Let us take a look at the Flint and Peoria morning soundings again, this time modified for Kalamazoo surface temperature and dew point at 3 p.m. Note that the surface temperature and dewpoint were modified while the levels just off the surface were not which results in a superadiabatic lapse rate. While this may not be a true representation of the low levels the modification of the surface temperature and dewpoint gives a sense for the potential instability that ‘may’ have been generated in absence of strong thermal advection. Utilizing this modified sounding instability parameters that may have been more representative of the environment on the afternoon of 13 May 1980 were calculated.
Modified 12 UTC FNT sounding for AZO surface temperature and dew point at 3 p.m. ½ hour before first tornado touchdown (Van Buren County).
Here we modified the 12 UTC FNT sounding for surface temperature (74) and dew point (55) in Kalamazoo at 3 p.m. This modification yields some instability. The LI is down to -1, total totals are up to 44, and MUCAPE is up to 371 J/kg. This was just enough instability to trigger thunderstorm development along the strong quasi-stationary frontal boundary draped across northern Van Buren and Kalamazoo counties and along and just ahead of the cold front. Note: We also know from the 3 p.m. surface observation in Kalamazoo of cloud base being broken at 1,800’ that this was the approximate LCL height (not in excess of 4,000’ as indicated in modified Flint sounding data). This low LCL height is also very consistent with our findings for all Type One events.
Modified 12 UTC Peoria, Illinois sounding for AZO surface temperature and dew point at 3 p.m. EDT, ½ hour before tornado in Van Buren County.
We also modified the 12 UTC PIA sounding for surface temperature (74) and dew point (55) in Kalamazoo at 3 p.m. The Peoria sounding was more representative of conditions in Kalamazoo, being south of the warm front. This modified sounding shows a larger degree of instability with the LI’s down to -7 and total totals of 45. This is certainly more than enough instability to trigger explosive thunderstorm development in the warm sector along and ahead of the cold front (which is exactly what happened). Note that this sounding is modified for temperature and dew point but not surface wind fields. So when you look at the wind profile with height in this image, keep in mind that the actual surface winds were actually SE or E.