Flood Potential Outlook
Issued by NWS St. Louis, MO

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Probabilistic Hydrologic Outlook
National Weather Service St. Louis MO
325 PM CST Thu Mar 02 2017

...Spring Flood and Water Resources Outlook Number 2...
...Elevated minor flood chances along the Mississippi River...
...Near normal flood chances along Missouri and Illinois Rivers...
...Below normal flood chances along local tributaries...

This outlook uses the term St. Louis Service Area to refer to the
Mississippi River from above Canton Missouri to above Cape Girardeau
Missouri, the Missouri River above Jefferson City Missouri to its
confluence with the Mississippi River, the Illinois River downstream
from Beardstown Illinois to its confluence with the Mississippi
River, and for tributary rivers in eastern Missouri, and west
central and southwest Illinois.

Although there is no ongoing flooding anywhere within the St. Louis
Service Area, current forecasts indicate a likelihood of minor
flooding in the next week along the upper Mississippi River from
Canton, Missouri through Winfield, Missouri, skewing flood
probabilities in this area.  Otherwise, the probabilities within
this outlook are not skewed by any ongoing flooding.

This outlook is based on current streamflows and soil moisture over
the area, upstream snowpack in the Mississippi, Missouri, and
Illinois river basins, and forecast rainfall over the next two weeks
to three months.  More than expected rainfall could cause additional
flooding over the area, while less than expected rainfall could keep
rivers from reaching expected crests.

...Low flood potential across local tributaries...

After more than 5 months of below average precipitation across
Missouri and Illinois, there are near to below average chances of
flooding along local tributaries in the St. Louis service area over
the next 90 days. In addition, this extended dryness has led to
moderate drought conditions acorss much of east central Missouri.
This drought may worsen without at least normal rainfall this
spring.  The least likely areas for flooding appear to be across
central Missouri, where probabilities for minor flooding range from
13 percent below average on the Gasconade River to 50 percent below
average along the Moreau River.  Flood probabilities are also low
across northeastern Missouri, ranging from 10 percent below the
seasonal average along the Cuivre River to 16 percent below the
seasonal average on the North River.  In the Meramec basin,
probablilites are closer to seasonal averages, ranging from just 1
percent below the average on the Meramec River near Steelville,
Missouri to 5 percent below at Pacific, Missouri.  Illinois
tributaries are also near to below seasonal averages.

...Normal to above average flood risk on area`s major rivers...

However, it`s a different story for the upper Mississippi River.
While the local area has experienced a pronounced precipitation
deficit with respect to seasonal norms, the upper Mississippi River
basin has experienced well above average snowfall this winter.  But
this snow has come with well above average temperatures, melting
much of the snowpack in these areas already.  This has left
Minnesota, Wisconsin, and northeastern Iowa with well below average
snowpack and snow water equivalent.  But with feeder streams already
flowing well above average for early March in these areas, the flow
in the Mississippi River is also running well above the seasonal
average. So the threat of minor flooding from Winfield to above
Canton, Missouri will remain high this spring, particularly during
March, as the latest daily forecasts indicate.  Along the Missouri
River, the flood risk below Yankton, South Dakota appears to be near
normal. As inflows into the Missouri River drop off due to the
recent dry weather across Missouri and Kansas, the flood risk is a
little below normal along the Missouri River from Jefferson City to
St. Charles.  For the Illinois River, there is a similar story. It`s
been fairly moist in the headwaters near the Chicago area, but
tributaries flowing into the Illinois south of Peoria are exhibiting
reduced inflow, leaving the Illinois River with a near normal spring
flood risk.

...Extended weather outlooks...

In the near term, the Climate Prediction Center calls for a
likelihood of above average temperatures in both the 6 to 10 day and
the 8 to 14 day outlooks, with precipitation probabilities
transitioning from near normal in the 6 to 10 day outlook to above
normal in the 8 to 14 day outlook.  For the month of March, the
outlook calls for better chances of continued above normal
temperatures and equal chances of being above, below, or near normal
precipitation. For the spring months of March through May, the 90-
day outlook calls for a higher chance of above normal temperatures
with equal chances of being above, below, or near normal
precipitation.

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.


...Table 1--Probabilities for minor...moderate and major flooding...
                    Valid Period:  03/05/2017 - 06/03/2017

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Mississippi River
Canton LD20         14.0   20.0   25.0 : >95   67   20   16   <5   <5
Quincy              17.0   22.0   26.0 : >95   67   28   30    8    8
Quincy LD21         17.0   21.0   25.0 :  71   62   28   28    8    8
Hannibal            16.0   22.0   24.0 : >95   69   19   17    8    8
Saverton LD22       16.0   20.0   22.0 :  79   65   37   38   21   24
Louisiana           15.0   20.0   25.0 : >95   71   32   36   <5    6
Clarksville LD24    25.0   31.0   33.0 : >95   72   31   30    9   13
Winfield LD25       26.0   30.0   34.0 : >95   69   38   39    8    8
:North Fabius River
Ewing               11.0   14.0   18.0 :  46   57   20   28   10   12
:Middle Fabius River
Ewing               12.0   17.0   19.5 :  34   49   13   14    9   10
:South Fabius River
Taylor               9.5   14.0   19.0 :  46   60   14   17   <5   <5
:North River
Palmyra             13.0   16.0   22.0 :  41   57   28   37   <5   <5
:Mid Fork Salt River
Holliday            17.0   22.0   26.0 :  36   50   <5   <5   <5   <5
:Salt River
New London          19.0   25.0   27.0 :  <5   <5   <5   <5   <5   <5
:Cuivre River
Troy                21.0   25.0   29.0 :  43   53   18   23    8    8
Old Monroe          24.0   27.0   30.0 :  51   61   28   26   10   11
:Dardenne Creek
St. Peters          18.0   20.0   23.0 :  24   24   15   15   <5   <5
:Bourbeuse River
Union               15.0   22.0   26.0 :  43   49   10   10   <5   <5
:Big River
Byrnesville         16.0   20.0   28.0 :  56   61   19   21   <5   <5
:Meramec River
Steelville          12.0   20.0   25.0 :  40   41   <5   <5   <5   <5
Sullivan            11.0   20.0   29.0 :  66   70   12   11   <5   <5
Pacific             15.0   23.0   27.0 :  38   43    9   10   <5   <5
Eureka              19.0   26.0   31.0 :  36   42   17   17    8   11
:Kaskaskia River
Vandalia            18.0   24.0   26.0 :  69   77   24   23    9   11
Carlyle TW         423.5  431.0  435.0 :  20   41   <5   <5   <5   <5
:La Moine River
Ripley              22.0   23.0   27.0 :  40   40   31   36   10   10
:Moreau River
Jefferson City      17.0   25.0   29.0 :  29   79   12   31    9   12
:Maries River
Westphalia          10.0   15.0   20.0 :  22   41   <5   11   <5   <5
:Gasconade River
Rich Fountain       20.0   25.0   30.0 :   9   22   <5    7   <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: 03/05/2017 - 06/03/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20          14.6   14.6   14.9   16.1   19.0   21.2   22.3
Quincy               17.5   17.5   17.8   19.2   22.5   25.1   26.5
Quincy LD21          16.3   16.4   16.7   18.0   21.3   24.0   25.6
Hannibal             16.2   16.2   16.5   17.8   21.1   23.0   25.0
Saverton LD22        15.8   15.8   16.1   17.8   21.7   23.5   25.4
Louisiana            15.8   15.9   16.3   18.0   21.0   22.4   24.3
Clarksville LD24     25.9   26.0   26.5   28.4   31.6   32.8   34.8
Winfield LD25        26.1   26.2   26.6   28.5   31.6   32.8   34.8
:North Fabius River
Ewing                 4.6    5.8    8.4   10.7   13.2   18.3   20.3
:Middle Fabius River
Ewing                 4.2    5.2    7.8   10.9   13.8   18.7   21.3
:South Fabius River
Taylor                4.3    5.1    7.0    9.1   12.0   14.8   17.3
:North River
Palmyra               6.0    6.4    9.3   12.0   16.4   20.1   21.1
:Mid Fork Salt River
Holliday              7.5    9.1   12.4   16.0   17.6   20.5   21.9
:Salt River
New London            2.8    3.8    6.6    9.1    9.9   13.9   16.2
:Cuivre River
Troy                  9.6   11.3   14.5   19.6   24.4   27.4   29.4
Old Monroe           20.9   21.0   22.3   24.1   27.2   29.9   30.7
:Dardenne Creek
St. Peters            9.1   10.3   12.1   14.8   17.6   20.9   21.5
:Bourbeuse River
Union                 7.9    9.3   11.2   14.3   18.5   22.2   24.6
:Big River
Byrnesville           6.7    9.7   12.9   16.4   19.7   21.9   24.2
:Meramec River
Steelville            2.5    3.6    7.3   10.8   13.5   15.8   18.4
Sullivan              5.6    6.9    8.8   13.2   17.0   20.8   24.4
Pacific               4.6    5.8    9.0   13.1   17.6   22.8   24.0
Eureka                7.5    8.4   11.0   15.3   23.4   30.3   32.9
:Kaskaskia River
Vandalia             11.5   13.5   16.1   20.2   23.9   26.0   26.7
Carlyle TW          415.4  415.6  417.3  419.7  422.8  423.9  424.5
:La Moine River
Ripley               10.6   12.7   16.3   19.8   24.9   27.0   28.4
:Moreau River
Jefferson City        2.5    3.9    5.4    9.3   18.4   28.0   34.2
:Maries River
Westphalia            1.0    1.3    2.2    3.0    6.5   13.5   14.9
:Gasconade River
Rich Fountain         4.2    5.2    6.8    8.9   14.3   19.5   23.3

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: 03/05/2017 - 06/03/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20          11.5    9.9    8.7    7.2    5.4    4.3    3.4
Quincy               14.8   13.4   12.8   12.5   12.0   11.7   11.1
Quincy LD21          12.9   11.1    9.4    7.8    5.9    4.9    3.9
Hannibal             14.3   13.1   12.2   11.4   10.7   10.1    9.9
Saverton LD22        12.7   10.8    9.3    8.1    6.7    5.7    4.8
Louisiana            13.3   12.2   12.1   12.0   12.0   11.9   11.9
Clarksville LD24     23.0   21.0   19.6   18.4   16.8   15.5   14.3
Winfield LD25        23.2   21.0   19.6   18.2   16.7   15.3   14.2
:North Fabius River
Ewing                 3.3    3.2    3.0    2.8    2.8    2.6    2.5
:Middle Fabius River
Ewing                 2.9    2.8    2.8    2.7    2.7    2.5    2.5
:South Fabius River
Taylor                1.5    1.4    1.2    1.2    1.1    0.8    0.8
:North River
Palmyra               3.3    3.2    3.0    3.0    2.7    2.6    2.6
:Mid Fork Salt River
Holliday              3.8    3.8    3.7    3.7    3.5    3.5    3.5
:Salt River
New London            5.3    4.9    4.5    3.6    2.1    2.1    2.1
:Cuivre River
Troy                  5.5    5.4    5.2    5.2    5.1    4.9    4.7
Old Monroe           18.1   16.1   15.1   14.2   12.7   11.1    9.8
:Dardenne Creek
St. Peters            1.7    1.6    1.5    1.4    1.4    1.3    1.3
:Bourbeuse River
Union                 2.2    1.8    1.6    1.6    1.5    1.4    1.4
:Big River
Byrnesville           2.4    2.0    1.7    1.7    1.6    1.4    1.4
:Meramec River
Steelville            1.7    1.6    1.4    1.3    1.2    1.2    1.2
Sullivan              3.3    3.1    2.6    2.6    2.5    2.5    2.4
Eureka                3.7    3.5    3.2    3.1    3.1    3.0    3.0
:Kaskaskia River
Vandalia              5.4    4.6    3.1    2.7    2.5    2.3    2.2
Carlyle TW          413.9  413.8  413.1  411.2  411.2  411.2  411.2
:La Moine River
Ripley                4.6    4.3    3.9    3.9    3.8    3.7    3.7
:Moreau River
Jefferson City        1.6    1.6    1.6    1.5    1.5    1.5    1.5
:Maries River
Westphalia            0.8    0.8    0.7    0.7    0.4    0.4    0.3
:Gasconade River
Rich Fountain         2.9    2.9    2.9    2.7    2.6    2.5    2.4

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/lsx for more weather and water
information.

The next routine monthly outlook will be issued at the end of the
month.

Fuchs

$$



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