The combination of tropical moisture from Simon and a slow-moving frontal zone will unleash heavy rain and the risk of localized flooding in a large portion of the central United States this week.
Leftover tropical moisture from Simon will impact parts of the Southwest this week. However, moisture will be strung along farther to the east over time.
Over the southern Plains, a great temperature contrast will develop prior to the breakout of heavy rain and drenching thunderstorms.
Temperatures in parts of Texas, Kansas and Oklahoma may flirt with record high levels. Meanwhile, cooler-than-average conditions will hold farther north over the Plains. The temperature contrast will provide extra energy for the upcoming rainfall.
The pattern has the potential to unload a general 1 to 2 inches of rain, but local amounts of 4 to 6 inches are possible.
While the exact track of the corridor of heaviest rain is uncertain, some areas in parts of the Plains and Midwest will be hit by drenching rain on multiple days during the pattern.
Cumulative rainfall over several days in part of the Central states can flood some agricultural areas and bring small streams out of their banks. Locally intense, short-term rainfall can lead to flash and urban flooding.
The corridor of the heavy rain will first likely extend across portions of Kansas, Missouri and Oklahoma Wednesday into Thursday.
Later in the week, the rain is likely to extend southward and eastward. From Thursday into Friday, heavy rain is likely to reach parts of northern Texas, Arkansas, southern Illinois, western Tennessee and the Ohio Valley.
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Rounds of less intense rainfall will extend eastward.
One batch of rain will soak part of the central Appalachians and mid-Atlantic Friday into Friday night.
Another batch of drenching rain is possible in parts of the East early next week, which could cause more travel delays.
Looking farther ahead to later next week, another storm system in parts of the Central and Eastern states may tap into tropical moisture from the Atlantic.
Part of the region in the South Central states forecast to be affected by the rain continues in long-term drought, while other areas on the Plains and Midwest have excess soil moisture.
Meanwhile, some areas in the East have been experiencing a rainfall deficit and a short-term dry spell.