Unimaginable

One of the most common threads on the Internet in recent days has been about how could so many people in 2011 die in a tornado outbreak?  Before the advent of advance radar coverage and our current warning system, tornadoes would frequently cause the deaths of 100s of people each year.  But in recent decades deaths from tornadoes have dropped dramatically until recent events.

The exact reasoning will take time to resolve as data and surveys are taken in the coming weeks.  Yet, there are likely some root causes.  First, the tornadoes and severe weather the previous day and earlier in that morning cut power to thousands of residents limited their access to the warnings that day.  Second, the tornadoes were moving exceptionally fast with forward speeds around 50 mph.  And lastly, EF-4 and EF-5 tornadoes are almost indescribably powerful and when mixed with an urban setting, the setup for a disaster is always going to be present.

Devastating Tornadoes

The first decade of our new century recorded a noticeable decrease in violent tornadoes in the United States.  The second decade so far has not been so kind.  Although through this writing it was not official, the first EF-5 tornado in three years and only the 3rd in the past decade may have been recorded this past Wednesday.  The horrific tornado outbreak that struck Mississippi, Alabama and Georgia killed over 200 individuals with over 1000 people injured.

That would place this event with the third highest death toll in the past 50 years.  Several long-lived tornadoes with damage paths over 50 miles long, with widths near 1 mile, devastated numerous communities as well as portions of the larger cities of Birmingham and Tuscaloosa, Alabama.

EF-4 and EF-5 tornadoes are rare, but when they occur, high casualty numbers are frequently observed, because even if you take proper shelter, some storms are sadly just too powerful to survive.

Perception v. Reality

As we finish April, nearly everyone will remember this month as being cold and damp, yet, when the official stats for the month are written about in this space in a few days, you will likely be surprised.

The reason?  Temperatures this month, although below average, have been well within the bounds of average.  The average temperature for April has only been around 2 degrees below normal.  The reason this month has felt cold can be wholly attributed to our high temperatures.  Our daily highs this month have been averaging around 5 degrees colder than the average, whereas our wake up temperatures have been consistently above average all month.  Our morning lows have been so mild, that frosts these past few weeks have been rare.

Although morning lows are noticed around planting and harvest times and of course in the dead of winter, the high seems to always be the temperature most people pay closer attention too.  By that standard, April was indeed a cool month.

Side Effect

One good side-effect of our cool and cloudy weather lately is the relative lack of windy days.  Fargo Moorhead is a very windy place and April is, on average, our windiest month of the year with an average wind speed of 14.4 mph for the entire month.  That is a full mph higher than the second and third windiest months, May and March.

During a more typical April, when fields are not flooded and skies are not perpetually cloudy, there will be a number of days with warm sunshine beaming down on dry fields, causing thermal updrafts which can rise hundreds of feet into the air.  These thermals create turbulence and if there is already a breeze going, by afternoon it is common to have winds in the Red River Valley gusting well over 40 mph.

But this year, the fields are wet or flooded and the skies have been frequently cloudy, so our windy weather has been purely due to the passage of weather systems, keeping our winds this April about the same as the rest of the year.

Say it ain’t Snow

Fargo Moorhead averages 3.2 inches of snow in April.  So far this month we have received 4.2 inches of snow which places the month right near the long term average.  Since accurate snow records began in 1893 Fargo Moorhead has recorded measurable snow during the month of April 84% of the time.

Although a high percentage of the April snow events have occur toward the beginning of the month, recent years have not been so kind.  In fact, 8 out of the last 10 days in April have a daily snowfall record that has been set in the last 20 years.  This includes the two latest 6 inch snow events in the record books that occurred on April 25-26, 2008 when 9.1 inches fell and a 7.5 inch event on April 26, 1994.

May averages 0.1 inches of snow with measurable snow being reported in 20% of Mays and when you include flurries the odds go up to nearly one in three.

Graupel Watch

There is no record of snow having ever fallen in Fargo Moorhead during the summer, although there are a number of stories floating around the local rumor world.  There are reports (very rare) of snow falling in other places around North Dakota during June, but not in either July or August.  We do live in a place that is prone to cold extremes, but it would be a genuine freak of nature to get actual snow to fall in North Dakota (or Minnesota) anytime in summer except maybe during the first ten days or so of June.

However, there is a type of precipitation known as graupel, which can been described as a kind of soft hail with a remarkable resemblance to Dippin? Dots ice cream, which can fall during some of our cooler summer weather.  Graupel showers are usually too brief for graupel to accumulate, but a longer shower of graupel could cause the ground to become covered with an icy, snow-like cover.  But this would be graupel, not snow.

Instant Weather

In October, 1780 over 22,000 people died in a hurricane that ravaged many of the islands in the Caribbean. The reports of that disaster took weeks to reach Europe and the United States.  The earthquake and tsunami that struck Japan in March was nearly instantly reported via text message alerts and via Twitter and other internet resources long before it was picked up by the traditional media outlets.

I mention this because the perception by many is that this past decade brought more tornadoes, hurricanes and floods than what has occurred in the past.   As it often the case, the perception does not much the data.  In fact, the number of violent tornados (EF3 and higher) in the past 10 years have been at historic lows, the number of hurricanes around the globe in the past few years have been at their lowest in 30 years and studies have shown that flooding has not been increasing.

Our instant access to weather information may make it seem like storms are happening more frequently, but it is not the weather changing, but our technology.

A Colder April

April, 1997 will always be remembered for the devastating flood that followed one of the worst winters in recorded history.  The winter of 1996-1997 did not end until well into April that year.  April 4-7, 1997 brought perhaps the worst storm of that winter to the area with a devastating blizzard and heavy rain event as many were frantically sandbagging to stem the rapidly rising water.  The storm was followed by a severe cold snap that brought January type temperatures to the area.

From April 6-9 the low temperature dropped into the singles digits, although, no records were broken.  The story was different with daytime highs.   The high temperatures on April 7, 1997 reached a meager 13 degrees.  That high of 13 degrees was the coldest maximum temperature recorded during the month of April in Fargo Moorhead since records began back in 1881.

To this day the daily highs from April 7-10, 1997 are still the lowest maximum temperatures on record for those dates.

Without Warning?

The severe weather outbreak last week across the United States brought many of the same quotes you often hear after such events.  Comments such as ?it came without warning? or the phrase ?unpredictable tornados? were widely used.  Such phraseology perhaps makes for a good sound byte after such devastation, but at the same time it perpetrates the myth that no one knew the storms were coming.

The reality is, the Storm Prediction Center issued statements of the threat of a major outbreak of severe weather and tornados several days before the event occurred.  The mornings of each day additional statements were made to where and when the storms were expected.  Then watches were issued before the storms formed, plus all storms had a warning issued before the storm arrived at each location.

So the storms were well advertised and accurately predicted and anyone that heard a forecast before the storms arrived should not have been surprised.

Short Memories

The recent snowfalls have prompted several individuals to inquiry about when was last time we had snow so late in the season.  Just three years ago, on April 24-25, 2008, Fargo Moorhead recorded 9.1 inches of snow.  That was the second major snow event that month as on April 6, 2008 we had a 6 inch event and in between those two snow storms, around 2 inches fell on April 10-11.  In fact, April 2008 was the 2nd snowiest April on record with a total of 16.9 inches being recorded.  That narrowly missed the record of 17.4 inches that was recorded in April 1904.

If you participated in the first Fargo Marathon on May 14, 2005 you likely remember the snow that fell just before the race started.  Although, the official reading that day was only a trace, 2-3 inches of snow was reported as close by as Horace that morning.

So although we may not enjoy them, late season snowfalls in North Dakota and northern Minnesota occur more frequently than most of us want to remember.