Flood Potential Outlook
Issued by NWS Chicago, IL

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FGUS73 KLOT 181105
ESFLOT
ILC007-031-037-043-053-063-075-089-091-093-097-099-103-105-111-
141-197-201-INC007-073-089-111-127-182315-

HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE CHICAGO IL
505 AM CST TUE FEB 18 2014 /605 AM EST TUE FEB 18 2014/

...INCREASING FLOOD POTENTIAL BY THURSDAY...

HIGH TEMPERATURES WILL WARM ABOVE FREEZING TODAY AND AGAIN ON
WEDNESDAY RESULTING IN SOME SNOW MELT. TEMPERATURES WILL DROP
BELOW FREEZING AT NIGHT AND HELP TO LIMIT THE RATE OF SNOW MELT.
TEMPERATURES AND DEWPOINTS BOTH ARE FORECAST TO CLIMB INTO THE 40S
ON THURSDAY...WITH 50S POSSIBLE SOUTH OF THE KANKAKEE. THESE VERY
MILD TEMPERATURES AND MOIST CONDITIONS WILL RESULT IN A GREATLY
ACCELERATED SNOW MELT AND INCREASED RUN OFF.

SNOW DEPTHS ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA
GENERALLY RANGE BETWEEN 10 AND 20 INCHES. MORE IMPORTANTLY...THE
WATER EQUIVALENT OF THE EXISTING SNOW PACK IS ESTIMATED BETWEEN 1
AND 4 INCHES...WITH THE HIGHER AMOUNTS CONCENTRATED MAINLY NEAR
THE WISCONSIN STATE LINE. FROST DEPTHS BELOW THE SNOW PACK RANGE
FROM 12 TO 16 INCHES. A DEEP FROST LAYER CAN INHIBIT THE
INFILTRATION OF WATER FROM SNOW MELT AND INCREASE THE RUNOFF INTO
AREA RIVERS AND STREAMS.

BASED ON CURRENT TEMPERATURE FORECASTS ALONE...RIVERS WILL LIKELY
START RISING DUE TO SNOW MELT DURING THE MID TO LATTER HALF OF THE
WEEK. THERE IS AN INCREASING POTENTIAL FOR MODERATE TO LOCALLY HEAVY
RAIN TO FALL LATE WEDNESDAY NIGHT INTO THURSDAY. IF HEAVY
RAINFALL MATERIALIZES THAT WOULD INCREASE THE RATE OF RUNOFF AND
SUBSEQUENT FLOODING. THERE ARE MANY FACTORS THAT CONTRIBUTE TO
THE SEVERITY OF THE FLOODING...AND AT THIS TIME IT IS DIFFICULT TO
DETERMINE PRECISELY HOW SEVERE ANY POTENTIAL FLOODING MAY BECOME.

ANOTHER MAJOR CONCERN IS THE AMOUNT OF ICE COVER ON RIVERS ACROSS
THE AREA. NATIONAL WEATHER SERVICE CHICAGO ICE SPOTTERS REPORT
MANY RIVERS HAVE 100 PERCENT ICE COVER. AS THE RUNOFF
BEGINS...STREAM FLOWS BENEATH THE ICE COVER WILL INCREASE WHICH
WILL LIFT AND BREAK THE ICE. AS THE ICE MOVES DOWNSTREAM...ICE
JAMS ARE POSSIBLE. ICE JAMS CAN RESULT IN RAPID RISES OF WATER
LEVELS AND SIGNIFICANT FLOODING IN THE VICINITY OF THE JAM.

PERSONS LIVING ALONG RIVERS AND IN FLOOD PRONE AREAS SHOULD
PREPARE NOW FOR THE POSSIBILITY OF RIVER FLOODING IN THE COMING
WEEKS. CONTINUE TO CLOSELY MONITOR THIS DEVELOPING SNOW MELT
SITUATION. ANY SIGNIFICANT CHANGES IN PRECIPITATION AMOUNTS OR
TEMPERATURES COULD AFFECT THE TIMING AND SEVERITY OF FLOODING.

FOR DETAILED RIVER FORECAST AND FLOOD INFORMATION GO TO
WEATHER.GOV/CHICAGO AND CLICK ON THE RIVERS AND LAKES LINK.

$$

IZZI




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