The coldest air of the season so far settled into the upper Midwest Wednesday morning. The featured maps present an analysis of available NCEP Real-Time Mesoscale Analysis (RTMA) hourly products. These hourly products are snapshots in time and not integrated over an hour, so they are not an exact accounting of minimum temperature nor hours below freezing. The top map presents the minimum temperature with some limited locations in northern Iowa reaching values below 30 degrees. The bottom map shows the number of hours below freezing. So it appears likely that this was a killing freeze over some portions of northcentral Iowa. Other places were likely more subject to micro-climate and highly localized effects that would not be well represented by this grid analysis product.

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