Storms with Names
What happened to late afternoon, garden-variety popcorn showers and T-showers? We still see them, of course, but now (increasingly) we have to be on the lookout for their mutant relatives: supercells, tornadoes, meso-convective swarms of T-storms that pop up at night, and derechos.
Last Friday's wind damage was triggered by a particularly aggressive bow echo, a powerful T-storm downdraft of rain and hail-cooled air that reached the ground and spread out, fanning straight-line wind damage.
Monday evening a much larger "derecho" swept into Chicago, a much larger boomerang-shaped swirl of thunderstorms. To be called a derecho a vast arc of storms has to travel at least 240 miles. June 29, 2012 one such derecho traveled 800 miles, from Iowa to Norfolk, leaving millions without power.
The threat of heavy storms diminishes today as a cool front turns on a drier northwest breeze. We salvage a dry sky Thursday and Friday; a few pop-up instability T-showers Saturday afternoon.
Sunday looks sunnier & drier. Keep your holiday weather expectations low & you'll never be disappointed. It's that kind of summer.
Right now models hint at 80s & isolated T-showers for the 4th. It may even feel like summer out there.
* image above courtesy of the Twin Cities National Weather Service, which has a good explanation of Friday evening's severe storm here.
4th of July Outlook. Here is the ECMWF model outlook for midday on the 4th of July (next Thursday), showing a few showers and T-storms over the central and northern Plains, with a risk of a shower or T-shower over southern Minnesota. It's way too early to get specific, but showers and storms seem likely east of the Appalachians, with a better chance of puddles south/west of Minnesota. We'll see. Model map: WSI.
Extra Severe. A radar loop from Friday evening's bow echo (courtesy of NOAA) shows a severe gust front as rain and hail-cooled air rushed east at 50 mph. A few thoughts from Friday's severe gust front:
* Sirens are not sounded for Severe Storm Warnings (with the exception of Dakota County).
* Tornadoes get more attention, but severe storms can be just as destructive. Damage is often more extensive, but not as severe as in a major tornado. To put things into perspective, the damage left behind from Friday's 70-80 mph gust front was roughly equivalent to an EF-0 tornado, one that was 15-20 miles wide. At some point it becomes a matter of semantics: did a tornado or a severe storm gust front bring down that big tree in your yard?
* The supercell thunderstorm that morphed into a bow echo raced east at 50 mph, moving faster than high-res models were predicting. Winds gusted over 60-70 mph over portions of Hennepin County for 10-15 minutes. The persistence of the high winds, coupled with wet, saturated ground from early morning storms, helped to bring down even more trees.
* This rotating supercell was able to sustain itself, keeping the rain and hail-cooled gust front intact for several hours, prolonging the damage. A typical thunderstorm self-destructs after 30-45 minutes, but spinning supercells can protect the warm updraft, sustaining a storm for a long period of time.
Photo credit: National Severe Storms Laboratory
(photo: littleleague.org)Lightning Safety. After concern was raised about recent Little League baseball games played during questionable weather (lightning observed nearby) I wrote this note to an ump who asked me about criteria for calling off a game, and when it's safe to resume play. Here is my reponse:
"With the recent spate of severe and damaging thunderstorms impacting the metro area, I wanted to drop you a quick note and remind you and your colleagues that lightning-related fatalities are most likely at the very beginning and tail-end of an outdoor event. This is where we see the most lightning-related injuries and fatalities, not during the height of the storm, when heavy rain/hail is falling.
Here’s the problem: lightning can travel 8-10 miles in a horizontal direction. In fact every year people are struck with blue sky overhead, a thunderstorm on the distant horizon. The National Weather Service’s “30-30 Rule” has become a defacto standard in the weather business. When you can count 30 seconds between lightning and thunder it’s time to head for shelter; and wait 30 minutes after the last thunderclap before resuming safe play on the field.
From a National Weather Service link focused on Lightning Safety and Outdoor Sports Activities:
“Because electrical charges can linger in clouds after a thunderstorm has passed, experts agree that people should wait at least 30 minutes after the storm before resuming activities”.
More information from NOAA here: http://www.srh.noaa.gov/jetstream/lightning/lightning_safety.htm
I realize the wet spring has compressed the season, and players (and their parents) are anxious to get these games in and complete the season. However the overriding goal should be safe play and lowering weather risk. Any temptation to “push the weather” and get coaches, players (and spectators) out onto a ball field within 30 minutes of the last report of thunder is not only unsafe, but a potential disaster in the making. From a litigation standpoint, there’s a large and growing body of evidence that waiting 30 minutes significantly increases safety margins and helps to avoid lightning-related disasters. Taking a chance and resuming play within that 30 minute window is a recipe for fatalities, life-long, chronic, lightning-related injuries, and litigation.
As an interested parent who spent many long weekends at the local ballpark with my two son (checking Doppler on my smart phone more often than I would have liked) I have an interest in safe play and taking any and all steps to reduce the potential for weather-related tragedy."
- Paul Douglas, CBM Meteorologist. Founder of Media Logic Group.
Photo credit above: "A flooded downtown Calgary, Alberta is seen from a aerial view of the city Saturday, June 22, 2013. The two rivers that converge on the western Canadian city of Calgary are receding Saturday after floods devastated much of southern Alberta province, causing at least three deaths and forcing thousands to evacuate." (AP Photo/The Canadian Press, Jonathan Hayward)
Google Maps image credit: "
* The Wall Street Journal has more on the alleged tsunami here (subscription may be required).
GWEN IFILL: The president today renewed a pledge he has been making since 2008 to reduce greenhouse gas emissions and slow global warming. This time, he plans to exert executive authority to force action. With today's announcement, the president zeroed in on the new and existing power plants that burn coal and turn out 40 percent of the nation's carbon dioxide emissions.
PRESIDENT BARACK OBAMA: As a president, as a father, and as an American, I'm here to say, we need to act...Right now, there are no federal limits to the amount of carbon pollution that those plants can pump into our air. None. Zero. We limit the amount of toxic chemicals like mercury and sulfur and arsenic in our air or our water, but power plants can still dump unlimited amounts of carbon pollution into the air for free. That's not right, that's not safe, and it needs to stop..."
Photo credit above: "Mantoloking, New Jersey on March 22, 2013." Reuters/Lucas Jackson.
Graphic credit: "
Albertans have also learned that climate change delivers two extremes: more water when you don’t need it, and not enough water when you do. The geographically challenged have also become learned, once again, that water travels down hill and even inundates flood plains.
So climate change is not a mirage. Nor is it weird science or tomorrow’s news. It is now part of the flow of daily life."Photo credit: "This undated photo provided by the Calgary Flames shows the inside of the Calgary Saddledome in Calgary, Alberta. The Saddledome, home to the National Hockey League's Calgary Flames, was flooded up to the 10th row, leaving the dressing rooms submerged. The two rivers that converge on the western Canadian city of Calgary are receding Saturday, June 22, 2013 after floods devastated much of southern Alberta province, causing at least three deaths and forcing thousands to evacuate." (AP Photo/Calgary Flames).