Text and images Copyright 2008, David R. Brooks, Institute for Earth Science Research and Education

Notes from a Temperate Climate

David Brooks

This page is dedicated to students, teachers, and all my friends in Thailand. Although I know that students living in Thailand's tropical climate study other climates in school, most of them have not yet had the experience of visiting or living in a place with a completely different climate. Over the next months, I will post photos taken from the front steps of my house and other places around our house. After a year, I hope you will have a better idea of what it is like to live in a temperate climate. If you have questions, you are welcome to send me an e-mail. For complete weather summaries, see this site, which is at a small commercial airport about 10 km from my house.

30 March 2008

These notes start on 30 March 2008, just as spring is beginning where I live in Pennsylvania, We have weather that is typical of much of the northeastern and midwestern United States. Our house is near the east coast of the United States, about 150 km from the Atlantic Ocean, at 40.2N latitude and 75.3 west longitude, at an elevation of 120 m. March marks the change from winter to spring weather in our climate. Because of the big change in weather, March is sometimes described as "In like a lion, out like a lamb." The air temperature at 15:30UT (11:30am, Eastern Daylight Time) was 7C. Temperatures may still drop to freezing at night, but the date of "last frost" is rapidly approaching. During March, the maximum temperature was 18C and the minimum was -4C. My wife, Susan, has already planted some cold-tolerant vegetables, such as peas, in her vegetable garden. She is starting other plants, such as tomatoes, indoors, but it is still too cold to plant them in the garden.

In temperate climates, there is a mix of evergreen and deciduous trees. Typically, deciduous trees lose all their leaves during the winter. Ground vegetation also dies, leaving only brown remains and last fall's leaves. In Figure 1, taken on 30 March 2008 at about 15:30UT, you can see many deciduous trees on our property. They may look dead, but they are not. On the right is an eastern red cedar, which stays green year-round. On the ground, there are only some clumps of green vegetation visible -- just a few weeks ago nothing green was visible. These are daffodils, very popular bulb-propagated plants which are among the first flowers to bloom in the spring -- a close-up is shown in in Figure 2. These flowers are about 6 cm in size. Some crocus, which are also bulb-propated plants, are shown in Figure 3, growing beside our patio. They start blooming a few weeks before daffodils and their flowers are about 3 cm in size. The bulbs of these plants lie dormant underground all winter. So, their emergence in the spring is triggered not by air temperatures or sunlight, but by warming soil temperatures. Unlike most vegetation, daffodils are not appealing food for the whitetail deer that are common in our area, so they remain unharmed.
      Figure 4 shows buds just forming on a Kousa dogwood, an ornamental deciduous tree native to Japan. Elsewhere on our property, forsythia, shown in Figure 5, are also flowering. These bushes are often planted in hedges along property lines. People like them because their small bright yellow flowers are a sure sign of spring. Later in the year, the bush is not nearly so attractive.
Figure 1. 30 March 2008.

Figure 2. daffodils.Figure 3. Crocus.Figure 4. Buds on Kousa dogwood.Figure 5. Forsythia.

05 April 2008

There is a rhyme about April: "April showers bring May flowers." But, April is not a particularly rainy month where I live. Figure 6 shows the monthly average precipication in our area -- we receive a little more than 100 cm of precipitation per year. Unlike the climate in southeast Asia, precipitation in temperate climates is more uniformly distributed over the year. The average number of days per month with precipitation is also shown in Figure 6. The rainiest month where I live is July, often with thunderstorms and heavy rain. February is the driest month, with precipitation typically in the form of snow, and April is about average. When precipitation falls in the form of snow, the number of centimeters is calculated as the rainfall equivalent of the melted snow. On average, there are no "dry" or "wet" seasons as there are in southeast Asia.
Figure 6. Average precipitation where I live, by month.
On this overcast day, the view from my front steps has changed only a little. Overall, in Figure 7, there is a slightly more greenish appearance as tree leaves start to appear. Figure 8 shows a close-up of some of these trees, with their small leaves. Figure 9 shows a larger area planted with daffodils, which are now at their prime. Figure 10 shows a view of the meadow behind our house. This photo helps to explain why agricultural burning is rarely used in my climate -- all the meadow grasses die during the winter. The new growth will start in a few weeks.
Figure 7. 05 April, 2008.
Figure 8. Leaves just starting to appear.Figure 9. Daffodils in full bloom.Figure 10. Meadow in early spring.

One of the differences between Thailand and where I live, much farther north, is the seasonal dependence of day length. Figure 11 shows the number of hours of daylight where I live at 40N and around Bangkok, at about 13N. At my latitude, the day length varies from a little more than 9 hours in the winter to a little less than 15 hours in the summer. In Thailand, there is always at least 11 hours of daylight, but never as much as 13 hours. At the Vernal and Autumnal equinoxes (the start of Spring and Fall in the northern hemisphere), there is 12 hours of daylight regardless of where you live. Another difference between Thailand and where I live is the position of the sun in the sky at noon. My latitude is well above the Tropic of Cancer and Thailand is well below. (The Tropic of Cancer is an imaginary line drawn around the Earth at a latitude of about 23.5N.) The solar zenith angle is defined as the angle between an imaginary line pointing straight up from an observer's location and an imaginary line to the sun, as shown in Figure 12. At my latitude, the noon-time solar zenith angle varies from about 63 in the winter to 17 in the summer. The sun is never directly overhead. In Thailand, the noon-time solar zenith angle is a maximum of about 37 in the winter and reaches 0 twice during the year when the sun's declination (its angular position north or south of the equator) passes through Bangkok's latitude. The strong seasonal variability in the day length (and the availability of sunlight) and the variation in maximum solar zenith angle are the most important reasons why there are much greater temperature differences between winter and summer in temperate climates than in tropical climates.
Figure 11. Hours of daylight in Philadelphia and Bangkokg.Figure 12. Solar zenith angle. Figure 13. Zenith angle at solar noon.

12 April 2008

Due to warmer weather and some rain, spring growth has accelerated. Figure 14 shows much more green on leaves and in ground vegetation. The Kousa dogwood buds are greener and starting to open, as shown in Figure 15. The Kousa dogwood is a late-flowering tree compared to many others in our area. Figure 16 shows new blossoms on a wild cherry on our property. Many trees have new leaves that were completely absent only two weeks ago, as shown in Figure 17.
Figure 14. 12 April 2008
Figure 15. Kousa buds, 12 April 2008.Figure 16. Flowering Cherry, 12 April 2008.Figure 17. New leaves, 12 April 2008.

19 April 2008

What a difference one week makes! In spring, changes happen quickly when temperatures get warmer and days get longer. In this photo, a wild cherry tree has blossomed with white flowers and a redbud tree has also blossomed. The Kousa dogwood buds are much greener, but are just beginning to open.

26 April 2008

An overcast day in late April. There has been much less than the average precipitation so far this month. The leaves on the Kousa dogwood are now open and the flower buds on the Kousa dogwood are clearly visible now, as shown in the middle photo.

03 May 2008

Another overcast day in early May.

10 May 2008

A bright but still overcast day in May.

17 May 2008

A sunny day in mid-May.

24 May 2008

The Kousa dogwood flowers are approaching their peak.

31 May 2008

The Kousa dogwood flowers are at their peak.

07 June 2008

The dogwood leaves are now a deep glossy green. The flowers are just starting to fade.

14 June 2008

The dogwood flowers are fading. There have recently been several days with temperatures in excess of 35C, which is unusual for this time of year -- not yet even officially summer.

21 June 2008

The dogwood flowers are now gone.

28 June 2008

The orange flowers in the lower left are day lilies.

05 July 2008

The flowers are purple cone flowers.

15 July 2008

The dogwood looks a little stressed from the heat.

20 July 2008

During the peak of summer heat, not much is happening.

26 July 2008

More of the same...

02 August 2008


09 August 2008


16 August 2008

The blossoms on the right are from a crepe myrtle.

25 August 2008

The purpose coneflowers are finally starting to fade.

06 September 2008

Following a short rain shower.

13 September 2008

The dogwood seed capsules are ripening. Some sources say the fruit is edible, but not very good.

20 September 2008


27 September 2008

The dogwood fruits are mostly gone. They just fall off and perhaps some are eaten by squirrels.

04 October 2008

The dogwood leaves are just starting to change color.

11 October 2008

Now you can start to see leaves changing color in the other trees.

18 October 2008


25 October 2008


01 November 2008

Now the trees are losing their leaves.

08 November 2008

This is the height of fall leaf color in our region.

15 November 2008

In just a few days, winds and colder temperatures have stripped most leaves from deciduous trees.

21 November 2008

An unusual early snowfall has blanketed our area. The snow is very "wet" and sticks to branches. The snow has not accumulated on the flagstones because the air is not very cold and the ground is still relatively warm.

29 November 2008

By the end of November, it is starting to look like winter.

06 December 2008


13 December 2008

NOTE: I missed photos this week. These are duplicates from 06 December. This time of year, not much has changed!

20 December 2008

Freezing rain has coated the bare tree branches with ice.

27 December 2008

Instead of a White Christmas, we had a relatively warm and wet holiday.

03 January 2009

NOTE: This photos are copies of the photos from 27 December 2008.

10 January 2009

A small amount of snow has fallen overnight. The bud photo is the same as on 27 December -- this tree is dormant now, and nothing is changing.

17 January 2009

Daytime maximum temperatures for the last several days have not risen above 0, but there has been little precipitation. Because it has been so cold, there is still a little snow and ice left over from the previous week.

24 January 2009

The snow from last week has completely melted except for a couple of small patches on our flagstone patio that never receive direct sunshine this time of year. So far this winter, there has been relatively little snow.
When the temperature is not too cold -- just below freezing -- and it is not too windy, snow clings to tree branches, giving this scene a silvery look. The photo is from 19 January.

31 January 2009

A winter storm during the night of 27-28 January has given us several centimeters of snow, topped with freezing rain. This makes roads very hazardous. Our driveway is coated with ice, which makes it accessible only for a 4-wheel drive vehicle. Snow and ice has coated everything, including the leaves of this magnolia tree near our house. This tree, which keeps its leaves year-round, is native to the southern part of our country, but it has managed to survive our more severe winters in its location at the southeast corner of our house.

07 February 2009


14 February 2009


21 February 2009

Daffodils grow from bulbs several centimeters underground. Nobody is quite sure how they know when it is time to start growing again, although ground temperature probably acts as a trigger. Whatever the mechanism, they are always a welcome and reliable indicator that winter is nearing an end.

28 February 2009


07 March 2009

This time of year the weather where I live, during the transition from winter to spring, can fluctuate wildly! Just a few days ago we had low temperatures below -13 and more than 25 cm of snow on the ground. Today all that snow has melted and the high temperature was almost 22.
(C) during the first week of March.

14 March 2009

The daffodils have grown quickly over the last few days. Temperature swings are still quite pronounced, from below freezing at night to 15C or higher during the day. These temperature swings are important to plant growth and agriculture in temperate climates, as the freeze/thaw cycles help to break up and aerate the soil.
These flowers, called snowdrops, are the first to bloom at the end of winter.

21 March 2009

Spring officially started yesterday, on the 20th. This is a beautiful day, with a high temperature around 10, although nighttime temperatures can still fall below freezing. At this time of year, gardeners have already started their season's vegetable planting indoors. They want to get the new seedlings out into their gardens as soon as possible, to get an early start on the growing season, but they need to be careful with temperature-sensitive plants such as tomatoes, which will not survive even a brief freeze.
Crocus have sprung up in just the last few days, another sure sign that spring is here.
Robins migrate south in the winter and their return is another sign of spring where we live. This female is looking and listening for worms and grubs in our yard. (The female's coloring is basically the same as the male's, but it is not as bright.) There are flocks of 10-20 robins around our house, looking a little thin from their journey. They will fatten up considerably during the next few weeks as they mate and start building nests.

This weekend marks the end of one complete yearI started these photos on 30 March, 2008. Note that the daffodils are just starting to bloom this year, just as they did last year.
Here is a close-up of the daffodils in our front yard.