Wednesday, November 7, 2012

Wednesday search challenge (11/7/12): How much DOES it rain in Northern California?

Sometimes the simplest questions can lead to relatively tricky searches.  This is usually the case when the data you’re looking for isn’t just lying around on the floor of the internet, but is something you might have to assemble yourself. 

I was standing in the microkitchen at work last week waiting to make my café latte when a couple of us started talking about the weather during the past month. 

“Seemed awfully rainy to me,” a friend pointed out.  “Is this something new?  Or has October always been rainy in Northern California?” 

I’ve lived just south of San Francisco for over 25 years, and MY opinion was that this October seemed rainier-than-usual as well.  But you know how impressions are—they’re notoriously subject to all kinds of mis-rememberings, and in particular, the human ability to give accurate summaries of events over the long scale is really quite poor.

So I thought I’d just look it up—but this bit of weather data turned out to be a bit tricky, and leads to this week’s Search Challenge…

Can you find OR create a chart like this one I've sketched below showing each year's total October rainfall at SFO to answer the question:  

Did it rain more in October, 2012 than in any October during the past 10 years? 

My ideal chart for October rainfall at SFO.  (This is made-up data for the purpose of illustration.)  

To make it simple, let’s check the rainfall during October at SFO.  I know that accurate weather data will be available at the airport.  (Although you need not limit your searches to only FAA data. Any reasonably reliable rainfall weather data will do.  It just has to be measured at SFO.)  

As usual, please let us know HOW and WHERE you found the info, along with an estimate about how long it took you to answer the question (or generate the graph). 

Search on! 


  1. I frequently work with historical weather data to model energy consumption and use so already knowing which tools are available (and free) is helpful here.

    Weatherunderground provides historical data for many locations. The reporting tool isn't the best for customized reports, but with a bit of patience you can usually find what you're looking for. Pulling up the drecipitation (rainfall only, exluding snowfall) data, we get the monthly totals for every October from 2001-2012 (see my table, and graph here:

    One of the better resources that aggregates several weather-related datasets is from the Utah Climate Center, at Utah State University:

    The map-based tool shows all available weather reporting stations for each of the datasets that they offer (about 5 or 10 total, some daily only, some hourly).

    It took a couple minutes to find a dataset for SFO that covered the span from 2000-2012 (the GHCN dataset appears to be the most reliable)

    There are some significant discrepancies between the WUnderground and GHCN data.

    Adding in the AWOS dataset from 2005-2012 doesn't help much, because it presents even more variation in the listed values.

    Its not so clear that accurate and consistent data is available for the airport.

  2. Searched[rainfalll october sfo]

    Monthly mean prcp(in) 1.0

    Searched [sfo october precipitation ]

    MAXIMUM 7.30 1962
    MINIMUM 0.00 2003,2002 and 1978.

    Searched [sfo monthly precipitation 1849..2012]
    Found with data since 1849:

    With the data from:

    Made graph but I don´t know how to upload

    Did it rain more in October, 2012 than in any October during the past 10 years?
    Answer: No. In 2009-2010 rainfall was the month in the ten years with more rainfall with 3.11 inches

  3. I googled [SFO "weather data"]. The first result is a page from the National Weather Service Forecast Office for the San Francisco Bay Area titled NOWData - NOAA Online Weather Data. You can generate tables of monthly avgs/totals of precipitation in SFO for 1981-2010 (avgs), 2011, and 2012. Copy/paste the data for October in Excel and you can generate a 3-point graph comparing the average precipitation, last year's, and this year's rainfall in inches.
    Granted, I was lazy as my graph doesn't detail the last 10 years. I could've dug more to get the info, but my lunch break is coming to an end.
    Total search time: 3 mins.

  4. Final answer: it rained more than average, but less than last year.

  5. I just go to and search for SFO. You can scroll back as long as there is data and it puts it on a pretty chart for you.

  6. I used Wolfram Alpha and changed the weekly chart to "Past 10 Years" and also chose "Show Annual"

  7. I used WolframAlpha and searched "San Francisco California Rainfall". I changed the chart to annual and Last 10 years.

  8. Easy, use Wolfram Alpha. It struggled with larger data sets, (when increasing the amount of years in a single query) probably because I'm using an iPad. If you can't get the results in a single query on a desktop machine, just repeat it ten times. :)

  9. Well Sacramento is actually Northern California :)

  10. And yeah, took about 5 minutes since wolfram generates graphs automatically.

  11. I went to Weather Underground, where I usually get my weather reports, and asked for San Francisco airport, which got me to weather station KSFO:

    I then asked manually for each October:
    2012 0.70in
    2011 1.18in
    2010 0.84in
    2009 2.96in
    2008 0.32in
    2007 1.97in
    2006 0.33in
    2005 0.08in
    2004 2.77in
    2003 0.00in
    2002 0.00in
    2001 0.33in
    1948 0.31in

    Since I don't really care about the data, I was too lazy to pick up all the numbers. They have a dump in comma-separated form for daily data up to a year at a time, but not for more customized reports.

  12. Any hydrologist would go straight to NOAAs NCDC.

  13. I'm sure I'm wrong because this search took me no time! I typed in "rain precipitation data SFO" which led me to the site (the second in the results). I used the double chevron to preview the page and thought this was a probable candidate for me to begin my search on. There I found some interesting links, like : "YEAR-TO-YEAR GRAPHS - COMPLETE SET OF LINKS" ranging back from 1921 through 2012. On each link a new tab opens up showing month by month data relating to daily temperature and precipitation. I then draw a table like the one you proposed, and found out that Oct 09 was the month with the most precipitation not only in all of 2009, but in all the ten-year span!

  14. Precipitation for this year, 2012, is about average, i.e., 1.24 inches. The rainiest year in the last decade was 2009 with 3.11 inches. I strated with a search for 'monthly rainfall SFO and landed at There I found everything except the data for 2012. That I found with another search specifying October 2012 findinfg the rainfall 1.24 inches for last month. BTW, not really very rainy at all, with about 2 weeks in the middle of the month with only clear skies!

  15. Answer No

    I used WeatherSpark. It's my go to place for weather related things.!graphs;ws=31587;t=328502;mspp=236153063;fcs=0;graphs=clouds:0,windSpeed:0,subZero2:0,stidpg:0,solarPosition:0,spaitg:1,windIcons:0,tiles:0,dewPoint:0,windDirection:0,temperature:0,smeisg:1,pressure:0,snowDepth:0,saf:0,precipitation:0,humidity:0,precipitationAmount:1,visibility:0,precipitationRate:0,sdpitg:0,cloudCeiling:0,siitg:1

  16. In short, the answer is no.

    This took me much much longer than necessary through my own desire for haste and confirming the data. I had the correct data (I think) within about 5 minutes but took me much another 30 minutes or so (whilst trying to do other things) to confirm.

    Started off with simple [rainfall sfo] type searches which gave no real information but brought up the term 'precipitation' which was useful. I then tried [monthly weather summary san francisco airport] because 'SFO' was proving a bit hit and miss. Halfway down the page was 'SAN FRANCISCO WSO AP, CALIFORNIA - Climate Summary'. Perfect data (albeit missing data for October 2012; looked up the NWS site for that) for what I wanted but I had to check where WSO AP was. Quick look around and it didn't appear to be at SFO ( so I restarted my search :(. This decision was further influenced by the fact that the data didn't seem to match the chart above (which I later noticed was only for illustrative purposes!!).

    Finally found myself at the WRCC site which had come up in a few searches. Looked at the climate summaries for Central California (, zoomed in on SF and clicked on San Francisco Intl Airport below...only to find myself looking at San Francisco WSO AP data again (argh).

    Lesson learned. Trying to search whilst devoting yourself to other tasks can detrimentally affect what you find.

  17. query [rainfall measurement] to get the technical term used in the industry which is precipitation.

    next query [precipitation SFO 2002..2012], led to me to this site:

    looked at the yearly graph, it turned out that October 2009 is the wettest period from 2002 to 2012 with the highest precipitation recorded of 2.50 inches, however, this year it only reached (highest) 0.75 inches.

    you can see the graph here:

    another challenge worth conquering!!!