Another Derecho, Anyone?

A derecho is defined as " a storm complex traveling more than 400 miles, producing damaging wind gusts of 58 mph (60 knots) or stronger along its path. Some gusts must exceed 75 mph. The width of the damage path must be at 60 miles wide."

The Storm Prediction Center (SPC) posted a Day 2 Enhanced Risk (Level 3 of 5) for central Iowa to eastern Indiana at 12:30 pm on Sunday, July 14, 2024. This prediction of a large swath of severe weather would indicate a confidence for a derecho-like event. 

11:31 am CDT, Monday, July 15, 2024. The SPC upgrades its outlook to a Moderate Risk (Level 4 of 5), a 10% hatched tornado probability stretching from eastern Iowa to northeast Indiana (above center), and a high probability of wind (above right). 

1:59 pm. Mesoscale 1630 is posted, outlining a 95% probability of the issuance of a severe thunderstorm watch in an area stretching from western Iowa to western Indiana. The actual watch would be issued a short time later.

4:14 pm CDT. Now at my stationary spotting location on Sutton Road (right) at Central City Road (background, left), west of Central City, Iowa in Linn County. A severe-warned storm is approaching from the west (left and left center in image). 

4:26 pm. Looking northeast at the underside of an enormous anvil cloud, ahead of the approaching severe-warned thunderstorm. My spotting vehicle, equipped with amateur radio and weather radio, is seen in the foreground. 

Radarscope image for 4:36 pm CDT, showing the approaching storm beginning to become more linear and bowing out just west of my location. 

4:50 pm. Tornado warning is issued, and sirens sound. Area that is tornado warned is toward the left in the image.

4:52 pm. Radarscope dual pane image, showing the tornado warning polygon, with reflectivity at top, and velocity at bottom.

5:23 pm CDT. Cell phone Emergency Alert sounds, valid until 6:00 pm. I decide to move back south toward Cedar Rapids, where a "tail-end Charlie" storm feature is approaching, which seems more "favorable" for significant severe weather.

5:28 pm Radarscope dual pane image, with a hot spot to my southwest. Now at my new stationary spotting location on North Marion Road, about a tenth-mile north of County Home Road, north of Marion, Iowa in Linn County.

5:31 pm CDT. Looking southwest toward tornado warned area, with the sky becoming very dark in a short amount of time. Nikon Z6ii camera.

5:31 pm. Go Pro Hero 4 Silver video frame capture. Lightning bolt. With the energy of the storm increasing, many positive CG lightning strikes were occurring in this area, including one that struck just 50 yards from this location, sending sparks flying from a telephone pole!

5:33 pm. Tornado warning polygon and my spotting location (blue target icon). 

5:35 pm. Cell phone Emergency Alert for a tornado warning sounds again. 

5:51 pm. Go Pro video frame capture showing estimated 70 mph winds and rain slashing my windshield. I reported this situation to the Linn County Amateur Radio Emergency Services (ARES) network via amateur radio. 

5:55 pm. Emergency Alert sounds again, warning of a severe thunderstorm warning with possible 80 mph winds. Thankfully my spotting vicinity was spared from significant wind or flood damage that impacted other areas, including a 97 mph wind gust reported near Holy Cross in Dubuque County. Some three tornado reports were also confirmed in the state from this storm that was later confirmed as a derecho.

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Sped-up Fireworks Display Before Storm

An annual private party fireworks display in rural Shueyville, Iowa on Independence Day started at the usual time but had to be sped up and shortened as a strong storm was pushing into the area and was just minutes away with its drenching rain. The above six images were captured from 10:01-10:02 pm on Thursday, July 4, 2024. All are 2 second exposures at f/4.5, ISO 100, 24mm focal length. The bursts are reflected in a large pond in the foreground.

This image, and the following two below it, are blends of two separate images processed in StarStax.

Minutes after these images were captured we made a mad dash for our cars as the deluge from the storm was about to begin! Nikon Z6ii camera.

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Tornado Threat Turns Linear

Tuesday, July 2, 2024 dawned with a significant chance of severe weather possible for most of the state of Iowa. Mesoscale Discussion 1511 (above left) posted the probability of wind, hail and tornadoes in southern and southeastern Iowa; and an expanded Storm Prediction Center (SPC) Enhanced Risk over the same area.

Ten minutes later, Tornado Watch 497 (5% Hatched) is issued, essentially in same region as the Enhanced Risk.

By 4:00 pm, I decided to attempt to intercept a large discrete storm tracking east from east of Des Moines. Around 4:40 pm the storm cell became tornado warned (Radarscope capture above). I hurried south on Interstate 380/US Highway 218 to get south of the cell, but now the storm was becoming outflow and linear.

5:39 pm. Radarscope capture. I have now reached my spotting location at the Phillips 66 Truck Stop just off US Highway 218 at Ainsworth, Iowa in Washington County. The severe-warned storm has lost its tornado warning and now is linear and bowing out (northwest of my location).

5:44 pm. Bowing linear storm with severe warnings all up and down its length.

5:56 pm. Looking northwest at an approaching shelf cloud, in the more intense area of the storm, as seen from the Phillips 66 Truck Stop. 

5:59 pm. Shelf cloud panorama. The tornado threat has now diminished, with only QLCS (Quasi-Linear Convective System) spin-ups possible.

Radarscope capture corresponding to the panorama image above it.

5:59 pm. Looking north at shelf cloud in the more intense region of this severe-warned storm as it begins to overtake my location.

6:01 pm. Close-up of the leading edge of the approaching shelf cloud looking northwest, showing the turbulent "whale's mouth" feature behind it.

6:02 pm. Leading edge of the shelf cloud in the western sky. Whale's mouth at background right.

6:02 pm. Looking northeast. The leading edge of the storm continues to overtake this Ainsworth, Iowa location. High winds are kicking up dirt in the parking lot at center.

6:20 pm. Looking northeast at the truck stop. At this location, wind speeds never surpassed 60 mph, and no hail fell here, despite heavy rainfall. A single (EF0) tornado touchdown was reported north of here, southwest of the Iowa City airport. Nikon Z6ii camera.

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