850 hPa Analysis The animation on the previous page contains a 850 hPa analysis, which has the parameters of geopotential heights, Precipitable Water and wind. The 850 hPa conditions that day were actually rather remarkable with regards to the formation of severe weather. First and foremost, the magnitude of the low level jet was incredible, with winds between 45 and 50 kts. In addition, the winds were roughly out of the south-southwest. This, like the intense 700 hPa winds, allowed for long, looping hodographs necessary for low level rotation within storms. In addition, as the 850 hPa low consolidates and moves eastward throughout the period, it “catches” and strong plume of moisture that comes off the Gulf of Mexico. Given the intensity of the low, and in consequence the magnitude of the low level jet, this plume of moisture actually wraps around the top of the low, causing very deep moisture to be ushered into eastern lower Michigan. Needless to say, this created very favorable thermodynamic conditions for the formation of strong to violent tornadoes throughout the entire region.

Surface (1000 hPa) Analysis

Surface Analysis

The animation on the previous page contains a 1000 hPa surface analysis, which has the parameters of geopotential heights, equivalent potential temperature and wind. Similar to the 850 hPa analysis, the parameters in the animation are rather remarkable when it comes to the formation of severe weather. First, winds are still strong, 25 kts, and now out of the southeast. Again, the winds helped in hodograph length and size, and were tremendously favorable for the formation of strong to violent tornadoes. There was more than 90º of turning between the surface and 500 hPa pressure surface over eastern Michigan, which allowed for tremendous bulk shear and helicity values to be in place. Additionally, equivalent potential temperature (theta-e) values are a big key here. Theta-e values were exceptionally high that day, implying a very warm, moist air mass was being advected into the area. This tells us that the airmass was also very unstable, and parcels probably had very little trouble rising rapidly. Finally, theta-e, as well as the placement of the winds, tell us that the storms formed near or on a warm front. This, like many of the other parameters in place, allowed for a very favorable environment for strong to violent tornadoes. The warm front undoubtedly added more helicity to any storm that could form on or near it.

Moisture Analysis (Surface)

The animation on the previous page simply shows how dewpoint temperatures were also advected northward by the surface low. Dewpoint is a good “absolute” indicator of atmospheric moisture content, as higher values imply higher moisture. It is also a good indicator of LCL height, as a good first guess for LCL is to subtract the dewpoint in Fahrenheit from the temperature, also in Fahrenheit, and divide by 4.5. Lower LCL’s allow for tornadoes to form more easily, as the storm-scale rotation is more easily transferred to the ground. On that day, dewpoints were very high, and as such, storms had a lot of moisture to use as fuel, in addition to probably what were very low LCL’s.

Sources %80%93_Beecher_tornado %80%93_Beecher_tornado devastating-tornadoes-in-history/ (picture) devastating-tornadoes-in-history/ IDV