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Extension > Mark Seeley's WeatherTalk > String of Days with High Dew Points

Friday, September 4, 2015

String of Days with High Dew Points

String of Days with High Dew Points:



August ended with a sultry day as dew points climbed into the 70s F on the 31st pushing Heat Index Values into the 90s F again.  It was the 6th day in August that dew points reached the 70s F in the Twin Cities.  Dew points also reached into the 70s F on Tuesday, Wednesday, and Thursday, September 1-3, marking the 17th, 18th, and 19th days this summer with such values in the Twin Cities. It is particularly uncommon to have 4 consecutive days with dew points in the 70s F.  In total roughly 120 hours this summer have brought a dew point of 70F or higher to the Twin Cities.  This is below the long term average of 171 hours for the summer, so our mutual discomfort has not been as frequent as many other summers, but we sure have felt it the second full week of the State Fair.  And the string of days with dew points in the 70s F was expected to last until Labor Day.  The highest measured dew point this summer in the Twin Cities was 76F on July 12th.

Thanks to dew points in the mid to upper 70s F, the Heat Index Values at St James, Willmar, Glencoe, Morris, Montevideo, and Litchfield exceeded 100F on Thursday this week, and such values may be observed in other places over the coming Labor Day weekend.

Provisional Climate Summary for August:


On a statewide basis the mean temperature for the month of August was just slightly cooler than average (less than 1F). Some northern Minnesota communities were slightly warmer than average for the month.  The weekend of August 14-16 brought the hottest weather of the summer for most Minnesota locations, with daytime temperatures reaching the 90s F accompanied by high, uncomfortable dew points. Heat Index values exceeded 100F at several Minnesota locations on those dates.  The extremes for the month ranged from 95F at Ada (Norman County) on August 14th to just 33F at Cotton, Brimson, and Embarrass on the 26th. 

The month of August was drier than normal for most climate observers in Minnesota, though there were some locations that reported above normal rainfall thanks to heavy thunderstorms.  On August 7th thunderstorms brought new record daily rainfall amounts to Morris (3.05"), Kimball (4.20"), and Big Lake (4.49"); on August 19th thunderstorms produced new daily rainfall records at Wolf Ridge (2.91") and at Madison (4.03"); and on August 23 thunderstorms brought record rainfalls to Hallock (2.60") and Warren (3.81").  Among those stations reporting more than 6 inches of rain for the month were: Big Lake (7.90"), Princeton (6.65"), Askov (6.60"), Wright (8.65"),  Pipestone (6.68"), Worthington (6.49"), New Ulm (6.41"), and St Peter (6.53"). 

The month of August was windier than normal and brought a number of days with high wind gusts.  Most locations reported wind gusts of 30 mph or greater on 6 to 8 days, and several locations reported wind gusts over 40 mph.

For the summer months of June through August, the statewide mean temperature was about 1F warmer than the historical average, and the statewide rainfall was about 0.5 inches above the historical average.

State Fair Weather:


The 12-day run of the Minnesota State Fair continues at the Fairgrounds in Falcon Heights this week, concluding on Labor Day.  For those who are interested I will be there at 11am on Friday, September 4th (today) at Carousel Park for an MPR broadcast of the Minnesota Weather Quiz with host Tom Weber.  I will also be doing a book signing (for 2nd Edition of Minnesota Weather Almanac) from noon to 1pm that day in the tent at Carousel Park.  Please stop by if you are at the Fair.

As for weather during the State Fair:  the historical average daytime temperatures are in the upper 70s to lower 80s F, with nights ranging from the upper 50s to low 60s F.  It typically rains on 3-4 days during the fair.  Current modeled forecasts favor near normal temperatures this weekend, warming to above normal conditions most of next week, with a cool down and chance of showers and thunderstorms for the Labor Day weekend.

Record climate values for the State Fair include:  a high temperature of 104F on September 10, 1931; a low of 33F on September 13, 1890; and rainfall of 4.06 inches on August 30, 1977.  Much more on the weather history of the Minnesota State Fair can be found at the DNR-State Climatology Office.

Appearance at Subtext Bookstore:

On Tuesday evening, September 8th, from 7pm to 8pm I will be at the Subtext Bookstore in downtown St Paul talking about the 2nd edition of the Minnesota Weather Almanac, answering questions, and signing copies of the book.  Please drop by if you are interested. 

Weekly Weather Potpourri:


In August the BBC announced that it was going to drop its contract with the United Kingdom Meteorological Office to provide weather forecasters for its broadcast services. Instead it was accepting bids for forecasting services from offshoots of Dutch and New Zealand meteorological offices.  This news was greeted with outrage and frustration across the United Kingdom where many citizens feel that the 93-year relationship between the BBC and the UK Met Office has provided excellent service to the public and should be respected.  I think it remains to be seen how this will be resolved.  You can read more from the Daily Mail and from the Mirror web sites.

In the weekly drought update from USDA's Brad Rippey he notes that drought in the Pacific Northwest has been exacerbated by heat stress (well above normal temperatures) which has contributed to many wildfires in the area.  One fire in the state of Washington burned more than 150,000 acres. 

In the Western Pacific Ocean Typhoon Kilo was churning between Wake Island and Midway Island generating winds over 100 mph and sea wave heights of close to 40 feet.  This storm was expected to strengthen but remain out to sea.  Meanwhile Hurricane Ignacio was moving north away from the Hawaiian Islands and expected to weaken, becoming extra-tropical in character as it reaches the Gulf of Alaska early next week.  Hurricane Jimena was east of Hawaii and remaining nearly stationary, but expected to move north next week and dissipate to tropical storm status.

A new study published in the Proceedings of the National Academy of Sciences by UC-Irvine scientists finds that simultaneous droughts and heat waves are occurring with an increased frequency over the years since 1960.  They examined global records of temperatures in the 90th percentile or higher from the historical records and extended periods when precipitation was 20 percent or less of the normal.

A recent study in the journal Geology documents the results of the famous September, 2013 flash flood in Boulder Canyon , CO.  The study found that this single event eroded the equivalent of 1000 years worth of sediment from the foothills west of Boulder, CO.  Further, they concluded that the erosive potential of these rare but severe flash floods has probably been under estimated in regards to the formation of natural landscape features across the Colorado landscape.

A new study from NOAA scientists shows that Barrow, Alaska experienced its warmest May in history this year, and one of its earliest every spring season ice melts.  This follows a trend in northernmost Alaska towards earlier loss of snow cover and sea ice. 

MPR Listener Question:

We are planning our trip up north later this month to observe the beautiful fall colors in Minnesota.  Do you think peak fall color will be earlier or later than normal this year?  

Answer:

It is always hard to say.  Temperature forecasts for the first half of September favor near normal to slightly cooler than normal conditions across the state, but this should not dramatically affect the pace of autumn color change.  Though prolonged heat stress has been absent this summer, some areas of north-central Minnesota (Beltrami, Itasca, and Koochiching Counties), as well as northeastern Minnesota (portions of St Louis, Lake, and Cook Counties) have had a drier than normal summer.  This may provoke a slightly earlier than normal color change in some areas there. Otherwise I think it would be wise to use the DNR autumn color web site to plan your trip

Twin Cities Almanac for September 4th:

Twin Cities Almanac for September 4th:

The average MSP high temperature for this date is 76 degrees F (plus or minus 9 degrees F standard deviation), while the average low is 58 degrees F (plus or minus 7 degrees F standard deviation).

MSP Local Records for September 4th:

MSP weather records for this date include: highest daily maximum temperature of 98 degrees F in 1925; lowest daily maximum temperature of 59 degrees F in 1920: lowest daily minimum temperature is 39 degrees F in 1885 and 1974; highest daily minimum temperature of 73 F in 1960; record precipitation of 2.08 inches 1911; and no snowfall has been recorded on this date.

Average dew point for September 4th is 55 degrees F, with a maximum of 74 degrees F in 1960 and a minimum of 35 degrees F in 1974.

All-Time State Records for September 4th:

The state record high temperature for this date is 103 degrees F at Beardsley (Big Stone County) in 1922 and at Pipestone in 1925. The state record low temperature for this date is 22 degrees F at Park Rapids (Hubbard County) in 1885 and at Grand Rapids (Itasca County) in 1918.  State record precipitation for this date is 5.53 inches at Chanhassen (Carver County) in 2005; and there has not been any snowfall on this date.

Past Weather Features:

September 4, 1918 was the coldest in history on a statewide basis.  Frost was observed as far south as Lynd (Lyon County) and lows in the 20s F were reported 15 other communities around central and northern sections of the state, including just 22F at Grand Rapids.

During the Heat Wave of September 3-7, 1922, Minnesota citizens endured day after day of 90F temperatures (warm nights too) without the modern convenience of air conditioning.  Many slept outside or on porches.  Observers from all parts of the state set new daily temperature records, including 96F at Babbitt and 100F or greater at 16 other locations around the state.

Widespread thunderstorms brought heavy rains to parts of Minnesota over September 3-4, 1941.  Many observers reported over 2 inches of rain, especially in the north.  Hallock (Kittson County) reported nearly 5 inches with some local flash flooding.

Over the week of September 4, 1998 many portions of central and northern Minnesota were plagued by poor air quality as smoke from wildfires in Alberta and Saskatchewan passed across the region limiting visibility and causing bright red sunsets.  A dry summer in western Canada contributed to a difficult wildfire season in Alberta where over 300,000 acres were burned by lightning caused wildfires.

Outlook:

Warm and humid over the weekend with chances for scattered showers and thunderstorms.  Greater chance for showers later on Sunday, then much cooler and less humid on Labor Day (Monday).   Generally dry with cooler than normal temperatures most of next week.

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