Could get bumpy as we transition from mild air to heat, humidity

Weather

ONE MORE MILD NIGHT

What a treat this has been as each of the past three mornings have opened in the 50s across central Indiana. For the second straight morning, Indianapolis started the day at 57° — the normal low for mid-September. The outlying areas were the coolest, and in western Indiana, Crawfordsville recorded a low of 50°.

The lack of humidity is one factor playing a part in the mild weather. The air is dry, and therefore it cools easily and quickly at night. The air is originating in northern Minnesota and Wisconsin where low temperatures were as cool as 36° Wednesday morning in Fond Du Lac! We are not quite severing ties with this flow of air just yet. For a fourth straight morning, lows in the 50s are expected to start the day Thursday.

STORMS PRECEDE SURGE IN HEAT AND HUMIDITY

It may be a bumpy ride as we make the transition from very mild air to the thick, tropical and uncomfortable air to end the work week. Around the periphery of a massive dome of heat out west, the development of thunderstorm complexes are looking more and more likely. We call this a “Rim of Fire” pattern when the storms develop into a cluster or complex and ride the jet stream, often diving in from the northwest. These prolific lightning, rain and often strong-wind producing clusters thrive on a nighttime jet stream that runs through the night then dissipates after sunrise. 

Such a scenario may be in the works before sunrise Friday just before the real jump in heat and humidity. We are NOT expecting storms on Thursday but will watch locations of Iowa and northern Illinois for such development after sunset Thursday night. Should a complex form, storms are possible early Friday morning with a possibility of damaging wind gusts. Stay tuned – our quiet severe weather season could take a turn.

With storms diminishing Friday morning, hazy sun is to emerge, and our temperatures are set to surge. With expected dry time Friday afternoon, the temperatures are expected to rise again into the lower 90s with a heat index climbing into the mid/upper 90s by afternoon. Scattered thunderstorms are possible in widely scattered fashion through Sunday. 

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