October is here and it may bring Denver's first taste of snow and freezing temperatures for the season. (iStockphoto / johnnyscriv)
With the first full month of fall here, October usually brings one of the quietest weather months in the Denver area with plenty of mild, sunny days and clear, cool nights. Certainly given our recent trend of well-above normal temperatures many are hoping for some relief.
The month actually has our second highest amount of sunshine with 72 percent with September having the most with 74 percent. Interestingly enough, the month following, November, is one of the lowest sunshine months with only 64 percent.
Typically October brings our first real taste of winter with the first freeze on average coming on the 7th of the month and the first snow on the 15th of the month.
You can get all the details including a look back at historical October weather and a look ahead at what October 2010 is expected to bring in our complete preview here.
Are you ready? As September comes to a close and with fall's arrival cold and snow aren't far behind usually.
Wednesday marked the first day of fall and while the forecast may not call for freezing temperatures or snow, it won’t be long before the Mile High City is faced with those conditions. We have in fact already passed the earliest dates Denver has seen freezes and snow so they can arrive at any time.
Denver has in fact seen snow as early as September 3rd and its first seasonal freeze as early as September 8th. Those are the extremes however. On average the first snowfall occurs on October 19th and the first freeze on October 7th.
How will we fare this year? La Niña conditions are strengthening and the outlook is for warmer than normal temperatures for the next few months. Colorado weather however doesn’t always follow an established pattern.
Below is a look at Colorado’s cold season statistics as provided by the National Weather Service. They provide a bit of historical perspective as to what we might expect this year.
The statistics below and many more are kept in our Climatology section. Check it out
Autumn First Freeze Information
Earliest Date of First Freeze: September 8, 1962
Latest Date of First Freeze: November 15, 1944
Average Date of First Freeze: October 7th
First Freeze Last 11 Years:
October 2, 2009
October 13, 2008
October 8, 2007
September 18, 2006
October 5, 2005
October 14, 2004
September 14, 2003
October 4, 2002
October 5, 2001
September 20, 2000
September 28, 1999
October 21st is the average date in which Denver’s normal overnight low temperature hits 32 degrees Fahrenheit for the first time.
Autumn First Snow Information
Earliest Date of First Snow: September 3, 1961
Latest Date of First Snow: November 21, 1934
Average Date of First Snow: October 19th
First Measurable Snow Last 11 Years:
October 21, 2009
November 14, 2008
October 22, 2007
October 18, 2006
October 10, 2005
November 1, 2004
November 5, 2003
October 25, 2002
October 5, 2001
September 23, 2000
September 28, 1999
Seasonal Snowfall Amounts
Greatest Seasonal Snowfall: 118.7 inches 1908-09
Least Seasonal Snowfall: 20.8 inches 1888-89
Average Seasonal Snowfall (1971-2000): 61.7 inches
Is it global warming at work? Probably not but the Mile High City experienced a very warm month of August that nearly ended up in the “top 10” statistical column. Were it not for things cooling down in the last week that almost certainly would have happened.
Denver’s average temperature for the month was 73.8 degrees – 2.1 degrees above normal. That put it 0.3 degrees shy of the number ten spot for warmest August on record which was in 1947 with an average temperature of 74.1. We should be thankful we didn’t reach near the top spot. The hottest August on record was in 1937 when we hit an average of 76.8 degrees.
In terms of extremes, the hottest day of the month occurred on the 22nd when the mercury climbed to 97 degrees. The coldest temperature recorded was on the 17th when we dropped to 47 degrees. Neither of those were records.
Overall we recorded 12 days with 90 degree or higher temperatures – three above normal. Similarly we have seen 41 ninety degree plus days this year which is 10 more than normal.
Only one temperature record was set for the month. That occurred on the 18th when a record high minimum of 67 degrees was recorded. This tied the previous record for the date set in 1986.
Here in Thornton we were a bit cooler than the Denver measurements. We saw an average temperature of 72.3 degrees with a high of 93.9 on the 18th and a low of 51.1 degrees on the 17th.
It may not have seemed like it as we did have quite a few days with thunderstorms but we in fact finished August with below normal precipitation. Denver recorded 1.05 inch but that was 0.77 inch below normal.
Most of that precipitation however fell within the first seven days of the month when 1.03 of the total was recorded. Of that, 0.68 inch was recorded on the first of the month. However, a mere 0.02 inch was recorded for the final three weeks of the month.
Thornton fared better than the official measurements in terms of precipitation. We recorded 1.41 inches for the month and the moisture we received was spread out across the month much better.
At the official Denver monitoring station at Denver International Airport they recorded 10 days with thunderstorms. The max wind gust was 45 mph recorded on the 12th and again on the 16th.
As temperatures start to drop, September reminds us that summer is at an end and fall is now here. Sunshine is predominant though as the month actually has the highest percentage of sun out of any month. Sunny days and clear, cool nights are the standard weather pattern for the month.
However that isn’t to say the weather can’t be a lot more “interesting.” Extremes can occur during September ranging from heat to cold to yes, even snow.
From the National Oceanic & Atmospheric Administration: The combined global land and ocean surface temperature made this July the second warmest on record, behind 1998, and the warmest averaged January-July on record. The global average land surface temperature for July and January–July was warmest on record. The global ocean surface temperature for July was the fifth warmest, and for January–July 2010 was the second warmest on record, behind 1998.
The monthly analysis from NOAA’s National Climatic Data Center, which is based on records going back to 1880, is part of the suite of climate services NOAA provides government, business and community leaders so they can make informed decisions.
Global temperature anomolies, July 2010. (NOAA)
Global Temperature Highlights
The combined global land and ocean average surface temperature for July 2010 was the second warmest on record at 61.6°F (16.5°C), which is 1.19°F (0.66°C) above the 20th century average of 60.4°F (15.8°C). The averaged temperature for July 1998 was 61.7°F (16.5°C).
The July worldwide land surface temperature was 1.85°F (1.03°C) above the 20th century average of 57.8°F (14.3°C) — the warmest July on record. Warmer-than-average conditions dominated land areas of the globe. The most prominent warmth was in Europe, western Russia and eastern Asia. Cooler-than-average regions included central Russia, Alaska and southern South America.
According to the Finnish Meteorological Institute, Finland set a new all-time maximum temperature on July 29 when temperatures soared to 99.0°F (37.2°C), surpassing the previous record set in July 1914 by 2.3°F (1.3°C).
Western Russia was engulfed by a severe heat wave during much of July. On July 30, Moscow set a new all-time temperature record when temperatures reached 102°F (39°C), exceeding the previous record of 99.0°F (37.2°C) set four days earlier. Before 2010, the highest maximum temperature recorded in Moscow was 98.2°F (36.8°C), set nine decades ago.
According to the Beijing Climate Center, the July 2010 average temperature across China was 73.0°F (22.8°C), which is 2.5°F (1.4°C) above the 1971-2000 average and the warmest July since 1961.
The worldwide ocean surface temperature was 0.97°F (0.54°C) above the 20th century average of 61.5°F (16.4°C) and the fifth warmest July on record. The warmth was most pronounced in the Atlantic Ocean.
La Niña conditions developed during July 2010, as sea surface temperatures (SST) continued to drop across the central and eastern equatorial Pacific Ocean. According to NOAA’s Climate Prediction Center, La Niña is expected to strengthen and last through the Northern Hemisphere winter 2010-2011.
For the year-to-date, the global combined land and ocean surface temperature of 58.1°F (14.5°C) was the warmest January-July period on record. This value is 1.22°F (0.68°C) above the 20th century average.
Global temperature anomolies, January through July, 2010. (NOAA)
Polar Sea Ice and Precipitation Highlights
Arctic sea ice covered an average of 3.2 million square miles (8.4 million square kilometers) during July. This is 16.9 percent below the 1979-2000 average extent and the second lowest July extent since records began in 1979. The record low July was set in 2007. This was the 14th consecutive July with below-average Arctic sea ice extent. July 1996 was the last year that had above-average sea ice extent.
Antarctic sea ice extent in July was above average, 4.8 percent above the 1979-2000 average—resulting in the largest July sea ice extent on record.
According to Australia’s Bureau of Meteorology, the continent received an average of 34.4 mm (1.35 inches) of precipitation during July 2010—this is 55 percent above the 1961-1990 average and the highest value since 1998.
Scientists, researchers and leaders in government and industry use NOAA’s monthly reports to help track trends and other changes in the world’s climate. This climate service has a wide range of practical uses, from helping farmers know what and when to plant, to guiding resource managers with critical decisions about water, energy and other vital assets.
Denver and Thornton's August weather preview and history.
As summer vacations wind down and families prepare to send their kids back to school in August, Colorado weather also starts to settle down. The chances for severe weather decrease markedly during August and by the end of the month daytime temperatures are dropping quite a bit as well.
At the start of the month Denver usually averages around 88 degrees for a high temperature. By the end of August that drops to 82 degrees. Similarly, nighttime lows drop from 60 to 53 from the start to the end of the month.
Generally clear skies can be expected between midnight and noon but the afternoon often brings showers and thunderstorms. These storms typically develop over the foothills then bring precipitation to the Denver metro area.
According to the National Weather Service, record-setting rain fell in Denver on the 4th of July. But is it accurate to say that? (ThorntonWeather.com)
Heavy rain showers put a damper on a lot of Independence Day celebrations yesterday. Thunderstorms moved across the Front Range dumping rain and hail across northeastern Colorado with enough rain falling to set a record for the 4th of July.
At Denver International Airport (DIA), 1.84 inches of rain was recorded. This easily eclipses the old 4th of July record dating back to 1909 when 1.44 inches fell.
Here in Thornton we weren’t nearly as wet having recorded 0.81 inches for the storms that moved through. Some of the other rainfall totals from across the metro area:
The rain yesterday was heavy in places but nowhere in the central Denver area measured anywhere near the amount DIA recorded (see map below). When the National Weather Service (NWS) announces a “record” like the rain yesterday, it is comparing the measurements at DIA to historical records taken at the old Stapleton International Airport from 1950 to 1995 and downtown from 1871 to 1949.
Is it accurate to claim a weather record when the station doing the recording is 12 miles away from where historical records were made? Of course not and this is a problem.
The National Weather Service either needs to start recording Denver’s official statistics from the new station or it needs to quit comparing data from DIA to that recorded before the move in 1995.
Denver’s climate records are forever being altered and the public is being misled.
June typically brings severe weather to Thornton and the Denver area.
June is historically Denver’s severe weather month and severe thunderstorms, tornadoes and hail are notorious visitors to Denver and across eastern Colorado during the month. In fact, over 40 percent of the tornadoes that occur in Colorado are observed in June and these are typically the most destructive of the year. Severe thunderstorms have also caused major property damage across the Front Range during the month.
In just the last 25 years or so, there have been some particularly notable storms in June. Tornadoes have struck the metro area including one that longtime Thornton residents will recall on June 3, 1981. 53 residents were injured, 25 homes were destroyed and 239 other structures were damaged. Others tornadoes in the metro area include southeast Denver and Aurora on June 8, 1986 and east Denver on June 13, 1984. Severe thunderstorms occurring on June 13, 1984 dumped large hail making it one of the worst and the second costliest storm in Denver history. More recently, on June 20, 2001, a major hail storm moved across Denver International Airport dropping hailstones as big as two inches in diameter. Damage was extensive on and near the airport.
According to data released by the National Oceanic and Atmospheric Administration (NOAA), the combined land and sea temperatures for last month were the warmest April temperatures on record. Individually, sea surface temperatures were the warmest for any April and surface temperatures were the third warmest.
Utilizing data from the National Climatic Data Center (NCDC), the agency reported that the combined temperature of 58.1°F (14.5°C) was 1.37°F (0.76°C) above the 20th century average of 56.7°F (13.7°C).
For the period from January to April, temperatures also were the warmest first quarter on record. NOAA said the combined temperature over the period was 56.0°F (13.3°C). That is 1.24°F (0.69°C) above the 20th century average.
In the United States, NOAA said that April featured above normal temperatures and below normal precipitation. Much of the eastern half of the nation experienced warmer than normal temperatures resulting in measurements 2.3°F above average and going down in the books as the 14th warmest April on record.
Colorado natives and those that have lived here long enough know that Denver and Colorado weather changes considerably throughout the year. The month of May almost seems to pack four seasons of weather conditions into 31 days. You name it, it can happen.
This being the latter half of spring, May does mean warm temperatures. Temperatures in the 80’s are common and reaching into the 90’s is not unheard of. The normal highs start out at 65 on the first but by the end of the month that climbs to 76. The record high for the month was recorded on May 26, 1942 of 95 degrees.
As temperatures start to drop, September reminds us that summer is at an end and fall is now here. Sunshine is predominant though as the month actually has the highest percentage of sun out of any month. Sunny days and clear, cool nights are the standard weather pattern for the month.
