Unusual Manitoba Tornado

During the late afternoon and evening of Monday, July 27, a tornado touched down in rural southwestern Manitoba and was tracked by tornado chasers for three continuous hours.  This is an extremely long time for a single tornado to remain in contact with the ground.  In fact, this is one of the longest continuous tornado touchdowns in North American history.

Along its path, the tornado felled trees and took down power lines and even destroyed one section of asphalt pavement.  Fortunately, it missed all towns and farmsteads so that not a single structure was damaged during the entire three hours.

Because there was so little damage, the tornado was only given a rating of EF2, indicating wind speeds of up to 135 mph.  It is possible the wind was stronger at times but there is no way to know.

Meteorologist John Wheeler

How Old is Arctic Ice?

The shrinking of the summertime Arctic Icecap in recent decades has left me wondering when the last time the Arctic was ice free.  Turns out this is a hard question to answer due to the fact that Arctic sea ice undergoes a little melting every summer from top (weather) and bottom (unfrozen ocean) which leaves a poor record.

The most accepted theory is that the North Pole has been capped in ice continuously or nearly continuously for 2.7 million years ago since the beginning of the present Wisconsonian ice age.  During the past 2.7 million years, there have been many periods of glacial advances in which ice has moved southward into the mid-latitudes and then retreated back to the Polar region during relatively brief interglacials.

The land-based and much colder Antarctic Icecap is thought to be around 34 million years old.

Meteorologist John Wheeler

Ice Age Primer

The present Ice Age, known as the Wisconsonian, began about 2.7 million years ago.  Since then, Earth has undergone a sequence of glacial advances and interglacial warm periods.  Approximately one million years ago, the frequency switched from about every 40,000 years to about every 100,000 years, during which time the cold periods became colder.

The present interglacial began about 12,000 years ago and is known as the Holocene Epoch.  The previous glacial period had lasted about 112,000 years.  The coldest point is thought to have been about 20,000 years ago when the globally averaged temperature was about 8-10 degrees colder than today.  The level of the sea was about 400 feet lower than today due to there being so much water locked in ice.

The previous interglacial is known as the Eemian and featured peak temperatures several degrees warmer and sea levels 20-30 feet higher than today.  There are at least four other known glacial periods in Earth’s past.   John Wheeler

 

July In Review

July was a very average month for Fargo Moorhead.  The average temperature was 72.5 degrees which is 1.5 degrees above the long term average.  Rainfall was 2.78 inches which was just 0.01 inches below average.

The warmest temperature was 91 on the 27th and the coolest was 42 on the 7th.  For the month, there was just one day with a high in the 60s, six days in the 70s, 21 in the 80s and just three in the 90s.  Low temperatures were in the 40s once, the 50s nine times, and the 70s 21 times.  Because daily records are kept midnight to midnight, the record does not reveal the three nights with overnight lows in the 70s because on all three occasions, the temperature cooled below 70 before midnight the following night.

The daily average temperature was above average 21 of the 31 days, indicating a month with consistently slightly above average temperatures but an absence of any truly “much above average” weather.

Meteorologist John Wheeler

Eerily Eemain?

A lot of climatologists are talking about the Eemian Period lately.  The Eemian is the name for the last great warming prior to the last glaciation.  It happened about 125,000 years ago.  According to ice cores and fossil records of the time, Earth was a few degrees warmer than the present period (The Holocene) and sea levels were about 20-30 feet higher than today.

The recent discussion revolves about a finding of a sudden warming late in the Eemian period that may have been related to a rapid ice melt and a sudden associated sea-level increase.  The thinking is that some of the glacial areas on Earth today are melting faster than the climate models have predicted, suggesting that the sea level rise in the next few hundred years could possible come faster and sooner than expected.

Not all climatologists agree with this idea.  The one part of this that concerns me is that there is more carbon dioxide level in the atmosphere today than there was in the Eemian.

Meteorologist John Wheeler

Humidity: It’s an AM/PM Thing

If you get your current weather information in the morning, you should know that the morning relative humidity is not a useful indicator of how humid the weather will be today.

In fact, the relative humidity is fairly useless as an indication of humidity discomfort because it tells us not the percentage of humidity, but the percentage of water vapor saturation.  The temperature is usually cooler in the morning and the relative humidity is usually 80 to 100 per cent because cooler air saturates more readily.  Later in the day, it might be 20 degrees warmer, and even with the same mass of water vapor in the air, the relative humidity usually is around 30-50 per cent.

The dew point temperature is a much better measure of humidity discomfort.  Air with dew points in the 60s and 70s feels increasingly humid.

Meteorologist John Wheeler

 

Season’s Wobbles

Someone asked the other day why it is warmer in the summer even though the sun is closer to us in winter.  First of all, yes, the sun is actually closer to us in winter.  Earth’s orbit around the sun is elliptical, not circular.

Winter is colder in the Northern Hemisphere because Earth’s Axis of Rotation points the Northern Hemisphere away from the sun in winter, giving us shorter days, longer nights, and more oblique solar radiation.  In the Southern Hemisphere, the sun is actually closer during the summertime.  But instead of having hotter summers and colder winters, the Southern Hemisphere is more temperate because there is a higher percentage of the surface covered by the ocean.

The Axis of Rotation slowly wobbles like a spinning top every 26,000 years.  Half of that time, the sun is actually closer to the Northern Hemisphere in summer.

Meteorologist John Wheeler

 

Sweating In the Humidity

When we humans are exposed to any combination of hot temperatures or high humidity, we become uncomfortable.  The amazing human body is able to acclimate somewhat, given enough time and exposure.

But hot and sticky weather always leaves us feeling, well, hot and sticky.  It is obvious why we have trouble keeping cool in the heat, but humidity is more complicated.  The external human body temperature is usually in the lower 70s Fahrenheit.  So when the dew point is around 70, moisture that forms on the surface of the skin (sweat) is much slower to evaporate and provide the cooling from evaporation.  We sweat but the sweat just makes us wet instead of evaporating and cooling us off.

Either way (heat or humidity), our bodies are in a constant state of perspiring and we need to drink extra water to stay hydrated internally.

Meteorologist John Wheeler

El Nino

Friday, July 31, 2015

El Nino continues to make weather news.  This change in atmospheric and sea-surface conditions in tropical regions of the Pacific happens every few years or so, but the one building now has the look of being a strong one.  El Nino’s impacts in the middle latitudes are more pronounced during the colder months.

What will the impacts be here?  It depends on other factors, of course.  This is weather which is highly dynamic.  But a strong El Nino can be statistically correlated to a stormier fall season, a much warmer than average winter with below average snowfall, and a colder but drier than average spring.

But it is important to understand that other factors can overwhelm the El Nino signal.  Of particular interest this winter is a large region of unusually warm water in the northeastern part of the Pacific Ocean.  What role this will play is interesting but unknown.

Meteorologist John Wheeler

Just Not That Hot

Our short summers give us little time to acclimate to sticky weather.  So if you find yourself complaining about the humidity, you are entitled.  But this summer, there has been as much hot air coming from the mouths of the complainers as from the weather, itself.

Through July 28, only four days have reached 90 degrees this summer, one in June and three in July.  It will take a serious stretch of hot weather in order for Fargo Moorhead even to achieve its average of 13 days at or above 90.

The average temperatures in June and July have been marginally above the long term average due mostly to slightly above average nighttime temperatures.  But, again, there has been very little in the way of truly high humidity.  Overnight lows have been mostly in the 60s these past few weeks with a few 50s and a couple of 40s thrown in.  We have mostly been spared those hot, sticky nights when dew points in the 70s keep the temperature from becoming comfortable.

Meteorologist John Wheeler