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

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

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 Reigns (Rains)

There were areas of heavy rain on Wednesday which was forecast well in advance.  The rain system had lots of humidity but it was not the humidity that could be felt by going outside and walking round.  It did not feel humid because the air was cool.  The dew point temperatures were not high and one did not develop excessive perspiration from exertion.  The temperature was mainly in the 60s which is cool enough that the body does not need to perspire.  But the quantity of water vapor in the atmosphere, top to bottom, was quite high.  Even though the air was not terribly humid in the lower atmosphere where we all experience it, there was an excessive amount of water vapor higher up.  This is why it was able to rain heavily on parts of the region despite it not “feeling” as if it would rain heavily.     Meteorologist John Wheeler

Drones to Fly into Hurricanes

The National Hurricane Center has plans for using drones to measure pressure and wind during this year’s hurricane season.  The automatic flying machines, called Coyotes, will be dropped out of hurricane hunter WP-3 aircraft from 10 to 12 thousand feet.  The drone’s spring-loaded wings will lock into place and its small electric motor will allow speeds up to 70 mph.  These drones will then be able to spend up to two hours flying around inside the eye of a hurricane, collecting data in a way no piloted aircraft can do safely.  The drones cost around $70,000 each, but the Hurricane Center plans on using several of them on any storm that looks big or threatens to make a landfall.  This new cost to hurricane forecasting is expected to easily be made up in money and lives saved from better forecasts.    Meteorologist John Wheeler

Heat Wave of 1988

So far this June there has been no hot weather.  It was a different story 22 years ago.  June of 1988 was the hottest June in the history of Fargo Moorhead weather.  The average high temperature that June was 85 degrees.  There were 13 days in the 90s, 14 days in the 80s, two days in the 70s, and one rainy day in the 60s.  Most of the days were sunny and stiflingly hot.  Rainfall was scant.  There were just five days with rain totaling just 1.24”.  The only significant rain of the month fell on June 14 when 0.69” fell.  That day was also the only day with a high temperature below 70 degrees.  The heat waves continued throughout the summer with a total of 39 days at or above 90 degrees compared to the average of 13 days.  There were also four days over 100 degrees.  In the more distant past, the summer of 1936 had ten days over 100 but only 38 days above 90.    Meteorologist John Wheeler

Tornado Raises Questions of Safety

The video of two oil workers unsure of what to do as the Watford City tornado approached them at very close range has initiated a lot of conversation around the country as to what to do when a tornado approaches.  Most often in a tornado warning, the tornado dissipates, never forms at all, or hits somewhere other than where you are. This can create the overconfident feeling that tornadoes “never” hit.  Yet they do.  And when a tornado hits your house is not the time to be deciding what to do. All families should develop a plan.  Where is the best place in your house to go?  Is this place ready?  Are there flashlights and shoes handy? How will you meet up if separated and cell phone service is disrupted?  Prepare now and be ready just in case.    Meteorologist John Wheeler

Smaller Weather a Communication Challenge

We have come to the time of the year when the weather gets smaller.  A shower or a thunderstorm that rains on Wahpeton or Valley City is likely to miss Fargo.  For that matter, it is not unusual for it to rain on the north side of Fargo and Moorhead but miss the south side altogether.  So when you see a forecast with a chance of rain in it on any given day, it does not necessarily mean it will rain where you are. Furthermore, if it does rain on you, it is not very likely to rain all day.  Many days that produce severe thunderstorms are beautiful days most of the day.  Likewise, just because the weather where you are is beautiful does not preclude the possibility of big, bad storms nearby.  We all know this to be true and yet if a forecast shows a chance of rain on Saturday most people seem to get the idea that their Saturday is ruined.  Remember that a chance of rain is only a chance.    Meteorologist John Wheeler

May In Review

The month of May, 2014, ended up being average but got there in a roundabout way.  The average daily high was 68.2 degrees and the average daily low was 45.8 degrees.  This works out to an average May temperature of 57.0 degrees, which is just 0.1 degrees cooler than average.  May is now the eighth consecutive month with a colder than average temperature.  However, December through April were all significantly colder than average whereas May was very nearly average.  The first two thirds of the month was cold with three mornings at or below freezing.  The coldest was 30 on May 4.  The final ten days of May were warm with two days in the 70s, five in the 80s, and three in the 90s including 93 on May 30.  Rainfall was 1.99 inches, which is 0.82 inches below average. There were 22 days with rainfall.  Thirteen of those daily rains were measurable.       Meteorologist John Wheeler

Suddenly Summer?

The sudden change to summer temperatures this past week was like an electric shock to those of us used to much below average temperatures over the past eight months.  But the current run of above-average temperatures is only eight days along and it is already showing signs of weakness.  In fact, the warm temperatures this past week were likely a temporary change in an ongoing cool weather pattern.  The summer, itself, is not likely to be as far below average as was the winter and spring.  Present global patterns suggest near-average or slightly colder than average temperatures for the summer overall.  Of course, we can expect the occasional warm spell, such as we had this past week.   Meteorologist John Wheeler