Past IEM Features tagged: hovmoller
Iowa's glorious most recent weekend was thanks to a strong high pressure system to our east that kept storms over the High Plains at bay. The featured chart displays NOAA MRMS precipitation estimates from Friday through Monday morning. The top panel is a simple map of precipitation totals showing the heavy amounts over Nebraska and South Dakota. The bottom panel is a Hovmoller diagram showing a time series of meridional averaged hourly precipitation over the domain shown in the top panel. This type of plot has some neat attributes as it shows the east/west progression of storms with time and with the east/west domain of Iowa shown, you can see how the areas of precipitation struggled to move east with time. Rain eventually did make into Iowa on Monday with totals mostly below an inch.
The featured chart is a called a Hovmoller Diagram. It displays the time evolution of some averaged field. In this case, each row represents the meridonal (north-south) average daily high temperature departure for the midwestern US. Time increases as you go down the chart. The two vertical lines represent the areal average that includes Iowa. Values on the left are to the west of Iowa and likewise values on the right are to the east of Iowa. A neat aspect of this chart is that you can visually see the movement and modulation of air masses. For example in September, you can see movement from upper left to lower right. This represents air masses going from the western part of the domain to the eastern part, with the slope representing the speed of movement. The plot also shows a difference during the summer months to what has happened since early September. The difference is due to having storm tracks every week or so as opposed to persistent air masses during the lazy days of summer. The very dark blues (cold departures) showing up in October are where the snow fell in western Nebraska and South Dakota.