...MINOR FLOODING POSSIBLE LATE SUNDAY INTO THE FIRST HALF OF THE
WEEK DUE TO A COMBINATION OF SNOWMELT AND RAINFALL...
AS AN EARLY SPRING STORM SYSTEM AFFECTS NORTHERN ILLINOIS AND
NORTHWEST INDIANA SUNDAY AND SUNDAY NIGHT...WIDESPREAD RAINFALL
WILL OCCUR. RAINFALL AMOUNTS THROUGH SUNDAY NIGHT OF AROUND ONE
AND A HALF INCHES WITH LOCALLY HIGHER AMOUNTS ARE EXPECTED OVER
THE ROCK RIVER BASIN. FURTHER SOUTH...ONE TO ONE AND A HALF INCHES
ARE LIKELY OVER THE ILLINOIS RIVER BASIN...WITH LESSER AMOUNTS SOUTH
AND EAST FROM THERE. THIS RAINFALL...COMBINED WITH SNOWMELT
RUNOFF...WILL LEAD TO RISES ON AREA STREAMS ALONG WITH PONDING OF
WATER IN LOW LYING AREAS. SOME OF THE RISES ALONG WATERWAYS MAY BE
QUICK.
RECENT WINTER STORMS HAVE DEPOSITED SIGNIFICANT AMOUNTS OF SNOW
ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA. SNOW DEPTHS
CURRENTLY RANGE FROM 1 TO 3 INCHES IN AREAS ALONG AND SOUTH OF
I-80. NORTH OF I-80...SNOW DEPTHS ARE BETWEEN 4 AND 10
INCHES...WITH THE DEEPEST SNOWPACK IN AREAS BORDERING THE
WISCONSIN STATE LINE. MORE IMPORTANTLY...WATER EQUIVALENTS OF THE
EXISTING SNOWPACK RANGE BETWEEN 1 AND 2.5 INCHES ACROSS MUCH OF
THE AREA.
ANOTHER CONCERN IS THE FROZEN GROUND BENEATH THE SNOWPACK. FROST
DEPTHS ARE CURRENTLY BETWEEN 6 AND 10 INCHES. THE KEY FACTOR THAT
WILL DETERMINE THE AMOUNT OF RUNOFF THAT OCCURS WILL BE THE RATE OF
FROZEN GROUND THAW LEADING UP TO AND DURING THE RAINFALL. AT THE
PRESENT TIME...THE THINKING IS THAT A SIGNIFICANT AMOUNT OF FROST
STILL REMAINS IN THE GROUND DURING THE HIGHEST SNOWMELT RATES LATE
TONIGHT INTO SUNDAY. THIS WOULD RESULT IN RUNOFF OF THE RAIN AND
SNOWMELT INSTEAD OF THAT WATER INFILTRATING INTO THE SOIL.
HOWEVER...THERE STILL IS UNCERTAINTY REGARDING THE AMOUNT OF FROST
THAW THAT WILL OCCUR. IN ADDITION...ANY HEAVY RAINFALL RATES THAT
OCCUR WITH THE ONGOING MELT WOULD RESULT IN HIGHER RUNOFF RATES
REGARDLESS OF THE FROST DEPTH.
PERSONS LIVING IN LOW LYING FLOOD PRONE AREAS SHOULD CONTINUE TO
MONITOR LATER FORECASTS AND STATEMENTS ON THE INCREASING FLOOD
POTENTIAL SUNDAY INTO THE FIRST HALF OF THE WEEK. SOME OF THE AREA
RIVERS THAT LOOK LIKE THEY COULD RISE TOWARD FLOOD STAGE INCLUDE
BUT ARE NOT LIMITED TO THE DES PLAINES RIVER...DUPAGE
RIVER...ILLINOIS RIVER...KISHWAUKEE RIVER...ROCK RIVER...AND SUGAR
CREEK.
