Wednesday, August 13, 2014

Hourly Temperature / Rainfall Numbers

One of the great data sets that NCDC archives is the hourly ASOS observations. These are particularly useful for developing climate descriptions and analyses on relatively short timescales. Much has been made of this summer's cool temperatures and excessive rains but little has been noted on these shorter time-scales.

I decided to compare last year's hourly observations with this year's hourly observations for the June 1 to August 10 time period. Instead of using the DS 3505 ISH data, I pulled the METAR observations directly. There are certain advantages to using the METARs instead of the DS 3505 data; e.g., the distinction between moderate and heavy rain.

From a temperature perspective, 2014 has been substantially cooler than 2013 in Fairbanks. Figure 1 shows the average hourly temperatures during the June 1 to August 10 time period for 2013 (orange) and 2014 (purple). The 25th percentile and 75th percentile lines are also shown. Interestingly, the warmest 25% of this summer's observations are about the same as the mean of last summer.

Figure 1. Average, 25th percentile, and 75th percentile temperatures for every hour of the day during the June 1 to August 10 time period for 2013 and 2014.

Of course this has been an exceptionally wet summer in Fairbanks. As we noted last week, the average day with precipitation has been quite wet. Looking at the hourly data, what we see is that not only have there been many more wet days this summer, but when it has rained, many more daily observations have indicated rain. Figure 2 shows some summary statistics for the number of rainfall observations. The last column on Figure 2 shows that days with rain have more than twice as many daily rainfall observations as last summer. In fact, 10 of the 71 days this summer have recorded rain for 12 or more of the 24 hourly observations. Last year, there were no such days.

Figure 2. Count of the number of rain observations during the June 1 to August 10 time period for 2013 and 2014.

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