Figure 3. Continuous map of wettest month of the year. Map surface generated from points in Figure 2. Individual Months Instead of trying to decipher often complicated patterns, I though it useful to have an individual map for each month of the year. In the following 12 figures Figures 4 through 15 , each month of the year is pulled out individually. Only those stations with a peak precipitation value in that month are shown. If a station has a tie for the peak month, it is shown in all months for which a tie exists.
Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure Intra-Annual Variability In many cases, there are substantial differences between wet and dry months. On the flipside, many stations in the Northeast and mid-Atlantic have precipitation evenly distributed across all months. The final map in this blog post Figure 16 shows the month-to-month variability in precipitation values across the year. In this case we used the Chi Square goodness-of-fit-test.
As you can see, some areas have low month-to-month variability and others have quite a bit. I initially assumed that all cold regions e. The other quite surprising finding is the low month-to-month variability in the Great Basin.
Perhaps this is an artifact of multiple synoptic-scale parameters in other regions all converging in this location. There are far too many patterns in this map to describe. It is worthy of its own blog post another day! Overall, the Northern Hemisphere receives more rainfall than its southern counterpart. But what exactly causes these spring-specific showers in areas north of the equator? Whether or not a region is particularly rainy depends on where you live: Factors like latitude, elevation, prevailing winds and topography influence precipitation.
This mix of ingredients positions the Northern Hemisphere to receive rain during springtime, especially the United States. As it turns out, the mystery behind seasonal rainfall is actually relatively simple. During the spring transition from cooler to warmer temperatures, the air around us heats up. The cool, dry winter air combines with warm, humid incoming summer air. The mix of temperatures causes this air to rise, and moisture escapes in the form of rain.
This leads to an especially wet spring in the Northern Hemisphere due to a combination of ideal temperature conditions, proximity to mountain ranges and prevailing winds.
And when summer finally approaches , the spring showers turn into occasional rainfall as temperatures increase. According to Trenberth, the configuration of continents versus ocean is rather different south of the equator: The continents are subtropical and the main storm tracks sit at higher latitudes than in the Northern Hemisphere, meaning that areas like New Zealand, Tasmania and southern Australia, southern Africa, and southern Chile and Argentina experience spring storms the most.
There are distinct dry seasons, where no rain will fall at all for months. Then short wet seasons, bringing heavy rains most afternoons, with hot, humid conditions throughout the rest of the day. Usually, countries located close to the equator with tropical climates have only two seasons, the dry season and the wet season.
During the wet season, just like in savannahs, there is typically heat build up over the course of the day. This allows thunderstorms to grow and eventually produce rain in the afternoon, continuing overnight. The magnitude of rainfall can vary from day to day but it can be expected at roughly the same time. It's best not to be caught in such conditions, as lightning can be violent and rainfall significant.
When is rainy season?
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