Another combination sundial

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

• More photos by North American Sundial Society members, Janet Jenkins and Mac Oglesby.
• Sundial frames skyline, by Michael Lee, amateur photographer.
• “Sister sundial” located at the Suffern Free Library, Suffern, NY. NASS Sundial Registry No. 411.

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

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

• NASS Sundial Registry No. 522
• Jefferson Spherical Sundial
• Henry Moore Sundial Sculpture
• Gnomonic horizontal sundials (plus Post Update)

Copyright © 2023 Walter Sanford. All rights reserved.

“Magic Mylar” diffusion material (plus Post Update)

So there I was, working on the next epic sundial-related blog post, when I realized two things: 1) The post needs to be too long to finish before Friday; and 2) The topic probably needs to be covered in a series of posts rather than one long post. Regrettable, because WordPress site statistics shows the sundial-related blog posts are popular with readers of my blog. Anyway, please stay tuned — I hope to finish the next post by Tuesday, 23 May 2023.

In the meantime, I decided to give you a quick update on my never-ending quest for good light diffusers.

“Magic Mylar”

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.

I should have taken some shots of the same subject with- and without diffused light, but I didn’t have time to do a proper test of the new diffusion material. Qualitatively speaking, I like the look and feel of the test shots in diffused light although I concede there are specular highlights that might require either double- or triple layers of diffusion, as recommended by my friend.

Here are a few shots from a quick studio session. The subject is a highly reflective plastic toy dinosaur. I used a small LED light panel (with added diffusion to supplement the built-in diffuser on the LED) and a Godox TT685C plus a small Altura flash modifier to light the scene. The output from the LED light panel is assumed to be constant, while I slightly increased the distance between the subject and the TT685C from the first to last shot. I estimate the front of the Altura was no more than say 5″ to 7″ from the subject. My assumption is the farther the TT685 was from the subject, the more the LED was the dominant light source.

Closest.

Mid-range.

Farthest.

Where can I get some “Magic Mylar?”

I don’t know whether the results of my test are so impressive that you would like to order some of the “Magic Mylar” STAT. The following image shows the label from a big roll of the mylar.

Comstoc Ink Jet Plotter Media | 3 MIL Double Matte

It’s unclear whether this specific product is discontinued. One source says the art supplier Dick Blick sells sheets of similar material. I will do some research and report my findings, if any. Please comment on this post if you find a source before I do.

Tech Tips

Disclaimer: The following photos show no evidence that I’m actually a fairly good photographer.

Here are two quick-and-dirty shots (taken with my Apple iPad mini 6) that show how I used the mylar to diffuse light from a Sunpak LED 160 light panel. I simply taped an ~8.5″ x 11″ sheet of the mylar to the LED. The first photo shows the LED off; the second shows the LED on.

Sunpak LED 160 light panel. (Off.)

Sunpak LED 160 light panel. (On.)

Looks like I didn’t place the subject at the center of the circle of light. In my defense, the circle of light wasn’t as apparent to me as it is in the photo. Hey, I told you it was a quick-and-dirty test!

More later after further testing.

Post Update

I’m a scientist. No really, I am. I know it’s easier to analyze the results of an experiment that has only one variable. My last experiment included another variable that made it impossible to objectively evaluate the quality of light diffused by adding “Magic Mylar” to a small LED panel.

So I ditched the Godox TT685C external flash unit and photographed the subject using only diffused light from the LED panel.

All photos were taken using my Apple iPad mini 2. Same subject, same “stage.” Notice the subject is closer to the center of the circle of light on the background.

Next I moved the iPad closer to the subject for a better look at the specular highlights, if any.

Finally, here’s the same shot cropped for a closer look at the subject. The white balance is way off, but hey, it’s an iPad camera photo! Otherwise the light has what I would describe as a “warm glow” with fewer glaring specular highlights than the shots from the first test. Maybe now you can see why I am excited by the results of my experimentation with the new mylar diffusion material.

Perhaps you’re wondering, “Why was it necessary to use an external flash unit when you took the first test shots?” I used my Fujifilm X-T5 and 80mm macro lens to take those shots. I wanted to use the same settings that I’ve been using for studio macro focus bracketing. Problem is, the photos were underexposed. Since I didn’t want to change the camera/lens settings, my only option was to add more light. And now you know the rest of the story.

Copyright © 2023 Walter Sanford. All rights reserved.

Gnomonic horizontal sundials (plus Post Update)

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.

EarthDial(s)

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.

• Sample calculations for constructing ED-7, using a rounded value of 39° N for the latitude, and a gnomon height of 10 cm.
• FCPS/NOVAC EarthDial Glossary
• How to Read the FCPS/NOVAC EarthDial
• Two motions — the rotation of the Earth around its axis, and the revolution of the Earth around the Sun — cause daily- and annual cycles in the Sun’s apparent path across the sky that can be observed indirectly using a horizontal sundial such as the FCPS/NOVAC EarthDial (ED-7). For details, see Observing Daily & Annual Cycles of the Sun.
• Earth’s Seasons – Equinoxes and Solstices, A One-Year Time Series of One-Day Time-Lapse Animations
• SCSA EarthDial Activity (teacher’s answer key available upon request)

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

GIFfun.app (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

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

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

• AMS interactive infrared [weather] satellite image – the American Meteorological Society (AMS) and the Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison.
• Weather Calculators, including temperature conversion – a page of interactive calculators that still work, rescued from the Wayback Machine Internet Archive.
• UTC/EST/EDT – a table listing equivalent times among Universal Time Coordinated (UTC), Eastern Standard Time (EST), and Eastern Daylight Time (EDT).
• AMS Interactive Infrared Weather Satellite Image – Making the Invisible Visible. Another resource rescued from the Wayback Machine Internet Archive. I created this activity as an extra credit opportunity for my Grade 8 Physical Science students when we were studying energy and energy transformations. In retrospect the activity is probably too long to use “as is,” but it might serve as a data bank of questions that teachers could use to create their own version of the activity. For non-educators, the activity questions can help to guide your thinking about what you can tell from the interactive infrared imagery.

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

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

• The John Garrey Tippit Memorial Sundial
• Sundial Plaza | University Libraries | University of Colorado Boulder
• North American Sundial Society Sundial Registry
• The Colorado Equatorial Sundial – NASA/ADS
• Diptics: University of Colorado Boulder

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.

 

Post update: What is it?

The mystery object shown in my last blog post is one of my prized possessions — an enamel lapel pin from the National Oceanographic and Atmospheric Administration (NOAA).

NOAA enamel lapel pin.

The About Me permanent page on my blog, linked from the top of the “Pages” section in the right sidebar, features the following quote.

For more than a decade, I was actively involved with several education outreach initiatives of the American Meteorological Society. Source Credit: About Me page.

As a result of generous funding from the National Science Foundation (NSF), the National Weather Service NWS), and the American Meteorological Society (AMS), I was able to participate in summer workshops for K-12 teachers at many NOAA/NWS facilities such as the National Weather Service Training Center, the NOAA/NWS Storm Prediction Center, the NOAA National Severe Storms Laboratory, the Cooperative Institute for Meteorological Satellite Studies, and the National Center for Atmospheric Research, to name a few. There I received training that enabled me to serve as an AMS Atmospheric Resource Agent for the Commonwealth of Virginia.

I don’t remember exactly when and where I was given the NOAA lapel pin but it’s a treasured memento of a period in my life when I learned a lot from some of the top experts in NOAA, and I experienced significant professional growth.

Copyright © 2023 Walter Sanford. All rights reserved.

What is it?

Ladies and gentlemen, children of all ages. It’s time for another exciting episode of “What is it?”

I will reveal that both photos are “one offs” (not focus stacked composite images) that show different parts of the same object, photographed with a 4x microscope objective mounted on my Fujifilm X-T3.

If you think you know what is shown in these photos, then please leave a comment. The answer will be revealed in a post update.

Copyright © 2023 Walter Sanford. All rights reserved.

Thunderstorms, mesocyclones, and tornadoes. Oh my!

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.

• How radar works
• Composite Reflectivity
• Storm Relative Velocity

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

• User’s Guide
• Information Articles
• RadarScope Blog

Copyright © 2023 Walter Sanford. All rights reserved.