Flood Potential Outlook
Issued by NWS St. Louis, MO

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ESFLSX

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE ST. LOUIS MO
1020 AM CST THU FEB 16 2017

...Spring Flood and Water Resources Outlook Number 1...
...Elevated flood chances along the Mississippi River...
...Lower flood chances along the Missouri and Illinois Rivers...
...Local tributaries have mostly below normal 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 from above Jefferson City,
Missouri to its confluence with the Mississipi River, the Illinois
River from Beardstown, Illinois to its confluence with the
Mississippi River, and the tributaries in central and eastern
Missouri, and west central and southwestern Illinois.

There is no ongoing flooding anywhere within the St. Louis Service
Area, hence the probabilities within this outlook are not skewed by
current 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 through the next 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 4 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
10 percent below average on the Gasconade River to near 40 percent
below average along the Moreau River.  Flood probabilities are also
low across eastern Missouri, ranging from 6 percent below the
seasonal average on the North Fabius River to 14 percent below the
seasonal average on the North River.  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 mid-February 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.  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 across eastern Missouri.  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 and above normal
precipitation in both the 6 to 10 day and the 8 to 14 day outlooks,
though the precipitation probabilities will be closer to normal in
the 8 to 14 day outlook. For the month of March, the outlook calls
equal chances of being above, below, or near normal for both average
temperature and 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:  02/19/2017 - 05/20/2017

                                       :    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 :  80   66   22   16   <5   <5
Quincy              17.0   22.0   26.0 :  78   66   28   26   11    8
Quincy LD21         17.0   21.0   25.0 :  67   57   27   25   11    8
Hannibal            16.0   22.0   24.0 :  80   67   21   17   11    8
Saverton LD22       16.0   20.0   22.0 :  75   62   33   35   25   20
Louisiana           15.0   20.0   25.0 :  82   70   31   32    6    6
Clarksville LD24    25.0   31.0   33.0 :  83   70   28   28   18   13
Winfield LD25       26.0   30.0   34.0 :  79   64   37   38   10    8
:North Fabius River
Ewing               11.0   14.0   18.0 :  50   56   20   32    9   11
:Middle Fabius River
Ewing               12.0   17.0   19.5 :  41   49   12   16    8    8
:South Fabius River
Taylor               9.5   14.0   19.0 :  51   62   17   16   <5   <5
:North River
Palmyra             13.0   16.0   22.0 :  45   59   28   41   <5   <5
:Mid Fork Salt River
Holliday            17.0   22.0   26.0 :  42   55   <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 :  40   49   18   25    7    7
Old Monroe          24.0   27.0   30.0 :  50   57   31   25   14   11
:Dardenne Creek
St. Peters          18.0   20.0   23.0 :  26   26   14   14   <5   <5
:Bourbeuse River
Union               15.0   22.0   26.0 :  42   52   10    9   <5   <5
:Big River
Byrnesville         16.0   20.0   28.0 :  54   63   20   21   <5   <5
:Meramec River
Steelville          12.0   20.0   25.0 :  35   40   <5   <5   <5   <5
Sullivan            11.0   20.0   29.0 :  59   70    9   11   <5   <5
Pacific             15.0   23.0   27.0 :  36   47    8   11   <5   <5
Eureka              19.0   26.0   31.0 :  33   45   15   15    7   10
:Kaskaskia River
Vandalia            18.0   24.0   26.0 :  72   80   27   28    9   12
Carlyle TW         423.5  431.0  435.0 :  20   42   <5   <5   <5   <5
:La Moine River
Ripley              22.0   23.0   27.0 :  39   41   34   34   10   10
:Moreau River
Jefferson City      17.0   25.0   29.0 :  38   79   16   35   10   15
:Maries River
Westphalia          10.0   15.0   20.0 :  23   45    5   13   <5   <5
:Gasconade River
Rich Fountain       20.0   25.0   30.0 :  11   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: 02/19/2017 - 05/20/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20          11.2   11.8   14.6   16.0   19.6   22.5   23.2
Quincy               14.4   14.9   17.6   19.2   23.3   26.5   27.5
Quincy LD21          12.5   13.3   16.5   18.0   22.0   25.6   26.8
Hannibal             14.0   14.7   16.5   18.0   21.4   24.7   26.9
Saverton LD22        12.3   13.3   16.0   18.0   21.9   25.0   26.9
Louisiana            12.8   13.8   16.2   18.0   21.4   23.9   25.7
Clarksville LD24     22.2   23.6   26.4   28.4   32.0   34.4   35.8
Winfield LD25        22.3   23.7   26.6   28.4   32.0   34.3   36.0
:North Fabius River
Ewing                 5.0    6.4    8.6   11.0   13.4   17.0   20.4
:Middle Fabius River
Ewing                 4.6    5.8    8.4   11.4   14.2   17.4   21.3
:South Fabius River
Taylor                4.5    5.3    7.3    9.5   12.3   15.1   17.4
:North River
Palmyra               5.9    6.9    9.2   12.8   16.4   19.7   20.8
:Mid Fork Salt River
Holliday              8.4    9.3   13.4   16.5   18.6   20.7   22.0
:Salt River
New London            3.0    3.5    6.7    9.2   10.8   13.5   17.0
:Cuivre River
Troy                  9.6   10.8   14.3   19.1   24.0   26.8   29.5
Old Monroe           17.7   19.2   21.9   23.9   27.5   30.4   31.7
:Dardenne Creek
St. Peters            8.0   10.3   12.4   14.7   18.1   20.7   21.1
:Bourbeuse River
Union                 6.0    8.0   11.9   14.4   16.9   21.9   24.5
:Big River
Byrnesville           7.3    8.9   12.0   16.1   18.9   22.1   24.5
:Meramec River
Steelville            1.6    2.3    6.3   10.0   13.6   15.2   18.6
Sullivan              3.4    5.9    8.8   12.6   16.2   19.8   24.6
Pacific               1.9    4.9    8.5   13.3   17.0   22.5   24.4
Eureka                6.6    7.6   10.7   15.2   22.6   29.6   33.1
:Kaskaskia River
Vandalia             12.0   13.8   16.8   20.8   24.2   26.0   26.8
Carlyle TW          415.2  416.0  417.6  420.3  423.0  423.9  424.9
:La Moine River
Ripley                9.4   12.2   15.5   19.8   24.6   26.9   28.5
:Moreau River
Jefferson City        3.7    4.3    8.4   13.1   20.9   28.8   34.5
:Maries River
Westphalia            0.7    1.2    2.5    3.2    9.2   13.2   15.1
:Gasconade River
Rich Fountain         4.2    5.7    7.7   10.7   15.3   21.0   24.0

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: 02/19/2017 - 05/20/2017
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20           7.4    7.4    7.3    7.3    6.6    4.9    4.1
Quincy               12.5   12.5   12.5   12.5   12.3   11.9   11.6
Quincy LD21           7.9    7.8    7.8    7.8    7.2    5.4    4.7
Hannibal             11.5   11.4   11.4   11.4   11.2   10.4   10.1
Saverton LD22         8.2    8.1    8.1    8.1    7.6    6.2    5.6
Louisiana            12.0   12.0   12.0   12.0   12.0   11.9   11.9
Clarksville LD24     18.6   18.6   18.3   18.2   17.8   16.1   15.3
Winfield LD25        18.4   18.4   18.1   18.0   17.6   15.9   15.1
:North Fabius River
Ewing                 3.5    3.3    3.0    3.0    2.9    2.9    2.6
:Middle Fabius River
Ewing                 3.0    2.8    2.8    2.8    2.7    2.6    2.6
:South Fabius River
Taylor                1.7    1.6    1.4    1.4    1.3    1.0    0.9
:North River
Palmyra               3.3    3.3    3.2    3.1    3.1    2.6    2.6
:Mid Fork Salt River
Holliday              3.8    3.8    3.8    3.7    3.7    3.5    3.5
:Salt River
New London            5.1    5.0    4.5    3.5    2.4    2.3    2.3
:Cuivre River
Troy                  5.6    5.4    5.3    5.2    5.2    5.0    5.0
Old Monroe           14.3   14.3   14.1   14.0   13.7   11.9   10.8
:Dardenne Creek
St. Peters            1.5    1.5    1.4    1.4    1.4    1.3    1.2
:Bourbeuse River
Union                 1.5    1.4    1.4    1.4    1.3    1.3    1.2
:Big River
Byrnesville           1.7    1.6    1.6    1.5    1.4    1.3    1.2
:Meramec River
Steelville            1.2    1.1    1.1    1.1    1.1    1.0    1.0
Sullivan              2.4    2.4    2.4    2.3    2.3    2.2    2.2
Eureka                3.2    3.0    3.0    3.0    3.0    2.9    2.9
:Kaskaskia River
Vandalia              5.8    5.3    3.2    2.8    2.6    2.4    2.2
Carlyle TW          413.8  413.7  413.3  411.2  411.2  411.2  411.2
:La Moine River
Ripley                4.2    4.0    3.9    3.9    3.8    3.8    3.7
:Moreau River
Jefferson City        1.6    1.6    1.6    1.5    1.5    1.5    1.5
:Maries River
Westphalia            0.7    0.7    0.6    0.6    0.5    0.3    0.3
:Gasconade River
Rich Fountain         3.0    2.9    2.8    2.7    2.5    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 update to this outlook will be issued on Thursday, March 2.

$$



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