All posts by Jim Woodmencey

The Arrival of Spring

The astronomical spring season officially began in the Rockies with the Vernal Equinox that occurred at 3:37 a.m. MDT on Saturday March 20th. It is that time of year when warm, sunny days can lull you into a bout of spring fever only to be squashed by a return to a stretch of winter-like conditions. Spring has a way of flopping back and forth between seasons in the mountains.

While this post can’t change the weather, it will explain what the Equinox signifies and how this new season changes the look of things in the Rockies and across the globe.

Vernal Equinox

“Vernal” is sometimes used to describe youth and vigor, something fresh. It also means, belonging to spring. When flowers begin to bloom, and everything starts fresh after the colder, snowier and darker winter.

“Equinox” is the Latin term for equal night (aequous nox). Around the date of the Equinoxes, both Vernal and Autumnal, nighttime and daytime are nearly equal everywhere around the globe.  From Ecuador to Alaska, from Nigeria to New Zealand, the sun is up for 12 hours and down for 12 hours. That is because on the Equinox the sun is directly overhead at the Equator, shining down on the disk of planet Earth evenly, from north to south.

Why is that? Because of the tilt of the Earth and its annual orbit around the sun.  At the Equinox, neither hemisphere is tilted away nor towards the sun.

Angle of the Sun

The big difference between how the day looks in Alaska versus the Equator is how high in the sky the sun gets at noontime. That is dependent upon the latitude and the curvature of the Earth.

Here in Jackson, the sun is about 46-degrees above the horizon at noon on the Equinox. Compared to only 23-degrees above the horizon on the Winter Solstice in December and around 70-degrees above the horizon on the Summer Solstice in June.

Up in Fairbanks, Alaska the sun angle on the Equinox is 25-degrees above the horizon at noon. On the Winter Solstice it barely cracks the horizon at 2-degrees. On the Summer Solstice in Fairbanks the sun only gets as high in the sky as it is here in March on the Equinox, around 47-degrees above the horizon. However, their length of day in Alaska increases exponentially between now and the Summer Solstice.

Length of Day

By mid-June, the length of our day in Jackson will increase almost three and a half hours from what we have right now. On the Summer Solstice, the time between sunrise and sunset will be 15 hours and 25 minutes. Add an extra 36 minutes on either end of the day for twilight, and barely leaves enough hours of darkness to get a full 8-hours of sleep here.

Whereas, up in Fairbanks, the length of day on the Summer Solstice is 21 hours and 50 minutes and twilight lasts for the remaining 2 hours and 10 minutes. It’s hard to get any shuteye up there in the summer.

In Ecuador, the days don’t change as dramatically, as a matter of fact, the length of day on the Equinox is just 11 seconds longer than it is on the Summer Solstice down there.

Changing Time

Many people ask why we change from Standard Time for the fall and winter months to Daylight Savings Time (DST) for the spring and summer months? The answer to that question involves some politics, some economics and some science. I’ll allude to the scientific reason here.

Our seasonal time change is mainly related to our biological clocks or more precisely our circadian rhythms. Where that time change is most effective though is between about 35-degrees and 55-degrees North latitude, roughly between northern Arizona and Southern Canada.

In Jackson Hole, Wyoming, where I sit at 43-degrees North latitude, if we remained on Standard Time all summer, we would see the sun rising at around 4:42 a.m. in mid-June, with twilight beginning just after 4:00 a.m. or an hour earlier than we currently have under Daylight Savings Time. That’s probably way too early for most folks to get out of bed.

Sunset here would also be an hour earlier if we stayed on Standard Time, on the longest days in mid-June sunset would be at 8:08 p.m. or similar to the sunset time in Jackson in mid-April, under Daylight Savings Time.

As it is now, sunset will be at 9:08 p.m. in mid-June, extending our playtime well into the evening in the summer. No matter which time we are under, Mountain Daylight Time (MDT) or Mountain Standard Time (MST), the amount of time we get between sunrise and sunset would remain the same. Most of us though would probably sleep through the first couple of hours of the day in summer, if the clocks didn’t change.

Jim is the chief meteorologist at and has forecast the weather in Jackson Hole for the last 30 years.

This article originally appeared in the Jackson Hole News and Guide.

2020: Another Cold & Snowy Year in Jackson Hole

This is a compilation of all of the weather stats for the Town of Jackson, WY for the year 2020, the stats that become part of the story of our local climate. Data presented comes from the from the Jackson Climate Station, located on the north end of town. As you will see, 2020 went down as another cold and snowy year here in Jackson.

The author skiing deep powder in the Tetons, February 2020. Photo Chris Harder.

Following this summary is a look back at the most significant weather events that occurred in 2020, what was unusual or outside what we consider “normal” weather.

High Temperatures 2020

The average high temperature for the entire year in 2020 was just under 52-degrees. That is two degrees colder than the long-term historic average annual high temperature of 54-degrees.

In 2019, the average high temperature was only 49-degrees. That was the coldest average annual high temperature, ever.

January, March and August of 2020 were the only months of the year that saw average high temperatures above normal. Every other month checked in with below normal high temperatures.

The hottest temperature recorded at the Jackson Climate Station in 2020 was 88-degrees on August 17th. There were no days that officially reached 90-degrees in town.

Low Temperatures 2020

The average low temperature for the entire year in 2020 was 23-degrees. That is precisely what the long-term average annual low temperature is for Jackson. In that respect, 2020 was totally normal.

January, March, May, June and August 2020 were all just above the average for monthly low temperatures. February 2020 was almost seven degrees colder than average; November was three degrees colder than average and December was around five degrees colder than average. The other months of 2020 were very close to the average monthly low temperatures.

The coldest day of the year back in 2019 was 25-degrees below zero on January 1st. In 2020, the coldest day of the year was also 25-degrees below zero, but it took until February 20th, 2020 to reach that same temperature.

Also of note was the coldest temperature ever recorded in the month of October, which occurred in 2020, when it dropped to 9-degrees below zero on October 26th. That beat the old October low temperature record that was set the previous year, when it dropped to 6-degrees below zero on October 30th, 2019.

Mean Temperature 2019

If you take the average of all the monthly high temperatures and all the monthly low temperatures for the year, you generate what is known as the annual mean temperature. This is the best gauge of the overall temperature for the entire year.

The annual mean temperature for Jackson in 2020 was 37.5-degrees. That tied for the 8th coldest year on record

In 2019, the annual mean temperature was 35.4-degrees. That was cold enough to qualify as the coldest annual mean temperature on record in Jackson.

The coldest year on record in Jackson prior to 2019 was back in 1944, which had a mean temperature of 35.5 degrees.

Keep in mind, to be in the competition for the coldest or warmest year ever, you need 12 months of complete weather data. Out of the last 97 years, dating back to 1923, there were 36 years with too many missing days or months of data to be able to calculate an accurate annual mean temperature. The year 2019 was the coldest out of the 61 years with complete data.

For trivia’s sake, the hottest annual mean temperature in Jackson’s climate record was 47.5 degrees, way back in 1933.

Precipitation and Snow

After a recent run of four years in a row with above normal annual precipitation, from 2016 to 2019, the Town of Jackson experienced a drier than normal year in 2020, but not by much. Total precipitation in Jackson in 2020 was 15.22 inches, compared to a long-term average of 15.83 inches.

Total snowfall in the year 2020 was a different story, we are presently on a five-year run with above average annual snowfall, and 2020 was the biggest of them all.

For the calendar year 2020, which actually accounts for parts of two different winter seasons, Jackson received 121 inches of snowfall. In 2019 we had over 111 inches. The average annual snowfall in the Town of Jackson is 77 inches.

I could only find three other years when the annual snowfall was greater than 121 inches in Jackson, the biggest of those years was in 1967, with 155 inches. The other two were in 1971 with 130 inches and 1973 with 123 inches. Again, these are among years that have complete records.


The weather in Jackson, WY for 2020 could be summed up as simply as this: it was colder and much snowier than normal, along with close to normal precipitation.

Everything was unusual in 2020, even the Weather

The pandemic created unusual circumstances that affected many aspects of our lives in 2020, the one thing it did not affect was the weather. Weather can be unusual all by itself.

Here, I will revisit Jackson’s weather from 2020 and focus on the more unusual events we had, in this most unusual year, season by season.

Winter 2020

January 2020 started out with a bang, when 32 inches of snow fell in the first two weeks of the year, in the Town of Jackson. That was big, considering the average snowfall for the month of January is 19 inches.

Rendezvous Bowl at the Jackson Hole Mountain Resort totaled up the most snowfall ever recorded in the first half of January. A total of 121 inches of snow was measured there between January 1st and January 15th, 2020. That’s 10 feet of fresh powder in two weeks.

The average snowfall for the month of January in Rendezvous Bowl is 86 inches. January 2020’s total snowfall ended up being nearly twice that, with 169 inches, establishing a new January snowfall record. The old record was 150 inches, set in January 1998. January 2020 was also the third snowiest month ever recorded at JHMR.

Chris Bellino on 25-Short, January 2020. Photo Jim Woodmencey

Spring 2020

Just as winter was waning the coronavirus was waxing, we received a big dump of snow. Between the morning of March 14th and the morning of March 15th, 2020 the Town of Jackson received 12 inches of snow, a record for a one-day snowfall total in mid-March.

That same day, the mountains received 23 inches of snow in 24 hours. That’s also the day the ski areas closed for the season.

As we all hunkered down in April, temperatures remained colder than normal. Jackson broke another record with a high temperature of only 28-degrees on April 13th, 2020. The low temperature that day was an unusually chilly 6-degrees. It was also snowier than normal during April 2020, in town and the mountains.

At the Rendezvous Bowl Weather Station (elevation 9,580-feet), at the Jackson Hole Mountain Resort, 74 inches of snowfall was recorded in the month of April 2020. Average snowfall there in April is listed as 33 inches.

Summer 2020

We started to dry out in May 2020. Precipitation this past May was only about one-third of the long-term average, 0.63 inches vs. 1.80 inches. June had more showers, but still checked in with just below average precipitation, 1.55 inches vs. 1.63 inches.

Then, in July and August it got really dry, with a little over half an inch of precipitation in July and less than a quarter inch in August. Correspondingly, there was also a noticeable lack of thunderstorms here in July and August 2020.

Temperatures were a bit at odds during the Summer of 2020, with cooler than average daily high temperatures, but slightly warmer than average overnight low temperatures. As a matter of fact, we went 91 days in a row without dropping below the freezing mark, between June 1st and August 30th. That is exceptional for Jackson.

Fall 2020

Over Labor Day Weekend the weather changed from warm and dry, with a high of 87-degrees September 5th, to cold and snowy, with a high of only 43-degrees on September 8th, 2020. That established a new record cold high temperature for that date.

Jackson also received one inch of snow on September 8th, 2020. That is the earliest in September that an inch of snow has been recorded in town. Prior to that, the earliest date for an inch of snow was September 17th, in 1944.

October 2020 also began relatively warm, then turned brutally cold during the final week of the month. On the morning of October 26th, 2020, the low temperature at the Jackson Climate Station dropped to 9-degrees below zero.

That established a new record cold temperature for the month of October. The old low temperature record for October, of minus 6-degrees, was from one year earlier, on October 30th, 2019.

October 26th, 2020 also established a new record cold high temperature for the month of October, of only 18-degrees. This was the first time in Jackson’s recorded weather history that a high temperature in October was in the teens.

November 2020 had its ups and downs temperature-wise, but as with October 2020, it checked in colder than average. November was also snowier than average in town.

In one 24-hour period from 9:00 a.m. on November 13th to 9:00 a.m. on November 14th, the Jackson Climate Station reported 7 inches of new snowfall. That much snow in a single day during the first two weeks of November is very unusual.

So far, December 2020 looks like it will finish up slightly cooler than normal overall, even with those few days of unusually warm temperatures around the Solstice.

Cam Fitzpatrick on Opening Day December 2020. Photo John Bowers.

Adieu to 2020

I tried to hit as many of this past year’s weather highlights as I could, although there are probably more that you might recall. For now, as most of us would probably like to do, let’s put 2020 in our rear-view mirror. Hopefully, 2021 will be a little less unusual for us, weatherwise and otherwise.

Post by meteorologist Jim Woodmencey.

Some of the above originally appeared in the Mountain Weather column in the Jackson Hole News & Guide