90°?

As many of you already know, the high temperature on Wednesday was 90 degrees.  Or was it?  The Moorhead airport recorded a high of 84 degrees that day, my home thermometer registered 86 degrees, our cooperative observer reported 88 degrees as did the reporting site at NDSU.

It was yet another example of differences in temperatures caused not only by natural variations, but more importantly where a thermometer is located.  The official site at the airport is located near the main runway to maximize safety for aircraft, not for registering the most accurate temperature reading.  Jet exhaust, a light breeze off the pavement nearby and other issues can cause that thermometer to be far different than what you may experience in your backyard.

Yet, the airport is the official reading in town and therefore it is accurate to say that the high on Wednesday was the latest 90 degree reading locally since 1993 and our 10th and probably last 90 degree day in 2011.

Never Ever

As many of our frequent readers to this space probably know, I love weather statistics.   Since the days of my first computer, downloading weather data and then parsing the numbers into averages, standard deviations and other not so common statistical properties has always been a hobby.  In fact, my Master’s thesis was a statistical analysis of weather data for portions of this region.

Yet, I have always understood the limitations of such data when it comes to one important element, time.  Good weather data only goes back approximately 150 years and in many areas the data is relevant for far shorter periods.  Therefore, you will frequently find me writing the phrase, “since 1881”, or another applicable year based on the subject.

Sadly, I hear or read the phrases “ever” or “unprecedented” far too frequently when weather events are mentioned.  Using past proxy data, dairies and other historical records,  clearly shows that those terms are highly misleading as our very meager weather records only give us a brief glimpse to all the possible weather variations that has impacted the planet over the millennia and should never be used to describe current weather events.

Dry But Wet

After a summer with the Red River in Fargo being above flood stage persistently, the past several weeks with the levels much lower has been a welcome sight.  Yet, by historical standards, the amount of water flowing through town is still extremely high.

For the past week, the Red River stage has consistently been just slightly above 16 feet.  Translated to cubic feet per second (cfs), approximately 2000 cfs is still flowing north as you read this.  The long-term median is only near 250 cfs.  So although the Red may look low in comparison to where we were, the amount of water in the river is still 8 times higher than normal for late September.

What this means is that even though the southern basin has been exceptionally dry in recent weeks, we are sadly still only one heavy rain event from the Red again reaching flood stage yet again.

The charts below are courtesy of gohydrology.org (I highly recommend reading this site).  Thanks for the graphics Robert!

Autumn Blue

Our recent stretch of sunny days has prompted many people to comment to me about how beautiful the sky is this time of year.  In some ways, the fall foliage show each year is spectacular not only because of the array of different colored leaves, but also because of the sharp crisp blue backdrop that enhances the view.

The autumn sky tends to look sharper and bluer this time of year for a couple of reasons.  During the summer, the dew point temperature tends to be much higher and this extra moisture makes the atmosphere hazy, giving the blue sky a dull, milky white appearance.  In the fall the moisture content in the air is much lower giving the sky a deeper blue appearance, especially when contrasted to what was seen all summer.

Plus, the lower sun angle this time of year enhances the scattering effect of the blue wavelengths that give the sky that classic autumn blue color.

Joplin

The National Weather Service released their assessment report for the Joplin,Missouri tornado last week.  That tornado was responsible for the death of 159 people and injured over 1000.  The report has a lot of analysis on how the public responded to the warnings issued during the storm.

Through numerous interviews, it was discovered that the vast majority of Joplin residents did not immediately take cover, or move to a safer location upon hearing a tornado warning was issued.  A high percentage of residents got their fist inclination of threatening weather when the sirens were activated, but this was taken as another false alarm by many.

The study concluded that sirens have lost credibility to most people, although it did prompt them to seek additional information.  The report offers some interesting insights as to how individuals perceive weather warnings and makes some very good recommendations to improve the weather warning system.

I highly recommend reading the assessment and we have a link to it at wday.com under the easy link tab.

Contrails Galore

A couple of weekends ago, when the weather was clear and near 90 degrees and so many of us were outside trying to soak up as much warm sunshine as we could, a lot of people noticed that jet trails (contrails) were crisscrossed across the sky all day long.

The reason for the long-lasting contrails is very simple and completely atmospheric.  That weekend, at altitudes above 30,000 feet, humidity levels were high and winds were very light, resulting in conditions which allowed contrails to form and linger.  That far up in the sky, the temperature is perpetually well below zero and the air is usually very dry.  So jet exhaust tends to disperse quickly.

But when conditions are just right, the moisture in the jet exhaust forms a cloud which will remain in place if there is not much wind.  We get the same effect sometimes on cold winter days when our own breath forms a lingering fog around our head.

Early Frost Means?

An early frost should not be taken as a sign that the upcoming winter will be a cold one.  Likewise, an early snow is not an indication of a snowy winter.  While these preseason jolts of weather can be a shock to the system, they are more the result of a random act of weather than a sign of impending doom.

In order to get temperatures to fall below freezing several weeks earlier than average, it takes a cool air mass that times itself just right so that light wind and clear skies happen right around sunrise.  A cold winter requires a weather pattern through the winter that frequently brings air from high latitudes into our region.  Similarly, an early snow is not an indicator of a persistent snowy pattern.

Note:  this is not to say that we will not have a mild winter.  This is just to say that an early frost is not a sign.

Stuck Weather

The summer edition of the Quarterly North Dakota Climate Bulletin, released last week by State Climatologist, Adnan Akyuz, has a report on the severe weather season across the state.  You will not be surprised to learn that there were many thunderstorms with damaging winds this past summer.

There were 177 reports of damaging winds along with 147 cases of damaging hail and 51 tornadoes.  These numbers are all higher than average, but the number of high wind reports is truly extraordinary.  The weather pattern which helped create the Memorial Day wind storm remained intact, more or less, throughout June and July, creating many opportunities for the same kinds of storms to form repeatedly.

This is similar to what happened to produce so much snow in the winter of 1996-97.  That winter, the storm track got stuck over our area whereas the remainder of the northern plains region did not have such a snowy winter.

Measuring Rain

Aristotle in is book Meteorologica, written in 340 BC, wrote about the different types of precipitation, yet, there was no mention of the actual measurement of rain or snow.    It would take well over another millennium before the concept of measuring rainfall would become an active practice.

The earliest known attempt to measure precipitation occurred inKoreaduring the reign of King Sejong who lived from 1397 to 1450.   King Sejong is credited with coming up with the idea of measuring rainfall in a standardize container.  This container was approximately 30 centimeters in depth and about 14 centimeters in diameter and stood on a pillar to measure the rainfall.  These containers were distributed to all the villages.  With this new knowledge of rainfall distribution, King Sejong could better estimate the potential harvest in each village and in turn, know how much the farmers should be taxed.

This first attempt to measure rainfall is credited to have occurred in the fourth month of 1441.

Moving Forward

As we move into the second half of September the number the truly mild days will decrease rapidly.  After today, Fargo Moorhead averages only 12 days with a high above 70 degrees with two of those days reaching 80 degrees or warmer.  If you long for one more 90 degree day before winter comes, the odds become even lower as that milestone has only occurred 39 times this late in the season since 1881.

Therefore, the 91 degree high on September 11 was likely our last such occurrence in 2011.  If the next several weeks are reasonably close to average, the high temperature that will be experienced the most will be in the 60s.  We average 16 days with a high between 60 and 69 the rest of the year.  Last year we recorded a remarkable 29 such days after this point, the 2nd highest on record.

Our average high and low will drop approximately a degree every other day for the next several weeks and on Halloween the averages will be 48 and 29 degrees.