May 3, 2026
I had my golf tournament in Delaware at the end of April. As an outdoor sport player, checking temperature is the first thing I usually do. The temperature during the tournament was not ideal. I had short sleeves and a winter coat on different days.
What made me curious was the relatively small temperature difference between day and night in Delaware.
Firstly, I would like to understand how temperature varies.
I read the article posted by a meteorologist, Peggy on www.globe.gov (1). Using the data in Southeastern Kansas, she explained the temperature in an interesting way: Heat Budget.
- Incoming radiation from the sun = save money
- Outgoing infrared radiation from the ground through convection currents (also losing energy through evaporation and heating up the cooler soil) = spend money
Peggy explained that the temperature reached the highest at 4p.m. Before that, the net radiation brings in more energy than convection currents remove. After that, convection carries away more heat than the radiation is bringing in. However, this time may shift depending on cloud cover or wind.
At night, the air and ground keep cooling off by giving off infrared radiation. It continues all night, the coolest temperature is in the early morning, near the time of sunrise.
This clarified why the temperature at noon is not the warmest, the temperature at midnight is not the coolest.
Secondly, I hope to explore the factors influencing the Diurnal Temperature Range (DTR).
If the Heat Budget is how we spend and save, the Diurnal Temperature Range (DTR) is the difference between our highest and lowest temperature in a 24-hour cycle.
In deserts, diurnal temperature range can be extreme, while in coastal areas, the change may be more moderate due to the influence of ocean currents(2). There are three primary scientific reasons for this moderation.
- High heat capacity of water
The heat capacity is the product of the specific heat and the mass (in g) of the material. Oceans have a greater heat capacity than land because the specific heat of water is greater than that of land, which causes land areas to heat more rapidly and to higher temperatures and also cool more rapidly and to lower temperatures, compared to oceans.
The high heat capacity of water keeps its temperature within a relatively narrow range, causing nearby coastal areas to have a narrow diurnal temperature range. In contrast, areas with similar weather conditions that are farther from the coast tend to have a much wider range of seasonal and daily temperatures. To summarize, large bodies of water tend to moderate the temperature of nearby land due to the high heat capacity of water. This high heat capacity results from both the higher specific heat of water and the mixing of heat throughout a greater depth over oceans(3). Unlike soil, water is transparent and mobile, allowing heat to distribute through a much larger volume.
- The “Blanket Effect” of Humidity and Cloud Cover
Water vapor is good at absorbing and giving off longwave radiation (energy that’s released from the Earth) as well as absorbing in the near-infrared part of solar radiation, which reduces the amount of daytime energy reaching the surface. Because of this, daily highs are typically lower in humid environments than in dry environments. This is the primary reason why desert regions experience some of the most extreme day-to-night temperature fluctuations(4).
Moist air slows both heating and cooling because water vapor absorbs and re-emits longwave radiation, which reduces the amount of daytime energy reaching the surface, and prevents heat from escaping into space to keep nighttime temperature from dropping sharply(5).
Cloud covers have similar effects.
- Sea and Land Breezes
Near the ocean, a cool sea breeze often blows inland during the day, capping the maximum daytime temperature. At night, the process reverses, but the lingering warmth of the ocean prevents the land from cooling too rapidly.
Finally, I would like to understand the reason for the relatively small diurnal temperature in the Rehoboth Beach area in Delaware.
The State of Delaware lies among the Atlantic coast of the United States, occupying the northern two-thirds of the Delmarva Peninsula. It is surrounded by water bodies including the Atlantic Ocean and Delaware Bay to the east, and Chesapeake Bay to the west(7).
This explains why Delaware has relatively small diurnal temperature.
However, even though Delaware’s temperatures are moderate compared with other states, the diurnal temperature in different areas of Delaware varies. For example, the Sussex Country near the ocean has smaller diurnal temperature than the New Castle County near the metropolitan area of Philadelphia.
The town, Rehoboth Beach, is located on the Atlantic Coastal Plain, which has moderate diurnal temperatures. Because it is a peninsula, air masses are almost always “conditioned” by water before they reach the golfer, regardless of wind direction.
In conclusion, while the maritime climate of Rehoboth Beach keeps the daily range narrow, the ‘Blanket Effect’ of high humidity means that even a small rise in temperature can feel much more taxing on an athlete’s body. Understanding the DTR doesn’t just help me pack my bag—it helps me manage my energy on the course.
Note:
The Rehoboth Beach Country Club photo was from American Junior Golf Association (AJGA ) website.
Reference:
(1) Peggy, How the Temperature Varies During the Day and Night https://www.globe.gov/explore-science/scientists-blog/archived-posts/sciblog/2008/02/27/how-the-temperature-varies-during-the-day-and-night/comment-page-1/index.html, posted on Feburary 27, 2008
(2) Diurnal Temperature
(3) Temperature Over Time, Climate Science Investigations (CSI)
(4) Understanding Diurnal Temperature Range
https://www.thoughtco.com/diurnal-temperature-range-3444244
(5) What is diurnal temperature range and why it changes as we move into spring
https://www.metoffice.gov.uk/blog/2026/what-is-diurnal-temperature-range
(6) Sea, Lake, & Land-Breezes
https://www.noaa.gov/jetstream/ocean/sea-breeze
(7) Delaware’s Climate
https://storymaps.arcgis.com/stories/6b5c6000896f483dbfd19b4e0af9a766
