Category Archives: Climatology

Thornton’s February weather preview: Typically a warmer, less snowy month

Thornton and Denver, Colorado February Weather Preview.February in Colorado typically brings to an end an extended period when average temperatures are at their lowest. Winter begins to loosen its grip and temperatures get warmer but precipitation is not a particularly common event during the month.

Thus far our snow season has been relatively dismal with the seasonal total in Thornton more than 10 inches below average.  In the high country, the snowpack is not faring much better.  February is only our sixth snowiest month so we may not see much snowfall for the balance of the month.

Temperatures however do usually see a nice rebound during the month. Average high temperatures climb from an average of 44 degrees at the start to 50 degrees by the end of February.

For the complete February preview including a look at historical averages and extremes as well as a look at what long range forecasts are predicting, click here. 

December 2017 recap: Despite cold finish, month was warmer and drier than average

With the last part of December fresh in our minds, it would not be surprising to think of the month as a cold one. However, reaching back, if you recall, we actually enjoyed a lot of mild days earlier and very little precipitation. As a result, December 2017 goes into the books as a warm and dry one.

The first half of the month was notable for stable conditions yielding above normal temperatures and no precipitation. Denver set a record high temperature on the 12th of 69 degrees which was also our warmest reading of the month.

Not long after the warmth came the cold.  Arctic air infiltrated from the north on the 21st resulting in much cooler temperatures and a pre-Christmas snow. This was followed by another snow on the 23rd that lasted into the early morning hours of Christmas Eve. Single digit lows were seen for seven days from the 21st to the 27th.

We then saw a brief warmup for the 27th to the 29th but that was short lived. We closed out the month with the final two days’ high temperatures failing to reach even the freezing mark.

On average, Denver’s temperature for December comes in at 30.0 degrees.  Both Thornton and the Mile High City came in above that with average readings of 31.8 degrees and 33.2 degrees respectively.

Thornton saw its warmest temperature reading of 69.1 degrees on the 12th and its coldest of 1.6 degrees on the morning of the 27th.  Denver’s warmest reading of 69 degrees also came on the 12th and its coldest of -4 degrees came on the 24th.

In terms of precipitation, Thornton saw a mere 0.16 inch of liquid in its bucket for the month. Denver was a bit better with 0.21 inches. Both were below the long-term Denver average of 0.35 inches.

December on average brings 8.5 inches of snowfall to Denver.  Thornton fell well short of that with 4.7 inches and Denver just a bit less with 4.0 inches.

Click here to view Thornton’s December 2017 climate report.

Thornton, Colorado's December 2017 temperature summary. (ThorntonWeather.com)
Thornton, Colorado’s December 2017 temperature summary. (ThorntonWeather.com)
Thornton, Colorado's December 2017 precipitation summary. (ThorntonWeather.com)
Thornton, Colorado’s December 2017 precipitation summary. (ThorntonWeather.com)
CLIMATE REPORT
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
645 AM MST MON JAN 1 2018

...................................

...THE DENVER CO CLIMATE SUMMARY FOR THE MONTH OF DECEMBER 2017...

CLIMATE NORMAL PERIOD 1981 TO 2010
CLIMATE RECORD PERIOD 1872 TO 2017

WEATHER         OBSERVED          NORMAL  DEPART  LAST YEAR`S
                 VALUE   DATE(S)  VALUE   FROM    VALUE  DATE(S)
                                          NORMAL
................................................................
TEMPERATURE (F)
RECORD
 HIGH              79   12/05/1939
 LOW              -25   12/22/1990
                        12/24/1876
HIGHEST            69   12/12        62       7       65  12/30
LOWEST             -4   12/24        -4       0      -15  12/17
AVG. MAXIMUM     48.3              42.8     5.5     42.7
AVG. MINIMUM     18.0              17.1     0.9     12.9
MEAN             33.2              30.0     3.2     27.8
DAYS MAX >= 90      0               0.0     0.0        0
DAYS MAX <= 32      4               5.8    -1.8        6
DAYS MIN <= 32     28              29.4    -1.4       30
DAYS MIN <= 0       1               2.0    -1.0        4

PRECIPITATION (INCHES)
RECORD
 MAXIMUM         5.21   1913
 MINIMUM         0.00   1881
TOTALS           0.21              0.35   -0.14     0.78
DAILY AVG.       0.01              0.01    0.00     0.03
DAYS >= .01         4               4.1    -0.1        6
DAYS >= .10         1               1.1    -0.1        2
DAYS >= .50         0               0.1    -0.1        0
DAYS >= 1.00        0               0.0     0.0        0
GREATEST
 24 HR. TOTAL    0.10   12/23 TO 12/23
 STORM TOTAL     0.10   12/23 TO 12/23

SNOWFALL (INCHES)
RECORDS
 TOTAL           57.4   1913
TOTALS            4.0   2017        8.5

DEGREE_DAYS
HEATING TOTAL     979              1086    -107     1146
 SINCE 7/1       2150              2468    -318     2042
COOLING TOTAL       0                 0       0        0
 SINCE 1/1        881               769     112      878

FREEZE DATES
RECORD
 EARLIEST     09/08/1962
 LATEST       06/08/2007
EARLIEST                        10/07
LATEST                          05/05
.................................................................

WIND (MPH)
AVERAGE WIND SPEED              10.0
RESULTANT WIND SPEED/DIRECTION   2/214
HIGHEST WIND SPEED/DIRECTION    37/270    DATE  12/04
HIGHEST GUST SPEED/DIRECTION    48/280    DATE  12/04

SKY COVER
POSSIBLE SUNSHINE (PERCENT)   MM
AVERAGE SKY COVER           0.50
NUMBER OF DAYS FAIR            8
NUMBER OF DAYS PC             18
NUMBER OF DAYS CLOUDY          5

AVERAGE RH (PERCENT)          49

WEATHER CONDITIONS. NUMBER OF DAYS WITH
FOG OR MIST                   12
FOG VSBY LESS 1/4 MI           4
THUNDER                        0
ICE PELLETS                    0
HAIL                           0
FREEZING RAIN DRIZZLE          0
DUST STORM                     0
SMOKE OR HAZE                  5
BLOWING SNOW                   0
TORNADO                        0

-  INDICATES NEGATIVE NUMBERS.
R  INDICATES RECORD WAS SET OR TIED.
MM INDICATES DATA IS MISSING.
T  INDICATES TRACE AMOUNT.

Thornton’s January 2018 preview: Cold but not always snow for first month of the year

Denver's January weather and climatology preview for 2013.As we begin the new year the winter chill begins to set in.  While January can see its share of extremes, the month historically sees stable temperatures and is usually relatively dry.

January ranks as the second coldest month in Denver next to December with average temperatures remaining virtually the same from the start to the end of the month.

In terms of snowfall, the month only ranks as the fourth snowiest and it is not uncommon for it to be quite dry.

What does January 2018 hold for us?  Follow the link to find out.

For the complete January preview including a look at historical averages and extremes, click here. 

Winter Solstice brings shortest day of the year, change of seasons

The Winter Solstice
Winter officially begins at 9:28am MST on Thursday, December 21, 2017. (NOAA)

Astronomical winter arrives in Thornton Thursday morning and with the solstice also comes the shortest day of the year.  Mother Nature as well appears set to bring in winter with a bit of a bang and a change in our recent mild, dry weather pattern.

Winter officially begins at 9:28am MST on Thursday, December 21.

The Winter Solstice occurs when the North Pole is tilted at its furthest from the sun – 23.5 degrees away. This results in the shortest day of the year in the Northern Hemisphere.

Here in Denver, with sunrise at 7:17am and sunset at 4:38pm, our day Thursday will be 9 hours, 21 minutes and 16 seconds long. The following day, Friday, it will be three seconds longer and each day from now through to the Summer Solstice in June will get gradually longer as well.

While we have a short day today, it is nothing like what will be experienced in the Arctic Circle.  Areas north of there to the North Pole will have no direct sunlight at all.  Conversely, areas south of the Antarctic Circle toward the South Pole will have 24 hours of daylight and have a midnight sun.

Did you know that there is a difference between the astronomical seasons that we are discussing here and meteorological seasons?

Meteorological seasons differ slightly and are geared toward matching the calendar with the annual temperature cycle. This is done primarily for meteorological observing and forecasting and in many ways it is more logical than the astronomical seasons.

For the Northern Hemisphere, the meteorological spring covers the months of March, April and May. Summer brings the hottest months of the year and so meteorological summer is June, July and August. Meteorological fall then is September, October and November followed by the coldest months of December, January and February as meteorological winter.

Thornton’s December preview: Will there be an end to the mild, dry conditions?

November proved to be an extraordinarily warm and dry month. Does December have hope for relief?

The month of December brings with it the official start of winter and oftentimes, colder and snowier weather conditions.

It however can also offer unseasonably warm temperatures and bone dry conditions.  Given our recent mild and dry weather, we are certainly hoping for a change in the coming month.

Overall December’s monthly mean temperature of 30.0 degrees (1981 – 2010 averages) makes it our coldest month.  Snow is always on everyone’s mind this time of year but December is only our 3rd snowiest month behind March and November with an average of 8.5 inches of the white stuff.

Get all the details on Thornton’s December weather including a look back at historical events and a look at the long range forecast in our December weather preview here.

  • Stay up to date with Thornton’s weather: Be sure to ‘like’ us on Facebook, follow us on Twitter and add us to your Google+ circles.

Thornton’s November 2017 preview: A fall month that can offer up just about anything

Thornton's November weather previewThe weather during the month of November in Denver metro area can offer just about anything.  While it is normally a quiet month, it can be prone to extremes.

November has historically been one of Denver’s snowiest months and major snowstorms are not entirely uncommon.  However conditions can also be quite dry.

Temperatures during the month continue to cool as we get closer to winter and by the end of the month the low temperatures routinely dip to 20 degrees or below.  At times it can in fact bring conditions more like what we see in January.

What lies ahead for November 2017?  Get all the details on November’s weather and what we can expect in our complete preview here.

September 2017 weather recap: Month starts warm and dry, ends cool and damp

The month of September 2017 saw significant differences between the start and the end.  The first two-thirds of the month were extraordinarily dry with temperatures well above normal. The last 10 days brought a big change though with damp conditions and much cooler conditions.

High pressure dominated the region for the first few weeks of the month.  During this period when we normally see cooler temperatures, we instead saw highs oftentimes at or above 90 degrees and a couple of record high readings.  Additionally, it was exceedingly dry with Thornton only received 0.03 inches of precipitation through the first 22 days of the month.

Big changes arrived and the last nine days of the month stood it stark contrast to the rest of September. Low pressure and a series of disturbances brought much cooler temperatures and much-needed precipitation, including snowfall in the high country. Seven out of the last eight days saw below normal high temperature readings and enough precipitation fell to push us to just above normal.

Thornton’s overall average temperature for the month came in at 62.4 degrees.  This was a full degree cooler than Denver’s long term September average of 63.4 degrees.  Out at DIA where Denver’s official measurements are taken, it was a good bit warmer with an average temperature of 65.1 degrees.

Temperatures in Thornton ranged from a high of 98.5 degrees on the third and a low of 40.9 degrees on the morning of the 29th.  Denver saw their high of 97 degrees on the third as well and their coldest reading of 40 degrees on the 20th.

Two record high temperatures were officially set or tied for the Mile High City.  The high temperature of 97 degrees on the third tied the record high for the date.  A reading of 92 degrees on the 21st set a new record high for that date.

In terms of precipitation, Denver averages 0.96 inches during September.  Thornton tallied 1.05 inches in the rain bucket while Denver bested us with 1.26 inches.

Click here to view Thornton’s September 2017 climate report.

Thornton, Colorado’s September 2017 Temperature Summary. (ThorntonWeather.com)
Thornton, Colorado’s September 2017 Temperature Summary. (ThorntonWeather.com)
Thornton, Colorado’s September 2017 Precipitation Summary. (ThorntonWeather.com)
Thornton, Colorado’s September 2017 Precipitation Summary. (ThorntonWeather.com)

From the National Weather Service:

CLIMATE REPORT
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
244 AM MDT SUN OCT 1 2017

...................................

...THE DENVER CO CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2017...

CLIMATE NORMAL PERIOD 1981 TO 2010
CLIMATE RECORD PERIOD 1872 TO 2017

WEATHER         OBSERVED          NORMAL  DEPART  LAST YEAR`S
                 VALUE   DATE(S)  VALUE   FROM    VALUE  DATE(S)
                                          NORMAL
................................................................
TEMPERATURE (F)
RECORD
 HIGH              97   09/03/2017
                        09/06/2013
                        09/05/2013
 LOW               17   09/29/1985
HIGHEST            97R  09/03        91       6       93  09/05
LOWEST             40   09/20        35       5       37  09/10
AVG. MAXIMUM     79.0              78.5     0.5     82.3
AVG. MINIMUM     51.3              48.3     3.0     49.7
MEAN             65.1              63.4     1.7     66.0
DAYS MAX >= 90      9               3.4     5.6        6
DAYS MAX <= 32      0               0.0     0.0        0
DAYS MIN <= 32      0               0.8    -0.8        0
DAYS MIN <= 0 0 0.0 0.0 0 PRECIPITATION (INCHES) RECORD MAXIMUM 5.61 2013 MINIMUM T 1892 1944 TOTALS 1.26 0.96 0.30 0.28 DAILY AVG. 0.04 0.03 0.01 0.01 DAYS >= .01         6               6.5    -0.5        4
DAYS >= .10         2               3.3    -1.3        1
DAYS >= .50         1               0.6     0.4        0
DAYS >= 1.00        0               0.1    -0.1        0
GREATEST
 24 HR. TOTAL    0.83   09/23 TO 09/23           09/12 TO 09/12

SNOWFALL (INCHES)
RECORDS
 TOTAL             0.0
TOTALS            0.0               1.3

DEGREE_DAYS
HEATING TOTAL     122               125      -3       64
 SINCE 7/1        130               141     -11       79
COOLING TOTAL     131                76      55       99
 SINCE 1/1        880               764     116      861

FREEZE DATES
RECORD
 EARLIEST     09/08/1962
 LATEST       06/08/2007
EARLIEST                        10/07
LATEST                          05/05
...................................................

WIND (MPH)
AVERAGE WIND SPEED              9.6
RESULTANT WIND SPEED/DIRECTION   2/165
HIGHEST WIND SPEED/DIRECTION    40/020    DATE  09/19
HIGHEST GUST SPEED/DIRECTION    48/030    DATE  09/19

SKY COVER
POSSIBLE SUNSHINE (PERCENT)   MM
AVERAGE SKY COVER           0.50
NUMBER OF DAYS FAIR            9
NUMBER OF DAYS PC             15
NUMBER OF DAYS CLOUDY          6

AVERAGE RH (PERCENT)     48

WEATHER CONDITIONS. NUMBER OF DAYS WITH
THUNDERSTORM              0     MIXED PRECIP               0
HEAVY RAIN                1     RAIN                       1
LIGHT RAIN               10     FREEZING RAIN              0
LT FREEZING RAIN          0     HAIL                       0
HEAVY SNOW                0     SNOW                       0
LIGHT SNOW                0     SLEET                      0
FOG                       8     FOG W/VIS <= 1/4 MILE      1
HAZE                     10

-  INDICATES NEGATIVE NUMBERS.
R  INDICATES RECORD WAS SET OR TIED.
MM INDICATES DATA IS MISSING.
T  INDICATES TRACE AMOUNT.

Thornton’s October weather preview: Fall arrives in earnest, tastes of winter

Thornton, Colorado October weather preview.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.

October is historically the second sunniest month and conditions are generally calm.

However we also will usually see our first taste of winter during the month with the first freeze and first snowfall of the season.

Temperatures as well will start to drop and by the end of the month the average nighttime lows are below freezing.

For complete details on our historical October weather and what we can expect in the coming month, read our complete October weather preview here.

  • Don’t miss a thing when it comes to our ever-changing weather! Be sure to ‘like’ us on Facebook, follow us on Twitter and add us to your Google+ circles.

Fall Colors 2017: Picks for the top Colorado Front Range spots for leaf peeping

Rocky Mountain National Park is a prime spot for viewing the fall foliage. (Tony's Takes)
Rocky Mountain National Park is a prime spot for viewing the fall foliage. (Tony’s Takes)

This time of year many folks start thinking about heading to the hills west of Denver in search of gold – fall foliage gold.

Where to go?  Below are five of ThorntonWeather.com’s favorite ones near Denver – plus a few further out and some bonus ideas.  After that, we will tell you where you can find a great website that provides regular updates on viewing conditions.

I-70 Corridor – If you’re looking for the easiest route, then this one is for you.  Simply head west on I-70 about 110 miles to Avon.  Between Vail and Avon, both sides of I-70 are lined beautifully with aspen.

Rocky Mountain National Park – One of the most popular summer destinations in the state is of course also a prime spot to view aspen in all their glory.  Once in the park head toward Bear Lake.  Glacier Gorge Junction provides a beautiful spot and you of course also get to enjoy all the splendor that Rocky Mountain National Park has to offer.  Extend your viewing by taking Trail Ridge Road all the way through to the west side of the park and the Grand Lake and Granby area.

Peak to Peak Highway – This little road trip can be a dual purpose trip – gambling and fall foliage viewing!  Take U.S. 6 through Clear Creek Canyon and then 119 through Blackhawk and Central City.  You can of course stop there if your wallet is fat enough and donate some money to the casinos.  From there continue on 119 toward Nederland.  Take highway 72 toward Ward and Allenspark.  There you will find more golden aspen than you can imagine, all with the Continental Divide nearby.

Colorado Fall Foliage - Average Date of Peak Aspen Colors. Click for larger view. (ThorntonWeather.com)
Colorado Fall Foliage – Average Date of Peak Aspen Colors. Click for larger view. (ThorntonWeather.com)

Poudre Valley Canyon –  Heading north on I-25 take Colorado 14 west and into Poudre Canyon and Roosevelt National Forest.  As you continue west you will come very near timberline as you come to Cameron Pass.  Amazing views abound!

Guanella Pass – This is a nice, relatively short drive from Denver.  From C470 take 85 through Bailey and Conifer, a nice drive unto itself.  When you come to the town of Grant, take the Guanella Pass Scenic and Historic Byway north to Georgetown.  The air is pretty thin along the way as you climb in excess of 11,500 views through the Pike and Arapahoe National Forests.

A couple other possibilities further from the Front Range:

Leadville / Aspen – From Denver take I-70 west to Copper Mountain and then Colorado 91 south over Freemont Pass to Leadville. Along the way there are plenty of viewing opportunities and Leadville is a nice little town to make a stop. From here you can take Highway 24 north back through Minturn and Vail. To extend the drive, take Highway 24 south to Colorado 82 and head toward Aspen. You can stop by the Maroon Bells in White River National Forest to view some of the most photographed mountains in Colorado.

Cottonwood Pass – From Denver take Highway 285 to Buena Vista. Head west on Main Street for seven miles then west on County Road 344 / Colorado 82. From there you start the climb up Cottonwood Pass with absolutely stunning views from the top. If you are up for it, you can continue down the west side of the pass into the Taylor Park area. Be forewarned though that the western half of the pass is unpaved and twisty.  Editor’s note: The west side of Cottonwood Pass is closed until Summer 2018 so that it can be paved.

Honorable mentions worth considering:

  • Boreas Pass between Breckenridge and Como (County Road 10)
  • Kenosha Pass on Highway 285 between Bailey and Fairplay
  • Independence Pass (Colorado 82 between Aspen and Twin Lakes)
  • Colorado 103 from Evergreen to Echo Lake. Throw in a drive up Mount Evans for a bonus.

If you do head out, be sure to send us your pictures for inclusion in our monthly photo slideshows!

For more information: