Flood Potential Outlook
Issued by NWS Chicago, IL

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FGUS73 KLOT 012146
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ILC007-011-031-037-063-075-089-091-093-097-099-103-105-111-
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Probabilistic Hydrologic Outlook
National Weather Service Chicago/Romeoville IL
325 PM CST Thu Mar 01 2018


...2018 SPRING FLOOD AND WATER OUTLOOK NUMBER 2...

This outlook is for streams within the National Weather Service
Chicago Hydrologic Service Area, which includes Illinois River
tributaries in Northeast Illinois and Northwest Indiana.  It
includes the Illinois River down to La Salle.  It also includes
streams within the Rock River basin in North Central Illinois and
the Rock River from Rockton down to Dixon, Illinois.  This outlook
is for the time period from early March through late May.

...OUTLOOK BRIEF SUMMARY UPDATE...

This update takes into account heavy precipitation that occurred
between February 15 and March 1.  At the lower range, Northern
Illinois received about 2.5 inches of rainfall, which is about 300%
of normal for the period.  At the higher range, east-central
Illinois and northwestern Indiana received 5 to 8 inches of
rainfall, which is 400 to 600% of normal.  This rainfall was in
addition to about 1.5 inches of liquid equivalent snowpack and 6
inch frost depth along and north of the Illinois and Kankakee
Rivers.  There was little or no snowpack south of the Illinois and
Kankakee Rivers

Based on current conditions, the risk of flooding this spring is now
normal to slightly above normal, which is a change from Outlook
Number 1 which indicated a slightly below normal risk of flooding.
The greatest risk is over the Kankakee, Iroquois and Illinois River
basins which were particularly hard hit by the late February heavy
rainfall.  The amount of additional rainfall or snowfall and
subsequent snowmelt in the coming weeks will determine the severity
of any future flooding.

The risk for ice jams and ice jam flooding is diminishing as
temperature climatologically rises through the spring.  However,
should a period of well below normal temperatures occur, ice jams
and ice jam flooding may be possible.  Ice jams can result in rapid
rises in water levels in a very short time.

This Spring Outlook Update is based on hydrologic conditions
including the current soil moisture, snowpack, and streamflow
conditions at the time of issuance.  It should be noted that
hydrologic conditions can change rapidly during late winter and
early spring.  These outlooks are issued each late winter and early
spring in addition to the 7 day river forecasts that are issued when
river forecast locations are in flood or are forecast to rise above
flood stage.

...CURRENT SNOW COVER AND WATER EQUIVALENT...

As of March 1st, there is no snow cover over northern Illinois and
northwestern Indiana.

...PAST TEMPERATURE AND PRECIPITATION...

Fall of 2017 concluded with temperatures 1 to 2 degrees above
normal.  Precipitation this past fall was near normal over north-
central and east-central Illinois and above normal over northeastern
Illinois and northwestern Indiana.  Fall started out very dry, with
precipitation well below normal, with only the Kankakee and Iroquois
Rivers and associated tributaries seeing precipitation in excess of
1 inch for the month.  Much of the remainder of the area saw 0.5
inch or less.  Precipitation for the region was near normal for the
month of November.  October was the wettest of the period with two
excessive rainfall events, with locations along and north of the
Kankakee and Illinois Rivers receiving precipitation 200 to 300% of
normal. Locations south of the Illinois and Kankakee Rivers saw near
normal precipitation.

For winter of 2017-18 so far, temperatures were 1 to 2 degrees below
normal.  The month of December started out unseasonably warm through
the 23rd and then a sharp drop-off in temperatures occurred with sub-
zero temperatures for the end of the month.  This lead to incidents
of freeze-up ice jam development.  January saw more variable
temperatures with alternating periods of very cold and very warm
conditions and the trends of quite variable temperatures continued
through February, with rapid swings between well below normal and
well above normal temperatures.  Total precipitation for the season
is now normal to above normal due to heavy rain that occurred in
late February.  Northern Illinois is now close to normal total
precipitation amounts ranging from 5 to 7 inches roughly west of I-
55 to the Wisconsin border. Northwestern Indiana and portions of
northeastern Illinois east of I-55 received 7 to 10 inches of
precipitation, which is 150 to 175% of normal.

...SOIL MOISTURE AND FROST DEPTH...

Soil moisture was near normal through Fall 2017 and Winter 2017-18
through mid February.  Following the heavy rain in late February,
soil moisture levels over northern Illinois and northwestern Indiana
are now above normal.  Little or no Frost remains as of March 1,
2018.

...RIVER CONDITIONS...

Streamflow on area rivers was below normal over much of the area
through the Fall and much of the winter.  The exceptions were some
of the flashier rivers of the Chicago Metro area where October heavy
rain and winter rain and snow had some rivers with above normal
streamflow.  Heavy rain in late February has left rivers with above
normal streamflow, which should continue well into March.  The
periods of cold conditions generated extensive ice cover on many
area rivers and ice jamming and break-up ice jam flooding occurred
during periods of wide temperature swings, particularly in December
and January.

...WEATHER OUTLOOKS...

The 7-Day WPC QPF Outlook through March 8 indicates the potential
for about 1 inch of rainfall over northern Illinois and northwestern
Indiana.

The 8 to 14 day CPC Outlook, valid March 8 to 14, indicates a chance
for Normal temperatures and a chance for Normal precipitation.

The March CPC One-Month Outlook indicates Equal Chances for Above
Normal, Normal or Below Normal temperatures and a chance for Above
Normal precipitation.

The March through May CPC Three-Month Outlook indicates Equal
Chances for Above Normal, Normal or Below Normal Temperatures and a
a chance for Above Normal precipitation.

...FLOOD POTENTIAL SUMMARY...

Based on current conditions, the risk for flooding this spring is
slightly above normal.  The greatest risk is over the Kankakee,
Iroquois and Illinois River basins which were particularly hard hit
by the late February heavy rainfall.

Ice jams and ice jam flooding remain possible, though chances will
diminish through the spring with the climatological rise in
temperatures.  Ice jams can result in rapid rises in water levels in
a very short time.

The amount of rainfall or additional snow and subsequent snowmelt in
the coming weeks will determine the severity of any future flooding.


In Table 1 below...the current (CS) and historical (HS) or normal
probabilities of exceeding minor...moderate...and major flood stages
are listed for the valid time period.

CS values indicate the probability of reaching a flood category
based on current conditions.

HS values indicate the probability of reaching a flood category
based on historical or normal conditions.

When the value of CS is more than HS...the probability of
exceeding that level is higher than normal. When the value of CS is
less than HS...the probability of exceeding that level is lower
than normal.

The Probabilistic Exceedance Outlooks for the Kankakee River at
Shelby, Indiana are listed as missing due to unrealistically high
values caused by the current high water levels.


...Table 1--Probabilities for minor...moderate and major flooding...
                    Valid Period:  03/11/2018 - 06/02/2018

                                       :    Current and Historical
                                       :     Chances of Exceeding
                                       :       Flood Categories
                                       :      as a Percentage (%)
                      Categorical      :
                   Flood Stages (FT)   :   Minor    Moderate   Major
Location           Minor   Mod   Major :  CS   HS   CS   HS   CS   HS
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Hart Ditch
Dyer                12.0   13.0   14.0 :  <5   <5   <5   <5   <5   <5
:Thorn Creek
Thornton            10.0   15.0   16.0 :   6    6   <5   <5   <5   <5
:Little Calumet River
Munster             12.0   14.0   17.0 :  37   41   11   16   <5   <5
South Holland       16.5   18.0   20.0 :  <5   <5   <5   <5   <5   <5
:North Branch Chicago River
Chicago Albany Av    7.0    7.5    8.0 :  <5   <5   <5   <5   <5   <5
:Kankakee River
Dunns Bridge        10.0   12.0   13.0 :  71   28   13   <5   <5   <5
Kouts               11.0   13.0   14.0 :  77   30   17   <5   <5   <5
Shelby               9.0   11.0   12.5 :   M    M    M    M    M    M
Momence              5.0    6.5    9.0 :  55   30   12   11   <5   <5
:Iroquois River
Rensselaer          12.0   14.0   15.0 :  28   28    8    9    7    7
Foresman            18.0   22.0   24.0 :  25   20   <5   <5   <5   <5
Iroquois            18.0   24.0   25.0 :  55   51   <5   <5   <5   <5
:Sugar Creek
Milford             18.0   22.0   26.0 :  52   47   12   14   <5   <5
:Iroquois River
Chebanse            16.0   18.0   20.0 :  14   12    7    8    6    6
:Kankakee River
Wilmington           6.5    8.0   10.0 :  15   15    8    8   <5   <5
:Des Plaines River
Russell              7.0    9.0   10.0 :  80   77   12   18   <5    7
Gurnee               7.0    9.0   11.0 :  41   40    6   11   <5    5
Lincolnshire        12.5   14.0   15.5 :  18   18   <5    8   <5   <5
Des Plaines         15.0   18.0   19.0 :  20   19   <5   <5   <5   <5
River Forest        16.0   17.5   18.5 :  <5   <5   <5   <5   <5   <5
Riverside            7.5    8.0    9.0 :  13   14    7    9   <5   <5
Lemont              10.0   11.0   12.0 :  54   43   20   16    6    6
:W Br Du Page River
Warrenville         11.5   14.5   17.5 :  17   13   <5   <5   <5   <5
:East Branch Du Page River
Bolingbrook         19.5   21.0   23.0 :  42   41   11    9   <5   <5
:Du Page River
Plainfield          12.0   14.0   15.0 :  <5   <5   <5   <5   <5   <5
Shorewood            6.5    8.0   10.0 :   8    8   <5   <5   <5   <5
:Mazon River
Coal City           12.0   14.0   17.0 :  14   15   <5   <5   <5   <5
:Fox River
Algonquin Tailwat    9.5   10.5   12.0 :  69   59   39   39   19   22
Montgomery          13.0   14.0   15.0 :  54   46    9   10   <5   <5
Dayton              12.0   14.0   24.0 :  53   43   16   14   <5   <5
:Vermilion River
Pontiac             14.0   15.0   18.0 :  11   12    8    8   <5   <5
Leonore             16.0   21.0   26.0 :  33   33   11   12   <5   <5
:Pecatonica River
Shirland            12.0   14.0   15.5 :  64   40   14   15    5   <5
:Rock River
Rockton             10.0   11.0   14.0 :  37   27   17   15   <5    6
Latham Park         10.0   11.0   14.0 :  38   28   18   15   <5   <5
Rockford             9.0   10.0   11.0 :  <5   <5   <5   <5   <5   <5
:Kishwaukee River
Belvidere            9.0   10.0   12.0 :  18   16    5    7   <5   <5
:South Branch Kishwaukee River
De Kalb             10.0   11.0   12.5 :  <5   <5   <5   <5   <5   <5
:Kishwaukee River
Perryville          12.0   18.0   22.0 :  32   38   <5   <5   <5   <5
:Rock River
Byron               13.0   14.0   16.0 :  21   15   13   11   <5    7
Dixon               16.0   18.0   20.0 :  15   15   <5    7   <5   <5
:Illinois River
Morris              16.0   18.0   22.0 :  44   38   21   21   <5   <5
Ottawa             463.0  466.0  469.0 :  79   33   23   14   10    6
La Salle            20.0   27.0   31.0 :  79   66   16   15   <5   <5

Legend
CS = Conditional Simulation (Current Outlook)
HS = Historical Simulation
FT = Feet

In Table 2 below...the 95 through 5 percent columns indicate the
probability of exceeding the listed stage levels (FT) for the valid
time period.

...Table 2--Exceedance Probabilities...

                               Chance of Exceeding Stages
                                  at Specific Locations
                          Valid Period: 03/11/2018 - 06/02/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Hart Ditch
Dyer                  3.4    3.6    4.6    5.5    6.4    7.2    8.2
:Thorn Creek
Thornton              4.6    5.1    6.2    7.2    8.3    9.4   10.7
:Little Calumet River
Munster               8.8    9.3   10.0   11.2   12.4   14.3   15.3
South Holland         9.1    9.7   11.1   12.3   13.8   14.5   15.1
:North Branch Chicago River
Chicago Albany Av     3.6    3.8    4.6    5.1    5.6    6.3    6.7
:Kankakee River
Dunns Bridge          9.0    9.1    9.9   10.7   11.6   12.3   12.8
Kouts                10.4   10.5   11.1   11.9   12.8   13.4   13.9
Shelby                  M      M      M      M      M      M      M
Momence               4.1    4.2    4.5    5.1    5.9    7.5    8.5
:Iroquois River
Rensselaer            7.0    8.4    9.7   11.0   12.3   13.5   17.9
Foresman             12.2   12.7   14.7   16.5   18.0   19.1   21.5
Iroquois             12.8   13.5   16.1   18.4   21.7   22.3   23.9
:Sugar Creek
Milford              11.3   14.4   16.9   18.1   19.8   22.5   24.6
:Iroquois River
Chebanse              8.5    9.6   10.7   12.6   15.2   16.6   20.4
:Kankakee River
Wilmington            3.4    3.7    4.4    5.3    6.0    7.3    9.2
:Des Plaines River
Russell               5.2    6.0    7.3    8.2    8.7    9.1    9.3
Gurnee                3.8    4.2    5.5    6.2    8.0    8.7    9.1
Lincolnshire          8.3    8.7    9.9   10.6   12.1   13.4   13.7
Des Plaines          10.4   10.9   12.5   13.4   14.7   16.6   17.4
River Forest          7.2    8.0   10.3   11.9   13.3   14.7   15.6
Riverside             3.8    4.2    5.3    6.4    7.0    7.8    8.1
Lemont                7.6    7.9    9.0   10.1   10.8   11.7   12.2
:W Br Du Page River
Warrenville           9.2    9.4    9.8   10.6   11.2   11.8   12.3
:East Branch Du Page River
Bolingbrook          17.5   17.7   18.7   19.3   20.2   21.0   21.3
:Du Page River
Plainfield            8.7    8.8    9.6   10.3   10.9   11.4   11.8
Shorewood             3.5    3.8    4.5    5.1    6.0    6.4    6.9
:Mazon River
Coal City             3.4    4.4    7.1    9.7   10.8   12.8   13.6
:Fox River
Algonquin Tailwat     8.8    8.9    9.4   10.0   11.5   13.4   14.7
Montgomery           12.6   12.6   12.8   13.0   13.4   13.9   14.1
Dayton                9.2    9.4   10.6   12.1   12.9   14.8   15.9
:Vermilion River
Pontiac               5.6    6.5    7.3    9.7   11.6   14.2   17.3
Leonore               7.8    9.3   10.7   14.0   17.4   21.1   22.3
:Pecatonica River
Shirland             11.4   11.4   11.6   12.5   13.5   14.5   15.5
:Rock River
Rockton               8.5    8.5    8.6    9.5   10.5   13.0   13.6
Latham Park           8.9    8.9    9.0    9.6   10.6   12.9   13.5
Rockford              3.9    3.9    3.9    4.2    4.8    6.3    6.8
:Kishwaukee River
Belvidere             3.1    3.8    5.0    6.5    8.2    9.6   10.1
:South Branch Kishwaukee River
De Kalb               4.3    5.1    6.0    7.1    8.2    8.8    9.4
:Kishwaukee River
Perryville            7.5    8.3    9.8   11.0   12.3   13.8   14.7
:Rock River
Byron                10.5   10.5   10.7   11.6   12.3   14.6   15.6
Dixon                12.6   12.6   12.7   13.7   14.7   16.9   17.8
:Illinois River
Morris                8.7    9.5   12.1   15.6   17.3   20.8   21.8
Ottawa              462.3  462.4  463.3  464.4  465.9  469.1  470.9
La Salle             15.9   16.7   20.2   23.8   25.2   28.7   30.1

In Table 3 below...the 95 through 5 percent columns indicate the
probability of falling below the listed stage levels (FT) for the
valid time period.

...Table 3--Nonexceedance Probabilities...

                            Chance of Falling Below Stages
                                 at Specific Locations
                          Valid Period: 03/11/2018 - 06/02/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Hart Ditch
Dyer                  2.1    2.1    2.0    2.0    1.9    1.9    1.8
:Thorn Creek
Thornton              3.0    2.9    2.9    2.9    2.8    2.8    2.7
:Little Calumet River
Munster               5.5    5.5    5.3    5.2    5.2    5.1    5.0
South Holland         5.7    5.6    5.5    5.4    5.3    5.3    5.2
:North Branch Chicago River
Chicago Albany Av     1.7    1.6    1.6    1.4    1.3    1.2    1.2
:Kankakee River
Dunns Bridge          5.6    5.3    5.0    4.7    4.4    4.1    3.8
Kouts                 6.3    6.1    5.7    5.5    5.1    4.8    4.6
Shelby                  M      M      M      M      M      M      M
Momence               2.6    2.5    2.4    2.2    2.0    1.9    1.8
:Iroquois River
Rensselaer            4.6    4.6    4.4    4.1    3.8    3.7    3.5
Foresman              7.6    7.5    6.9    6.5    6.0    5.8    5.4
Iroquois              7.1    7.1    6.5    6.1    5.6    5.3    4.9
:Sugar Creek
Milford               4.4    4.2    4.0    3.8    3.6    3.4    3.2
:Iroquois River
Chebanse              4.6    4.4    4.1    3.8    3.5    3.4    3.0
:Kankakee River
Wilmington            2.1    2.0    1.8    1.7    1.5    1.5    1.3
:Des Plaines River
Russell               3.4    3.2    3.1    2.9    2.7    2.6    2.5
Gurnee                2.5    2.4    2.2    2.0    1.8    1.6    1.5
Lincolnshire          7.1    7.0    6.8    6.6    6.4    6.2    6.1
Des Plaines           9.1    9.0    8.7    8.6    8.3    8.1    8.0
River Forest          5.1    4.7    4.4    4.1    3.6    3.2    2.9
Riverside             2.6    2.5    2.4    2.2    2.0    1.9    1.7
Lemont                6.7    6.6    6.5    6.3    5.8    5.5    5.3
:W Br Du Page River
Warrenville           7.5    7.5    7.4    7.4    7.3    7.2    7.2
:East Branch Du Page River
Bolingbrook          15.1   15.0   14.9   14.9   14.8   14.7   14.7
:Du Page River
Plainfield            7.0    7.0    6.9    6.8    6.8    6.7    6.7
Shorewood             2.4    2.4    2.2    2.2    2.1    2.1    2.1
:Mazon River
Coal City             2.0    2.0    1.9    1.7    1.5    1.3    0.8
:Fox River
Algonquin Tailwat     6.2    5.8    5.5    5.3    5.1    4.8    4.8
Montgomery           11.7   11.5   11.4   11.4   11.3   11.1   11.1
Dayton                7.0    6.8    6.4    6.2    5.8    5.4    5.4
:Vermilion River
Pontiac               3.7    3.6    3.5    3.4    3.2    3.1    3.0
Leonore               4.7    4.5    4.3    4.2    4.0    3.8    3.5
:Pecatonica River
Shirland              7.4    7.1    6.4    5.7    5.2    4.8    4.7
:Rock River
Rockton               5.3    4.8    4.3    3.5    2.9    2.6    2.5
Latham Park           6.1    5.6    5.2    4.7    4.2    4.0    3.9
Rockford              3.2    3.1    3.0    2.8    2.6    2.5    2.5
:Kishwaukee River
Belvidere             2.5    2.2    2.1    1.9    1.7    1.6    1.5
:South Branch Kishwaukee River
De Kalb               3.4    3.3    3.3    3.2    3.1    3.0    3.0
:Kishwaukee River
Perryville            6.7    6.4    6.3    6.1    5.9    5.7    5.6
:Rock River
Byron                 8.1    7.5    7.0    6.4    5.9    5.6    5.4
Dixon                10.4    9.9    9.5    8.9    8.5    8.2    8.1
:Illinois River
Morris                5.7    5.7    5.5    5.3    5.2    5.0    4.8
Ottawa              460.8  460.7  460.6  460.5  460.4  460.4  460.4
La Salle             12.2   12.1   11.9   11.6   11.3   11.1   10.9

These long-range probabilistic outlooks contain forecast values that
are calculated using multiple season scenarios from 30 or more years
of climatological data...including current conditions of the
river...soil moisture...snow cover...and 30 to 90 day long-range
outlooks of temperature and precipitation. By providing a range of
probabilities...the level of risk associated with long-range planning
decisions can be determined. These probabilistic forecasts are part
of the National Weather Service`s advanced hydrologic prediction
service.

Visit our web site weather.gov/lot for more weather and water
information.

The next outlook will be issued toward the end of next month.

$$

Krein



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