Record Warmth and Record Low Humidity

Record Warmth and Record Low Humidity:

The warm start to the month of May which I wrote about last week really ramped up even more this week as temperatures around the state average 12°F to 20°F above normal. Afternoon high temperatures in the 90s F were quite common. Within the Minnesota climate station network, there were many new high daily maximum temperature records set over May 11 to May 14.

On May 11th at least 20 climate stations reported record high temperatures, including 96°F at International Falls and Baudette.

On May 12th at least 40 climate stations reported record high temperatures, including 94°F at Granite Falls.

On May 13th at least 15 climate stations reported record high temperatures, including 93°F at Thief River Falls.

On May 14thth at least 10 climate stations reported record high temperatures, including 93°F at Red Lake Falls.

International Falls reported record high maximum temperatures of 90°F or greater on four consecutive days, May 11-14.

Minnesota’s geographic air conditioning was in evidence on most of these days as well. While many areas sweltered in the 90s F, temperatures at Two Harbors and Grand Marias remained in the 50s F and low 60s F. Afternoon temperatures near the Duluth Harbor were over 30 degrees F cooler than those at the Duluth Airport.

Coupled with the warm temperatures were record-setting low relative humidity values, ranging from just 6 percent to 19 percent during the afternoon hours on some days. These conditions combined with moderate winds caused the National Weather Service to issue Red Flag Warmings on several days this week, covering 85 of Minnesota’s 87 counties. Under these conditions, wildfires broke out in northeastern Minnesota earlier this week. Most of the concern was focused on the Camp House Fire, the Jenkins Creek Fire, and the Munger Shaw fire, all located many miles west and northwest from Duluth. These three fires had burned over 50 square miles as of Thursday of this week.

Later on Thursday, some severe thunderstorms crossed Minnesota bringing rain, some hail, strong winds, and even some tornado reports (at least in Swift, Stearns, and Polk Counties). Many areas of the state reported between 0.35 inches and 1.25 inches of rain from these thunderstorms. With most of the annual crops already planted in the state, farmers welcomed the rain, but not the severe weather elements.

Weekly Weather Potpourri:

The NOAA Climate Prediction Center released new seasonal outlooks this week. The summer outlook covering June-August calls for a warmer and drier than normal period in Minnesota, with drought persisting in western parts of the state.

A recent study published in the journal Theoretical and Applied Climatology suggests that reducing the urban heat island effect in major cities may reduce the frequency of occurrence of extreme heavy precipitation. Researchers studied the urban heat island effect of Osaka, Japan and by modeling evaluated its impact on localized heavy precipitation. Their results indicate that the reduction of sensible heat flux from urban areas would stabilize the lower troposphere and hence would lead to reducing cloud formation and precipitation.

MPR listener question:

With the exceptional dry air this week, we wondered when is the lowest relative humidity on an annual basis in Minnesota?

Answer:

Based on long term measurements, the average daily relative humidity is typically lowest in the month of April, before the native vegetation begins to green up. Highest overall relative humidity is usually in the month of December.

However, in recent decades sometimes the months of October and May can bring extraordinary low relative humidity readings in the single digits and teens, just like we experienced this week. This is especially true in years where drought has persisted in Minnesota.

Twin Cities Almanac for May 16th:

The average MSP high temperature for this date is 69 degrees F (plus or minus 11 degrees F standard deviation), while the average low is 50 degrees F (plus or minus 8 degrees F standard deviation).

MSP Local Records for May 16th:

MSP records for this date: highest daily maximum temperature of 94 degrees F in 1934; lowest daily maximum temperature of 48 degrees F in 1968; lowest daily minimum temperature of 31 degrees F in 1929; highest daily minimum temperature of 68 degrees F in 1962; and record precipitation of 1.10 inches in 1905. Record snowfall is 0.1 inches also in 1929.

Average dew point for May169th is 42°F; the maximum dew point on this date is 71°F in 1962 and the minimum dew point on this date is 16 degrees F in 1973.

All-time state records for May 16th:

The state record high temperature for this date is 100 degrees F at Artichoke Lake and several other western Minnesota communities in 1934. The state record low temperature for this date is 12 degrees F at Meadowland (St Louis County) in 1929. The state record precipitation for this date is 5.00 inches at St Cloud in 1894. The statewide snowfall record for this date is 3.0 inches at Leech Lake in 1915.

Past Weather:

By far the coldest May 16th in state history was in 1929 when most of the state awoke to a frosty morning. Over much of the state morning temperatures were in the twenties, and up north several climate stations reported teens. The afternoon high temperature at Grand Marais only reached 41°F.

The hottest May 16th was in 1934 when over 40 climate stations reported afternoon temperatures of 90°F or greater. Milan (Chippewa County) reported a 100°F high temperature and a 34°F low temperature on this date

On the morning of May 16th in 1950 snow was reported across northern Minnesota from Bemidji to Duluth. Many observers reported 1 to 2 inches of snowfall, one of the latest seasonal snowfalls in state history.

Outlook:

Much cooler over the weekend with temperatures below normal. Increasing cloudiness in the north late Saturday and into Sunday with chances for rain showers, even rain/snow mix in the far northeast where there will be chances for frost Saturday, Sunday, and Monday nights. Continued cooler than normal temperatures Monday with a chance for showers and thunderstorms late. Continuing chance for showers off and on through next Thursday with cooler than normal temperatures.