The Milwaukee/Sullivan National Weather Service Office was notified by Milwaukee TV stations and the Wisconsin DNR that citizens in the counties
of Milwaukee, Ozaukee and Waukesha reported a layer of red dirt on vehicles (Image 1/ Image 2). The red dirt was
deposited by the rain during the mid-moring hours of Tuesday, December 16, 2003.
The red dirt, which appears to be clay-based, originated from west central Texas and eastern New Mexico. Strong west winds gusting to 55
to 65 mph for serveral hours in that region the previous day, lifted the red dirt into the atmosphere. Poor visibilities were noted over
parts of the Texas Panhandle into Oklahoma Monday (12/15/03) afternoon and evening.
The wind flow associated with a low pressure system lifted the dirt to a high altitude and brought the red dirt into southeast Wisconsin
as the low pressure system moved northeast through Wisconsin Tuesday morning.
The soil in eastern New Mexico and west Texas was very dry, allowing it to be easily lifted by the strong winds.
The satellite image above shows the turbulent winds lifting the dirt and pushing it northeast.
The Hysplit Computer Model
The Hysplit computer model, normally used by the NWS to predict the spread of hazardous material
in the atmosphere, was used to see where air parcels, originating at different altitudes over
Lubbock, TX at 600 A.M Monday, December 15, 2003, would end up at 600 A.M. Tuesday, December 16, 2003.
The resultant plot clearly shows that wind currents, associated with a low pressure moving
northeast from the Kansas area to Wisconsin, transported the lofted red dirt from eastern New Mexico and
western Texas, northeast to southeast Wisconsin, northeast Illinois and Lower Michigan. Rain showers
associated with the low pressure washed the red dirt out of the atmosphere over a large area.
The red line shows the track an air parcel, at 1000 meters above the ground over Lubbock, TX,
would take during the 24 hour period ending 600 A.M Tuesday morning. The blue line represents
what happened at 2000 meters above the ground, and the green line indicates activity at 3000 meters
above the ground. Note that the air parcels at all three levels continue to mix and rise to higher
altitudes as they appoach the deposition area.
The amount of deposited dirt and the widespread nature of the deposit was very unusual for the Upper
Midwest. It has happend before, but not on the scale of what occurred during the morning hours of
Tuesday, December 16, 2003.