Flood Potential Outlook
Issued by NWS St. Louis, MO

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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE ST. LOUIS MO
500 PM CST THU FEB 19 2015

...Spring Flood and Water Resources Outlook Number 1...
...Flood chances below average along the big rivers...
...Local tributaries have near average flood chances...

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.

There is no flooding anywhere within the St. Louis Service Area, so
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
rivers from reaching expected crests.

There are near to below average chances of flooding along most
rivers in the St. Louis Service Area over the next 90 days.  Across
Central Missouri, flood chances are between 4 and 7 percent below
the seasonal average on the Maries River, the Gasconade River, and
the Moreau River.  However, after several recent snow events, flood
chances along tributaries in northeastern Missouri are mostly 8 to
14 percent above the seasonal average.  Thanks to several inches of
snow water equivalent across much of north central Illinois, flood
chances along the Illinois River are also above average, though the
chances of significant flooding from Meredosia south remain low.  In
the Meramec and Kaskaskia River basins, the flood chances are within
6 percent of seasonal norms.  This reflects the typical lack of
significant snowpack and near normal soil moisture.  And along the
Black River, flood chances are below average this spring.

Meanwhile, this year`s outlook along the Mississippi River indicates
minor flooding is likely from Canton, Missouri to Winfield,
Missouri, but this chance of flooding is about 4 to 10 percent below
the seasonal averages.  And while minor flooding is probable,
moderate flooding is unlikely along the upper Mississippi.  While
snowpack in the upper Mississippi River basin is widespread, it is
also quite shallow.  Simply put, this has been a lean year for
snowfall across the upper Midwest, and most of the upper Mississippi
River basin has much less snowpack on the ground than we typically
see.  In the Missouri River basin, snow depths are also below the
seasonal average.  This combined with a variety of soil moisture
conditions over the lower Missouri River basin leads to near normal
chances of flooding along lower Missouri River this spring.  As with
both the Mississippi and Illinois Rivers, this means minor flooding
will be likely, but significant moderate flooding is unlikely.

In the near term, the Climate Prediction Center calls for a strong
likelihood of below average temperatures in the 6 to 10 day and 8 to
14 day outlooks.  Precipitation in the 6 to 10 day outlook should be
below average to the north and east of St. Louis and near average
elsewhere, and near average throughout the service area during the 8
to 14 day period.  For the month of March, temperatures will most
likely be below average to the north and east of St. Louis with
equal chances of being above average, average, or below average
elsewhere in the St. Louis service area, and there will be equal
chances of precipitation being above average, near average, or below
average.  For the period March through May, there are equal chances
that temperatures and precipitation will be above average, near
average, or below average. 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:  2/23/2015 - 5/24/2015

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Dardenne Creek
St. Peters          18.0   20.0   23.0 :  43   43   29   27   15   13
:Mississippi River
Canton LD20         14.0   20.0   25.0 :  55   63    9   15   <5   <5
Quincy              17.0   18.0   22.5 :  52   61   43   58   12   24
Hannibal            16.0   22.0   24.0 :  55   64    9   16    9    7
Saverton LD22       16.0   20.0   22.0 :  50   60   24   33   10   21
Louisiana           15.0   20.0   25.0 :  63   67   21   33   <5   <5
Clarksville LD24    25.0   31.0   33.0 :  63   67   18   27    9   12
Winfield LD25       26.0   30.0   34.0 :  60   64   26   38    6    7
:North Fabius River
Ewing               11.0   14.0   18.0 :  58   46   24   27    9    9
:Middle Fabius River
Ewing               12.0   17.0   19.5 :  61   47   15   15    9    7
:South Fabius River
Taylor               9.5   14.0   19.0 :  64   55   15   15   <5   <5
:North River
Palmyra             13.0   16.0   22.0 :  52   44   23   24   <5   <5
:Mid Fork Salt River
Holliday            17.0   22.0   26.0 :  53   52    7   <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 :  55   47   32   30    7    6
Old Monroe          24.0   27.0   30.0 :  41   56   21   23   <5   10
:Meramec River
Steelville          12.0   20.0   25.0 :  43   40   <5   <5   <5   <5
Sullivan            11.0   20.0   29.0 :  64   70   16   15   <5   <5
:Bourbeuse River
Union               15.0   22.0   26.0 :  53   49    7    7   <5   <5
:Meramec River
Pacific             15.0   23.0   27.0 :  50   56    9   10   <5   <5
:Big River
Byrnesville         16.0   20.0   28.0 :  67   64   32   29   <5   <5
:Meramec River
Eureka              18.0   25.0   30.0 :  50   50   21   16   12    9
:Kaskaskia River
Carlyle TW         423.5  431.0  435.0 :  33   55   <5   <5   <5   <5
Vandalia            18.0   24.0   26.0 :  75   78   30   27   13   10
:La Moine River
Ripley              22.0   23.0   27.0 :  53   43   44   36   10    9
:Moreau River
Jefferson City      17.0   25.0   29.0 :  73   80   31   33   13   13
:Maries River
Westphalia          10.0   15.0   20.0 :  33   37   10   11   <5   <5
:Gasconade River
Rich Fountain       20.0   25.0   30.0 :  13   21   <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: 2/23/2015 - 5/24/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Dardenne Creek
St. Peters            9.4   10.6   12.7   16.3   21.6   24.0   24.4
:Mississippi River
Canton LD20           9.4   10.0   12.2   14.3   17.4   20.2   22.2
Quincy               13.1   13.5   15.2   17.4   20.8   24.1   26.3
Hannibal             12.8   13.4   14.8   16.4   19.6   22.8   24.7
Saverton LD22        10.3   11.2   13.5   16.0   19.9   23.3   25.1
Louisiana            12.2   12.3   13.9   16.4   19.5   22.6   23.9
Clarksville LD24     20.8   21.3   23.7   26.7   30.1   33.2   34.4
Winfield LD25        20.9   21.5   23.9   26.8   30.3   33.1   34.3
:North Fabius River
Ewing                 6.5    8.0    9.7   11.9   14.5   18.3   20.7
:Middle Fabius River
Ewing                 6.2    8.2   10.2   12.9   15.8   18.9   21.4
:South Fabius River
Taylor                6.2    7.2    8.8   10.6   12.6   15.7   18.9
:North River
Palmyra               7.3    8.5   10.8   13.5   15.8   20.2   21.2
:Mid Fork Salt River
Holliday             11.7   12.6   15.6   17.3   18.9   21.1   22.5
:Salt River
New London            8.1    9.3    9.6   10.2   12.7   14.4   16.6
:Cuivre River
Troy                 13.1   14.0   17.4   22.7   25.7   28.2   30.1
Old Monroe           17.3   17.8   20.6   23.0   26.4   29.2   30.3
:Meramec River
Steelville            3.1    4.5    8.1   11.4   13.8   16.3   19.0
Sullivan              5.0    6.9    9.9   14.3   17.5   22.0   25.6
:Bourbeuse River
Union                 9.3   10.7   12.8   15.4   18.2   21.2   24.0
:Meramec River
Pacific               6.2    7.0   11.1   15.3   18.6   23.1   24.6
:Big River
Byrnesville          10.8   12.5   14.5   18.0   20.9   23.3   25.8
:Meramec River
Eureka                8.7   10.1   13.6   18.3   23.8   30.3   33.1
:Kaskaskia River
Carlyle TW          417.7  418.3  420.3  422.0  424.4  425.2  426.2
Vandalia             14.2   14.6   18.1   22.1   24.6   26.5   28.5
:La Moine River
Ripley               13.5   15.7   19.3   22.4   25.0   27.2   28.8
:Moreau River
Jefferson City        7.5   10.3   17.0   20.5   25.7   30.5   34.8
:Maries River
Westphalia            3.1    3.6    5.7    8.5   12.1   15.1   17.3
:Gasconade River
Rich Fountain         6.4    6.8    8.7   12.0   17.8   23.1   24.9

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: 2/23/2015 - 5/24/2015
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Dardenne Creek
St. Peters            3.2    3.2    3.2    3.2    3.1    3.1    3.0
:Mississippi River
Canton LD20           2.6    2.6    2.6    2.5    2.5    2.5    2.4
Quincy               10.9   10.9   10.9   10.9   10.9   10.9   10.9
Hannibal              9.7    9.7    9.7    9.7    9.7    9.6    9.6
Saverton LD22         4.2    4.2    4.2    4.2    4.1    4.1    4.1
Louisiana            11.8   11.8   11.8   11.8   11.8   11.8   11.8
Clarksville LD24     14.0   14.0   14.0   13.9   13.7   13.6   13.6
Winfield LD25        13.9   13.9   13.9   13.8   13.6   13.5   13.4
:North Fabius River
Ewing                 3.2    3.2    3.1    3.0    2.9    2.9    2.7
:Middle Fabius River
Ewing                 3.2    3.1    3.0    3.0    2.9    2.9    2.8
:South Fabius River
Taylor                2.2    2.1    2.1    2.0    1.9    1.7    1.7
:North River
Palmyra               4.4    4.3    4.3    4.3    4.1    4.0    3.9
:Mid Fork Salt River
Holliday              4.4    4.4    4.4    4.4    4.4    4.3    4.2
:Salt River
New London            5.7    5.2    4.9    3.6    2.2    2.2    2.1
:Cuivre River
Troy                  5.3    5.2    5.2    5.2    5.1    5.0    4.9
Old Monroe            9.5    9.5    9.5    9.5    9.5    9.4    9.4
:Meramec River
Steelville            1.6    1.6    1.5    1.5    1.5    1.5    1.5
Sullivan              2.1    2.1    2.0    2.0    2.0    2.0    1.9
:Bourbeuse River
Union                 1.8    1.7    1.6    1.6    1.6    1.4    1.4
:Big River
Byrnesville           3.1    2.4    1.9    1.9    1.9    1.9    1.8
:Meramec River
Eureka                2.4    2.3    2.1    2.1    2.1    2.1    2.0
:Kaskaskia River
Carlyle TW          413.6  413.5  413.4  412.3  411.1  411.1  411.1
Vandalia              4.3    4.3    3.3    3.0    2.7    2.6    2.5
:La Moine River
Ripley                4.9    4.8    4.8    4.7    4.6    4.3    4.2
:Moreau River
Jefferson City        1.7    1.7    1.7    1.7    1.7    1.7    1.7
:Maries River
Westphalia            1.5    1.5    1.5    1.5    1.4    1.3    1.2
:Gasconade River
Rich Fountain         2.7    2.7    2.6    2.6    2.6    2.6    2.6

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 update to this spring flood outlook will be issued March 5.

Fuchs
$$









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