...MINOR FLOODING POSSIBLE LATE SUNDAY INTO NEXT WEEK DUE TO A
COMBINATION OF SNOWMELT AND RAINFALL...
A LOW PRESSURE SYSTEM WILL BE AFFECTING NORTHERN ILLINOIS AND
NORTHWEST INDIANA BEGINNING LATE SATURDAY. THIS SYSTEM HAS THE
POTENTIAL OF PRODUCING RAINFALL OF BETWEEN 0.75 AND 1 INCH. THIS
RAINFALL...COMBINED WITH SNOWMELT RUNOFF...COULD LEAD TO SIGNIFICANT
RISES ON AREA STREAMS ALONG WITH PONDING OF WATER IN LOW LYING AREAS.
RECENT WINTER STORMS HAVE DEPOSITED SIGNIFICANT AMOUNTS OF SNOW
ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA. SNOW DEPTHS
CURRENTLY RANGE FROM 3 TO 6 INCHES IN AREAS ALONG AND SOUTH OF I-80.
NORTH OF I-80...SNOW DEPTHS ARE BETWEEN 6 AND 12 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.
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 THAT OCCURS BEFORE AND DURING THE PERIOD WHEN
SNOWMELT AND RAINFALL IS IN PROGRESS. AT THE PRESENT TIME...THE
THINKING IS THAT A SIGNIFICANT AMOUNT OF FROST WILL STILL REMAIN IN
THE GROUND DURING THE HIGHEST SNOWMELT RATES. THIS WOULD RESULT IN
RUNOFF OF THE RAIN AND SNOWMELT INSTEAD OF THAT WATER INFILTRATING
INTO SOIL. HOWEVER...THERE STILL IS UNCERTAINTY REGARDING THE AMOUNT
OF FROST THAW THAT WILL OCCUR. IN ADDITION...HEAVY RAINFALL DURING
THE MELT PERIOD 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 LATER THIS WEEKEND AND INTO NEXT WEEK.
