Baltimore and Washington: Extreme Precipitation Within Their Political Boundaries

Baltimore and Washington: Extreme Precipitation Within Their Political Boundaries

Most larger U.S. cities have one “official” National Weather Service (NWS) weather station for which climate data is recorded and archived. As we weather geeks know, that one location can be very unrepresentative of weather conditions compared with other parts of a city, especially as related to precipitation. Elevation and varying urbanization can provide great differences in temperatures while thunderstorms can drop prodigious amounts of rain in one part of a city, while other areas stay dry. This got me thinking that I had never seen data for either Baltimore or Washington (cities where I grew up), in a format that provided a broader view of these cities’ data. To that end, I decided to undertake the research required using the available climate data of both cities to find out, historically and currently, what other “official” stations (mainly NWS Cooperative Observer Network locations) are available to provide a more comprehensive view of the precipitation records of both locations.

Officially, the National Weather Service (previously known by numerous names and under various Federal Government departments, including the Dept. of Agriculture) began recording official data around 1870. There is available data for various locations prior to this time but the many standards set by NWS might not have been followed, therefore cannot be considered as reliable/official.

Since the late 1800s, both Baltimore and Washington have had nearly a dozen other official stations within their political boundaries recording data for various time periods, some short-term, some longer-term. Additionally, in many instances, the official downtown locations have been discontinued and the new official locations have been moved to nearby airports that could be outside of the city borders. Much of this historical data is now available digitally in website databases (NWS, NCEI/NCDC, ACIS) but much of the older information is not, requiring me to review old paper versions or scanned versions containing handwritten entries. This was very tedious work at times but, being a data wonk, I was determined to provide the best information possible for both cities. Therefore, I began researching state and city publications, dating back to 1870 to find the extremes. This required even reading every page, month-by-month (and annual publications) to make sure I was finding the most accurate, complete data, even the errata that was published in one issue, then corrected in a subsequent issue. This brought up another problem, the fact that the digital databases often contained errors, requiring even more research to figure out what data was correct and where it went wrong. The current results for both Baltimore and Washington can be found in the links below, containing precipitation records for daily/24-hour, monthly, and annual amounts. I’ve also provided the names of all of the stations for which data was reviewed, along with their periods of record.

Baltimore City Limits: Record Precipitation – Daily, Monthly, Annual Amounts

Washington, DC City Limits: Precipitation Records


I’ve also been researching temperatures for both cities and will publish that information at a later date.


Take care,



Map image courtesy of Bing Maps.

7 thoughts on “Baltimore and Washington: Extreme Precipitation Within Their Political Boundaries

  1. Thanks for this great collection of data Jeff. It looks really good and complete at my first glance. I will be studying it further as the days go by, and noting any comments about it to you.

  2. Thanks for the reply, Kevin. It’s certainly been a labor of love working on this historical data for the last 15 or so years. As I continue to format new things to post for Maryland, I would like to start working more fully on the State of Oregon’s historical data.

  3. Awesome post Jeff! I thought local climatological differences in Seattle were huge, but I think they are even bigger in Portland due to the Columbia River Gorge. I’m in Northeast PDX, so we are windier and cooler during gorge outflow events, and our freezing rain lasts far later than downtown.

    One thing that would be really interesting is finding the rate at which local differences in weather stations change over the climatological record. I assume it would be greatest in periods of concentrated urbanization around the applicable weather stations.

    Thanks for all your hard work, and I look forward to your temperature findings and eventually your Oregon data!

  4. Thanks, Charlie! It’s been interesting learning and observing the local climatological differences here in the Portland area. The Gorge certainly has a huge influence with those strong easterly winds bringing inland colder winter air and warmer summer air. Here in Happy Valley we’re somewhat protected compared to you as the hills tend to block the strongest winds and sinking cold air. Of course, the coastal waters certainly have an impact as well from the other direction.

    Another thing I’m interested in finding out is why the Portland Airport (PDX), right on the Columbia River, experiences less precipitation, on average, than other parts of the Metro area (10% or more), even compared to the long-term downtown weather station(s). Local Annual Means for the 1981-2010 period are thus:

    PDX: 36.03″
    Downtown (KGW-TV): 42.85″
    Portland WFO: 43.47″
    Hillsboro AP: 39.90″
    Oregon City: 44.21″
    Troutdale: 46.97″
    Beaverton (Nature Park): 40.06″
    Vancouver AP: 39.14″
    Happy Valley: (no COOP station here but I continually record more, on average)
    Is there a valid difference or is there an issue with siting or instrumentation at PDX?

    One other thing that interests me here is why we get so much small hail! Prior to moving here, I had never heard or even thought that the Willamette would get much hail at all. In the 3 1/2 years that I’ve been observing here, I have actually observed 25 hail days and 37 separate events (4 events in 1 day and 3 events two other days). I know atmospheric lift is required and I’m assuming the coast, coastal mountains and the Cascades are a major player but I’d like to hear/see an expert explanation from a meteorologist such as yourself!

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