Incredibly Low Wind Chill Values Impact the Texas and Oklahoma Panhandles

The following article will discuss our recent wind chill outbreak.  Click on any image to view a "bigger picture".

Observed Wind Chills from Early February 2011
(Image 1 - Lowest observed wind chill values from February 1 through February 3, 2011)

Wind Chills

Over the past few days (January 31st through February 3rd) much of the United States felt the impact of a major winter storm. We were lucky here in the Panhandles to miss the multiple feet of snow or inches of ice, but we did experience something possibly record setting.; On the morning of February 1st, 2011 the Boise City, Oklahoma Mesonet site (an automated weather observing station) reported a wind chill of -36 degrees (image 1).By our best observation, this was the lowest wind chill ever recorded by an Oklahoma Mesonet site.

Before we get too excited, there are a few issues with that last statement. First, the Oklahoma Mesonet has only been operational since the early 1990s so they do not have any data before about 1993. Second, the wind chill formula changed in 2001 when scientists from Canada and the U.S. developed a more accurate method for calculating wind chill. Third, the original wind chill formula was developed in 1945 so we did not keep wind chill records prior to that date.

However, we can determine the wind chill for a particular period in time (even before 1945) if we know the air temperature and wind speed. That is a problem though since we did not always have accurate wind measurements. So finally, the biggest problem is that the National Weather Service just has not kept accurate wind chill records.

With that being said, we can make a few general observations about our recent cold outbreak. The widespread wind chill observations of around -30 degrees or less is extremely low and certainly abnormal for the Texas and Oklahoma Panhandles. Also, the period of time that we experienced wind chills below -15 degrees (which is the point when we issue a Wind Chill Warning) was well over 24 hours. This is also rare. In fact, many forecasters in our office could not remember the last time we issued a Wind Chill Warning.

Typically, we struggle to reach low wind chill values in the Panhandles because you need both cold temperatures and strong winds to produce low wind chills. Many times, we experience our coldest temperatures on clear, dry mornings with calm winds. Calm winds and dry air allow a process called radiational cooling to take place. When the winds are strong, this causes a process called mixing to take place. Mixing prevents the cold, dense air from settling on the ground and thus, keeps the ground temperature slightly higher than expected during radiational cooling.

This was a unique air mass though. The source air mass descended from the arctic region and drove quickly south into the Panhandles. Not only was the air near the ground very cold, but the air above the ground was cold as well. So even with the mixing taking place, the end result was just plain cold.

Temperatures

In addition to dangerously low wind chill values, temperatures have remained below freezing for a prolonged period of times during the current arctic outbreak. By the time temperatures rise above freezing on Friday, Amarillo will have remained below freezing for approximately 112 hours (about 4.7 days). To put this into perspective, the table below shows the most consecutive days that temperatures have remained below freezing along with the average temperature during those days.

Days Below Freezing

Dates

Average Temp. (F)

12
Dec 1978-Jan 1979
20.1
10
Feb 1895
15.5
9
Dec 1892
26.4
8
Dec 1983
9.5
8
Jan 1960
25.0
5

Jan 31-Feb 4, 2011

11.6

Clearly, our current cold snap does not even come close to the length of sub-freezing temperatures observed from December 1978 through January 1979. Arguably, however, the most impressive arctic outbreak occurred in December of 1983 when temperatures remained below freezing for 8 days and the average temperature during that time period was only 9.5 degrees!

The reason for the unusually prolonged and extreme cold weather observed in December of 1983 can be explained by looking at the upper air pattern across the United States (image 2). Typically, temperatures underneath ridges of high pressure experience above normal temperatures while temperatures underneath troughs of low pressure are below normal. In December of 1983, a stronger than normal ridge of high pressure was located in the eastern Pacific and extended well northward into Alaska. At the same time, an abnormally strong and persistent upper level trough of low pressure extended from Canada southward through the southern Plains. This pattern allowed very cold air to dive south from the arctic into the Texas and Oklahoma Panhandles.

Average 500mb flow pattern
(Image 2 - Average 500mb Pattern for Dec - Jan, 1984 to 1984.)

Departure from normal surface temps graphic(Image 3 - Departure from normal Surface Temperatures for Dec - Jan, 1984 to 1984.

Although the trough of low pressure weakened in January of 1984, it generally remained in place across the same area. As a result, surface temperatures were well below normal across a large portion of the central United States. In fact, the average temperatures in the Texas and Oklahoma Panhandles were on the order of 2-4 degrees below normal (image 3).

The result has generally been warmer than normal surface temperatures in the western half of the United States and below normal temperatures in the eastern half of the United States. The Texas and Oklahoma Panhandles have experienced temperatures between 1 and 2 degrees warmer than normal.

Average 500mb pattern for winter 2011
(Image 4 - Average Observed 500mb Pattern for Dec. - Jan. 2010 - 2011)

Average Surface Temp Departure from Normal Winter 2011
(Image 5 - Average Surface Temperature Departure from Normal from Dec. - Jan. 2010/2011)

Within the last week, however, a stronger than normal ridge of high pressure began to nose northward into Alaska while a stronger than normal trough of low pressure migrated across the Four Corners region. The end result has been well below normal temperatures for the Panhandles during the first few days of February. The image on the left (image 5) shows the average temperature variation from normal from December through January (this winter). Notice that the Panhandles experienced temperatures that were one to two degrees above normal. Despite the recent cold wave, since December 2010, temperatures have generally been much warmer than the same time period from December of 1983 through early February of 1984. 

The three graphs below compare the daily observed maximum, minimum and average temperatures from the 1984 winter season to the current winter season. You will notice more frequent periods of cold air during the 1984 winter with a sharp drop in temperatures at the end of the graph for the current winter (images 6, 7 and 8).

Max Temp Comparison Max Temp Comparison Max Temp Comparison
(Image 6 - Camparison of Observed Daily Maximum Temperatures between the Dec./Jan. of 1983/84 and Dec./Jan. of 2010/11.) (Image 7 - Camparison of Observed Daily Minimum Temperatures between the Dec./Jan. of 1983/84 and Dec./Jan. of 2010/11.)

(Image 8 - Camparison of Observed Daily Average Temperatures between the Dec./Jan. of 1983/84 and Dec./Jan. of 2010/11.)

Another interesting issue with image 5 from above, is the particularly warm air located in the arctic region and northeast Canada.  While at the same time, there is colder than normal air sitting across much of the eastern United States.  This seems a bit counterintuitive.  Why would it be colder than normal in the eastern U.S. if the air across the arctic region is warmer than normal?  Well, a simple explanation is that the cold air is being displaced from the arctic region into the middle latitudes (Continental United States).  While there are multiple causes for this displacement, one of the primary factors is the consistent “blocking” high pressure that has formed over the arctic region.  This high pressure center has essentially redirected the cold low pressure system further south.
You can note this general theme on the image to the right (image 9) which shows the departure from normal of the average 500mb pattern during December and January.  The 500mb level is a good measure of the center of the atmosphere and we use this level to find high and low pressure systems.  Notice the warm colors over the arctic region.  This graphic indicates the 500mb pressure level was much higher than normal during the winter months.  You can also note that the 500mb level was lower than normal across the eastern United States.  In other words, the low pressure systems were moving across the eastern U.S. more frequently providing colder air and more winter storms. 

500mb departure from normal chart
(Image 9 - 500mb Departure from Normal Chart for Dec./Jan. 2010/11)

La Nina

The pattern this year fits very close to the expected conditions during a La Nina pattern.  During a typical La Nina season, ocean waters in the Pacific Ocean along the equator are colder than normal.  This slight decrease (or increase in the case of El Nino) in sea surface temperature creates significant effects on the North American weather patterns.  The graphic below demonstrates how the jet stream reacts during a La Nina pattern (image 10).  Notice the large blocking high pressure centered over the Pacific Ocean with the trough of low pressure (where the purple jet stream line makes a dip) over the north to northeastern United States.  Compare the typical La Nina pattern to the average pattern observed during December and January (image 11).
  Average 500mb chart for winter 2011 
(Image 10 - The Typical Weather Pattern for La Nina)  (Image 4 - Average Obs. 500mb Pattern for Dec./Jan. 2010/11)

Temperature is Weather’s Silent Killer

Pop quiz: What is the leading cause of weather-related deaths?  Tornadoes?  Nope.  Hurricanes?  Wrong again.  Lightning?  Getting closer.  Flooding?  Yes and no.  Flooding is often cited as the #1 weather killer, but the truth is, you could combine flooding, lightning, tornadoes, and hurricanes and you would just reach the number of deaths caused by heat alone.  Then if you add deaths associated with cold, it is clear that air temperature is in fact the leading cause of weather-related fatalities. 

But air temperature is not glamorous.  Air temperature does not destroy homes, throw large objects through the air with ease, or gain round the clock news coverage.  You can’t see it coming like a tornado, or hear it like thunder, but it is more dangerous than any other type of weather.

There are a number of ways that air temperature can be dangerous, both directly and indirectly.  Prolonged heat spells can cause heat exhaustion, heat stroke, or dehydration.  Long periods of exposure to the extreme cold can quickly cause frost bite or hypothermia.  These heat waves or cold outbreaks impact the vulnerable populations, such as the elderly or those with special needs, more frequently but they are not the only people at risk.  
The Center for Disease Control (CDC) reports that on average, about 180 people in the United States die every year from Carbon Monoxide poisoning by non-automotive products.  These products include malfunctioning fuel-burning appliances such as furnaces, ranges, water heaters and room heaters; engine-powered equipment such as portable generators; fireplaces; and charcoal that is burned in homes and other enclosed areas.  These fatalities peak during the winter months, specifically in December and January, when fuel-burning appliances are used more frequently for home heating purposes (image 13). 

During the rest of the year, Carbon Monoxide related deaths often coincide with bouts of severe weather.  Power outages caused by strong winds, lightning strikes or other weather related issues lead some people to run generators to provide power to their home.  If these generators are run inside the home, the expelled Carbon Monoxide can quickly turn dangerous.  As an example, the CDC noted that in 2005, 47 people died from Carbon Monoxide poisoning during the power outages caused by severe weather, including Hurricane Katrina.
Monthly Carbon Monoxide Related Deaths

The Bottom Line

Just remember that when the weather turns cold, don’t use Carbon Monoxide producing products to heat your home unless you use proper ventilation.  Make sure the flue is open in your gas burning fireplace (I can speak from personal experience that failing to open your flue while running your fire place will cause your Carbon Monoxide detector to alarm.  Thankfully, my CO alarm was in proper working order or I might be writing this article for an entirely different audience.). 

Stay warm out there!

Please contact Justyn.Jackson@noaa.gov or John.Brost@noaa.gov for questions. 


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