A rare, meteorological phenomenon observed on the western Lake Michigan
shoreline during the warm season is the pneumonia front. These fronts
are defined as lake modified synoptic scale cold fronts that result in
one-hour temperature drops of 16 degrees F or greater. Further knowledge
of pneumonia fronts is not only important for the efficiency of commerce
(aviation and marine), but also essential for sensible weather forecasts
for the dense population base along the Lake Michigan coast. Examining
surface temperature data from Milwaukee and Madison, Wisconsin resulted in
a set of 25 cases from the period 1948 through 2003. Further investigation
of these cases resulted in the identification of two main synoptic patterns
coincident with pneumonia front events. Analysis suggests that these
synoptic patterns are necessary but not sufficient in the forecasting of the
pneumonia front phenomenon. Mesoscale controls of pneumonia front events were
examined through the use of a simple model, and sensitivity simulations of
a specific event (17 July 2003) using the PSU-NCAR mesoscale model (MM5).
The simple advection model showed the following: reduced roughness over a
north-south lake allows for stronger impact in the southern lake and
shoreline; zonal and northwest-southeast cold fronts are more conducive for
pneumonia front cases; and colder lake temperatures in the north increase the
near-shore temperature gradient and frontal propagation. The results of the
MM5 sensitivity tests suggested the following in regards to the 17 July 2003
pneumonia front: orography had little influence on pneumonia front generation
and maintenance; temperature falls relating to the pneumonia front were
strongly dependent upon landmass diurnal heating; and Lake Michigan surface
water temperatures impacted pneumonia front strength. The insights gained
from this research should allow operational forecasters to reliably assess
the likelihood of pneumonia front events in the short-range.