The past few days have been a welcome relief from much warmer weather in July and the first few days of August. The featured chart compares the July average temperature departure from average against the following August departure. The low correlation and visual appearance would indicate that one does not necessarily beget the other. The departure so far this August is about the same as July. The forecast has temperatures near average for the next week or so.

Voting:
Good = 18
Bad = 8

Tags:   jul   aug  

It is hard not to keep featuring interesting stats from July after such an exceptional month! The featured chart displays the July high and low temperature departures from long term average for Des Moines. The bottom plot displays the monthly high versus low departure with a good correlation of 0.6 shown, which means warm highs usually mean warm lows and vice versa. The red dot on the scatter plot shows how exceptional this year was for low temperature.

Voting:
Good = 10
Bad = 6

Tags:   jul   jul11  

NOAA recently released estimates of July average temperatures and put this year as the 7th warmest on record for Iowa. The featured chart presents an analysis of hourly temperature departures and percentiles based on hourly data for Des Moines. The plot clearly shows the most exceptional temperatures occurring during the night time hours, which indeed tells the story of this month having very warm low temperatures. This was a result of the record amount of humidity in the state this July helping to keep temperatures warm overnight. Based on some IEM calculations: this July was the warmest on record for low temperatures statewide, but only the 40th warmest for highs (since 1893). The average of those two values gets us to 7th warmest.

Voting:
Good = 14
Bad = 5

Tags:   jul   jul11  

Thankfully, July of 2011 is history, but the heat and muggy weather looks to continue. The featured chart presents the number of hours during July for the past 40 years that the heat index was above 100 degrees for Des Moines. This year's total comes in slightly higher than 1999. The average during this period is just over 28 hours as shown by the blue line.

Voting:
Good = 19
Bad = 2

Tags:   jul11   jul  

This month has seen a remarkable amount of humidity in the area as shown by the featured chart comparing average mixing ratio for July since 1951 at the Des Moines Airport. Last year had been the previously most humid for July, but this year has soundly beat it by a full gram! Of course, there is still a few days left in this July, but judging by the forecast, the sticky weather looks to stick around until the end of the month.

Voting:
Good = 39
Bad = 6

Tags:   jul   jul11  

This July has been one of the warmest we have seen in a very long time. As measured by average daily low temperature, this year comes in second behind 1936 based on IEM statewide estimated data as shown by the featured chart. Years above average are shown in red and the 1930s really stand out. One reason why overnight lows have been so warm is the vast amount of moisture in the air this month (more on this tomorrow). The warm weather is expected to continue until the end of the month.

Voting:
Good = 56
Bad = 3

Tags:   jul11   jul  

The middle of July is the warmest time of year and has been no exception this year. A boundary will try to sink south today and bring some relief for Friday with highs in the mid 80s.

Voting:
Good = 15
Bad = 3

Tags:   jul  

The featured chart is an attempt to determine the relationship between observed July air temperatures and wind directions at 4 PM from the Des Moines Airport. The contour plot is a density field with the red area representing the 90th percentile (most common). Focusing on that area, we see a clear trend for increasing temperatures as winds switch from the SE to SW. The side histograms show the distribution of the observations with the dark green showing the distribution of winds while the temperature is above 90 degrees. Again, the SSW and SW winds are the most frequent when temperatures are the warmest. So what is the moral of the story? Having winds from the SW are an important factor to drive temperatures into the mid and upper 90s.

Voting:
Good = 32
Bad = 11

Tags:   jul