Denver’s April 2013 Climate Summary With A Bonus

During the month of April 2013, Denver, CO (link updated monthly) recorded a 74°F difference between maximum and minimum temperatures.  This fact tells us nothing about how temperatures compare to climatological norms however.  For the entire month, Denver was 5.7°F below normal (41.7°F vs. 46.4°F).  The maximum temperature of 80°F was recorded on the 29th while the minimum temperature of 6°F was recorded on the 10th.  Here is the time series of Denver temperatures in April 2013:

Figure 1. Time series of temperature at Denver, CO during April 2013.  Daily high temperatures are in red, daily low temperatures are in blue, daily average temperatures are in green, climatological normal (1981-2010) high temperatures are in light gray, and normal low temperatures are in dark gray. [Source: NWS]

There is a big disparity between 2013 temperatures and normal temperatures, especially daily maxima.  Three outbreaks of Arctic air impacted Denver during the month, which set record low temperatures on four different days.  This graph also shows something else that is eye-opening: five daily maximum temperatures were equal to or lower than the climatological daily minimum temperature!  As someone who was ready for spring to spring, April was a disappointing weather month.

But it also got me to thinking about the difference between spring 2013 and spring 2012.  As many of us remember, temperatures in the US in 2012 were very warm compared to climatological norms.  So how different were temperatures in Denver in February-March-April 2013 versus 2012?  I decided to take a look.  Let’s start with extending the dates in Figure 1 back to the beginning of February 2013:

Figure 2. Time series of temperature at Denver, CO during February-April 2013.  Daily high temperatures are in red, daily low temperatures are in blue, climatological normal (1981-2010) high temperatures are the top dark gray line, and normal low temperatures are the bottom dark gray line. [Source: NWS]

This graphic simply demonstrates the same story that I wrote above as well as in my March and February Denver Climate Summary posts.  February was obviously colder than normal due to extended cold air masses over the area.  March and April were also colder than normal, but this was due to vigorous mid-latitude cyclones that brought Arctic air masses south over the area.  This is evident by the significant dips in both maximum and minimum daily temperatures: there was one in the beginning of March, another in the end of March, and three in April.

With this chart in mind, let’s look at the difference between 2012 and 2013.  First, daily maximum temperatures:

Figure 3. Time series of maximum temperature at Denver, CO during February-April 2012 and 2013.  2013 temperatures are in brick-red, 2012 temperatures are in red, and climatological normal (1981-2010) high temperatures are the dark gray line with green crosses. [Source: NWS]

My memory of 2012′s maximum temperatures was close to reality.  February 2012 was colder than I remember, but this was likely affected by the warmth of April 2012 and the record-setting daily highs in the summer of 2012.  Figure 3 shows a very large difference between daily maximum temperatures in 2012 and 2013, especially after the 22nd of March.  I didn’t remember the cold snap on April 3, 2012.  This graphic shows, by proxy, the lack of spring synoptic storms in 2012.  Daily maximum temperatures rarely fell below the normal for the date.  Instead, April temperatures were as much as 20°F warmer than normal on some dates, but regularly 10°F warmer than normal.  In contrast, 2013 temperatures were often 25-30°F colder than normal.  The difference between two years’ temperatures is a measure of interannual weather variability.  I have more on that below.

Figure 4. Time series of minimum temperature at Denver, CO during February-April 2012 and 2013.  2013 temperatures are in blue, 2012 temperatures are in green, and climatological normal (1981-2010) high temperatures are the dark gray line with brown pluses. [Source: NWS]

Again, February 2012′s temperatures were similar to February 2013′s.  The specific dates of temperature swings obviously varies between the two years.  March 2012 and March 2013 also look similar, up until the 22nd of March (see maximum temperatures above also).  Thereafter, the time series diverge with much colder air in place over Denver four different times through the end of April.  2012 had warmer than normal minimum temperatures through most of April.  The combination of warmer than normal nights and days, combined with a relative lack of precipitation in 2012 set the stage for the record-setting warmth in the summer as well as the rapid decline in drought conditions, which are still largely present now.

Interannual Variability

I have written hundreds of posts on the effects of global warming and the evidence within the temperature signal of climate change effects.  This series of posts takes a very different look at conditions.  Instead of multi-decadal trends, this series looks at highly variable weather effects on a very local scale.  The interannual variability I’ve shown above is a part of natural change.  Climate change influences this natural change – on long time frames.  The climate signal is not apparent in these figures because they are of too short duration.  The climate signal is instead apparent in the “normals” calculation, which NOAA updates every ten years.  The most recent “normal” values cover 1981-2010.  The temperature values of 1981-2000 are warmer than the 1971-2000 values, which are warmer than the 1961-1990 values.  The interannual variability shown in the figures above will become a part of the 1991-2020 through 2011-2040 normals.

Precipitation

Precipitation was above normal again during April 2013, extending this new trend to three months.  During the month, 1.87″ of liquid water equivalent precipitation fell, compared to 1.71″ normally.  The wettest April on record was in 1983 when 4.56″ of precipitation fell.  There were three notable weather events during April: a 6″+ snowstorm on the 9th, a 7″+ snowstorm on the 15th, and a 5″+ snowstorm on the 22nd.  In total, the NWS recorded 20.4″ of snow.

The recent precipitation surplus reduced northeast CO drought severity in the last three m months, but did not break it yet.  Above-average precipitation will have to fall for longer than three months for that to happen.  The NWS expects continued drought conditions across most of Colorado through the next three months.  Additional improvement in eastern Colorado might occur, but NOAA and the CPC expects western Colorado drought  to remain the same or worsen.

Denver’s March 2013 Climate Summary

During the month of March 2013, Denver, CO (link updated monthly) recorded a 74°F difference between maximum and minimum temperatures.  This fact tells us nothing about how temperatures compare to climatological norms however.  For the entire month, Denver was 2.7°F below normal (37.7°F vs. 40.4°F).  The maximum temperature of 76°F was recorded on the 15th while the minimum temperature of 2°F was recorded on the 25th.

Figure 1. Time series of temperature at Denver, CO during March 2013.  Daily high temperatures are in red, daily low temperatures are in blue, daily average temperatures are in green, climatological normal (1981-2010) high temperatures are in light gray, and normal low temperatures are in dark gray. [Source: NWS]

Precipitation was above normal again during March 2013, making a two-month trend.  During the month, 1.47″ of liquid water equivalent precipitation fell, compared to 0.92″ normally.  The wettest March on record was in 1983 when 4.56″ of precipitation fell.  There were two notable weather events during March: a 6″+ snowstorm on the 9th and the 23rd.  In total, the NWS recorded 23.5″ of snow, 13.5″ more than the normal of 10.0″ for the month.

While more precipitation fell than normal during the month, the drought impacting the region was still not broken.  Above-average precipitation will have to fall for longer than one month for that to happen.  The NWS expects continued drought conditions across most of Colorado through the next three months.  Some improvement in northeast Colorado might occur.  In contrast to February and March, the NWS projects warmer and drier than normal conditions over Colorado during the next three months.

Denver’s February 2013 Climate Summary

During the month of February 2013, Denver, CO recorded a 58°F difference between maximum and minimum temperatures (20°F less than January!).  This fact tells us nothing about how temperatures compare to climatological norms however.  For the entire month, Denver was 2.4°F below normal (30.1°F vs. 32.5°F).  The maximum temperature of 63°F was recorded on the 17th while the minimum temperature of 5°F was recorded on the 22nd.

Figure 1. Time series of temperature at Denver, CO during February 2013.  Daily high temperatures are in red, daily low temperatures are in blue, daily average temperatures are in green, climatological normal (1981-2010) high temperatures are in light gray, and normal low temperatures are in dark gray. [Source: NWS]

Precipitation was finally above normal again during February 2013.  During the month, 0.77″ of liquid water equivalent precipitation fell, compared to 0.37″ normally.  For the first time in my life, rain fell across the Denver metro area in February!  On the 6th, it rained very lightly, just enough to make the streets and plants wet.  To add to the oddity and rarity of the situation, the ground was still wet with liquid on the morning of the 7th – it wasn’t cold enough to freeze the rain overnight. A similar event occurred in late January.  Conditions returned to normal in the second half of the month.  Measurable snow finally fell on the 20th and 21st of the month.  Then a significant winter storm hit the area on the 24th, dropping ~9″ of snow across the metro area.  In total, the NWS recorded 14.1″ of snow, 8.2″ more than the normal of 5.9″ for the month.

While more precipitation fell than normal during the month, the drought impacting the region was not broken.  Above-average precipitation will have to fall for longer than one month for that to happen.

Denver’s January 2013 Climate Summary

During the month of January 2013, Denver, CO recorded a 78°F difference between maximum and minimum temperatures.  Does that tell you anything about whether it was warmer or colder than normal?  No, it does not.  For the entire month, Denver was 0.4°F below normal (30.3°F vs. 30.7°F).  But the maximum temperature of 66°F was recorded on the 24th while the minimum temperature of -12°F was recorded on the 12th.

Figure 1. Time series of temperature at Denver, CO during January 2013.  Daily high temperatures are in red, daily low temperatures are in blue, daily average temperatures are in green, climatological normal (1981-2010) high temperatures are in light gray, and normal low temperatures are in dark gray. [Source: NWS]

Precipitation was below normal again during January 2013.  0.31″ of liquid water equivalent precipitation fell during the month, compared to 0.41″ normally.  For the first time in my life, rain fell across the Denver metro area in January!  Two days after hitting the high for the month, the National Weather Service recorded 0.01″ of rain on the 26th.  I haven’t read anything regarding historical rain in Denver in January, but I think such an event is very rare indeed.  4.6″ of snow fell, which was 2.4″ below the normal of 7.0″.

2012: Hottest Year On Record For United States

It’s official: 2012 was indeed the hottest year in 100+ years of record keeping for the contiguous U.S. (lower 48 states).  The record-breaking heat in March certainly set the table for the record and the heat just kept coming through the summer.  The previous record holder is very noteworthy.  2012 broke 1998′s record by more than 1°F!  Does that sound small?  Let’s put in perspective: that’s the average temperature for thousands of weather stations across a country over 3,000,000 sq. mi. in area for an entire year.  Previously to 2012, temperature records were broken by tenths of a degree or so.  Additionally, 1998 was the year that a high magnitude El Niño occurred.  This El Niño event caused global temperatures to spike to then-record values.  The latest La Niña event, by contrast, wrapped up during 2012.  La Niñas typically keep global temperatures cooler than they otherwise would be.  So this new record is truly astounding!

The official national annual mean temperature: 55.3°F, which was 3.3°F above the 20th century mean value of 52°F.

Figure 1 – NOAA Graph showing year-to-date average US temperatures from 1895-2012.

This first graph shows that January and February started out warmer than usual (top-5), but it was March that separated 2012 from any other year on record.  The heat of July also caused the year-to-date average temperature to further separate 2012 from other years.  Note the separation between 2012 and the previous five-warmest years on record from March through December.  Note further that four of the six warmest years on record occurred since 1999.  Only 1921 and 1934 made the top-five before 2012 and now 1921 will drop off that list.

Figure 2 – Contiguous US map showing state-based ranks of 2012 average temperature.

Nineteen states set all-time annual average temperature records.  This makes sense since dozens of individual stations set all-time monthly and annual temperature records.  Another nine states witnessed their 2nd warmest year on record.  Nine more states had top-five warmest years.  Only one state (Washington) wasn’t classified as “Much Above Normal” for the entire year.  The 2012 heat wave was extensive in space and severe in magnitude.

Usually, dryness tends to accompany La Niña events for the western and central US.  This condition was present again in 2012, as the next figure shows.

Figure 3 – Contiguous US map showing state-based ranks of 2012 average precipitation.

As usual, precipitation patterns were more complex than were temperature patterns.  Record dryness occurred in Nebraska and Wyoming.  Colorado and New Mexico saw bottom-five precipitation years.  Severely dry conditions spread across the Midwest all the way to the mid-Atlantic and Georgia continued to experience dryness.  Washington and Oregon were wetter than normal as a result of the northerly position of the mean jet stream in 2012.  Louisiana and Mississippi saw wetter than normal conditions, largely as a result of Hurricane Isaac.

Figure 4 – Contiguous US map showing state-based average actual precipitation.

I always find it useful to know the magnitude of measurements as well as how they stack up comparatively.  Figure 4 provides the former while Figure 3 provides the latter.  “Normal” precipitation varies widely across the country and even between neighboring states.  How much precipitation fell to allow NE and WY to record driest years on record?  13.04 and 8.03″, respectively.  Another useful map would be state-based difference from “normal”.

So the brutal heat that most Americans experienced was one for the record books.  As the jet stream remained in a more northerly than usual position, heat across the country dominated.  More heat and fewer storm systems in 2012 meant widespread and severe drought expanded across the country.  That drought tended to reinforce both the temperatures recorded (drying soils meant incoming solar radiation was more easily converted directly to sensible heat) and the lack of precipitation (dry soils required extra moisture to return to normal conditions).

Thankfully, record-setting temperatures didn’t occur all over the globe in 2012 (although Australia is having their own problems now in 2013).  I therefore don’t expect 2012 will be the warmest year on record globally, but a top-10 finish certainly is not out of the question.  Again, this is significant because of the extended La Niña event that ended in mid-2012.  Without the influence of anthropogenic (man-made) climate change, 2012 probably would have been cooler than will be recorded.  The background climate is warming and so La Niñas today are warmer than El Niños of yesterday.

These warming and drying conditions have massive implications for our society.  The drought that afflicted the Midwest in 2012 helped push up commodity prices as crops failed.  If that trend continues into 2013, prices will rise further, which will pinch all of our finances.  Drought in the Southwest and Midwest impacted flows in rivers (Colorado & Mississippi, among others).  The former could mean imposed restrictions in 2013 while the latter could mean reduced river transportation, which puts further pressure on goods sold in the US.  Conditions aren’t the worst recorded yet, but it is imperative that we examine resource management policies.  Are policies robust enough to handle the variability of today’s climate?  If not, they probably aren’t equipped to address future variability or change either.  What systems are critical to today’s society?  If the Southwest remains dry, does agriculture (largest user of CO river water) reduce its use or do urban users?  What sets of values guide these and other decision-making processes?

Colorado’s Hot, Dry September Follows Hot, Dry Summer: Get Used To It

For those of us living in Colorado, we know that this summer was warmer and drier than normal.  We further know that September was one of the warmest and driest on record.  And just like the rest of the world, if we don’t stop forcing the climate system with our global warming pollution, this summer and this September will become the new normal.  Even hotter and drier years are on tap if that happens. I’m going to start on a local level.  The Denver metro area recorded its 5th driest and 7th warmest September on record in 2010.  The climatological period is 1971 to 2000; the length of reliable records date back to 1872.  September 2010 was thus in the top 5 driest and top 10 warmest out of more than 125 other Septembers.  In other words, it was very significant.  Some of the details of that warmth should be noted:

THERE WERE 8 NINETY DEGREE DAYS WHICH WAS 6 ABOVE THE NORM. FOR THE SEASON NOW…THERE HAVE BEEN 49 90 DEGREE DAYS WHICH IS 16 ABOVE NORMAL. ONE NOTEWORTHY STATISTIC WAS THAT DURING SEPTEMBER 2010 THERE WERE 25 DAYS THAT RECORDED TEMPERATURES OF 80 DEGREES OR HIGHER. ACCORDING TO LOCAL CLIMATOLOGICAL RECORDS…THAT IS THE HIGHEST NUMBER OF 80 DEGREE TEMPERATURES FOR SEPTEMBER IN DENVER SINCE 1872.

That’s part of how you get the 7th warmest September on record.  More importantly, overnight lows tend to drive records like this.  Higher overnight lows help keep daytime highs higher and month-long temperatures on pace for record highs. And how dry was it?

BETWEEN THE 18TH AND 22ND OF SEPTEMBER…THE DENVER INTERNATIONAL AIRPORT COLLECTED A TOTAL OF ONLY 0.06 INCH OF MOISTURE. THE REMAINING 25 DAYS OF THE MONTH WERE TOTALLY DRY…NOT EVEN A TRACE OF LIQUID. BETWEEN AUGUST 8TH AND SEPTEMBER 30TH ONLY 0.08 INCH OF RAINFALL WAS TALLIED.

Eight-hundredths of an inch of precipitation is incredibly low for a nearly two-month time period.  Combined with the heat, it’s what has led to my lawn and garden to nearly stop growing and turn brown.  Obviously, it also puts stress on local water supplies. Let’s look at this in a slightly different way.  When all the hourly temperature readings are averaged over the entire month of September, the average temperature for the month registered 67.0F.  Compared to 30 years of climatological records, that was 4.6F above normal.  When you read a number like that, you should keep in mind that the most likely set of climate model solutions project that level of warming for Colorado to become the new normal this century.  Left unchecked, global warming will make this September’s near-record heat and lack of precipitation just an average year in just a few decades’ time.  I want to share this graphic again, which shows the number of weeks per year which have high temperatures over 100F. I don’t think 2 months of 100F highs sounds like a future that I want to experience. How about you? Changing gears a little bit, I wanted to discuss Colorado temperatures and precipitation for September and the summer. According to NOAA’s NCDC, Colorado recorded its 112th warmest out of 116 Septembers.  So the heat didn’t just affect Denver or the Front Range metro area.  Colorado also recorded its 18th driest out of 116 Septembers.  A quick aside: Wyoming recorded its all-time driest September in 2010 while Minnesota recorded its all-time wettest September.  Those kind of seemingly paradoxical simultaneous conditions are exactly the kind of phenomenon projected to occur more and more often in the upcoming decades.  In other words, get used to it. Additional data from the NCDC shows that Colorado recorded its 106th warmest July-September on record.  In fact, take a long look at the map at that link.  An overwhelming majority of states across the continental U.S. had above average Jul-Sep temperatures.  A majority of states had their top-10 warmest Jul-Sep temperatures out of the past 116 years.  Two saw their all-time warmest Jul-Sep periods ever.  Again, these kind of conditions are only expected to occur with more frequency in the future … unless we stop our global warming pollution.  Colorado’s Jul-Sep precipitation was much closer to normal.  How is that, you might ask, when September was so dry?  Because July and August both came close to being notably wetter than normal. Some of these numbers may not seem that impressive or may not trigger some level of concern by themselves.  Think about them in context of water supplies, agriculture and ecosystem health and they should become worrisome.  These trends aren’t likely to go away.  In fact, just the opposite, they’re likely to get worse and do so soon.  How will millions of Front Range residents cope with dwindling water supplies, especially when farmers will want and need to grow crops for food.  While we might be able to adjust, countless flora and fauna species are accustomed to long-term stable climate conditions.  They’re not going to be able to adjust to radically different conditions on time-scales of years to decades.  Their health and survival now largely depend on our decisions and actions. You can do something tomorrow.  Find a 350.org event near you and help put pressure on decision makers to actually start making some decisions. Cross-posted at SquareState.

AMS’ State of the Climate in 2008

I got my AMS State of the Climate in 2008.  I’m browsing through it now.  I’ve come across a number of interesting results – mostly about the wide-ranging impacts the moderate La Nina had on the planet’s weather patterns and observations last year.  With the La Nina over and a new El Nino continuing to intensify, 2009 and 2010 will hold interesting phenomena as well.

I plan on posting some tidbits about 2008 results and put them in context with how things have developed so far this year.  Between sorting through the big report, work and a modeling class, I might not post as often or as much as I’d like.  We’ll see what happens.

Denver Weather & Climate: July 2008

Crossposted at SquareState.

I’m sure those of us in the Denver metro area have noticed that July has been pretty warm this year. For those that are interested in details, a large ridge has established itself over these and other parts (a ridge is the opposite of a trough; troughs move air-masses around and ridges keep them in place). The result has been higher than climatological average temperatures and less than average precipitation.
The local NWS office has officially recorded 15 consecutive days of high temperatures of 90 degrees or more for Denver (at DIA). The record streak for Denver is 18 days. I’ve seen observations over 90 at Denver today, so add one to the streak. The high temperature should exceed 90 the rest of this week, so the record could be broken in a big way. Before I count those chickens, however, it’s instructive to look at the years still officially with longer streaks: 1987 (16 days), 2000 (17 days), 1874 and 1901 (18 days each). 2000 had a second streak later the same summer of 12 consecutive days of 90+ degrees.

If you were around in 2005, you probably remember July of that year was warmer overall. It didn’t have very long streaks of high temperatures, but it did have the most 100+ degree days in Denver history with seven, five of which happened in a row. Ugh!

What about precipitation? That’s not looking so good for Denver (again, officially at DIA now). As of the beginning of this year, 2002 stands as the driest year in Denver’s history. So far, this year is drier. And not only is it drier, it’s significantly drier. Take a look:

2002 2008 (inches)

Jan 0.48 0.08

Feb 0.32 0.18

Mar 0.53 0.17

Apr 0.23 0.32

May 0.94 1.56

Jun 1.45 0.73

July thru 26th 1.39 0.24

————————————————————————————-
Total 5.34 3.28

Difference -2.06

Keep this in mind: one or two storms can make up this entire difference. A heavy rainstorm or snowstorm right over the station at DIA can significantly add to this year’s total. 2008′s numbers aren’t the end of the world. But they’re definitely worth noting.

I’m also left wishing once again for a robust mechanism to get town-by-town results from across Colorado. How do Durango, Grand Junction, Pueblo and Greeley compare, for instance? Such things take money and time, though…

Sweet Modeling Video

I found a very nicely put together short video that shows some of the parameters considered in general climate models. Go to the following blog:

Ice Blog

It’s in French, so look for the term “ici” in parentheses. It’s a link that will allow you to download the video (36.4MB). Play it in your favorite software and enjoy the show!

Climate Updates 6/14/08

Did you know that

as far back as 1995, analysis by the National Climatic Data Center showed that over the course of the 20th century, the United States had suffered a statistically significant increase in a variety of extreme weather events, the very ones you would expect from global warming, such as more — and more intense — precipitation.

You can see an example of the U.S. Climate Extremes Index at Climate Progress. The plot shows twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events. Note that 2007 had the second most extreme precipitation over the U.S. in the historical record, close behind 1998. Note further that the 5-year moving average is now high above the long-term average. Put another way, the findings in the 1995 analysis are not only still valid, but are actually more applicable today. Extreme weather events such as intense precipitation are increasing in frequency.

***

One of the leading climate stories from last year was the record melt of the Arctic ice sheet. The Northwest Passage even opened. So one big question for this year is will Arctic ice in 2008 melt more than it did in 2007? The answer so far isn’t so good.

As the graph shows, the ice extent this year has been well below the climatological average and has been nearly as low as last year’s record. In March, conditions weren’t quite as bad as they were last year, but the degree of melting by the end of May put the ice extent to the same value as is normally seen near the end of June. One of the commenters after the post points out that the graph that is updated daily. As of 14Jun08, the ice extent is slightly less than it was at the same point in 2007, a bad signal for the rest of this year.