Recipe for heavy rain in October

On Thursday (Oct. 24th), strong storms and heavy showers swept across Central Texas with widespread rain totals of 1″ to 3″ and isolated amounts up to 7″. Everything came together for a heavy rain event, a somewhat common occurrence this time of year in this part of Texas. But why is that? And what do we need to get this kind of weather set-up? Let us break down the “recipe”:

INGREDIENTS:

1. ENERGY: an upper level trough or low pressure system provides the energy we need to get storms and showers fired up. We want the atmosphere energized… free of sinking air and an upper-level pattern favorable for instability.
2. LIFT: we can think of lift as a trigger… or some sort of mechanism that will push air upwards. An example of this? A cold front. A cold front is just a boundary between colder air and relatively warmer air. As the cold front moves in, the colder, denser air behind the front will lift the warmer, moist air already in place.
3. MOISTURE: we can’t get rain if we don’t have clouds… and we don’t see clouds if we’re stuck with dry air. To see a heavy rain event in Central Texas, we usually see moisture pulled in off the Gulf of Mexico or Pacific Ocean (or both!) This increase in moisture can be from a tropical disturbance in the Gulf/Pacific or even a strong low pressure system over the Desert Southwest pulling in moisture around the bottom of it.

In the case of this week, a low to our west provided the energy and helped set the stage for active weather. We pulled in moisture off the Pacific and Gulf, as moisture from what would become Tropical Storm Olga was brought in by south/southeasterly winds. The trigger was a strong cold front that dropped in from the north Thursday night. Heavy showers and strong thunderstorms developed in front of and along the front as it moved northwest to southeast across Central Texas. In the matter of just a few hours, many locations picked up a couple inches of rainfall. (Fortunately, only minor to moderate flooding resulted with one water rescue and a handful of stalled vehicles.)

When all three ingredients (energy, lift, moisture) come together like they did this week, we prime the atmosphere for abundant rainfall. So be on the lookout for this type of set-up and stay with KXAN for all your weather information.