The National Weather Service (NWS) has issued a flood watch for Lake and surrounding Illinois counties through Friday morning, July 29^th. Parts of Lake County have been impacted by flash flooding caused by intense thunderstorm rainfall over the past several days, leading to localized flooding of roads, streets, yards, and in some cases, the basements or lower levels of homes. Heavy rains have filled many stormwater basins and road ditches, leaving limited capacity for additional rainfall. The Lake County Stormwater Management Commission has instituted a Green Flood Alert, meaning that current and forecast conditions may lead to flooding.

The current weather situation includes a large area of very moist air over northern Illinois, and additional warm humid air feeding into the area. Storms are expected to develop to our west later today, and then move east. The convective nature of thunderstorms often produces very intense rainfall over a relatively localized area, and within a given storm there is often a wide variation in measured rainfall amounts from point to point. Because of the high moisture content of the atmosphere, storms that develop later today will be capable of producing rainfall rates of one to three inches of rain per hour, which could easily lead to localized flash flooding.

Flash flooding is one of the leading causes of weather-related injuries and deaths in the United States, with most deaths caused by people driving into flooded roads. We join the National Weather Service in reminding anyone that drives upon a flooded road or street to "turn around, don't drown," since water can hide damage to the underlying road surface and only six inches of flowing water can sweep a car or truck off the road. Additional information about the "turn around, don't drown" campaign can be found in the NWS brochure available at

http://www.weather.gov/os/water/tadd/images/NSC_FinalVersion1-4.pdf

The Lake County Division of Transportation provides the most complete listing of road information through the Lake County Passage traffic management center, available at 1620 on AM radios, or at the website

http://www.lakecountypassage.com/index.jsp

The Stormwater Management Commission encourages community officials and homeowners to make sure that storm drain grates, drainage ditches, culverts, and swales are not blocked by debris from the recent windstorms. Branches, limbs, leaves, and wood chips can wash downstream and lodge against bridges or culverts, causing water to back up very quickly in areas where flooding may not typically occur.

If you're experiencing flooding, please report the situation to the Stormwater Management Commission at 847-377-7700. Residents or businesses that need assistance should first contact their local municipality or township. Partner organizations that need assistance should contact the Lake County Emergency Management Agency at 847-377-7100 during business hours, or after-hours through the Lake County Sheriff's 9-1-1 Dispatch Center at 847-549-5200.

The text of the NWS flood watch provides some additional information:

AFTER A LULL IN THE THUNDERSTORM ACTIVITY LATE THIS MORNING AND EARLY AFTERNOON... STRONG THUNDERSTORMS ARE EXPECTED TO DEVELOP LATE THIS AFTERNOON OVER EASTERN IOWA AND NORTHWEST ILLINOIS. THESE THUNDERSTORMS WILL THEN SLIDE EAST ALONG A NEARLY STATIONARY FRONTAL BOUNDARY THIS EVENING AND OVERNIGHT. VERY MOIST AND UNSTABLE AIR FEEDING INTO THESE STORMS FROM THE SOUTH WILL LIKELY RESULT IN EXCESSIVE RAINFALL. THIS COULD RESULT IN RAINFALL RATES FROM 1 TO 3 INCHES PER HOUR IN THE HEAVIER STORMS. THE WATCH AREA HAS ALREADY EXPERIENCED VERY HEAVY RAINFALL IN RECENT DAYS AND ANY ADDITIONAL HEAVY RAIN COULD LEAD TO RAPID FLOODING. AREAS ALONG AND NORTH OF INTERSTATE 88 AND INTERSTATE 290 APPEAR TO HAVE THE GREATEST THREAT FOR RECEIVING THE HEAVIEST RAINFALL. AREAS TO THE SOUTH OF THESE HIGHWAYS DOWN TO THE INTERSTATE 80 CORRIDOR DO HAVE SOME RISK FOR HEAVY RAINFALL AND FLASH FLOODING AS WELL.