A destructive windstorm – Derecho


Several authors have conducted studies on derechos, but what is a Derecho?

Figure 1 – Photo taken by Doug Berry of the very impressive shelf cloud on the leading edge of the “People Chaser” Derecho of May 27, 2001 near Fort Supply, Oklahoma by NOAA



Derecho is a large-scale and long-lived straight-line convective windstorm, i.e., a family of strong winds produced by moving thunderstorms system (namely, mesoscale convective system, MCS) (3,4). A derecho is so declared if it follows 4 requirements, here summarized:
1) the area of convectively induced wind damage should have a major axis longer than 400 km and wind gusts of at least 93,6 km/h along most of its length;
2) wind gusts can be related to the same event so that a chronological progression of singular wind swaths or a series of wind swaths is indicated;
3) at least three reports of wind gusts of at least about 120 km/h (and/or related wind damage) separated by 64 km or more within the area of severe wind gusts;
4) all wind reports have to occur within 3 h of the other wind reports of the same derecho event.

Among some products that monitors the weather there is the radar that show the precipitation on a given area and through it a derecho can be seen as a bow, which is formed by strong winds coming from the rear of the storm.

Figure 1 – Derecho progression on Radar by Weather.gov

Fig. 2 – Radar Animation From the Advanced Weather Interactive Processing System (AWIPS) display inside KDVN. Severe Thunderstorm Warnings are lined in yellow, with Tornado Warnings in red. by Weather.gov



The environment promoting such a windstorm is characterized by strong winds speeds and/or particular wind rotation with height and all this is accompanied, even though not always, by hot and humid air in the lower atmospheric levels. Derechos are frequent in the U.S. where ≥15 events happen every year (4, 5, 6). In Europe only a few derechos occur each year (7, 8, 9) and only several of them were studied in detail [see, e.g., (10, 11, 12, 13, 7)]. Curiously, the term derecho is still not common in Europe, although several events can be classified as such (10, 13, 7), and in Germany such events was not classified as derechos before 2004.

Derechos can bring several damages and fatalities with it (4,7,15)

Figure 3 – The Commercial Appeal staff photo by Mike Maple- Two children examining the root structure of an uprooted tree on Belvedere Boulevard in midtown Memphis. – 2003

Figure 4 – Medium Tree – One of the 200 year-old trees uprooted in the old north town part of Sherbrooke, Quebec (facing south) (From Mainville 1999)






although its effects are directed along a relatively straight line (16,17).

Figure 5 – Straight damages – Street – The Commercial Appeal staff photo by Mike Maple- View of Linden Avenue west of Barksdale Street on Friday afternoon, July 25, 2003, (three days after the derecho), showing pole-top capacitors and associated switching equipment still littering the street. – 2003



In the U.S. it was seen that its effects are similar to those of tornadoes and tropical storms, except for the strong ones (18) , then the importance to make a correct forecast to avoid a sudden and unexpected occurrence (16,17) but this type of forecast is not easy to make. For example, a study on a derecho event in the US (1) highlighted the challenges in forecasting warm-season derecho of a particular type.

In another study (2) was conducted a diagnosis and a modelling of 2 destructive, first-time documented derechos that interested European Russia in 2010 and was found the importance of large-scale atmospheric configuration on the formation and development of severe convective storms in the first place which, next, led to the derechos in those cases, a similar result was found by another study on derechos in Germany (14). Also, some model simulations underestimated wind gusts (2), so we can guess a potential danger forecast underestimation.

Derecho can happens in both cold and warm season (14) with the latter prevalent in Europe (13, 7), for example in Germany it was found that in summer a relatively strong winds speed and particular wind rotation with height was present, together with a contribution from insolation, indeed such events tended to start between 12 and 17 UTC (14:00-19:00 CEST ) (8). On the other hand in winter, apart for the derechos detected in the warmer hours ( 12-15 UTC, 13:00-16:00 CET), they was also discreetly present in cold hours (18-06 UTC , 19:00-07:00 CET) (8). Moreover, although the winter derecho type has a similar intensity as the summer type, it presents the highest intensity peaks and path length. (8)

Anyway, we can’t help but to look up to this nature-made , although dangerous, beauty.

Figura 6 – Photo 198961984 © John Sirlin | Dreamstime.com

References

  1. Ribeiro, B. Z., Weiss, S. J., & Bosart, L. F. (2022). An Analysis of the 3 May 2020 Low-Predictability Derecho Using a Convection-Allowing MPAS Ensemble, Weather and Forecasting, 37(2), 219-239.
  2. Alexander Chernokulsky, Andrey Shikhov, Alexey Bykov, Nikolay Kalinin, Michael Kurgansky, Boris Sherstyukov, Yulia Yarinich,
    Diagnosis and modelling of two destructive derecho events in European Russia in the summer of 2010, Atmospheric Research, Volume 267, 2022, 105928, ISSN 0169-8095
  3. Fujita, T. T., and R. M. Wakimoto, 1981: Five scales of airflow associated with a series of downbursts on 16 July 1980. Mon. Wea. Rev.,109, 1438–1456.
  4. Johns, R.H., Hirt, W.D., 1987. Derechos: widespread convectively induced windstorms.
    Wea. Forecast. 2, 32–49.
  5. Ashley, W.S., Mote, T.L., 2005. Derecho hazards in the United States. Bull. Amer. Meteor.
    Soc. 86 (11), 1577–1592.
  6. Coniglio, M.C., Stensrud, D.J., 2004a. Interpreting the climatology of derechos. Wea.
    Forecast. 19, 595–605.
  7. Taszarek, M., Pilguj, N., Orlikowski, J., Surowiecki, A., Walczakiewicz, S., Pilorz, W., Piasecki, K., Pajurek, L., Połrolniczak, M., 2019. Derecho evolving from a
    Mesocyclone-A Study of 11 August 2017 severe weather outbreak in Poland: event
    analysis and high-resolution simulation. Mon. Weather Rev. 147 (6), 2283–2306.
  8. Gatzen, C.P., Fink, A.H., Schultz, D.M., Pinto, J.G., 2020. An 18-year climatology of derechos in Germany. Nat. Hazards Earth Syst. Sci. 20 (5), 1335–1351.
  9. Surowiecki, A., Taszarek, M., 2020. A 10-year radar-based climatology of mesoscale convective system archetypes and derechos in Poland. Mon. Weather Rev. 148 (8), 3471–3488.
  10. Gatzen, C., 2004. A derecho in Europe: Berlin, 10 July 2002. Wea. Forecast. 19, 639–645.
  11. Lopez, J.M., Arús, J., 2004. A Mediterranean Derecho: Catalonia (Spain). In: 17th August
    2003 Preprints, Third European Conf. on Severe Storms, Leon, Spain, CD-ROM, p. 53.
  12. Punkka, A.-J., Teittinen, J., Johns, R.H., 2006. Synoptic and mesoscale analysis of a high-
    latitude derecho-severe thunderstorm outbreak in Finland on 5 July 2002. Wea. Forecast. 21 (5), 752–763.
  13. Celi´nski-Mysław, D., Matuszko, D., 2014. An analysis of selected cases of derecho in Poland. Atmos. Res. 149, 263–281
  14. Gatzen, C. P., Fink, A. H., Schultz, D. M., and Pinto, J. G.: An 18-year climatology of derechos in Germany, Nat. Hazards Earth Syst. Sci., 20, 1335–1351, https://doi.org/10.5194/nhess-20-1335-2020, 2020.
  15. Mathias, L., Ermert, V., Kelemen, F. D., Ludwig, P., and Pinto, J. G.: Synoptic Analysis and Hindcast of an Intense Bow Echo in Western Europe: The 9 June 2014 Storm, Weather Forecast., 32, 1121–1141, 2017.
  16. Doswell, C. A.: Severe convective storms – An overview, in: Severe convective storms, 1–26, Springer, 2001.
  17. Dotzek, N., Groenemeijer, P., Feuerstein, B., and Holzer, A. M.: Overview of ESSL’s severe convective storms research using the European Severe Weather Database ESWD, Atmos. Res, 93,
    575–586.
  18. Ashley, W. S. and Mote, T. L.: Derecho hazards in the United St

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