Good morning,
I hope this email finds you well! The atmosphere is primed across much of Iowa for all modes of severe weather later this afternoon through the overnight hours. The development of severe thunderstorms, specifically where and when, has been impacted by the continuing shower/thunderstorm activity across central Iowa. When thunderstorms rain out, they put out boundaries of rain-cooled air called “gust fronts.” These boundaries will be important later this afternoon, as they are a means of forcing thunderstorms in an unstable environment. These outflow boundaries can last for several hours and act as micro-scale cold fronts.
Instability is another variable … current thunderstorms are limiting the amount of sunshine hitting the surface, which limits the amount of instability that can build up through the day; turn off the flame under a boiling pot of water and it stops boiling. If the clouds burn off, the atmosphere will destabilize faster, allowing thunderstorms to form along and south of a warm front or existing gust fronts. We also have strong winds aloft and in the mid-levels that are moving in different directions; this is called “wind shear” and it causes thunderstorms to rotate. These types of thunderstorms are known as “supercells” and can produce tornadoes, hail and high winds. Heavy rain and flash-flooding are also possible with this event.
Taken together, an Enhanced Risk of severe weather exists basically south of I-80 to St. Louis. Within this region, a few tornadoes are possible, though the main threat appears to be straight-line winds and hail. Current high-resolution model solutions that are updating with existing thunderstorm activity show discrete storms forming later this afternoon and then coalescing into a line later tonight. Again, multiple factors are at play, so uncertainty exists. I have included the NWS Situation Report. Stay up-to-date via local media and the NWS as conditions can change rapidly this afternoon and evening.
State Climatologist.
I hope this email finds you well! The atmosphere is primed across much of Iowa for all modes of severe weather later this afternoon through the overnight hours. The development of severe thunderstorms, specifically where and when, has been impacted by the continuing shower/thunderstorm activity across central Iowa. When thunderstorms rain out, they put out boundaries of rain-cooled air called “gust fronts.” These boundaries will be important later this afternoon, as they are a means of forcing thunderstorms in an unstable environment. These outflow boundaries can last for several hours and act as micro-scale cold fronts.
Instability is another variable … current thunderstorms are limiting the amount of sunshine hitting the surface, which limits the amount of instability that can build up through the day; turn off the flame under a boiling pot of water and it stops boiling. If the clouds burn off, the atmosphere will destabilize faster, allowing thunderstorms to form along and south of a warm front or existing gust fronts. We also have strong winds aloft and in the mid-levels that are moving in different directions; this is called “wind shear” and it causes thunderstorms to rotate. These types of thunderstorms are known as “supercells” and can produce tornadoes, hail and high winds. Heavy rain and flash-flooding are also possible with this event.
Taken together, an Enhanced Risk of severe weather exists basically south of I-80 to St. Louis. Within this region, a few tornadoes are possible, though the main threat appears to be straight-line winds and hail. Current high-resolution model solutions that are updating with existing thunderstorm activity show discrete storms forming later this afternoon and then coalescing into a line later tonight. Again, multiple factors are at play, so uncertainty exists. I have included the NWS Situation Report. Stay up-to-date via local media and the NWS as conditions can change rapidly this afternoon and evening.
State Climatologist.
