How do severe weather events form?

  The same conditions that cause ordinary thunderstorms also cause organized severe weather: atmospheric moisture, lift (often from thermals), and instability. Severe weather is caused by a wide range of factors. Thunderstorms can become severe weather due to a variety of factors.

Explanation: Hope this helps

Organized severe weather occurs from the same conditions that generate ordinary thunderstorms: atmospheric moisture, lift (often from thermals), and instability. A wide variety of conditions cause severe weather. Several factors can convert thunderstorms into severe weather.

Explanation:

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.