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Late-day pop-up showers

“Now is the summer of our discontent….”

If Bill Shakespeare was hanging out in Minnesota this summer he might have a few choice words to describe our manic summer. Our stunted, illegitimate, slimmed-down “Calgary Summer.” Forget 90. Now we’re all (secretly) relieved with the afternoon high reaches 80. July temperatures are averaging 3-4 degrees cooler than normal. More fun facts….

Only 4 days so far this month with temperatures above average in the metro area.

2 days with highs stuck in the 60s, another 9 days with highs in the 70s.

Moderate/severe drought conditions extend across central Minnesota – driest weather over the Twin Cities metro area.

“Why has it been so cool and dry?”

A lot of theories – no single, definitive smoking gun. Proving cause and effect with the weather is an exercise in futility. A lack of sunspots? A brewing El Nino in the Pacific? Recent volcanic eruptions from Alaska to Russia? All of these factors could be in play – it may be a combination of multiple triggers. One thing I have discovered studying Minnesota weather for the better part of 25 years: the atmosphere is more likely to slip into a rut, stuck in a repetitive pattern, when the Pacific Ocean is unusually warm (El Nino) or unusually chilly (La Nina).

For some reason the arctic region/North Pole has been unusually mild. This, in turn, has pushed the “polar vortex”, the coldest air over the Northern Hemisphere, a few hundred miles farther south, closer to Hudson Bay – a pattern we’d expect to see in April or October, not the middle of the summer. This southward shift in the jet stream means that storms that should be tracking across central Canada are diving farther south, each one tugging a reinforcing shot of chilly air unusually far south of the US/Canada border. That’s why it hasn’t been much of a summer from the Upper Midwest and Great Lakes into New England.

Does this mean that climate change is a sham – proving once and for all that global warming is a crock of hooey? Not necessarily. Most important: this is still weather, not climate. A pattern that lingers for a few weeks, for a portion of a continent, does not mean the entire globe is feeling the chill. In fact I was surprised to see that this past June the combined average global land and surface temperature was the SECOND WARMEST ON RECORD! BTW, these climate records date back to 1880. Here are more climate headlines from NOAA:

Global Climate Statistics

  • The combined global land and ocean surface temperature for June 2009 was the second warmest on record, behind 2005, 1.12 degrees F (0.62 degree C) above the 20th century average of 59.9 degrees F (15.5 degrees C).
  • Separately, the global ocean surface temperature for June 2009 was the warmest on record, 1.06 degrees F (0.59 degree C) above the 20th century average of 61.5 degrees F (16.4 degrees C).
  • Each hemisphere broke its June record for warmest ocean surface temperature. In the Northern Hemisphere, the warm anomaly of 1.17 degrees F (0.65 degree C) surpassed the previous record of 1.12 degrees F (0.62 degree C), set in 2005. The Southern Hemisphere’s increase of 0.99 degree F (0.55 degree C) exceeded the old record of 0.92 degree F (0.51 degree C), set in 1998.
  • The global land surface temperature for June 2009 was 1.26 degrees F (0.70 degree C) above the 20th century average of 55.9 degrees F (13.3 degrees C), and ranked as the sixth-warmest June on record.

Notable Developments and Events

  • El Niño is back after six straight months of increased sea-surface temperature anomalies. June sea surface temperatures in the region were more than 0.9 degree F (0.5 degree C) above average.
  • Terrestrial warmth was most notable in Africa. Considerable warmth also occurred in Siberia and in the lands around the Black and Mediterranean Seas. Cooler-than-average land locations included the U.S. Northern Plains, the Canadian Prairie Provinces, and central Asia.
  • Arctic sea ice covered an average of 4.4 million square miles (11.5 million square kilometers) during June, according to the National Snow and Ice Data Center. This is 5.6 percent below the 1979-2000 average extent. By contrast, the 2007 record for the least Arctic sea ice extent was 5.5 percent below average. Antarctic sea ice extent in June was 3.9 percent above the 1979-2000 average.
  • Heavy rain fell over central Europe, triggering mudslides and floods. Thirteen fatalities were reported. According to reports, this was central Europe’s worst natural disaster since the 2002 floods that claimed 17 lives and caused nearly $3 billion in damages.

Thanks to storm chaser (and all-around great guy) Tad Parris, who was tracking “supercell” thunderstorms near the Minnesota/Iowa border Friday afternoon. Hail up to 2″ in diameter was reported in Dodge county. I saw some 4-5″ diameter hail in eastern Iowa, associated with a supercell storm that went on to spawn tornadoes. This reinforces one of my fairly reliable warning signs: the larger the hail, the greater the risk of a tornado. The reason: to keep a 4″ diameter ball of ice suspended in the air requires a SEVERE thunderstorm updraft. A tornado is more of a process than an object, the visible manifestation of an especially severe updraft. Remember, baseball-size hail = enhanced tornado risk. I’ve seen it time and time again.
WRF/NMM Model Output for 7 pm this evening. This shows accumulated rain between 1 pm and 7 pm. After a dry, sunny start, the combination of low-level moisture and lingering instability aloft will mean building PM clouds, and a few scattered showers, even a stray thundershower after 3 pm. Clouds and showers will keep temperatures cooler, holding in the upper 60s north to low/mid 70s south.

WRF/NMM Model Output for 7 pm Sunday, showing predicted temperatures in degrees F. The bright red-shaded areas are for 80 degree+ temperatures, anticipated over the southwestern third of Minnesota. The Brainerd and Alexandria Lakes area should see highs in the upper 70s to near 80 with more sun Sunday than today. That said, we still can’t rule out an isolated late-day thundershower Sunday, especially between 4 pm and 7 pm.

GFS Prediction for 500 mb Winds, 7 pm Saturday. This graphic shows forecast wind direction/speed at approximately 18,000 feet above the ground. Note the giant “cut-off-low” forecast to be located just north of Minnesota, centered over southwestern Ontario – next weekend. That’s about 500 miles farther south than it SHOULD be in late July. Yes, that will mean chilly, unstable air over Minnesota, with any fleeting morning sun giving way to PM clouds and showers, highs possibly stuck in the 60s – even some 50s far north? Yes, I too am mildly disgusted by this pattern. I miss the Dog Days….

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