Forecast Exercise: Question 2

To answer this question and others that follow, you first need to open the Interactive Skew-T with this sounding.

It is always important to take into account factors that may change the sounding during the day. These changes can substantially alter the stability and/or shear profiles and significantly impact the potential for severe weather.

1. Modify the lower part of the sounding to reflect the predicted maximum surface temperature of 83°F (28°C). How does this affect the stability and severe weather potential?
Enter your response in the text box below, then click Done to see an expert opinion.

The surface heating to 28°C, and subsequent modification (heating) of the lower levels of the sounding up to at least 850 hPa have significantly increased the instability and further enhanced the severe weather potential. This is reflected in a number of sounding parameters, including increases in CAPE, TT, and SWEAT, and a decrease in LI, all of which indicate an increased potential for severe convection.

2. Now further modify the sounding, drying the lowest 100 hPa by lowering the Td by 5°C. How does this affect the stability and severe weather potential?

Drying of the lowest 100 hPa results in a significant decrease in CAPE and an increase in the LI, both reflective of a diminished severe weather potential. The lesson here is that it is important to look at how both temperature and moisture affect the stability. While daytime heating may destabilize the sounding, drying due to mixing or the passage of a dryline may act to increase the stability and counteract the effects of heating. Conversely, an increase in low-level moisture can significantly destabilize a sounding, even in the absence of surface heating. (Prove this to yourself using the interactive skew-T diagram).
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