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

 

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

Warmer, Yet Not So Hot

There is an interesting trend regarding our summer temperatures.  Over the past few decades, the summertime average temperature for Fargo Moorhead has risen slightly.  However, there is an opposite trend of there being fewer days with high temperatures in the 90s and 100s.

From 1980 through 1989 there were 15 days in the 100s.  But in the 26 years since 1989, there have been just four days in the 100s. Meanwhile, the average temperature has risen, particularly the average daily low temperature.

What gives?  More humidity and more rainfall yield warmer nights which raises the average temperature but also allow for fewer really hot days which are more likely when the soil is dry.  Prior to 1990 when there was generally less rainfall, there were more hot days even in a cooler climate.

Meteorologist John Wheeler

Not So Hot

In our part of the country, many people associate temperatures of 90 degrees or higher as being a sort of statistical boundary between our regular warm summer weather and what is considered “hot.”  Fargo Moorhead experiences an average of about 13 days a year at 90 degrees or higher.  The greatest number of 90 degree days was 39 in 1988.  Last summer there were only three.

Days of 100 degrees or hotter have historically occurred at a pace slightly lower than once every two summers.  However, these hottest of hot days are tied closely to soil moisture and there have been so many wet summers in recent years that 100 degree weather has become rare.  Since the summer of 1989, there have only been four days of 100 degree heat. The last was July 20, 2012.  Previous to that, there were two century days in July of 2006, and one in June of 1995.

Meteorologist John Wheeler

 

El Nino 2015-16

A very strong El Nino appears to be developing in the Pacific Ocean. El Nino is a reversal of weather conditions across the tropical Pacific.  Areas near South America get warmer and wetter while areas near Australia become very dry.  This affects the weather around the world by deflecting the Jet Stream.

But the effects around the world (including around here) are hard to predict because other large-scale patterns also influence the storm track.  The biggest concern for our area would be the potential development of a blocking pattern which could bring either persistently wet weather or drought, depending on the shape of the Jet.

At present, a large region of anomalously warm water off the coast of Oregon, Washington, and British Columbia, adds to the uncertainty.  If the strong El Nino continues to develop in conjunction with this warm blob, it could mean a very interesting winter for some parts of the world.

Meteorologist John Wheeler

When to Interrupt the Show?

Television meteorologists always struggle with the question of when to break into regular programs for important weather announcements.  WDAY’s policy is to interrupt for all Tornado Warnings, but only the most severe of non-tornadic storms; the ones with life-threatening winds or extreme flooding.

Wednesday afternoon, a thunderstorm was rolling into Fargo Moorhead with heavy rain, gusty winds, and lots of lightning.  The National Weather Service criteria for a Severe Thunderstorm Warning is a wind of 58 mph or greater or one inch diameter hail.  This storm had neither although it did have heavy rain, moderately strong wind gusts, and intense lightning. We elected to not interrupt the show.  As the storm passed into south Moorhead, rainfall intensified and there was street flooding.

In hindsight, perhaps we should have interrupted for this one even though it was not really life-threatening.  It’s always a tough call because those not in the path of the storm would have wondered why we were interrupting their show.

Meteorologist John Wheeler

Will the Warming Return?

The globally averaged temperature rise in the Twentieth Century leveled off following the extremely warm El Nino year in 1998.  Since then, Earth’s atmosphere has remained very warm, but has shown little or no warming.

An article in Science Daily reveals a possible explanation for the warming hiatus.  An international group of scientists have discovered that volcanic aerosols in the atmosphere have been reflecting twice as much solar radiation that previously thought.  The study found no increase in aerosols from 1999-2002, but a tremendous increase starting in 2005.  Kasatochi in August 2008, Sarychev in June 2009, and Nabro in June 2011; are the three biggest contributors of sulphur dioxide which is a well-known reflecter of solar radiation.

A cooling of the Pacific Ocean and a drop in El Nino frequency has also added to the lack of warming.  If the present building El Nino turns out to be a big one, it is likely that modern-day world temperature records will be broken next year.

Meteorologist John Wheeler

Not Just Hot Air

Most of the energy from the sun’s rays passes right through the air onto the ground. There, depending on the radiative qualities of the particular surface, it can get really hot.

A metal car hood or an asphalt parking lot might be too hot to touch even with the air temperature in the 80s or low 90s.  The temperature of some surfaces, especially those colored black, can get as hot as 150 to 200 degrees.  The air adjacent to these surfaces can be very warm, too.

When we report the current temperature, we are reporting the temperature at a precise location at a certain height above the ground in the shade.  This is required in order to have some uniformity when comparing temperatures.  But the actual temperature of the air can vary greatly from spot to spot.  And the temperature of objects can vary even more.  Meteorologist John Wheeler