Weather Word of the Week: Moisture Return

Weather Word of the Week

Moisture, a word that some people can’t stand the sound of. Despite this fact, it is a VERY important ingredient for weather more specifically for storms. In this episode of Weather Word of the Week we are going to explore the return of this ingredient and where it comes from.

Moisture Sources

Gulf of Mexico– This is our primary source of moisture for the Natural State. The warm waters of the Gulf create quite a bit of evaporation into the atmosphere. Given the right type of weather patterns, we can see this massive amount of water vapor pumped right up into Arkansas.

Plants– The evaporation of water from the surface of plants (evapotranspiration) provides the second highest amount of moisture to our atmosphere. We will explore this topic further in an episode of Weather 101.

Favorable Weather Patterns for Moisture Return

There are multiple patterns that can lead to a moisture increase across our region. The most favorable set-up involves a high pressure anchored over the Tennessee Valley, and a low pressure across the panhandles of Texas and Oklahoma. Being located on the western periphery of the high pressure allows rich Gulf of Mexico moisture to flow into our viewing area. The low to our west can increase the rate of moisture transport, but can also bring dry air into the region as well.

Favorable Set-Up for Moisture Return

The drier air located at about 5,000 ft above the ground often caps the atmosphere across our area. The strength of this cap is important. If the cap is too strong, no storms will be able to overcome the inhibition. If the cap is too weak, then storms will form too early before the instability has time to build.

If we increase the low level (below 5,000 ft) moisture across our region, that will effectively increase the instability of the atmosphere as well. The greater the amount of instability the more severe the storms become.

Seasonable Variability in Moisture Return

It should come as no surprise that the greatest moisture return from the Gulf occurs in the summer. The Gulf of Mexico has heated up quite a bit by this time, and readily provides us with the sultry moist summer evenings!

The springtime also pumps quite a bit of moisture our way with the stronger Canadian highs providing a stronger return flow from the Gulf. The dew points climb fast, and can increase the thunderstorm fuel across the area. The strong leeside Rocky low pressures can also increase the rate of moisture return as well!

The fall does see moisture return patterns as well, but they tend to be much weaker. This weaker set-up does not bring the dew points up quite as high. Unusually strong Canadian high pressure systems can still bring in plenty of moisture in the fall. When this occurs it can help fuel our fall severe weather season.

Fall Moisture Return Set-Up

As odd of a word as it is, moisture is a very important ingredient to the weather across the area. Without moisture return, there would be no storms, clouds, or rain to keep our crazy weather interesting!

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