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THE WINDS OF CHANGE WILL BE WHISTLING THIS WEEKEND...

NASA Researchers Help Analyze a Historically Powerful, Costly Storm


A team of NASA researchers used this satellite and radar imagery to help officials in Iowa better understand the effects of a derecho that ripped through the state in August.

The intense storm gave many Iowans a brief sense of what it might feel like to experience the strong winds of a hurricane.


To help officials in Iowa better understand the scale and scope of the disaster, a team of NASA researchers, led by Kris Bedka, a severe storm expert at NASA's Langley Research Center in Hampton, Virginia, and colleagues at NASA's Marshall Space Flight Center in Huntsville, Alabama and the University of Oklahoma, analyzed the storm using data and imagery from multiple Earth-observing satellites and weather radars on the ground.


“We’re trying to understand and demonstrate how state-of-the-art satellite and radar data can be used to identify the most intense areas of the storm and the damage they produced,” said Bedka.

His team's analysis is helping to reveal a layered picture of a storm that was historically intense — even for a derecho.


"There's evidence based on damage patterns in pockets throughout the state of Iowa that they saw winds exceeding 140 mph, which is extremely uncommon in these derecho systems," said Bedka. "I mean, 100 mph is usually kind of your upper end. When you get to 140, that's just a whole new level."


My new book Derecho 911, Iowa's Inland Hurricane explores issues such as while providing a comprehensive look at this one of a kind weather event. You can get you copy at derechobook.com


The imagery Bedka and his colleagues analyzed — visible in the compiled image series above, with the swath of the state that took the most damage outlined in white — showed remarkable agreement between what was happening in the clouds and the damage patterns the ground.


The first two images in the series are color composite synthetic aperture radar visualizations of ground vegetation taken by the European Space Agency's Sentinel-1 satellite — the first before the storm, the second after. In the second image, the lighter green and some brown areas show large areas damaged by wind and, in some cases, hail, which can strip vegetation of its leaves.


The third image in the series superimposes ground wind reports, radar-detected swaths of possible hail and National Weather Service (NWS) wind estimates with the damage patterns visualized in the second image.


In the fourth image, which comes from several NWS NEXRAD Doppler weather radars, the maroon and pink represent areas of high reflectivity, a telltale signature of hail. Also, the pattern of the radar echoes changed as the derecho moved across Iowa, becoming more arc-shaped. The arc, often referred to by meteorologists as a “bow echo,” indicates where the strongest winds were occurring, which is aligned well with NWS estimates and damage evident in the Sentinel-1 data.


“Because of how the instrument aboard Sentinel-1 collects data, we were able to compare data acquired both pre- and post-derecho to understand how the structure of vegetation, especially mature agricultural crops, were impacted and changed,” said Jordan Bell, research scientist in the Earth Science Branch at Marshall. “Synthetic aperture radar is being used for more and more applications, so it was exciting to provide impactful analysis for this event.”


The cool blues in the next-to-last image from the National Oceanic and Atmospheric Administration's Geostationary Operational Environmental Satellite East-16 (GOES-16) represent areas where tall, cold clouds that penetrated deep into the stratosphere were likely driving powerful wind downbursts. These are also areas where updrafts suspend water droplets long enough to form hail.


The warm yellows and reds in the final image, also from GOES-16, are areas of high lightning flash density, another indicator of storm intensity.


This layered analysis has been a valuable resource to Justin Glisan, state climatologist in the Iowa Department of Agriculture and Land Stewardship, as he continues to unravel what happened.


“The remote sensing products produced by the NASA team have given us a tremendous set of tools to study the agricultural damage produced by the Aug. 10 derecho event that impacted 57 of Iowa’s 99 counties, one of the most significant weather events Iowa agriculture has experienced," said Glisan. "As state climatologist of Iowa, having these additional and remarkable products in the toolbox will provide excellent guidance as we continue analyzing this catastrophic event.”


THE WEEKEND AHEAD


That brings me to the weather at hand this weekend and we start a rapidly deepening cyclone that travels from Iowa into Wisconsin Saturday night. Depending on your model of choice the pressure deepens as low as 980mb as it travels over Lake Superior. It all adds up to a period of rain later Saturday and lots of wind.


Starting with the wind, it blows from the south Saturday tapping moisture and warmer air. Highs have a pretty good chance of reaching into the 50s from about HWY 30 south thanks to gusts that reach 30 mph. The deepening pressure gradient also transports moisture rapidly north on the low level jet. Showers and even a few thunderstorms are expected to develop as the storm gets its act together. At 9pm the surface low is centered near Dubuque with a cold front cutting through extreme SE Iowa.

Since moisture is initially lacking and the system is moving fast rainfall amounts should not get out of hand but 1/2 to 1/2" amounts should be common. Perhaps a bit more in any spot that can scare up a thunderstorm. The GFS shows this for totals.

The EURO has this for the same time period.

As the storm wraps up Saturday night in Wisconsin strong W/NW winds will bring the rain to scattered showers Sunday morning. But more importantly it will bring colder air and very blustery conditions late Saturday night and Sunday. Gust to 40 are expected with the potential of some as high as 50. A wind advisory appears likely. Below you can see the 10 meter max gusts the EURO is indicating.

With spotty morning showers and temperatures in the 40s, the blustery conditions support wind chills Sunday that will be well into the 30s in most areas, maybe the upper 20s in my far NW counties. It will not be a nice day.

Fortunately, the cold air retreats and by Tuesday we begin a warming trend that should yield highs close to 60 towards Thursday of the coming week. That's the latest and greatest. Have a terrific weekend and roll weather...TS

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