Archive for the ‘education’ Category

Henry Moore Sundial Sculpture

June 9, 2023

The Henry Moore Sundial Sculpture is located at Sundial Plaza alongside the Adler Planetarium & Astronomy Museum in Chicago, Illinois USA. (41° 52.006′ N latitude, 87° 36.426′ W longitude.)

Bowstring Equatorial Sundial

This type of sundial is a variety of the classic equatorial sundial, often referred to as a “bowstring equatorial sundial” because it looks somewhat similar to the “bow” in “bow & arrow.”

Remember, an equatorial sundial is a reduced model of the Earth. (More about that in a follow-up blog post.) A bowstring equatorial sundial is a “reduced equatorial sundial” — think of it as a kind of skeleton equatorial sundial.

The large red circle shown in the following annotated photo represents the Earth.

The dial plate (representing the equatorial plane) has been reduced to a semi-circular band that represents approximately one-half of the Earth’s Equator, This part of the sundial is referred to as the “equatorial band.” The equatorial band serves as the “time scale.”

Parts of a “bowstring equatorial sundial.”

The gnomon (or style) is a thin rod (the “bowstring”) representing the Earth’s axis of rotation.

The vertically-oriented “bow” represents a single meridian (line of longitude) and is referred to as the “meridian band.” The bowstring is connected to the bow at the equivalent of the Earth’s North and South Poles.

The bow is attached to a pedestal or “foot” (ped- is Latin for foot).

Time scale or time band, showing time of day.

The hour lines for the bowstring equatorial sundial are laid out on the inner surface of the equatorial band. Every hour is 1/24 of a day, or exactly 15 degrees wide. The shadow of the gnomon (or style), cast among the hour lines on the equatorial band, shows the time. The meridian band (“bow”) bisects the equatorial band (“time scale”); the 12 o’clock noon hour line is located on the time scale where the two bands intersect (since solar noon occurs when the Sun crosses the observer’s meridian). Facing north, morning times are located on the left side of the equatorial band; afternoon times are on the right.

In contrast to the classic equatorial sundial, the primary advantage of the bowstring equatorial sundial is that the style shadow is cast upon a single time scale all year long (regardless of whether the Sun is north or south of the Celestial Equator). Unlike the classic equatorial sundial, the bowstring equatorial sundial should work on the day of the equinoxes (although the author has not witnessed this firsthand).

Setting the Sundial

Similar to setting the correct time on an analog clock or wristwatch (by moving the hands of the timepiece into proper position), properly orienting an equatorial sundial will move the gnomon (or style) shadow into position so that the time scale displays the correct time of day.

The gnomon should be parallel to the Earth’s axis, inclined at an angle equal to the latitude of the observer.

41° 52.006′ N latitude.

North American Sundial Society member Fritz Stumpges is shown using a “SmartTool” to measure the angle of inclination of the gnomon (“bowstring”).

41.9 degree angle of inclination.

The dial plate/equatorial band should be parallel to the plane of the Earth’s Equator (perpendicular to the gnomon), inclined at an angle equal to the complement of the observer’s latitude — the angle that when added to the angle of the observer’s latitude equals a right angle in measure (90°). This angle is also known as the colatitude.

Colatitude 48.1 degrees.

Place the sundial on a horizontal surface; the top of the gnomon should point toward the Celestial North Pole (i.e., Polaris, the North Star). More simply, the sundial should be set so the 12 noon hour line is aligned with your local meridian.

Related Resources

Tech Tips

When I visited this sundial in 2005, I owned almost no photography gear. I used a one-time use film camera to shoot the photographs featured in this blog post. After I returned home, I had the film processed, digitized, and saved to a photo CD. The photo of the time scale/time band has a resolution of 3091 x 2048 pixels.

Copyright © 2023 Walter Sanford. All rights reserved.

“Magic Mylar” Moonlight

June 6, 2023

In a recent blog post entitled “Magic Mylar” diffusion material (plus Post Update), I shared the results my initial experimentation with a new material for light diffusion. Since then I added more mylar for multiple layers of diffusion and I must say I’m liking the results!

Toy dinosaur.

I used single point focus, positioned over the eye of the dinosaur. See why it’s necessary to use focus bracketing/focus stacking?

By now, some of you might be tired of looking at my toy dinosaur. That’s OK, he has thick skin [Get it?] and can withstand a little good natured griping. But seriously, he’s the perfect model for testing light diffusers due to the highly reflective plastic of which he is made.

“Magic Mylar” — where it all began

A friend and expert in macro photography kindly shared several sheets of diffusion material with which he is getting great results. The material is made of mylar plastic, matte on both sides.

Tunnel of Light II

I created a variation of my friend’s “Tunnel of Light.” Using my set-up, the mylar is almost perfectly round and surprisingly rigid.

Tunnel of Light (front/side view). Don’t mind the background clutter!

A single sheet of mylar is clamped to the white plastic top from a big jug of pretzels. The round top is ~4.5″ in diameter.

The jar top is held in place by a Wemberley The Plamp II. At a price point of $49.00, I don’t recommend buying a Plamp in order to make your “Tunnel of Light” — I just happened to have one on-hand and it does the job. I’m sure you can find a suitable clamp using off-the-shelf materials.

Tunnel of Light (rear/side view).

Three Impact ABS 3.75″ Small Spring Clamps (6-Pack) are used to hold the mylar in place. The orange “pivoting nylon pads for uneven surfaces” snap on/off, and as you might expect, tend to snap off at the worst times! For that reason, I DO NOT recommend these clamps. The price was right [$5.40] but you can’t count on them to perform in a pinch without fail. [See what I did there?]

I’m thinking about replacing the white plastic jar top with a PVC pipe fitting, the advantage being it would support the mylar while allowing a view of interchangeable backgrounds through the tunnel of light.

“Magic Mylar” everywhere …

How I got the shot

The toy dinosaur was placed inside the “Tunnel of Light II.” Two small LED light panels were used to light the scene for both setting exposure and focusing. Two external flash units were added for “pop.” All of the light sources were diffused with “Magic Mylar” plus one or more additional light diffusers such as the Altura flash modifier, shown in the preceding photo.

The goal is to use several light sources, set for low power, that add up to nice soft light that’s both bright and relatively free of specular highlights. Looks like I’m on the right track.

Copyright © 2023 Walter Sanford. All rights reserved.

Helicon Focus: Rendering in action (plus Post Update)

June 2, 2023

In my last blog post, I shared a composite image that was created using Helicon Focus to focus stack 99 JPG photos taken automatically using my Fujifilm X-T5 set for AUTO FOCUS BKT.

The following video demonstrates two strengths of Helicon Focus.

  1. It’s relatively simple to use. Creating a focus stacked composite image can be as easy as a two-step process: add source images to Helicon Focus by drag-and-drop; click the “Render” button.
  2. Rendering works quickly. For example, 99 photos focus stacked in ~50 seconds! (~00:08 s to ~00:58 s.)

The main window features two panels: the panel on the left shows the source images as the focus stack is created; the panel on the right shows the final output.

The right sidebar shows a list of filenames for the source images. When a filename in the list is highlighted, the corresponding image is displayed in the left panel of the main window.

Look closely at the final output, shown in the right panel in the main window. Notice the “ghost” artifact that’s visible near the tip of the toy dinosaur’s tail. Otherwise, the composite image looks perfect.

Click here to see a Screen Recording of the Rendering process.

I have no idea what caused the artifact. For whatever reason, some of the composite images I have created using Helicon Focus have one or more artifacts.

In contrast, every time I have used Fujifilm AUTO FOCUS BKT it has worked perfectly. (He said with fingers crossed.)

Related Resources

  • When dinosaurs attack! – This blog post shows the final image after I used Helicon Focus “Retouching” to fix the “ghost” artifact.
  • Focus bracketing and focus peaking – When I watched the real-time display of Helicon Focus rendering “Method C” for the first time, I was reminded of a blog post featuring two videos I created to demonstrate how focus peaking can show the way focus bracketing works. Those videos aren’t as steady and smooth as I’d like, but hey, not bad for a manual focus rail!

Post Update

When I tested the link to the video I noticed a problem with “flash dropout.” Two small LED panels and two external flash units were used to light the scene. Notice the flash on the right side of the subject didn’t fire in photo DSCF1214.JPG. That flash was a Godox MF12. Up until now, the MF12 flash has never failed to fire. For those who might be wondering, the Lithium Ion battery in the MF12 was fully charged before I started the focus bracket. I’ll watch it more closely to see whether reliability is an issue.

Copyright © 2023 Walter Sanford. All rights reserved.

Another combination sundial

May 26, 2023

The Hyatt Regency Jersey City Sundial, designed by Robert Adzema, is a combination “bowstring equatorial sundial,” “noon mark solar calendar,” and “horizontal sundial.”

Bowstring Equatorial Sundial

The Hyatt Regency Jersey City Sundial is a variety of the classic equatorial sundial, often referred to as a “bowstring equatorial sundial” because this type of sundial looks somewhat similar to a “bow & arrow.”

A bowstring equatorial sundial is actually a reduced model of the Earth: visualize a bare-bones globe for which all that remains is one-half of the Equator, one-half of a meridian (line of longitude), and the Earth’s axis of rotation.

  • The time band, also known as the “equatorial band,” represents one-half of the Equator. This stainless steel equatorial sundial features a wide “time band” showing hours from 6 a.m. to 6 p.m.
  • The vertically-oriented “bow” (as in “bow & arrow”) represents one-half of a single line of longitude, and is referred to as the “meridian band.”
  • The gnomon (or style) is a thin rod (the “bowstring”) representing the Earth’s axis of rotation. The bowstring is connected to the bow at the equivalent of the Earth’s North and South Poles.

Facing north-northeast.

Noon Mark Solar Calendar

At the noon hour is a “noon mark solar calendar” — an analemma illuminated by a ray of sunlight passing through an “aperture” mounted along the gnomon (rod), used to determine both the Equation of Time and the approximate day of the year.

Close-up, noon mark solar calendar.

Plaque explains how to tell time and date.

View of the underside of the “aperture.”

Horizontal Sundial

The pedestal supporting the time band and gnomon (rod and aperture) is designed to do double-duty as the gnomon (style) for a larger horizontal sundial that surrounds the equatorial sundial at ground level.

The hour lines on the dial face of the horizontal sundial are made of stainless steel bars embedded in concrete pavement.

The time of day is told by looking at either the shadow of the equatorial sundial gnomon (rod) on the time band, or the shadow of the horizontal sundial gnomon (style) on the dial face.

The following photos show the view from the west, facing due east (toward the New York City skyline, across the Hudson River). Notice the style of the triangular shaped gnomon is inclined at an angle equal to the latitude of the sundial (~40.7° N).

View from the west, facing due east.

Closer view, facing due east.

Related Resources

Tech Tips

When I visited this sundial in 2004, I owned almost no photography gear. I used a one-time use film camera to shoot the photographs featured in this blog post. After I returned home, I had the film processed, digitized, and saved to a photo CD. The last photo in the set has a resolution of 3072 x 2048 pixels.

Copyright © 2023 Walter Sanford. All rights reserved.

Combination sundial

May 23, 2023

The following set of annotated photos shows a combination sundial located at  Park Side Elementary School in Sebastopol, California USA. (Latitude and Longitude: 38° 24.005′ N 122° 49.724′ W.)

The unique design of this sundial is comprised of three types of dials: a “globe- or spherical sundial”; a small “bowstring equatorial sundial”; and part of a “gnomonic horizontal sundial” marked on the fan-shaped concrete pad in front of the dial pedestal.

Combination sundial located at Park Side Elementary School.

Globe-/Spherical Sundial

When the Sun shines on an object such as planet Earth, half of the object is in sunlight while the other half is in darkness. On Earth, we call this “day” and “night.”

The sundial is a cement globe of the Earth 28 inches in diameter inclined at 40 degrees, a bit off the site’s 38′ 20″ N latitude. The globe is oriented with the site longitude on the upper meridian so that shadows across the globe represent the true sun angle at that moment. Source Credit: NASS Sundial Registry No. 522.

The cement globe is oriented to show true day and night in Sebastopol.

The axis of the globe is inclined at an angle equal to the latitude of the dial, in this case ~40°. As a result, Sebastopal, CA is located at the top of the globe.

The meridian line (longitude line) that passes through Sebastopal is marked on the following annotated image. It is local solar noon when the Sun is directly over that meridian.

Globe-/Spherical Sundial.

Some globe-/spherical sundials — such as the Jefferson Spherical Sundial — feature a thin, movable meridian vane that can be used to show where it is local solar noon on Earth; this dial does not.

Bowstring Equatorial Sundial

A small “bowstring equatorial sundial” is located below the concrete globe.

In recent blog posts, I have described a bowstring equatorial sundial as a “reduced equatorial sundial.” Think of it as a kind of skeleton equatorial sundial.

For more information about how bowstring equatorial sundials work please refer to my blog post related to the Henry Moore Sundial Sculpture, archived on the Wayback Machine Internet Archive.

Bowstring Equatorial Sundial.

The “bowstring” on the Park Side ES dial was cut and sharpened to a point that serves as a nodus that indicates both the time of day and date of the year.

Gnomonic Horizontal Sundial

The concrete pad in front of the dial pedestal is marked to show part of a “gnomonic horizontal sundial.” I describe this type of sundial as a “reduced horizontal sundial.”

Please refer to Gnomonic horizontal sundials (plus Post Update) for more information about how this type of sundial works.

Gnomonic Horizontal Sundial.

The concrete pad is marked with both hour lines and date curves: the hour lines run north-south; the date curves run east-west.

A rod through the globe casts a shadow onto the north polar regions in the summer. Source Credit: NASS Sundial Registry No. 522.

The aforementioned “rod” is sharpened to a point (nodus) that indicates both the time of day and date of the year.

Notice there’s a badly worn analemma located along the meridian line (12 noon hour line). “Analemma.” There’s that word again. Look for more information about “date curves” and the “analemma” in a follow-up blog post.

What are the take-aways?

The clever design of the combination sundial at Park Side ES provides several ways for teachers and students at the school to make the Sun-Earth connection — I sincerely hope they take advantage of this excellent tool for teaching and learning located literally in their front yard!

Related Resources

Copyright © 2023 Walter Sanford. All rights reserved.

Gnomonic horizontal sundials (plus Post Update)

May 16, 2023

In my last blog post, I mentioned that relatively simple sundials such as “equatorial sundials” (including “bowstring equatorial sundials” as well as “globe- or spherical sundials,” distant cousins of equatorial sundials) and “gnomonic horizontal sundials” are better for making the Sun-Earth connection with K-12 students than more complex sundials. In this blog post, we will take a deeper look at “gnomonic horizontal sundials.”

Many, if not most people are familiar with the appearance of a horizontal sundial such as the one shown below. Typically, horizontal sundials have a triangle-shaped shadow caster mounted on a base plate.

Christ Church sundial | Alexandria, Virginia USA

In contrast, most people are unfamiliar with the names for the parts of a horizontal sundial.

The triangle-shaped shadow caster is known as the “gnomon.” The upper edge of the gnomon is the “style“; the “nodus” is a point located anywhere along the style, including the tip of the gnomon. The gnomon is mounted on a base called the “dial face/plate.”

Sunnymead Elementary School

A “gnomonic horizontal sundial” — such as the one located at Sunnymead Elementary School in Hillsborough, New Jersey USA — is a reduced horizontal sundial with a vertical gnomon.

In this case, “reduced” means all of the gnomon is removed except for the nodus — a single point along the style that is supported by a vertical pole. The nodus casts a shadow on the dial plate that indicates both the time of day and the date of the year.

The first two annotated images show the part of the gnomon that is removed, highlighted in translucent red.

Photo Credit: Chi-Lian Chiu.

Photo Credit: Chi-Lian Chiu.

Notice the hour lines radiate outward from the “dial center,” like the ribs on a Japanese fan, and the date curves run east-west. Time of day is read from the numbers above the upper date curve when Standard Time is in effect; read the numbers below the lower date curve when Daylight Saving Time is in effect.

As of 2007, Daylight Saving Time begins in the United States on the second Sunday in March and ends on the first Sunday in November. On the second Sunday in March, clocks are set ahead one hour at 2:00 a.m. local standard time (which becomes 3:00 a.m. local Daylight Saving Time). On the first Sunday in November, clocks are set back one hour at 2:00 a.m. local Daylight Saving Time (which becomes 1:00 a.m. local standard time). Source Credit: Daylight Saving Time, Astronomical Information Center, U.S. Naval Observatory.

The next annotated image shows the “analemma,” the odd looking figure eight located along the noon hour line (also known as the meridian line) on the dial face. In a nutshell, the analemma is used to correct Local Solar Time for Local Standard Time.

Photo Credit: Chi-Lian Chiu.

Look for more information about “date curves” and the “analemma” in a follow-up blog post.

Putting it all together, the last annotated image shows the nodus indicates the time of day is approximately 11:30 a.m. EDT on June 21.

NASS Sundial Registry No. 504 | Hillsborough, NJ | Sunnymead ES

The following resources are specifically related to the Sunnymead Elementary School gnomonic horizontal sundial.

  • Sample calculations for constructing the Sunnymead sundial, using a rounded value of 40.5° N for the latitude, and a gnomon height of 100 cm (1.0 m).
  • Here’s a link to a horizontal sundial template (PDF) for Sunnymead Elementary School, Hillsborough, New Jersey USA (40°31’53” N latitude). Instructions for assembly: Print the PDF; cut out the gnomon and dial plate; glue the gnomon to the dial plate.


EarthDials are also “gnomonic horizontal sundials.” EarthDials? Yep. The EarthDial Project began in 2004.

The EarthDial Project is a partnership between The Planetary Society (the world’s largest space interest group), Bill Nye, the Science Guy® and Nye Labs, and Professor Woody Sullivan at the University of Washington. Source Credit: The EarthDial Project, The Planetary Society (archived by the Wayback Machine Internet Archive).

The FCPS/NOVAC EarthDial (ED-7) was located in Fairfax County (Alexandria), Virginia at the Thomas Jefferson High School for Science and Technology (TJHSST) Planetarium.

ED-7 | 38° 49′ N latitude, 77° 12′ W longitude

The following resources are specifically related to EarthDials in general, and ED-7 in particular.

Related Resources

  • British Sundial Society Glossary (complete version)
  • SCSA Pole-to-Dial Converter Calculator – Use the SCSA “Pole-to-Dial Converter-Calculator” to convert any vertical pole (e.g., a flagpole, utility pole, etc.) into a fully functional sundial featuring “date curves” (declination lines) for the equinoxes and solstices.
  • Motions of the Sun Simulator – can be used for open-ended exploration of daily and annual motions of the Sun. Configure the simulator as shown in the following screen captures and click “start animation.”

Daily motion.

Annual motion.

Post Update (for MacOS) was used to create the following animation of screen captures from the “Motions of the Sun Simulator.”

Save a time-series of screen captures as PNG files; use Apple Preview to convert the PNGs to GIFs. Suggested GIFfun setting(s): Delay = 200 (or 500).

Copyright © 2023 Walter Sanford. All rights reserved.

My favorite types of sundials for K-12 education

May 12, 2023

There are two types of relatively simple sundials that I think are better for making the Sun-Earth connection with K-12 students than some of the more complex types of sundials.

Equatorial Sundials

Equatorial sundials” and “bowstring equatorial sundials” are by far my favorite types of sundials. (“Globe- or spherical sundials” are distant cousins of equatorial sundials.)

An “equatorial sundial” is actually a reduced model of the Earth, similar to a globe with its upper and lower halves removed. This design enables students to make the connection between time and time-keeping and the Earth’s rotation.

A “bowstring equatorial sundial” is a reduced equatorial sundial — you might think of it as a kind of skeleton equatorial sundial.

Gnomonic Horizontal Sundial

My second favorite type of sundial is known as a “gnomonic horizontal sundial.” Say what? Rest assured it’s easier to understand how this type of sundial works than its name suggests. For now let’s just say it’s a reduced horizontal sundial — very reduced!

Previews of coming attractions

Please stay tuned for upcoming blog posts related to my favorite types of sundials for K-12 education. The posts will focus upon sundials that are located at schools, including one at an elementary school in California, another at an elementary school in New Jersey, and one that was located at a high school in Virginia. Suggested student activities will be included with each post.

I have been able to recover some of the original photos of the aforementioned sundials, including many that are annotated. I’m still searching for similar blog posts that were published many years ago. Needless to say, I hope I’m able to recover those older blog posts. Otherwise, it will take a lot longer to write text for the new posts.

Related Resource: Sundials – a new permanent blog page.

Copyright © 2023 Walter Sanford. All rights reserved.

Interactive infrared weather satellite image

May 9, 2023

The AMS interactive infrared [weather] satellite image resulted from the collaboration between the American Meteorological Society (AMS) education initiatives and the Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison.

Infrared imagery is one of three types of weather satellite imagery. Black, white, and shades of gray are used to represent temperatures from the tops of clouds and the land & water surfaces on Earth. Black is the hottest temperature; white is the coldest. Sometimes this type of weather satellite imagery is color-enhanced for use by broadcast meteorologists.

The first image (shown below) is the non-interactive version of two screenshots from my Apple iPad mini 6. All three images in this blog post are from the same date and time.

08 May 2023 at 19:00 UTC (03:00 pm EDT).

As you move the cursor (red reticle) over the interactive image, the temperature (in degrees Celsius) and location (latitude and longitude) are listed.

The first screenshot shows the cursor (red reticle) over a dark area located somewhere along the Florida peninsula where the temperature is 27°C (78.8°F or 299.2 K). At such a warm temperature, we are almost certainly looking at land rather than water.

Cursor (red reticle) located somewhere along the Florida peninsula.

The the second screenshot shows the cursor (red reticle) over a bright white area located somewhere in/above Alabama where the temperature is -55°C (-67°F or ~218.2 K)! At such a cold temperature, we can be certain we are looking at the tops of very high clouds. This could indicate hazardous weather is occurring at the Earth’s surface.

Cursor (red reticle) located somewhere over Alabama.

Science can and should be fun. Have fun exploring using the AMS interactive infrared [weather] satellite image!

Related Resources

Tech Tips

The interactive infrared [weather] satellite image was tested using my Apple iPad mini 2 and 6, Apple MacBook Air (13″, M1, 2020), and Apple iMac desktop computer (vintage 2009) and is compatible with all of those devices.

Did you notice both the non-interactive and interactive infrared images are GIF files?

The [GIF] format supports up to 8 bits per pixel for each image, allowing a single image to reference its own palette of up to 256 different colors chosen from the 24-bit RGB color space. Source Credit: GIF, by Wikipedia.

In the old days before the AMS interactive infrared [weather] satellite image, we would use a scientific image-processing tool such a NIH Image (now ImageJ) to infer temperature from pixel values (0-255). Labor intensive, but it was fun!

Copyright © 2023 Walter Sanford. All rights reserved.

Sundials – a new permanent blog page

May 5, 2023

In my last blog post I mentioned that I was fortunate to participate in a summer workshop for K-12 teachers at the National Center for Atmospheric Research, located in Boulder, Colorado USA.

We stayed in student housing at the University of Colorado Boulder. During a walk around the beautiful campus, I discovered a large sundial near the Norlin Library. I’d never seen a sundial quite like it, so I bought a one-time use film camera and shot some photographs.

John Garrey Tippit Memorial Sundial, Boulder, Colorado USA.

After I returned home, I learned the John Garrey Tippit Memorial Sundial is an equatorial sundial. My discovery of the sundial in Boulder, CO led to a long period in my life when I was really into sundials and created a lot of Web pages focused on informal education about sundials.

Unfortunately, most of those resources were lost when my personal Web server went dark after the sudden death of a dear friend. Fortunately, many of those resources are archived in the “Wayback Machine Internet Archive.”

I just started what will be a long work-in-progress to recover those resources and add them to “Sundials,” a new permanent page in my blog. At the moment, the “Sundials” page is a placeholder that will be updated frequently during the coming months. I invite you to check out the resources currently listed on the page — there are lots of links to explore now, with more in the pipeline.

Related Resources

Tech Tips

When I visited this sundial in 2000, I owned almost no photography gear. I used a one-time use film camera to shoot the photograph featured in this blog post. After I returned home, I had the film processed, digitized, and saved to a photo CD. The original version of the photo (shown above) has a resolution of 2048 x 3072 pixels.

Copyright © 2023 Walter Sanford. All rights reserved.


Thunderstorms, mesocyclones, and tornadoes. Oh my!

April 25, 2023

As a weather enthusiast, RadarScope is my go-to weather app for tracking the approach and passing of weather systems such as the line of strong thunderstorms that affected the Washington, D.C. metropolitan region on Saturday, 22 April 2023.

Animated GIF created by RadarScope app. (11:44 AM to 11:58 AM)

The following annotated screenshot shows a few basic buttons; their function is described below the graphic.

My location, radar sites, and warnings. (12:01 PM)

  1. My location. (See blue reticle, center screen.)
  2. Radar sites. (KWLX, located in Sterling, Virginia, is the National Weather Service radar site nearest to my location.
  3. Warnings. (Two warnings were in effect when this screenshot was captured.)

A fly-out panel appears when you click on the Warnings button. As you can see, there were two Severe Thunderstorm Warnings in effect at the time of the screenshot. If you click on one of the warnings then RadarScope automatically takes you to a zoomed-in view of the warning area. Click on the button for “My location” to return to your home location.

Warnings. (11:58 AM)

Tornado Warning

Soon afterward, a Tornado Warning was issued for Culpeper- and Madison Counties in Virginia, as indicated by the red polygon. Notice the red polygon is nested inside a yellow polygon that outlines an area where a Severe Thunderstorm Warning was issued.

Tornado Warning (red polygon). (12:30 PM)

Click on the red polygon for more information about the Tornado Warning.

Tornado Warning (information). (12:30 PM)

The next screenshot shows the “Super-Res Reflectivity” radar product, zoomed in on the Tornado Warning area. With a lot of imagination, you can almost see something that looks a little like the classic “hook echo” associated with tornadoes. Almost, but not quite.

Super-Res Reflectivity. (12:30 PM)

Time to switch to the Storm Relative Velocity radar product, shown below. This is where Doppler weather radar really shines. Greens indicate radar echoes moving toward the KWLX radar site; reds indicate radar echoes moving away from the radar site (like brake lights on a car driving away from you).

The following image shows the thunderstorm cell is rotating counterclockwise — this is known as a mesocyclone and is the reason for the Tornado Warning.

Storm Relative Velocity. (12:27 PM)

Within the broader area of counterclockwise circulation there is a tighter area of greens and reds, as shown more clearly in the Super-Res Storm Relative Velocity radar product.

Super-Res Storm Relative Velocity. (12:32 PM)

It’s important to note that the orientation of side-by-side greens and reds typical of rotating thunderstorm cells varies depending upon the location of the storm cell relative to the weather radar site. In the example shown above the greens are on the right and the reds are on the left because the warning area is located to the southwest of KWLX. In contrast, if the warning area were located to the northeast of the radar site, then the reds would be on the right and the greens on the left.

As it turns out, there were’nt any official Tornado Reports for Virginia. Later the same day, a small F0 tornado touched down briefly in Montgomery County, Maryland.

Related Resources

The following resources from the National Weather Service provide excellent background information about Doppler weather radar.

More RadarScope-specific resources are available from the creators of the app.

Copyright © 2023 Walter Sanford. All rights reserved.

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