How to make your own cheap weather station


Though the prices for personal weather station have dramatically dropped (around $100) over the past few years, I decided to work on making my own. The primary measurement I wanted was temperature given this is the specific one that could be dramatically different from my neighbors (or neighborhood weather station) given the many unique microclimates your yard can have.

Step 1: Create an account and weather station at Weather Underground. This will allow you a place to view your weather station results as well as a permanent storage location for your data. After you have created your account it is really easy to create a weather station after clicking this link you just need to enter some basic information such as address and time zone click “Submit” and you have yourself a weather station. Now this is not very exciting unless data is being updated so we will look at this next.

image Step 2: Get some data. Hear is a point where you can go all out with every weather measurement sensor imaginable, though if this was your intent I would recommend saving some money and getting a personal weather station, but in my case all I really wanted to track was the outdoor temperature. To get this temperature I used a DirectTemp USB waterproof temperature probe from Quality Thermistor, Inc. All you need to do is plug this into an open USB port and with some simple serial communication you can start getting temperature results. This can easily be done using a language like C# with just a few lines of code:

SerialPort serialPort = new SerialPort(“COM5”, 9600); serialPort.Open(); serialPort.WriteLine(“2”); double responseValue = Convert.ToDouble(serialPort.ReadLine()); serialPort.Close();

You could also use something similar to my homemade waterproof digital thermometer and an arduino to get your outside temperature.

Step 3: Log your results. WeatherUnderground makes submitting data to them very easy. All that is required is a specially formatted query string request which you could do in any internet browser…though updating this manually every 5 minutes would be very tedious this is how can do this also using C#. All that is required is to replace the “ID” with your weather station created in Step 1 and your password used when you created your account.

string submitUrl = “[password]&”; submitUrl += “dateutc=” + DateTime.UtcNow.ToString(“yyyy-MM-dd hh:mm:ss”) + “&”; submitUrl += “tempf=” + GetOutdoorTemp(); // Using code above WebClient webClient = new WebCLient(); webClient.DownloadString(submitUrl);

Now by calling the above code every 5 minutes using an infinite loop with some delay you can now log your temperature results and have current and historical data to have some better info to better guess your first/last frost dates or when it is safe to bring out your tender seedlings you are growing indoors.

Step 4 (optional): Leverage external weather data. As you may have noticed my weather station has more weather data than just temperature. I did this by leveraging (nicer word than stealing) some data from a weather station at a school in my neighborhood. Now this is not quite as accurate as if I was getting this information from my backyard…it is pretty safe to assume that the humidity, rain, and wind velocity and direction should be pretty much in the same ballpark. The process is pretty simple here where I extract this from a request to the external weather station and include these into my submission, which you can see in the code sample below.

   1: using System;

   2: using System.IO.Ports;

   3: using System.Xml;

   4: using System.Net;


   6: namespace WeatherStation

   7: {

   8:     class Program

   9:     {

  10:         private static WebClient webClient = new WebClient();


  12:         static void Main(string[] args)

  13:         {

  14:             while (true)

  15:             {

  16:                 SubmitWeatherInfo();


  18:                 System.Threading.Thread.Sleep(300000);

  19:             }

  20:         }


  22:         public static void SubmitWeatherInfo()

  23:         {

  24:                 string submitUrl = "[password]&";

  25:                 submitUrl += "dateutc=" + DateTime.UtcNow.ToString("yyyy-MM-dd hh:mm:ss") + "&";

  26:                 submitUrl += "tempf=" + GetOutdoorTemp() + "&";

  27:                 submitUrl += GetExternalWeatherData();


  29:                 webClient.DownloadString(submitUrl);

  30:         }


  32:         private static double GetOutdoorTemp()

  33:         {

  34:             SerialPort serialPort = new SerialPort("COM5", 9600);

  35:             serialPort.Open();

  36:             serialPort.WriteLine("2");

  37:             double responseValue = Convert.ToDouble(serialPort.ReadLine());


  39:             serialPort.Close();


  41:             return CelsiusToFahrenheit(responseValue);

  42:         }


  44:         public static double CelsiusToFahrenheit(double temperatureCelsius)

  45:         {

  46:             return (temperatureCelsius * 9 / 5) + 32;

  47:         }



  50:         private static string GetExternalWeatherData()

  51:         {

  52:             string externalWeatherStation = "";

  53:             externalWeatherStation += "ID=[ExternalWeatherStationId]";


  55:             XmlDocument xmlDoc = new XmlDocument();

  56:             xmlDoc.LoadXml(webClient.DownloadString(externalWeatherStation));


  58:             string externalData = "&winddir=" + xmlDoc.SelectSingleNode("//wind_degrees").InnerText;

  59:             externalData += "&windspeedmph=" + xmlDoc.SelectSingleNode("//wind_mph").InnerText;

  60:             externalData += "&windgustmph=" + xmlDoc.SelectSingleNode("//wind_gust_mph").InnerText;

  61:             externalData += "&baromin=" + xmlDoc.SelectSingleNode("//pressure_in").InnerText;

  62:             externalData += "&humidity=" + xmlDoc.SelectSingleNode("//relative_humidity").InnerText;

  63:             externalData += "&dewptf=" + xmlDoc.SelectSingleNode("//dewpoint_f").InnerText;

  64:             externalData += "&rainin=" + xmlDoc.SelectSingleNode("//precip_1hr_in").InnerText;

  65:             externalData += "&dailyrainin=" + xmlDoc.SelectSingleNode("//precip_today_in").InnerText;


  67:             return externalData;

  68:         }

  69:     }

  70: }

How to determine your own personalized last frost date from local weather station

There was a discussion in comments on my previous average last frost post on how to determine an accurate last frost.  A great point was made by Daphne where every garden can have its own microclimate so the date you find online or in a book could be many weeks off for your microclimate in neighborhood.

To be able to predict your last frost date accurately it takes some history, if you have lived in your current residence and happened been capturing your temperature data accurately by memory or paper you may the information to predict your last frost date.

For people that are relatively new to their residence, like myself, I felt there I had very little information to determine an accurate prediction of my last frost date.  This was until I remembered Weather Underground which logs results of schools or private individual that register their weather stations.

After a quick search I was able to find someone who had a weather station in my neighborhood.  After doing a custom query of the full range of the of the weather station, which in my case was a little over 4 years, I had all the information I needed.  By carefully adding a horizontal line at freezing using a graphics program (Microsoft Paint) I could easily see where the low temperature dipped below the freezing mark.


From a quick glance at the data it appears that the first week of April is a pretty safe date for past few years.  But if you look the the irregular low temperatures we have had this month this might be harder than I thought.

Now of course your neighbor may a different microclimate than you, but should get you in a better ballpark than the generic number you find fro your city.  You could always spend $500-$1000 on your own weather station to get some better accuracy, but for me seems close enough to me.  Though the weather station would be a really cool gadget to have.

Last frost dates are not the same

It came to my attention it seemed every time I see my average last frost date it comes up as a different date.

Average Frost Date (Seattle, WA) Location
3/10 The Old Farmer’s Almanac
4/20 Victory Seed Company
3/22 Ed Hume’s Seeds
4/15 USDA Zones
5/14 USA Gardener
3/25 Clyde’s Garden Planner
3/24 Garden Web








Now the humorous part of this is I didn’t go out trying to find as many non-matching dates as I could, these came in order from my Google query for “last frost dates”.

Under conventional wisdom, this number should be simply an average of the last frost dates for the past 30-40 years to give you about a 50% chance of avoiding frost given past history.  So it seems really strange why these numbers vary so much.

Then I came across U.S. Climate Normals this site includes no only the dates but the probability of them being true.  So if you are a betting man/woman (or just impatient) you can press your luck and plant with variable odds.

For my area (Seattle, WA) I have the following options:

Probability Level
Threshold (°F) 90% 50% 10%
36 °F Mar 27 Apr 11 May 18
32 °F Feb 13 Mar 10 Apr 22
28 °F Jan 01 Feb 25 Mar 20
From the information above, only The Farmer’s Almanac had the number I was really expecting.  But given the information above and how late frosts have “bitten” me in the past I think I will give myself a couple extra weeks and plan on my last frost being Mar 24th to hopefully avoid and hard frosts for tender seedlings.
%d bloggers like this: