...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 NORTH INTO THE REGION ON TUESDAY.
THE TYPE OF AIR THAT IS EXPECTED TO SLIDE OVERHEAD TUESDAY IS MORE
COMMON WITH MID SPRING LIKE AIR. THIS ABNORMALLY WARM AND MOIST
AIR 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.
