Wake Low Wind

On Thursday, July 24, an area of 50-60 mph winds developed over a large area south of Fargo Moorhead eastward across parts of Becker and Otter Tail counties.  The winds were especially problematic around Minnesota lakes, causing high waves to wash over shorelines.  The wind was caused by a condition known as a wake low.  Wake low winds sometimes form in the wake of a squall line.  The combination of adjacent areas of warm and and rain-cooled air creates a localized tight pressure field which makes it windy.  Wake low winds usually affect an area the size of two or three counties and last for one to three hours.  Winds of 40-60 mph are common but stronger winds are possible.  Wake low events defy National Weather Service storm warning products because they are not associated directly with the thunderstorms which cause them but are of too short a duration and too small in area for a high wind warning.  They happen most summers somewhere in our region but several years may pass between wake low winds at any one spot.  This makes them rare enough to be unfamiliar to the public as well.    Meteorologist John Wheeler.

Rain-Wrapped Tornado

The National Weather Service found evidence of a tornado within the widespread straight-line wind damage left behind after the Monday night storm.  The damage path is approximately 28 miles long through Polk and Red Lake counties and was discovered by the nature of the damage; debris was lifted higher and thrown further in a manner usually associated with tornadoes.  No one actually saw the tornado because it was entirely wrapped in heavy rain and was surrounded by a large area of very strong non-tornado wind.  A few people along did report hearing the “freight train roar” often associated with tornadoes, butthis sound can sometimes be heard in strong straight line wind storms as well.  Rain-wrapped tornadoes are not common in the northern Plains but are more common in the South where more humid environments often produce more widespread rain around tornadoes.  Rain-wrapped tornadoes are often difficult to detect except by Doppler radar, and the National Weather Service did have a tornado Warning in effect at the time.  This illustrates the need for people to take all Tornado Warnings seriously.  Fortunately, there were no injuries Monday night.

The tornado was a part of a huge thunderstorm complex which produced wind damage along a more than 500 mile path through North Dakota and Minnesota into northern Wisconsin and northern Michigan.  It began Monday afternoon and lasted into early Tuesday.  The storm complex, called a derecho, happens from time to time when hot and humid air in the lower atmosphere is topped by an upper air disturbance of higher winds and cooler temperatures.  The cool air aloft makes the air very unstable.  As the developing thunderstorms form into a line, some mechanism forces some of the stronger upper-level wind down to the ground. This condition can continue for hours, causing near-continuous wind damage.  In the Monday night storm, the mechanism responsible for forcing the wind was a small area of low pressure which formed over northeast North Dakota and then continued to move east with the storm.

By far, most of the wind damage Monday night was due to straight-line wind.  There were many reports of wind speeds estimated to be in the 60 to 80 mph range.  The tornado produced wind in this range as well, along with a few locations of 110-120 mph wind, all in Polk County near and southwest of Crookston.  The 110+ mph wind allow for the tornado to get an EF-2 rating.

Meteorologist John Wheeler

What Really Is the Record?

Fargo Moorhead weather data has been measured and recorded at Hector Airport since February of 1942.  Prior to that, our weather was recorded at the National Weather Bureau Office in Moorhead, in what is now the Rourke Museum.  But I recently learned from Daryl Ritchison of the North Dakota Climate Office that sporadic record keeping actually had begun at the Fargo Airport in 1930, and meticulous, hourly weather records from Hector started in 1932.  This means there is a period of ten years during the Dust Bowl when there is a complete other set of weather records for this area.  The Moorhead data are the numbers used for the official record because that was the official site until 1942.  But the Fargo data appear to be good data.  One item that stands out is July 6, 1936.  The all-time record high for Fargo Moorhead of 114 degrees was set that afternoon.  However, over in Fargo, the unofficial instrument at Hector recorded 115 degrees for two consecutive hours that day.    Meteorologist John Wheeler

The Worst Heat Wave

At this time in 1936, our region was in the about to begin its most extreme heat wave on record.  For eleven straight days, from July 6-16, the high temperature in Fargo Moorhead was at least 99 degrees.  The average high during the period was 104 degrees.  Nine of the eleven days were in the 100s.  The hottest temperature during the heat wave was the 114 reading on July 6 which is still the hottest on record for Fargo Moorhead.  There was little relief at night, either.  Most morning lows were in the 70s and two mornings, July 10 and 11, were 82 and 80 degrees.  The heat withered crops and tested the endurance of people.  Most rural areas still had no electricity so there was not even a fan to use.  The remainder of that summer was hot and dry and there was one more 100 degree day on September 21.  The ten days of 100 degree weather are the most recorded in Fargo Moorhead  in one year.     Meteorologist John Wheeler

Cold Winters, Cool Summers

From now through the middle of August is the hottest time of year in our region.  And that is not saying much.  The smoothed daily average high temperature is in in the 80s, peaking at 83 degrees for about three weeks from mid-July into August.  Even during our summer peak, any day is statistically more likely to be in the 70s than in the 90s.  We average 13 days a year of 90 degree temperatures.  On average, eleven of those days happen during July and August.  We only get to 100 degrees once every few years.  The last time was in 2012 and the last time before that was in 2006.  Before 1993, when it started raining more, 100 degree days were more common, but still happened less than once a year on average.  People say we live in a region of cold winters and hot summers.  They are right about the winters but our summers are generally quite cool.     Meteorologist John Wheeler

Where’s the Heat?

If you are as yet unsatisfied with our northern summer and require some real heat to get yourself into a summer frame of mind, may I recommend Las Vegas, Nevada or the surrounding desert of southern Nevada and California?  During June, 21 of the 30 days of the month were in the 100s, the hottest being 111 degrees June 30.  Nearby Needles, California, had just one day at 99 degrees and the other 29 were in the 100s.  At the weather station in Death Valley, the coolest day of the month was 103 and the hottest was 120 degrees.  Death Valley holds the record for the hottest properly measured (and officially recognized) temperature on Earth of 134 degrees set July 10, 1934.   Meteorologist John Wheeler

June Temperatures

June temperatures were close to average.  The average high was 77.5 degrees which is 0.1 degree above the three-decade mean.  The average low was 56.8 degrees which is 1.9 degrees above the three-decade mean.  This continues the trend observed over recent years of having the low temperatures warmer than the high temperatures, relative to the long term average.  This is another representation of our local climate being wetter than in the past.  The increase in rainfall leads to higher humidity and more clouds, all of which has a bigger impact on temperatures at night and less of an impact in the daytime.  The increase in average humidity also leads to fewer really hot days.  June had two days with highs in the 60s, 15 with highs in the 70s, and thirteen with highs in the 80s.  The warmest day last month was 89 on June 21. The coolest day was 66 degrees on June 6.  June had 12 mornings with lows in the 60s, 15 with lows in the 50s, and three with lows in the 40s. The coldest temperature was 44 degrees on June 8.  The warmest night was 69 degrees on June 27.   Meteorologist John Wheeler

June Wet and Stormy, Kind Of

June was a wet and stormy month.  Rivers are high from Manitoba to Tennessee.  Almost every evening on the national news there is coverage about all the severe storms this summer.  But the national tornado count on the Storm Prediction Center’s Annual Storm Summary web page shows that the last year to have had so few tornadoes through July 1 was 2005.  What about all the rain?  It has been wet but nowhere nearly as wet as it was in 1993.  June was a bad month in the Great Plains and Midwest for storms.  But June was certainly not record bad and it wasn’t really even unusually bad.   Instead, network news is just covering the heck out of stormy weather.  It is riveting and extremely popular.  Weather is good for ratings.  And while the coverage is well-intended and truthful, the viewers should not be persuaded by the sheer volume of storm coverage into thinking this summer is out of the ordinary.   Meteorologist John Wheeler

High Humidity Makes Storms More Chancy

When the weather becomes humid, it is intuitive that there is an accompanying increase in thunderstorm activity.  But trying to forecast the timing and location of storms during humid weather is often very hard.  Storms do well in humid environments.  In addition to helping it rain, the evaporation and condensation process adds tremendous amounts of energy to the atmosphere, making storms explosive.  But storms also need a trigger; something to get them started.  Usually when we get our most humid summer weather, the fronts, lows, and other dynamics are weak.  This leads to forecasts of widely scattered storms, possibly severe, and some with very heavy rain.  And if people hearing the forecast gloss over the qualifying, “widely scattered,” they can get the impression that heavy rain is a certainty.  In reality, these humid weather patterns produce a few heavy storms and a lot of fine weather over the rest of the area.    Meteorologist John Wheeler


Humidity Facts

Here are a few sticky thoughts to keep the sweaty weather stuck in your mind for a while.  Humid air may feel heavy, but dry air is actually denser and heavier than humid air.  Humid air we get here in the North usually comes from the Gulf of Mexico.  But that air can actually pick up humidity on its way due to evapotranspiration of corn and bean fields.  The relative humidity percentage is a percentage of saturation, not a percentage of humidity.  The condition of 90 degrees and 90 per cent humidity is a condition rarely found on Earth. On a humid, 90 degree day, the relative humidity is usually around 40 to 50 per cent.  The 90 per cent humidity happens in the morning when the air is cooler. The relative humidity is usually higher in winter but we don’t notice it in the colder air.   Meteorologist John Wheeler