MCS is labeled.  You can enlarge the image by clicking on it.

With the upper level winds out of the west on Thursday, high clouds blowing off the tops of thunderstorms drifted over southeast Wisconsin giving us a mostly cloudy day.

An MCS often forms near a warm front as very warm and moist air to the south rides up and over the warm front.  Once the thunderstorms form, they warm front can act like railroad tracks, as the thunderstorms ride along it trying to stay near the warm and moist air.

With a warm front lifting north tonight into Friday, another MCS should form.  Below is the surface map at 7 a.m. Friday.  A few thunderstorms may be occurring over parts of our viewing area at this time.

Now where might an MCS form in this type of setup?  The 12z GFS computer model forecast for 7 a.m. on Friday indicates from northern Nebraska to southwest Minnesota.  If this occurs it would then likely travel off to the east and try to stay near the warm front.

Also on the map above, notice the green shades near Milwaukee, this idicates the chance of thunderstorms Friday morning.  Not only will t-storms be possible Friday morning, but also with the peak of daytime heating in the afternoon.  Any thunderstorms that form Friday afternoon thru Saturday could contain hail and strong winds.  The timing for thunderstorms on Saturday looks greatest during the afternoon and early evening.  This is something we will keep a very close eye on, so make sure to watch WISN 12 News for the latest!

You can also stay up-to-date with rain chances and our forecast in several ways!

  • Facebook: Weather Watch 12
  • Twitter: WISN12News
  • iPhone App: WISN
  • Interactive radar  www.wisn.com/irad

If thunderstorms do find your backyard, please send us your rain totals and any pictures that you may safely take during the storm!   We may show your reports on WISN 12 News! 

Jeremy Nelson


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