Iowa Flood Studies: Waiting for the Rain near Traer, Iowa
May 1st, 2013 by Walt PetersenFrom May 1 to June 15, the Iowa Flood Studies, or IFloodS campaign is taking place in eastern Iowa. NASA and the Iowa Flood Center at the University of Iowa are measuring rainfall with ground instruments, ground radar, and satellites, and then evaluating flood forecasting models and precipitation measurements from space.
We have been waiting for rain at the NPOL site. Yesterday evening it got very close- within 50 km or so. In the interim, we were waiting for convective cells to develop along what is called a radar “fine-line”. Fine-lines are little boundaries in the lowest part of the atmosphere associated with small changes in wind, temperature and/or humidity that often work to focus bugs. They are very visible to the radar and are often (though not always) associated with a line of cumuliform clouds which will sit over the top of the boundary. The clouds form in response to convergence and mixture of the moisture along the fine line and tend to “ride” it as it propagates along. Often, deeper more vigorous rain cells will develop along these lines as they intersect other cloud rolls or boundaries.
May 1, 2013. Clouds along the “fine-line”, a boundary that means a change in wind, temperature and/or humidity is occurring. Credit: Walt Petersen / NASA
At any rate, we watched one of these boundaries for quite some time yesterday with the radar. It passed NPOL in the afternoon (below) and I went out to take a quick picture of the clouds along it (above; which were unimpressive…..alas). However, southwest of Des Moines there were a few severe storms that developed along the same line; just didn’t happen in our area.
NPOL radar view of the “fine-line.” Clouds and rain are shown in blue. The NPOL position is labeled in white and the line of green sites show where the ground instruments are located. Credit: NASA
Today (currently) we are awaiting a major storm system that is sitting just to our west and northwest and producing rain mixed with snow in the northwest corner of Iowa — the same system that was producing snow in Colorado early this morning. It looks to be wet and cold here for the next few days after the storm arrives. If and when we get the rain/snow mix, we will focus very hard on coordinated scanning with the D3R as this will be a very unique opportunity for us to collect data in a mixed-phase event with three different radar frequencies at dual-polarization. Since this situation happens more often in the mid-latitudes, and GPM will extend our rain and snowfall measurement capability into the mid-latitudes, this could be a great case for looking at the famous “rain-snow line” transition and how our GPM radar and radiometer algorithms will work in this situation.
Walt Petersen is the Ground Validation Scientist for the Global Precipitation Measurement (GPM) mission, based at NASA’s Wallops Flight Facility in Virginia.
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