Today's feature continues the recent series looking into the record setting dew point temperatures from earlier this week. Dew point extremes are not an official climate metric tracked by the National Weather Service, so entities like the IEM create period of record statistics based on hourly observations. So while there is no official Iowa dew point temperature record, discussions with various Iowa climate experts have often concluded that 87°F on 13 Jul 1995 for Cedar Rapids is it. Three airport weather stations reported maximum dew point temperatures above 87°F earlier this week, but yesterday's IEM feature attempted to explain those away as just bad data / poor sensor performance. Today's featured chart takes another look into one of the problematic maximum dew point readings (Algona). It is compared with a nearby ISU Soil Moisture station (Kanawha) and the Ames airport station over Sunday and Monday. Ames reported a maximum of 86°F, so it is good to inspect the three time-series to see if the patterns make sense. Two areas are shaded each day as informative times to observe temperature and dew point changes. The light red area (7 AM - noon) represents a period of increasing net radiation and vertical air mixing. The light blue area (6-8 PM) often represents a period of stabilization as air temperatures start to decrease but evapo-transpiration may still be on-going. The top two subplots present coherent depictions of increasing day time temperatures allowing for a vapor pressure deficit that can support evapo-transpiration increasing the dew point. For the second day, a drier air mass was working its way into Iowa during the afternoon hours and you can see rather poor sensor performance at the Algona site vs nearby Kanawha. The Ames 86°F reading appears to be associated with the aforementioned early evening brief period with on-going transpiration and reduced vertical mixing. The "Generate This Chart" button takes you to the ASOS one minute plotting tool for Ames, which provides some more clues to what drove the 86°F dew point.

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Tags:   awos   dewpoint   jul26