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Weather Chart FAQs

What's the past and future for this site?
How do I install this?
How do I make a chart?
What's new?
What are the data sources?
How do I get the freshest data?
What is the "24h" checkbox?
What is the "RA" checkbox?
What is all that stuff in the URL?
Why does a two-day chart has fewer points than a one-day chart.
What data is shown in the table?
How should I interpret the time axis?
When plotting wind speed, what is the secondary-y axis?
Why are there two wind options, Wind (0-36) and Wind (0-40)?
Why do some charts grow taller?
What is the delta-P charting option (Columbia Basin sites)?
How is the direction data aggregated, especially when the wind is out of the north?
What kind of software is used to make this all work?
What are the little numbers, in the upper left hand corner, to the right of the home link?


What's the past and future for this site?  top

For nearly 20 years Waconia has been hosted by PNNL or Gustavus. With my retirement comes an end to this free hosting for the database and the server-sided scripting that was behind the charting page. (If you would like to host Waconia inside your local network, here is the installation guide.)

I plan to make a new charting page that will have a user interface built around Google Charts and will query weather data stored in Google's Fusion Tables. All client sided; all without hosting costs.

The gleaner scripts will continue to run, but will feed to the Google Fusion tables, and be hosted on a little Intel NUC existing quietly on my home network.

The scripts will also feed a local database for my at-home version of the old Waconia. So the old site lives on in the comfort of my basement. The current sample charts are produced by posting to this at-home Waconia and then sending them to my free internet hosting service using FTP (yes, another Python script...).

How do I install this? top

If you would like to try running the gleaners and the Waconia web site on your local network, here is the installation guide.

How do I make a chart?  top

First you'll need to install some stuff to support the gleaners and the rosy.asp charting page. Then come back here...

Use the five drop-down lists to control what data is presented. Click the "Update" button to refresh the plot. The drop-down lists set the following parameters (from left to right):

The "<" and ">" buttons (to the right of the "Days" control) step the chart backward ("<") or forward (">") in time. The size of the step is determined by the value of the "Days" control. The ">" button (to the right of the stations select list) acts to step through the stations list.

Select the "24h" checkbox to display single-day data in the 24-hour mode. When viewing today's data, this mode will present the most recent 24 hours of readings, including some of yesterday's data.

Select the "Timer" checkbox to put the chart into auto-update mode.

A brief help tip for each control can be viewed by letting the mouse cursor remain (still) on it for about one second.

What's new?  top

What are the data sources?  top

Data is collected from four sources:

How do I get the freshest data?  top

You can set Waconia to auto-refresh every 5 minutes by selecting the "Timer" checkbox. This feature automatically syncs your browser to refresh 10 seconds after the 5-minute updates on the Whitebear server and insures that you have the freshest data available. Another useful indicator is the difference (in minutes) between the current time and the time stamp on the latest data record. This is shown in the last set of parentheses in the string of numbers to the right of the home link.

What is the "24h" checkbox?  top

Selecting this option enables the 24-hour mode for the 1-day plot. This displays the most recent 24 hours of data including readings from yesterday. The effect of this mode is only apparent when selecting the most recent day in the day list.

There are two black vertical lines that indicate the time of the most recent reading (left line) and the current time (right line). The distance between these two lines indicates the age of the most recent data. Note that this "age" is also indicated by the minutes in parentheses () just to right of the server time. Readings from yesterday are displayed to the right of the most-recent-reading line. Yesterday's data is indicated with thinner trace lines and the direction markers are gray.

Why do this? First, it gives you a complete diurnal cycle in one consistant view. Also, it presents a contrast between today's latest reading and what was happening at that same time yesterday. The two vertical lines give a quick visual indication of the lag in the most recent reading. You can think of the left-vertical line as painting over yesterday's data as the day progresses (as it slowly moves from left to right throughout the day).

What is the "RA" checkbox?  top

Selecting this option smooths the data with a 3-point running average. This feature uses a special technique to deal with near-North wind-direction data. It converts individual wind-direction observations into x and y components, averages the components, then calculates the wind direction from the component averages.

What is all that stuff in the URL (web address)?  top

The URL (web page address) is now parameterized. This allows you to e-mail a link for a particular day and location, or to save a shortcut that will give you the latest data at your favorite site.

To create a URL that gives the latest data, just trim the URL back to the sensor parameter. For example, here is a URL string for the latest wind data for the Faribault, MN airport:

rosy.asp?region=MN&jS=T&hT=T&pT=F&Location=KFBL&Sensor=Wind40

Why does a two-day chart has fewer points than a one-day chart?  top

Charts of two or more days of data will show hourly aggregates of the raw 15-minute data. For example,  if the HMS web site presents data at 14:00, 14:15, 14:30, and 14:45, the chart will represent those four points with a single aggregate point at 2 p.m. PST (14/24 = 0.583 day fraction).

What data is shown in the table? top

The table at the top shows today's latest reading for the selected site. This is a raw fifteen minute reading and is equivalent to the current data shown at the source site. It is also equivalent to the last point on a one-day chart.

How should I interpret the time axis? top

Here are a few things to remember when interpreting the time axis on the chart:

When plotting wind speed, what is the secondary-y axis? top

The y-axis on the right side of the plot is for wind direction. This scale is used to determine the values of the square point markers. Also see the discussion in the next FAQ.

Why are there two wind options, Wind (0-36) and Wind (0-40)? top

Both options provide wind direction and wind speed information. The direction is defined by the secondary y-axis on the right side of the chart.

The 0-40 option is the most used wind direction charting option. In this case the direction data is scaled so that the compass points correspond with the 5 mph grid lines on the chart.

The 0-36 option is a good choice for people that are comfortable thinking of direction in terms of degrees (0-360). 180 degrees on the right axis corresponds with 18 mph on the left axis; a scaling factor of 1/10. One frequent user, a sailplane pilot, prefers this wind charting option.

In either case, the secondary-y axis makes it straightforward to interpret the direction data.

For the curious, some history and development details: The chart-image module used in Waconia (ASPChart) unfortunately does not have an option for a secondary y-axis. The secondary axis that you currently see is actually a hand-built static image (a transparent gif), overlaid on the chart. Through the magic of HTML, CSS, and JavaScript, the two images are revealed simultaneously to the give the appearance of a single image. In earlier releases of Waconia, a simple compromise (using no secondary axis and no overlay image) was implemented, through which the wind-direction data was scaled by the ratio 40/360 (for the 0-40 option) or 1/10 (for the 0-36 option). Without a secondary axis, the user was left to interpret the direction points using only the speed axis and the clues in the image legend. Thanks to the image overlay in the current release, the legend has now been simplified; it's way better.

Why do some charts grow taller ?  top

There is an image scaling feature for the wind, temperature and delta-p charts.  

What is the delta-P charting option (Columbia Basin sites)?  top

This option plots differential pressures between four sites: Portland, The Dalles, Roosevelt, and Richland. The differentials are defined in the chart legend. For example, the trace named "Portland - The Dalles" is calculated as the pressure difference between Portland and TheDalles (using sea-level corrected pressures).

Pressure differentials can be useful in predicting wind at Roosevelt WA. Pressure gradients often move from west to east so a good differential between Portland and The Dalles can be a good indicator of wind to come at Rosy. Differentials over about 0.05 inches Hg generally indicate sailable wind.

How is the direction data aggregated, especially when the wind is out of the north?  top

For charts of two or more days, I have not implemented a method for aggregating near-North direction data (that is, directions that are bouncing back and forth between slightly greater than 0 and slightly less than 360). So I simply use the average of the 4 direction readings. This method can produce an erroneous result of approximately 180 (or 20 using Waconia direction notation) if the direction is near North (example:  (3 + 359 + 2 + 358)/ 4 = 180.5).

In the one-day charts this is not an issue because there is no aggregation of the HMS 15-minute data.

Note that the RA feature properly performs a running average on direction data for one-day charts.

What kind of software is used to make this all work?  top

ASP (Active Server Pages), Perl, Python, JavaScript, and VBScript  are the main tools. For a little more detail, take a look at the "about the technology behind the viewer" page and the installation page.

What are the little numbers in the upper left hand corner, to the right of the home link?  top

There are three categories of information in this string of numbers:

  1. The first set indicates the number of image requests in the last 24 hours (1d = one day) and the last 72 hours (3d = 3 days).
  2. And just to the right of these numbers is the time on the server when the page was generated.
  3. And farthest to the right, in parentheses, is the difference in minutes between the server time and the time stamp of the latest data record.

 

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