Why summer rainfall is so tough to predict

TULSA, Okla. — Most of us are familiar with the terms popcorn thunder storms or hit-or-miss showers — and those descriptions explain the very nature of much of our summer rainfall in Oklahoma. Due to how localized rainfall is this time of year, predicting amounts for any exact location is nearly impossible. It boils down to three main reasons:

1. Upper-level winds are light. The jet stream has shifted north of us, and we get light flow aloft. This causes any storms that form to move only a short distance before they rain themselves out. That means the rain footprint is generally pretty small from any given cell.
2. Storms tend to form at random. Due to light winds aloft, storm systems and surface boundaries are not always clearing defined. This means there’s less predictability on where updrafts that lead to storms will occur. This is why summer storms are often of the popcorn or “hit or miss” variety.
3. Hot air holds more moisture. The warmer the atmosphere, the more moisture it can contain. This means our air is loaded with potential rainfall when humidity is running high on a summer day. If and when storms, form, significant rainfall rates are likely to occur. With the slow movement of those cells, high rain totals can occur in a small space. Just down the road, however, it may barely rain at all. Ultimately, this gives us a big disparity in totals. In other words, it is feaost or famine with rainfall.

At the end of a summer day, the rainfall map will look bespeckled with pockets of high totals instead of showing smooth gradients of rainfall like the forecast maps often show.

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