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Roller coaster temperatures July 18-21

Roller coaster temperatures July 18-21

Thursday, July 18th brought very warm temperatures, oppressive dewpoints and high Heat Index Values (ranging from 98 F to 107 F) across southern Minnesota counties. Record tying and record setting warm overnight low temperatures were also noted by some observers including MSP Airport with 80 degrees F (tied 2011), and Thielman, Melrose, and Isle with 73 degrees F (new record warm lows). If you want to read more about some of the history of warm nights in the Twin Cities when the temperature does not fall below 80 degrees F the Minnesota State Climatology Office has posted a narrative on their web site.

Just 3-days after July 18th, on Sunday (July 21st), a cool, dry Canadian air mass brought some near-record setting low temperatures to northern Minnesota observers, with many readings in the low to mid 40s F. International Falls tied a record low on Sunday with 41 degrees F (matching 1947), while Crane Lake reported a new record low of 39 degrees F. Such remarkable swings in temperature values are more common in late summer than mid-summer in Minnesota. 

Unusual tornado on July 22nd

The NOAA-National Weather Service Grand Forks Office reported on an unusual tornado earlier this week that struck between Mahnomen and Zerkel (Mahnomen County). This storm was unusual in several aspects: firstly it struck between 1:50 AM and 2:30 AM on July 22nd (Monday), a very rare time of day for tornadoes in our region (less than 2 percent of all tornadoes occur at that time of day); second, wind speeds were estimated to range from 110-120 mph (EF-2 strength), unusually strong for an overnight storm; thirdly, the storm path was nearly 18 miles in length (though intermittently on the ground), a relatively long storm path for an overnight storm. Thankfully this tornado did not cause any deaths or injuries, but it did damage a home, a number of farm structures, along with some farm equipment. It also caused a good deal of tree damage, especially around Roy Lake. This was the 6th confirmed tornado of the year so far in Minnesota. You can read more about the 2013 tornado season in Minnesota at the MN State Climatology Office web site.

Thunderstorms on July 25th

Strong thunderstorms visited parts of the state on Thursday, July 25th and overnight into Friday. There were numerous reports of damaging winds, hail (0.25 to 1.50 inches in diameter), and heavy rainfalls in some northern and southeastern counties. Some observers reported near record or record-setting rainfall amounts for July 25th including 2.47 inches at Spring Valley, 2.23 inches at International Falls (a record amount), 2.11 inches at Lanesboro (a record amount), 1.94 inches at Flag Island, 1.87 inches at Babbitt (a record amount), 1.62 inches at Long Prairie, and 1.55 inches at Grand Meadow. Some farmers were disappointed to see the rain fall on fresh cut hay fields, and a few in Fillmore County reported hail damage to crops.

Preliminary July climate summary

July's mean temperature for most observers in Minnesota was near normal or warmer than normal. The middle part of the month was very warm with many observers reporting daytime temperatures in the 90s F. Extremes for the month ranged from 96 degrees F at Little Falls, Gaylord, and Forest Lake on the 18th to just 38 degrees F at Brimson (St Louis County) on July 2nd. Even low temperatures in the mid to high 30s F may occur this Saturday morning (July 27) in northeastern counties. Several observers reported dewpoints in the 70s F which pushed the daytime Heat Index Values from 95 F to 105 F on some days. The warm temperatures produced higher than normal Growing Degree Days which boosted crop development, allowing late planted fields to catch up in their growth, and most corn fields went through the silking and pollen shed phase of development during the 3rd and 4th week of the month.

Precipitation for July was high variable around the state. Many observers in southwestern Minnesota counties reported less than normal precipitation. But for many locations intense thunderstorms brought heavy rainfall and these places finished the month with above normal precipitation totals. In the north International Falls and Gunflint Lake reported nearly 7 inches, Grand Marais over 7 inches, and Tofte nearly 5 inches. In central counties a number of observers reported over 5 inches, while in the south Wells and Dundas reported over 6 inches. Soil moisture reserves were adequate to surplus in most places as the month wraps up.

Weekly Weather potpourri

Colleagues at the Midwest Regional Climate Center have collaborated to produce a nice feature on their web site, called "Weather on the Day You Were Born." You can find out what the weather was like on your birth date and print out a certificate verifying it. Of course this can likely be verified by your parents as well! If you are interested in this feature click here.

Tropical Storm Flossie in the Eastern Pacific Ocean is headed towards Hawaii. By early next week it is expected to bring some heavy rain, 45-55 mph winds, and 15-20 foot seas to the islands. Flossie is the 6th named storm of the Eastern Pacific Tropical Storm season. In the Atlantic Ocean the National Hurricane Center was also tracking Tropical Storm Dorian, not expected to approach the Bahamas until the middle of next week.

Drought has taken a strong grip on southwest China this month, drying up lakes and reservoirs and causing some water rationing in other others. The rice crop has been negatively affected and some farmers have had difficulty keeping livestock fed and watered. The Chinese Meteorological Service says that some areas of seen their driest month of July since 1961. You can read more here.

A recent paper by scientists from Oregon State University published in the journal Nature explains the dynamical mixing of ocean waters in the central Pacific Ocean and how the sea surface temperature fluctuations influence large scale atmospheric patterns. You can read more about their work here.

MPR listener question

With the cool temperatures expected for Saturday morning and some daytime highs forecasted to only reach the 60s F I was wondering what the coolest July daytime high has been for the Twin Cities area, and also on a statewide basis?
Answer: The coolest daytime high for July in the Twin Cities climate record (1872-2012) is 58 degrees F on July 4, 1967. It was completely cloudy that day, all day, and with a low cloud ceiling. Winds were from the north and it was definitely jacket weather. On a statewide basis the north shore along Lake Superior usually records the coldest temperatures in July. On July 2, 1950 Grand Marais reported a morning low of 36 degrees F and an afternoon high of 49 degrees F, more November-like temperatures, but occurring in July. That day was dominated by wind off the lake, low overcast and light rainfall, again a definite jacket day.
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