The cold front will move slowly enough that we can expect chances for showers and thunderstorms for the next three days. It will not rain the entire time, in fact some might not get any rain at all. However, the chances are there area-wide. This morning there is some thunderstorms moving into northwestern Missouri. While these will die out before reaching central Missouri, they will develop boundaries that will slide into the region.
It will be along these boundaries that have the greatest chances for thunderstorms. These should be quite isolated, with most of us remaining dry for Sunday. A slightly more organized chance of thunderstorms is possible on Monday as the actual cold front moves into the area. This cold front will be weakening as it moves through, so it will not provide much forcing to get storms going, therefore they will be widely scattered with little organization to them. Where exactly these storms could develop will depend on where the front is, right now locations south of I have the greatest chance of these storms but they are possible area-wide.
As the front moves to the south, we could still see some lingering showers and thunderstorms into Tuesday as well. Particularly in the morning. No severe weather is expected, although in some of the stronger storms heavy rain, frequent lightning, and wind gusts up to 40mph are possible. Thunderstorms seldom occur on the West Coast where the temperature contrast between the water and the land is minimal. A more uniform temperature area, doesn't create the instability to develop severe thunderstorms.
In Iowa thunderstorms can occur at any hour of the day. During the summer thunderstorms usually occur at night. This contrasts with storms along the front range of the Rockies and Florida, where thunderstorms are usually afternoon events. The maximum in afternoon heating leads to convection and the production of thunderstorms in these two areas and most of the rest of the United States.
Often these storms are air mass thunderstorms. Iowa thunderstorms and one in most of the Upper Midwest usually require the additional forcing caused by low level winds which occurs at night to produce thunderstorms which are more severe and longer lived storms. This marks the beginning of the second stage mature. The term downdraft is used to describe the rain and the cool air that begins to descend from the thunderstorm.
Downdrafts can change the temperature rapidly in an area in a short amount of time. For example, during a hot, summer afternoon in Sattley, California, the temperature was a blazing 97 degrees at P. However, after a thunderstorm passed through the area, the downdraft dropped the temperature to a cool 57 degrees by P. However, most storms cool things off a more modest degrees because of evaporative cooling.
Figure B. The mature stage of a thunderstorm. When the downdraft hits the ground, it begins to spread out in all directions. When this happens, a gust front can form. The gust front is basically a boundary that separates the rain-cooled air from the surrounding warm air shown in Figure C.
Sometimes, a menacing-looking shelf cloud or roll cloud will form along the gust front. As you can imagine, the wind behind the gust front can be very strong, sometimes even reaching severe levels. Figure C. A Gust Front located ahead of an approaching thunderstorm. During the mature stage, the heaviest rain and sometimes hail fall from the storm.
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