The above image is a visible satellite image from GOES at 2031UTC on 8/9/11. It shows a line of thunderstorms from southern Lake Huron to southeast lower Michigan into far northwest Ohio and far northeast Indiana. This convection was observed along a cold front advancing east through the area. Now, compare the above image to the image below:
The above image is the Theta-E Nearcast product at 2030UTC on 8/9/11. The green areas indicated unstable conditions (low level theta-E minus mid-level theta-E), and the blue areas indicated stable conditions. Note how this product clearly shows the unstable conditions along and ahead of the cold front, and this area corresponds to the convection shown in the 2031UTC visible satellite image. This also showed the stable airmass behind the cold front. Given that this product can be viewed several hours into the future, this product could have given a forecaster more confidence to diagnose the best areas for convection to initiate and grow.
The above image is the visible satellite image from GOES at 1445UTC on 8/9/11. Note the large area of VFR to MVFR ceilings over nothern and central Minnesota into far northwest Wisconsin. Also of note is a smaller area of MVFR to IFR ceilings over southern Wisconsin. Now, compare the visible image above to the image below:
This image is the MODIS Probability of MVFR Ceilings product, at 1445UTC on 8/9/11. Two things of note here are 1) the high probabilities of MVFR ceilings across northern Minnesota into far northwest Wisconsin, and 2) the strip of low probabilities of MVFR ceilings across southern Wisconsin. This product had a very good depiction of the MVFR ceilings over central/northern Minnesota into far northwest Wisconsin. Some VFR ceilings were also mixed in with the MVFR ceilings.
Another interesting note was this product showed low probabilities of MVFR ceilings over southern Wisconsin, where MVFR to IFR ceilings were observed. These low probabilities could have helped give an aviation forecaster some confidence that low ceilings were possible across TAF sites in this area. These clouds formed quickly after sunrise, as a cold front was moving southeast through the area.
J. J. Wood
National Weather Service
Milwaukee/Sullivan, Wisconsin
8/9/11