Autumn 2011 Forecast

Wednesday is the last day of meteorological summer.  After 6 straight months with below average temperatures, the past three months all finished warmer than normal. With the autumn season beginning tomorrow, many people have asked if this warmer than average stretch will continue.

This area has experienced a number of mild autumns in recent years; in fact, the past 8 have finished with above normal temperatures and going back even farther, 13 out of the last 14 autumns finished with above average temperatures.  By analyzing past years with similar atmospheric and oceanic conditions to what has been occurring in 2011, the odds seem to favor this area enjoying another fall season with above average temperatures.

Although using the same techniques would lead me to believe precipitation trends may be favorable as well, our current wet phase has made it difficult to have confidence in any precipitation forecast besides a wet one.

A Touch Drier

Have you noticed that it isn’t raining as much the last couple of weeks?  We were already assured of above-average August rainfall when it rained 2.87 inches on the first day of the month.  After one more heavy rain and a few glancing blows, Fargo Moorhead stands at a little more than four inches for the month.

But the last significant rain to hit the city was back on August 6.  Lawns are starting to turn a little yellow and brown for a change.  But do not confuse short term dryness with truly dry weather.  The soil is only dry on the very top and rivers are still bank full.  Even if we have a dry fall season we will still be on pins and needles all winter worrying about the spring flood.  But the sunny and dry weather is at least a pleasant offering of normal, late-summer weather.

There might even be an opportunity to run along the bike path beside the river between midtown and Lindenwood, a path used only by catfish so far this summer

Weather Control

Does anyone else remember the idea back in the 1970s that Soviet Union scientists were controlling our weather?  The theory, which achieved some popularity, was that the Russians had found a way to project standing wave patterns into the atmosphere causing drought in the United States in a grand scheme to raise the price of Russian wheat.

It always was a dumb theory.  For one thing, during the mid-70s drought across America, there was a simultaneous drought across Russia.  So if the Soviets were controlling our weather, they were having trouble controlling their own.  The preoccupation of finding a scapegoat for bad weather remains a popular red herring today.

People look to find a blame for every drought, flood, storm, and earthquake without realizing that bad weather and other natural disasters have always happened and will continue to happen from time to time.

Infrared

William Herschel, a famous astronomer of the mid 1700s through the early 1800s, is probably most famous for discovering the planet, Uranus, the first planet discovered with the use of a telescope.

He was messing around with prisms and sunbeams one day in the year 1800 when he noticed that the air in the red part of the spectrum seemed warmer than the other colors.  Intrigued, he measured the spectrum of prism colors with a thermometer, and soon discovered that the air was actually warmest just outside the red light.  He declared that there must be some sort of invisible light being refracted onto that spot and he called this light calorific from “calor,” the Latin word for heat.

We now call these rays “infrared” and we now understand that this is how heat is radiated.  When the sun feels warm on your skin, you are experiencing infrared radiation from 93 million miles away.  This heat, however, does not cause sunburn.  Rather, it is the ultraviolet (UV) rays at the other end of the spectrum which are dangerous.

90s Gone Missing

This past Tuesday, Fargo Moorhead recorded our 8th 90 degree day of the year, although, just barely as the high only reached 90 degrees that afternoon.  With our 90 degree season winding down, it seems likely we will finish the year with a below average number of 90 degree days for the 4th year in a row.

During our current wet phase we have been averaging 10 such days, a subtle, yet noticeable departure from the historical average of 13.  More cloud cover and moister soils conditions can be blamed for our reduction of hot days in the region.   Although the decades of the 1960s and 1970s were generally cooler overall than recent years, even those two decades saw an average of fifteen 90 degree days per year.  Those years would be an example of how drier soils and sunnier sky conditions can lead to more extremes in our climate.

Once this wet phase ends, more abundant hot days will return, until then, more summer with fewer extremely hot days will probably continue.

Moving Pole

Modern day GPS units have made the old fashioned compass almost obsolete.  It is just as well, really.  Compasses never really pointed true north, anyway.  Technically, a compass points not to the North Pole, but to the Magnetic North Pole.

It turns out that the Magnetic North Pole is almost due north from Fargo Moorhead, anyway.  It is currently located near Ellesmere Island in far northern Canada, which is certainly not where the North Pole is.  Fargo Moorhead is located near what is known as an agonic line; a line due south of the Magnetic North Pole, so a compass works pretty well here.  However, on the eastern or western coasts of the country, compass needles point a direction about 15 degrees off of true north.

Not only that, but Earth’s magnetic poles are not permanent.  In fact, their rate of movement is accelerating.  They are presently shifting about 37 miles per year which amounts to around 15 feet an hour.

Fireball!

Tuesday evening, around 9:45 pm. a large number of people all over the region saw a bright flash of light move quickly across the sky.  What they saw was a kind of glorified meteor called a fireball.  Most meteors are made of a rock from space smaller than a pea.

As they enter Earth’s atmosphere at an extremely high velocity, these pebbles burn up quickly, usually at an altitude of 40 to 75 miles, producing what we call a shooting star.  A fireball happens when a larger rock, fist-sized or larger, moves into the atmosphere.  These produce a more spectacular, fiery display as they burn up.  Only very rarely do meteors reach the ground.  The Barringer Crater near Flagstaff, AZ, is a mile wide, 500 foot deep hole from a meteor impact some 50,000 years ago.

That meteor is thought to have been about the size of half a football field before the impact.

Severe Weather Rests on Weekends?

This summer it has been common for there to be thunderstorms, often with severe weather, in this area on one of the two days of nearly every weekend since Memorial Day.  Plus, conventional wisdom is that it always rains on weekends.  Yet, statistically there is not an increase in rain during weekends; in fact, just the opposite may be true.

A recent paper published in the Journal of Geophysical Research found evidence that in the United States during the summertime, tornado and hailstorm activity peaks during the workweek in the same time frame that atmospheric aerosols (think manmade pollution) peak.  It is thought that this increase in particulates in the air invigorate thunderstorm activity.  According to this study, Saturday and Sundays have the lowest probability of severe weather of all the days of summer.

The study looked at data between 1995 and 2009.  Perhaps if the summer of 2011, at least in our area was included in this study, it may have skewed the data toward the weekends just a bit.

Tomato Summer

During the three months of meteorological summer, the high temperature in Fargo Moorhead is in the 80s, on average, 40 percent of the time.  This summer the temperature has been in the 80s very persistently.  In fact, since June 1, the high has been in the 80s on 56 percent of the days.

Extreme heat this summer has been relatively rare, through yesterday, the official high has been at or above 90 degrees only 8 times.  Yet, this summer is currently ranking as the 8th warmest on record.  There are two main reasons for this.  First, those frequent days with highs in the 80s have kept our daily high temperature a few degrees above normal.  Plus, as of yesterday, this summer is currently ranked as the warmest summer on record for the average low temperature.

The frequent nighttime rain and severe weather events have been a key factor in keeping our lows very mild this summer and our soils very wet.

Postitive Lightning

We tend to think of all lightning strikes as being the same, but as is the case with other electrical currents, lightning comes in two flavors, negative polarity strikes and positive polarity strikes.  The strong turbulence within thunderstorms tend to separate electrical charges in a storm leaving the lower portions of the cloud base with a negative charge and the upper reaches of a cumulonimbus cloud with a positive charge.

Because similar charges will repel, the ground tends to become positively charged eventually leading to the negatively charged cloud base to discharge to the ground.  On occasion, usually less than 5% of all cloud to ground lightning, the positively charged upper portion of a thunderstorm will also send a lightning stroke to the ground, often well away from the base of the storm (where the ground tends to be more negatively charged).

These so called positive strikes last longer and are many times more powerful than a negative strike.   Positive strikes are therefore more lethal and cause far more damage to our electrical grid than the weaker more common negative strikes.