...HEAVY RAINFALL POSSIBLE TUESDAY INTO TUESDAY NIGHT WITH
INCREASED RISK OF FLOODING...
A SLOW MOVING AND STRONG STORM SYSTEM IS FORECAST TO TRANSPORT
UNSEASONABLY WARM AND HUMID AIR NORTHWARD INTO THE REGION ON
TUESDAY. IN FACT...APRIL LEVEL VALUES OF MOISTURE ARE FORECAST TO
MOVE INTO THE AREA...AND WHEN COMBINED WITH A SLOW MOVING AND
STRONG FRONT COULD RESULT IN WIDESPREAD HEAVY RAINFALL OVER
PORTIONS OF THE REGION. AT THIS TIME...THE GREATEST THREAT OF
HEAVY RAINFALL LOOKS TO BE IN NORTHWEST INDIANA AND SOUTHEAST OF
INTERSTATE 55 IN ILLINOIS WHERE 1 TO LOCALLY OVER 2 INCHES OF
RAINFALL COULD OCCUR. ELSEWHERE...MODERATE RAINFALL TOTALS OF ONE
QUARTER TO THREE QUARTERS OF AN INCH ARE FORECAST OVER THE NEXT 48
HOURS.
THIS RAIN WILL FALL ON FROZEN GROUND RESULTING IN VERY HIGH RUNOFF
RATES WHICH WILL RESULT IN A FASTER THAN NORMAL RESPONSE ON AREA
STREAMS AND RIVERS. THE QUICKLY INCREASING STREAM FLOW AND RECORD
OR NEAR RECORD WARM TEMPERATURES WILL RESULT IN A RAPID BREAK UP
OF ICE ON RIVERS AND AN INCREASED RISK OF ICE JAM FLOODING ACROSS
THE ENTIRE REGION. IF CURRENT FORECASTS FOR HEAVY RAINFALL VERIFY
THEN THE GREATEST RISK OF FLOODING WILL BE OVER THE VERMILION...
IROQUOIS...AND KANKAKEE RIVER BASINS.
IN ADDITION TO THE USUAL UNCERTAINTIES WITH RESPECT TO THE
RAINFALL FORECAST...THERE ARE SOME ADDITIONAL UNCERTAINTIES
REGARDING THE FLOOD POTENTIAL. FIRST...STREAM FLOW ACROSS THE AREA
IS CURRENTLY BELOW TO MUCH BELOW AVERAGE WHICH SUGGESTS A LOWER
FLOOD THREAT THAN WOULD NORMALLY BE EXPECTED WITH RAINFALL OF THIS
MAGNITUDE IN JANUARY. TEMPERATURES ARE FORECAST TO FALL BELOW
FREEZING AGAIN WEDNESDAY...WHICH COULD SLOW OR STOP THE RUNOFF AS
STORM WATER AS IT FREEZES. DESPITE THESE UNCERTAINTIES THERE DOES
APPEAR TO BE A HEIGHTENED RISK OF FLOODING THIS WEEK...PARTICULARLY
IN AREAS THAT ARE MOST PRONE TO ICE JAMS. PERSONS IN FLOOD PRONE
AND LOW LYING AREAS SHOULD MONITOR LATER FORECASTS AND STATEMENTS
ON THE HEAVY RAIN AND FLOOD POTENTIAL.
