Record Low Temperatures for Denver, CO Today

An arctic air mass plunged down the east side of the Rocky Mountains in the past day.  This air mass will cause record low temperatures for the Denver, CO area.  According to the NWS, the record low maximum temperature for April 9th is 27F, which was set in 1973.  The record low minimum temperature for April 9th is 12F, which was set in 1959.  The temperature at DIA at midnight this morning was 24F.  The maximum temperature during the day today will not be higher than 20F, which means the calendar day’s maximum temperature has likely already been set.  It’s 15F right now, which is quite frigid for April in Denver.

The storm system that brought this cold air to the area was also supposed to bring considerable snow.  Yesterday’s forecast predicted up to 12″.  Because of the chaotic nature of the atmosphere, Denver will not receive 12″ of snow.  The upper level low split into two smaller pieces as it tried to traverse the intermountain west.  This development is not unusual, but numerical models have a hard time handling this behavior due to their limited resolution.  When upper level lows split, the energy associated with the storm also splits.  So instead of 12″ over the Denver area, lower amounts will be spread over a larger area.  The timing of vertical lift and the passage of a series of cold fronts through Denver also affected the beginning of precipitation.  Rain was supposed to fall starting around 6P last night, then switch to snow between 9P and midnight.  Instead, light snow started to fall around 10P.

This storm system is part of a different pattern than what occurred last year.  During early April 2012, record maximum temperatures were set.  Most of the change is due to simple interannual weather and climate variability, including low-frequency climate oscillations like the El Nino-Southern Oscillation and the Interdecadal Pacific Oscillation.  We can attribute part of the change to the underlying warming climate, which impacts those climate oscillations.

Climate change skeptics will likely point to this storm and the record lows that the NWS will record as “proof” that a warming climate is not occurring.  To the contrary, there is a climate-related reason why this storm system is impacting the western US today and bringing record warm temperatures to the eastern US.  The following plot shows today’s jet stream configuration:

The strength of the jet stream is characterized by the speed of the winds.  As the figure shows, there are very fast winds on the west side of the trough over the western US (red-filled contour where winds are in excess of 125 knots).  There are very slow winds south of Louisiana and east of northern Florida.  I have included an arrow on this figure to highlight the climate-related impact.  As the Arctic warmed more than the equatorial region, the temperature gradient weakened.  Temperature gradients cause pressure and density gradients (Ideal Gas Law).  As the average annual equator-pole temperature gradient weakens, the average pressure gradient similarly weakens.  This reduced pressure gradient causes the west-to-east movement of storm systems to slow down.  The arrow above highlights the amplitude of the current wave traversing North America.  This wave’s amplitude is characterized as high due to its large latitudinal extent (it stretches from Mexico to northern Canada, which is a very large distance).  This high amplitude simultaneously causes cold air to move from the Arctic to more southerly locations, such as Denver, CO, and warm air to move from the sub-tropics to more northerly locations, such as the eastern US.

Absent long-term anthropogenic climate change, this storm system would be much less likely to move slowly and bring record low temperatures to the middle of the US.  Instead, the storm would move quickly across the country.  Denver would receive cooler than average temperatures, but not record cold temperatures.  The cold air would remain further north and impact Canada and the northern US.

To summarize, climate change will not banish record low temperatures.  They will become more rare, however.  Winter will still occur in the mid- and high-latitudes.  But those winters will, on average, become warmer in the future.  Precipitation that would have fallen as snow in the 20th century will be likelier to fall as rain as the 21st century progresses.  More precipitation will likely fall during each event, but there will be longer time periods between precipitation events.  Overall, aridity will increase and flash flooding could become a more common problem for communities.

Thankfully, the NWS predicts temperatures to return to normal by this weekend.  I’m sure happy to receive the precipitation, but I wish it came as rain and left the Arctic air up in the Arctic.

Graphical History of 100 Degree Days in Denver & Possible Warmest July/Month

After a little bit of digging, I found the local NWS Office’s list of 100 degree days in Denver since 1872 – a 140 year history.  I’ve graphed number of occurrences by year:

The data is valid through the 28th of July, 2012.  As I’ve stated in previous posts, the previous yearly maximum number of occurrences took place in 2005 with 7.  So far this year, the temperature has exceeded 100°F 13 times.  At this point, I do not expect the NWS to record another 100°F day during the rest of this year.  While it has been warmer than normal in Denver, the North American monsoon season has kicked into gear, which suppresses daily maximum temperatures due to cloud formation.  The afternoons cannot get as warm with widespread, thick clouds as they could prior to the monsoon when the sun warmed the ground throughout the day.

Note that while 100°F day incidence appears to be increasing, I am not making any claim as to the statistical significance of such a development.  The linear trend (not shown) over the entire dataset is slightly positive, but these events are too rare from which to draw robust conclusions.

That said, the average temperature through the 28th of July in Denver is 78.9°F.  The Denver/Boulder NWS Office has the top-10 warmest Julys list:

10 WARMEST JULS
(1872-2011)

77.8 1934 #
77.7 2005
77.6 2008
77.3 1936
77.1 1939
76.9 1966, 2003
76.8 1954
76.7 2000, 2001
76.6 1901
76.4 1980

With only three days remaining, July 2012 has a very legitimate shot at the hottest July in 140 years’ of record-keeping.  If the average temperature remains near 78.9°F, 2012 will also beat out 1934′s 77.8°F by over 1°F!!  And while the 1930s were a very warm decade, note further that 5 of the warmest Julys on record occurred during the 2000s.

What is the `#` symbol in the table?  The NWS notes this:

# Warmest Month in Denver History.

If July remains anomalously warm from today through Tuesday, July 2012 will be the warmest month in Denver history.  This follows on the heels of the hottest June on record: 75°F, which beat the old record of 73.5°F (June 1994).

41st Day of 90°F+ Heat In Denver, CO

While 90°F might sound like a low threshold for many across the US Midwest, the total number of 90°F days for Denver in 2012 is racing for the record books.  An average year yields 32 90°F days in Denver – or at least an average year in a cooler climate.

Through the 26th of July, 2012, Denver, CO has recorded a total of 41 days of 90°F+ maximum temperatures.  Wednesday was the last day that could have registered a sub-90°F temperature, but 90°F was the recorded high for the day.  As such, the latest streak of 90°F+ days continues: 16!  That streak edges out the 15-day streak Denver already recorded earlier this summer.  So not only have temperatures been warmer than normal more often than normal, they’ve been warmer than usual for extended periods of time.  That means that ecosystems haven’t had their normal chance to recuperate from such high temperatures – a point that I will spend more time on in an upcoming post.
That streak is likely to continue: the forecast for the next 7 days includes highs in the mid- to upper-90s.  Denver could witness a July with only 4 days below 90°F.  So far this month, the average temperature departure from average is +4.7°F.  That isn’t as high as June (+7.6°F), but the general trend is clear: 2012 is very warm for Denver, CO and other locations across the mid-section of the US.

13th Day of 100°F+ Heat In Denver, CO

This is a short update to a recent series on this topic (last post here).

Through the 23rd of July, 2012, Denver, CO has officially recorded a total of 13 days of 100°F+ maximum temperatures.  The previous year with such heat was 2005, when the NWS recorded 7 such days.  We are on the cusp of doubling the previous number of 100°F+ days.  Due to Denver’s latitude (~40N) and altitude (~5,200 ft. above sea level), 100°F days are rare.  This year is developing a series of very anomalous heat and drought observations.

Denver has also now recorded 38 days of 90°F+ days, so only 12 more such days need occur the rest of this year to make the top-9 list.

Denver is also in the midst of another consecutive 90°F+ day streak: 13 through yesterday (11 Jul – 23 Jul).  That is in addition to the previous 15-day streak the city recorded from late June through early July.  The streak will continue through today before slightly cooler temperatures (only 89°F?) occur Thursday, then right back into the 90s starting Friday.

The thought of autumn and cooler temperatures is very appealing.

10th Day of 100F+ Heat In Denver, CO

Through the 19th of July, 2012, Denver, CO has officially recorded 10 days of 100F+ maximum temperatures.  The previous year with such heat was 2005, when 7 such days were recorded.  Due to Denver’s latitude (~40N) and altitude (~5,200 ft. above sea level), 100F days are rare.  This year is developing a series of very anomalous heat and drought observations.

Denver typically experiences 32 90F+ days per year.  With most of the summer still to go, Denver has already surpassed that mark.  It appears the city is targeting the top-10 90F days in a year.  That record is held by 2000 when there were 61 days of 90F maximum temperature or higher.  Note that six years since 2000 populate the top-9 list: 2000, 2002, 2005, 2006, 2007, and 2011.  There are only four years prior to 2000 in the top-9 (three are tied for 9th): 1994, 1978, 1964, 1960, and 1874.  The 9th place years recorded 50 90F days.

So far in 2012, there were 2 90F+ days in May, 17 in June, and 15 so far in July, for a year-to-date total of 34.  Denver likely recorded an additional 100F day today and will do the same thing tomorrow.  The extended weather forecast doesn’t call for a high less than 90F for the next 7 days.  Beyond that, above-average temperatures are forecasted for both the next month and the next 3 months.  90F daily maxima are not unheard of in the first couple weeks of September and I don’t at this point expect conditions to be cooler than that this year.

15 consecutive days were 90F+ from the 22nd of June (102F!) through the 6th of July.  If all those records hold up to quality control, that should tie for 7th on the list of most consecutive days with 90F or higher:

2008 JUL 13TH — Aug 5th……24
2011 JUL 15th — AUG 1st……18
1901 JUL  6TH — JUL 23RD…..18
1874 JUL  1ST — JUL 18TH…..18
2000 JUN 29TH — JUL 15TH…..17
1987 JUL 18TH — AUG  2ND…..16
1934 JUL  7TH — JUL 21ST…..15

Notice how the majority of these dates begin in July, not June.  Note further that there were three other times when such a streak began within one day of June 22nd (see full list).  The reason the streak stopped on the 7th of July was a temporary appearance of North American monsoon moisture that made its way from the Gulf of Mexico around the western periphery of the massive high pressure system that is at the heart of the record setting heat wave and drought afflicting the US this year.

So: will 2012 challenge 2000 for the most 90F days in one year?  There are only 16 more days before Denver makes the top-9 list, then 11 more to tie for 1st place.  This isn’t a record most of us want to see happen, of course.  I would much rather see the monsoon return with a vengeance and alleviate the precipitation deficit under which the area is suffering this year.

Will another noteworthy consecutive 90F streak occur?  Denver has 9 in a row through yesterday.  With today’s likely 100F, another streak of 10 joins the list.  As mentioned earlier, conditions don’t look like they’ll change any time soon.  2012 could see two extended streaks of 90F+.  Stay tuned.

8th Day of 100F+ Heat In Denver, CO

This is just a short update to my post yesterday about the early-summer heat wave affecting Denver, CO.

With the 101F maximum temperature yesterday (a new daily record), Denver has hit at least 100F 8 days already in 2012.  That might not sound like much to folks in Arizona or Texas, but 100F days are rare in Denver due to both our latitude and altitude.

As the 2nd link is kind enough to describe, the 8 days now exceeds 2005, which saw 7 such days.  One big difference between 2005 and 2012 is that in 2005, the 7 days of 100F+ heat occurred near the end of July, not prior to July 4th.  Put simply, not only is this heat wave anomalous in and of itself, but the timing of the heat wave is especially anomalous.  As I wrote in the post yesterday, June 2012 was the warmest June on record for Denver by a significant margin: +7.6F.  June 2012 beat out the previous record average June temperature by 1.5F (1994).  That is a significant margin of heat over an entire month.  It also follows an anomalously warm May and April.

There is good news: the string of consecutive 90F+ days might end this weekend.  Any temperature relief may not be accompanied by precipitation relief, which is also desperately needed.

7th Day of 100+F Heat In Denver, CO; June 2012 Hottest On Record

It’s official: June 2012 was the hottest June on record in Denver, CO (dating back to 1872) with an average temperature of 75F, 7.6F above normal!

Yesterday’s high of 101F added to the total number of days of 100F+ temperatures: to date, there are now 7.  Last week, there were 5 days in a row of 100F+ heat, matching the all-time record for Denver.  The streak included 2 105F readings, which tied for the all-time hottest temperature recorded for Denver.  There was also a 100F+ reading a few days prior to that streak.  For completeness, I want to point out that the 27th through 30th of June weren’t much cooler: it was 97, 97, 98, and 99 on those four days, so we didn’t miss 100 by much.

Here are a few pictures demonstrating the intensity and extent of the heat that not only affected Denver, but much of the High Plains prior to the impacts east of the Mississippi over the weekend:

Figure 1. Contour plot of surface maximum temperatures for July 1, 2012.

Figure 2. Plot of surface maximum temperatures by station for July 1, 2012.

Figure 3. Contour plot of surface maximum temperatures for June 30, 2012.

Figure 4. Contour plot of surface maximum temperatures for June 29, 2012.

Figure 5. Plot of surface maximum temperatures by station for June 26, 2012.  This is one of the two dates that Denver’s temperature tied for the all-time recorded high of 105F.

Context

Last year, there were 50 consecutive days of 90F+ maximum temperatures at Denver, which tied for 9th-longest in our recorded history.  With 7 additional days, it would have been the 3rd-longest streak; 11 more days would have tied the longest streak on record, set in 2000.  Note also that 6 of the 11 longest streaks have occurred in the 21st century!  Normally, Denver experiences ~34 days of 90F+ maximum temperatures.

So far this year, we are in the middle of a 10-day streak.  Today, the temperature has already been over 90 for over 4 hours (now 2:30P local) and the forecast calls for 90F+ for at least the next 5 days.

I couldn’t find records on the average number of 100F days in Denver in a year.  I would venture a guess and say that is because the number is less than one.  I’ll do some more digging and see if I can find out one way or the other.

Climate Projections

It wasn’t that long ago that I first saw projections of potential future climate maps for the US and didn’t think I could imagine what it would be to live through such conditions.  I’m sure there are many people who either similarly couldn’t imagine it because it hasn’t happened yet or who are simply unaware of such projections.  Take a look at the following graphic:

Figure 6. Projection for 2090-2099 of the number of weeks per year where maximum daily temperatures exceed 100F.  This projection used the A1FI SRES scenario, which best represents the globe’s current emissions path.

For the sake of conversation, I will assume that Denver has so far this year experienced 1 week (7 days) of 100F+ temperatures, and will further assume that no additional 100F days will occur in the rest of the year.  Under the A1FI scenario, by the end of this century, such a year would be considered relatively cool!

This shift toward more extreme temperatures can also be represented in this graphical manner:

This graphic shows that the increase in average temperature does not have to be that large in magnitude in order for a sizable number of events at the tail of a distribution (e.g., temperature) to occur.

Millions of people are currently without power (due to violent thunderstorms) and are experiencing 100F+ temperatures in the eastern US.  How many more summers like this do they want to have?  They’re going to find out, that’s very nearly certain now.

Record Warmth For US In March 2012 & Jan-Mar 2012

The statistics have been compiled and now the analysis and discussion will really start.  It was so warm across the US in March 2012 that the average US March temperature was 8.6 degrees F warmer than any other March on record (dating back to 1895).  The beat out March 1910, the previous warmest March on record (by a decent margin).  If I were to cherry-pick climate records like many skeptics do, I could easily claim that there is global warming from 1910 to 2012.  Actually, I don’t have to cherry-pick the data.  The fact that the 2000s were warmer than the 1990s which were warmer than the 1980s and so on does that for me.  Also, Jan-Mar 2012 saw an average of 42 degrees F across the US – which is 6 degrees F warmer than normal.

Figure 1. Depiction of divisional ranking of March 2012 temperature anomaly [Courtesy NOAA].

Figure 2. Statewide rankings of average March 2012 temperature.  Note the number of states setting all-time warm temperature records (labeled `118` on map with red state backgrounds) and the additional near-records set in another 16 states.  Note also only 1 state had below normal temperatures for the month.  [Courtesy

Figure 3. Statistical deviation from normal conditions for March 20th, 2012 as calculated by the GFS model.  This day occurred at the peak of the heat wave and was illustrative of the kind of conditions that were found for days in a row.

Figure 4. Anomalous temperature readings across the US for the week of March 8-16, 2012.

And while it is accurate to say, “This is exactly the kind of scenario which ‘loaded climate dice’ says should occur as the planet continues to respond to man-made greenhouse gases,” that isn’t exactly true in the sense that we can’t show that these conditions won’t occur in climate projections.  Scientists do acknowledge that this warmth is in response to the GHG levels that existed ~25-30 years ago: the accumulation of gases and absorbed energy since then won’t be felt for another generation.

The Summer in March 2012 raises another interesting question: what would have happened if this heat wave occurred instead in July or August – the hottest months of the year for the US?  Moreover, what would have happened if that hypothetical heat wave occurred instead during an El Nino and most of the US happened to be a little warmer than usual anyway, instead of during a moderate La Nina?  If these different phenomena occur at the same time, what will happen in the US; or Europe; or Asia?  We’re simply not prepared for that kind of event.  Of course, the warmth last month is projected to become “normal” for March in the US by the end of the century.  That sounds good until you think about the simultaneous lack of precipitation across much of the country.

I’ll have more on this information later this week.

Possible Record Heat In Denver Area Today

I’d bet a good number of metro area folks have heard the forecast for today: HOT! The record high of 98F for the day will likely be challenged. Here is the official forecast discussion from the Denver-Boulder NWS office this morning (sorry for the all-caps, it’s what the NWS text products actually look like):

SHORT TERM…A HOT AND DRY DAY IS IN STORE FOR THE FORECAST AREA TODAY WITH RECORD OR NEAR RECORD HEAT. THE UPPER LEVEL RIDGE WILL AMPLIFY A BIT OVER THE STATE WITH WARMER TEMPERATURES ALOFT. MOST SHORT RANGE MODEL GUIDANCE SHOWS 2-3C OF WARMING ACROSS NORTHEAST COLORADO FROM 24 HOURS AGO. AT THE SAME TIME…THE AIRMASS WILL BE DRYING AND THIS HAS ALREADY COMMENCED PER THE LATEST GPS INTEGRATED PRECIPITABLE WATER DATA. THIS ALL SUPPORTS RECORD OR NEAR RECORD HEAT. DENVERS RECORD IS 98F SET IN 1986…AND AT THIS POINT SEE NO REASON WE SHOULDNT AT LEAST TIE THIS RECORD GIVEN THE ABOVE MENTIONED FACTORS. THERE IS A SLIGHT RISK WE COULD REACH 100F…AND IF WE DID THAT WOULD BE THE LATEST IN THE SEASON A 100F DEGREE READING HAS BEEN OBSERVED. THE LATEST RECORDED 100F WAS ON AUGUST 16TH IN 2002.

There have been 38 90F+ days recorded at DIA so far this summer. That isn’t enough to crack the top-10 summers of all time since the 10th place year had 50 90F+ days, but it is above average (33 days). Last year, DIA recorded 49 90F+ days.

As the NWS office notes, this would be the latest calendar date which recorded a 100F+ day. While we haven’t experienced the ridiculous heat wave and drought that has afflicted Oklahoma (which set the record for hottest month for any state in the American history in July) or Texas, the total number of 90F+ days is significant for us considering how abnormally cool May was.

The relatively high number of 90F+ days in recent years (5 of the top 10 have occurred since 2000) and the late date at which 100F+ days occur are exactly the kind of events that have and will continue to become more prevalent as climate change effects take hold. After all, would dozens of 90F+ days be piling up with “global cooling”, especially when dozens of 32F- days are not piling up? Additionally, the precipitation extremes that occurred last month around the metro area (i.e., 7″+ of rain in 9 days) will also become more common.

Eastern 3/4 Of U.S. Roasted In July 2011

Thanks to global cooling (not!), the eastern 3/4 of the U.S. was much warmer than normal in July 2011.  In fact, Oklahoma set a record for the warmest month of any state in American history: an average of 88.9F.  Which kind of makes sense, when you think about it.  After all, it was the preeminent expert on climate, Sen. Jim Inhofe (R TB-OK), whose grandchildren built an igloo on the National Mall back in February 2010 – because mocking Al Gore is the top responsibility of a sitting U.S. Senator.  Maybe his family should have spent less time making fun of things they can’t or don’t want to understand but more time praying for rain this summer.  In the end, the solution is simple: stop polluting heat-trapping gases and the atmosphere will trap less heat!  Imagine that!

Back to the state of U.S. climate in July 2011.

July 2011 was the fourth warmest July in NOAA’s records: 77F.  It was the fourth warmest month all time.  Here is what that looks like graphically: