It Hasn't Rained as Much as You Think it Has in Denver (Officially)

DIA precipitation totals lagging rest of city
Back in March we laid out many reasons for why Denver International Airport is a poor representative location for Denver's official weather station to be located. For some background on today's post, check it out first.

There's probably no need to remind you, but we're in the midst of an impressive stretch of wet weather. The only problem is, while those of us that live in Denver have been soaked under records rains, those traveling through our fine airport to the east have actually been noticeably drier.

Since January 1st, 2015, DIA has recorded 11.07" of precipitation. That's compared to the NWS COOP station at City Park which has recorded 15.27", and an average of Denver-based CoCoRaHS reporting stations which average 16.21" of precipitation (which is 68% more precipitation than DIA). The greatest CoCoRaHS station of the bunch is reporting whopping 19.61", with just two of the 32 Denver stations recording less than 12" on the year.

The map below show's the regions year-to-date precipitation totals from CoCoRaHS. In the white square is the city of Denver proper, where the overwhelming majority of Denver residents live, while the circle is where DIA is located. Most of Denver proper has seen >15" of precipitation since January 1st, 2015.

The Long-term average year-to-date precipitation for Denver is 6.53" across several locations. With 11.07" recorded at DIA to date, that alone is an impressive 169% of normal. Meanwhile, if the City Park station were Denver's official station – Denver would be running 233% of normal as of June, 15th. Some CoCoRaHS stations in the city are reporting >19" on the year, or nearly 3 times the 'normal' amount!

Year to date temperature and precipitation for Denver (Jan 1 - Jun 15)

For even more perspective, the average CoCoRaHS precipitation totals in Denver of 16.21" is actually MORE than the 14.49" seen annually on average in Denver. The 11.07" meanwhile, is still 3.42" below the annual average (though impressive in its own right, see chart above).

May 1st through June 15th by the numbers
If we look specifically at the last six weeks, the precipitation differences between DIA and Denver proper are even more extreme.

In May, DIA recorded a respectable 3.76" of precipitation, which is 1.64" above normal for the month. Remarkably, given how wet it seemed, this didn't even put Denver in the top 20 for wettest Mays on record, officially. The station at City Park on the other hand recorded 5.03" of precipitation, ranking it #5 on the wettest Mays list. (Precipitation records are taken from all three historic official station locations for Denver: downtown, Stapleton, and DIA).

Through the first 15 days of June we see a similar disconnect. DIA has recorded 2.24" of precipitation (again, above normal, but not even in the top 20 wettest), while downtown has seen 5.39", which would make it the wettest June on record with still half the month to go!

June and May precipitation comparisons DIA/City Park vs average and record for Denver, CO | Averages and records considered for Denver as whole, as City Park history is not as long.

Hyperbole or just right?
Admittedly, it'll take one storm to change all of this. In fact, the storm on Saturday almost did. That said, DIA is enough of an outlier right now that 1) it made sense to bring up to boost the argument for why the station should move, and 2) there's enough consistency in the totals from the rest of the city which would lend one to believe it's not 'just' a missed cell or two causing the mismatch. Only one of the CoCoRaHS reporting stations in Denver is reporting less than DIA, the rest are far ahead (DIA total in yellow):

Comparing DIA and CoCoRaHS year to date precipitation totals for Denver

If we drop the two lowest outliers from the CoCoRaHS dataset we see the average jump to 16.61" in Denver, over 5" more precipitation than DIA since January 1st.

So yes, while one good storm could theoretically erase the DIA deficit, it's still a notable difference in precipitation over the last two months in what has been a great stretch of moisture for the city. While some stations around the Denver are already one good storm away from the all time wettest year on record for Denver, DIA is less than halfway there.

2015 precipitation in Denver compared to wettest year on record for the city

Nevertheless, it's not like DIA has been dry either. Officially Denver is still running nearly twice as what as 'normal' for this time of year, just maybe not as wet as you think it has been (officially).

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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