Rainfall totals year-to-date (2016) as Houston prepares for a big rain event

I don’t normally blog.  But when I do, I prefer to discuss the weather.  More specifically, I like discussing weather around Southeast Texas and the Houston area.

According to the Houston/Galveston National Weather Service office, southeast Texas is in store for a good soaking this weekend.  Much of the area may see around 1″-2″ of rain, but some areas may see as much as 9″ of rainfall, according to latest graphic from the NWS:

2016.12.02 NWS heavy rain threat image.png

Spacecityweather.com, which provides excellent no-nonsense weather forecasts and updates, provided a good update on the forecast here earlier today.

As this heavy rain event begins to unfold, I wanted to look at rainfall totals across Southeast Texas – including at my CoCoRaHS location in West University Place, TX – to see where we stand in 2016.

Rainfall totals around the area in 2016 have been mostly above normal through November 30th, with the exception of Galveston:

2016-11-30-rainfall-totals-around-area

In fact, if these locations received no rainfall for the rest of 2016, Houston IAH and College Station would finish 15% and 10% above normal (see “Normal Rainfall” column in table above), respectively, Houston Hobby would finish about 3% below normal, while Galveston would finish about 10% below normal.  With this weekend’s potential for heavy rains across all of these locations, it is very likely that all locations listed above will be in a position to finish 2016 with above normal rainfall totals, regardless of what happens the rest of the month.

Taking a step back, I looked at annual rainfall totals at Houston IAH going back to 2008.  I chose 2008 since that was the last year that IAH had a surplus of rainfall for the year before six straight years of below normal rainfall totals:

2016-11-30-rainfall-totals-iah-cumulative-since-2005

For six straight years (2009-2014), IAH recorded deficit annual rainfall totals, which added up to a cumulative rainfall deficit of close to 60″ (59.44″).  Drought-busting rains in 2015 halted that consecutive deficit streak at six years as IAH recovered over 20″ of the cumulative deficit.  Coming into 2016, the seven year cumulative rainfall deficit stood at just over 39″, and with a second straight year of above normal rainfall, 2016 will definitely put an additional dent into that cumulative rainfall deficit.  At the end of November, the cumulative deficit was just under 28″ (27.81″):

2016-11-30-cumulative-rainfall-deficit-graph

Experiencing multi-year periods of below normal rainfall is not new to Houston. The graph below illustrates annual rainfall totals as a percentage (%) of normal at Houston IAH.  Green bars in the graph represent years in which the annual rainfall amount was above average, while red bars in the graph represent years in which the annual rainfall amount was below average.

2016-11-30-annual-rainfall-amounts-1949-thr-2016

As can be seen in the graph above, since 1949, Houston has experienced other episodes of below-average rainfall for extended periods: a 7-year consecutive period in the 1950s; a 6-year consecutive period in the 1960s; and a 5-year period in the 1980s.

Taking a closer look at 2016, it has been a tale of two halves.  The first half of 2016 was downright wet as 42.07″ of rainfall fell at Houston IAH during the first half of the year.  To put that into perspective, IAH received an amount equivalent to nearly 85% of the average rainfall IAH expects to receive for the entire year!  In addition, the 42.07″ received was 17.75″ above the normal amount of rainfall for the first half of the year.  But, as soon as June ended, the virtual spigot was turned off.  By contrast to the first half of the year, IAH received only 15.33″ of rainfall during the second half of the year through November 30th.  That 15.33″ is 6.38″ below normal for the five months ending November 30th.  The highlight of the second half of 2016 so far was a long, dreary, 17-day stretch in August with at least a Trace of rain recorded.  During that 17-day consecutive streak, IAH recorded 10.40″ of the 15.33″.

Another key difference between the two halves of 2016 thus far is the days of precipitation count, especially the number of days with greater than 2″ of rain.  During the first half of 2016, there were five occurrences when Houston IAH reported greater than 2″ of precipitation.  During the second half of 2016, only 1 occurrence has seen greater than 2″ of precip.  The table below shows the comparison between the “days with precipitation” statistics for Houston IAH:

2016-11-30-days-with-precipitation-amounts

Bottom line: notwithstanding the contrast between the two halves of the year, 2016 will go down as another wet year, overall, for Houston and other areas in Southeast Texas, and the potential for additional, possibly heavy rainfall, will continue to erode away at the multi-year cumulative rainfall deficit.

Stay dry, my friends.

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