“Derecho” Pattern: Damaging wind event possible along I-90 corridor overnight

derecho

A widespread convectively induced straight-line windstorm.

Specifically, the term is defined as any family of downburst clusters produced by an extratropical mesoscale convective system. Derechos may or may not be accompanied by tornadoes. Such events were first recognized in the Corn Belt region of the United States, but have since been observed in many other areas of the midlatitudes.

Johns, R. H., and W. O. Hirt 1987. Derechos: Widespread convectively induced windstorms. Wea. Forecasting. 2. 32-49. -AMS Glossary of Meteorology

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Image: NOAA via Brittney Misialek

Severe Overnight Potential:

This looks like a bumpy overnight and early Wednesday AM for folks along the I-90 corridor.

An overnight Mesoscale Convective System (MCS) is likely to develop in South Dakota and roll along I-90 through southern Minnesota overnight. Most of the storms should occur after midnight. Storms may rumble through the Twin Cities early Wednesday AM, but the biggest severe threat appears to be focused on southern Minnesota.

The T-Storm complex looks potentially severe…and may form a “Derecho”…a long lasting bow shaped cluster of severe storms notorious for producing widespread straight line wind damage.

Damaging winds may approach 60 to 100 mph in some areas with the overnight storms.

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-Latest Sioux Falls radar loop

-Latest Twin Cities radar loop

-Sioux Falls NWS

-Twin Cities NWS

NOAA’s SPC has put out slight and moderate risk areas for parts of South Dakota into southern Minnesota overnight into early Wednesday.

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Here’s some attention getting wording from NWS.


Meteorologists are tracking a so-called derecho weather pattern in the Midwest that could spawn severe windstorms in major metropolitan areas with gusts as strong as 100 mph.

The National Weather Service says derechos occur once or twice a year in the central U.S. with winds of at least 75 mph. The storms maintain their intensity for hours as they sweep across vast distances, and can trigger tornadoes and large hail.

Meteorologists say the wind storms could hit from South Dakota to Pennsylvania over the next two days, including the Milwaukee, Chicago, Detroit, Cleveland and Pittsburgh metro areas.

Meteorologist Bill Bunting says there’s a 30 percent chance of severe wind storms capable of damaging homes and knocking down trees. Bunting says residents need to closely watch severe-weather warnings.

And some concern from the Twin Cities NWS in the late Tuesday forecast discussion.


AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN

323 PM CDT TUE JUN 11 2013

.SHORT TERM…(THIS EVENING THROUGH WEDNESDAY) ISSUED AT 323 PM CDT TUE JUN 11 2013

SIGNIFICANT WIND EVENT EXPECTED ALONG I-90 LATE TONIGHT. LOOKING AT THE BIG PICTURE…AN UPPER LOW CURRENTLY SPINNING OVER NORTHERN UTAH IS EXPECTED TO SLOWLY WEAKEN AS IT LIFTS ACROSS SD AND INTO SOUTHERN MN ON WED. AS OF THE 12Z SUITE OF MODELS…THIS LOW WAS INITIALIZED TOO WEAK…AND MAY AFFECT THE EVOLUTION OF STORMS OVERNIGHT AND INTO WED. A SURFACE LOW DEEPENING IN NE COLORADO WILL MOVE TO NEAR OMAHA BY 12Z WED WITH THE BULK OF TSTMS FORMING ON THE NORTH SIDE OF THE LOW. UPSLOPE FLOW ALONG THE BLACK HILLS OF SOUTH DAKOTA IN CONJUNCTION WITH THE SHEAR ASSOCIATED WITH THE SFC LOW AND AMPLE DAYTIME HEATING WILL LEAD TO SUPERCELL DEVELOPMENT BY EARLY THIS EVENING. THESE SUPERCELLS ARE EXPECTED TO CONGEAL INTO A FORWARD-PROPAGATING SEVERE MCS ACROSS SOUTH CENTRAL SD LATER THIS EVENING.

DRIVEN BY A 50KT MID-LEVEL JET, THIS COMPLEX WILL SPEED ALONG I-90…ARRIVING INTO SW MN ~10Z…EXITING SE MN ABOUT 6 HRS LATER. ALTHOUGH HAIL AND HEAVY RAIN ARE ALSO THREATS WITH THE STORMS TONIGHT…THE MAIN IMPACT WILL BE WIND GUSTS POSSIBLY EXCEEDING 60KTS. NUMEROUS LOCAL/MESO- SCALE MODELS ARE IN PRETTY GOOD AGREEMENT WITH THE TIMING AND PLACEMENT OF THIS COMPLEX SO CONFIDENCE IS RELATIVELY HIGH.

Derecho Season:

June and July are prime derecho season in the Upper Midwest. Here’s a look at derecho “climatology” in the summer months.

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Minnesota is prone to derechos and has had some famous storms like the BWCA Blowdown event on July 4th 1999.

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Minnesota in “Derecho Alley?”

Minnesota may not be in the heart of tornado alley…but there is a pretty strong frequency signal for derechos in Minnesota. We spend our summers near the edge of the “Bermuda High” and derechos like to run the edge of the developing heat dome.

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Anatomy of a “Bow Echo”

Early studies noted how these long-lived damaging wind storms showed up as a “bow echo” on radars. Heres’ a look at the anatomy of these storms.

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Heres’ more from NOAA on derechos:


Definition of a derecho

A derecho (pronounced similar to “deh-REY-cho” in English, or pronounced phonetically as “”) is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of tornadoes, the damage typically is directed in one direction along a relatively straight swath. As a result, the term “straight-line wind damage” sometimes is used to describe derecho damage. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.

Origin of the term “derecho”

The word “derecho” was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, in a paper published in the American Meteorological Journal in 1888. A defining excerpt from the paper can be seen in this figure showing a derecho crossing Iowa on July 31, 1877. Hinrichs chose this terminology for thunderstorm-induced straight-line winds as an analog to the word tornado.

“Derecho” is a Spanish word that can be defined as “direct” or “straight ahead.” (Click here to hear a pronounciation of the word “derecho”). In contrast, the word “tornado” is thought by some, including Hinrichs, to have been derived from the Spanish word “tornar,” which means “to turn.” Because derecho is a Spanish word, the plural term is “derechos;” there is no letter “e” after the letter “o.”

Bottom Line: People in southern Minnesota should be alert for damaging T-Storm clusters overnight. Keep the NOAA Weather Radio on and handy…and be ready if you need to take shelter overnight.

Paul Huttner