Flash flood warning issued as heavy rain hits East Helena area
Flash flooding already hit parts of East Helena as thunderstorms dropped 3.70 inches near town and sent 0.41 inches into Helena Regional Airport in an hour.
A flash flood warning covered East Helena and parts of southeastern Lewis and Clark County on July 1 as thunderstorms dumped rain fast enough to send water into low spots, underpasses and small streams. Trained weather spotters recorded thunderstorms producing heavy rain, and flash flooding was already occurring across the affected area.
The National Weather Service in Great Falls included Helena, East Helena, Townsend, Winston, Goose Bay, Silos, York and Spring Meadow Lake State Park in the warning area, which also reached north-central Jefferson County and northwestern Broadwater County. Rainfall rates could reach 0.5 to 1.5 inches in an hour, with up to another inch possible, a pace that can overwhelm drains and send water across roads in a matter of minutes.
Helena Regional Airport recorded thunderstorm rain during the period, including 0.41 inches in one hour around mid-afternoon. Local spotters also measured 3.70 inches of rain near East Helena.
Slow-moving thunderstorms with heavy rain posed a flash flood threat through the evening, especially in the Sapphire Mountains and southwest Montana. The storms were moving northeast at about 12 to 20 mph, a slow pace that allowed them to keep dropping rain over the same ground, and the HREF model showed the potential for up to 0.80 inches in under an hour in limited areas.
The main concern was flooding of small creeks and streams, urban areas, highways, streets, underpasses and other low-lying or poor-drainage spots. That put the heaviest risk on daily travel in and around Helena and East Helena, where runoff can quickly turn into standing water on local roads and choke drainage channels after a burst of rain.
Lewis and Clark County Emergency Management manages its Emergency Operations Center from Helena Regional Airport during emergencies, and the county uses an Emergency Alert System and a target notification system through the Lewis and Clark County Sheriff's Office, Helena Police Department and 911 Dispatch Center for evacuation orders and other urgent alerts. The flash flood risk would ease day by day as the system weakens and moisture gets worked out, but the storm pattern remained active across Montana through the week.
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