Flood Potential Outlook
Issued by NWS St. Louis, MO

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ESFLSX

Probabilistic Hydrologic Outlook
National Weather Service ST. LOUIS MO
425 PM CST THU FEB 15 2018

...Spring Flood and Water Resources Outlook Number 1...
...Near normal flood chances along the Mississippi and Illinois
Rivers...
...Below normal flood chances along the Missouri River...
...Local tributaries have 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 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 drought
conditions ranging from abnormally dry over portions of west central
Illinois and northeastern Missouri to extreme drought over portions
of east central and southeastern Missouri, particularly in the
Meramec River watershed.  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 flood risk on area`s major rivers...

However, it`s a different story for the upper Mississippi, Missouri,
and Illinois rivers.  While the local area has experienced a
pronounced precipitation deficit with respect to seasonal norms, the
upper Mississippi River basin has experienced near normal snowfall,
on average, this winter.  In Minnesota and northern Wisconsin, snow
water equivalents and snow depths are well below what is typically
observed.  This deficit is compensated, in part, by near normal to
above average snow water equivalents and depths over Iowa, southern
Wisconsin, and northern Illinois.  In spite of the low snow totals
across the upper Midwest, soil moisture across the upper Mississippi
watershed is mostly near to above seasonal norms. In addition, where
bigger streams are not frozen, observed streamflow is near to above
the seasonal flows. This will leave the Mississippi River from near
Canton, Missouri south to Winfield, Missouri with a near average
chance of flooding the next 3 months.  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.  Along the lower Missouri
River, the flood risk across central and eastern Misouri appears to
be below normal. Precipitation this winter has provided above normal
precipitation from Nebraska into western Iowa and northwestern
Kansas, but below average across the remainder of Kansas into
western Missouri.  With normal discharges expected out of Gavins
Point Dam near Yankton, South Dakota, this translates into below
normal chances of flooding this spring along the lower Missouri
River from Jefferson City to St. Charles, Missouri.

...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.
For the month of March, the outlook calls a equal chances of being
above, below, or near normal precipitation. For areas north of I-44
in Missouri and west of I-55 in Illinois, the temperature outlook
for March indicates temperatures will mostly likely be colder than
average, with equal chances of below, above, or near normal
temperatures across southern Missouri and south central Illinois.
For the spring months of March through May, the 3-month outlook
indicates a better chance of above normal precipitation, with the
best chances of above normal precipitation to the east of St. Louis.
This same outlook calls for a better chance of above normal
temperatures south of the Missouri River in Missouri and south of I-
64 in Illinois, with equal chances of below, above, or near normal
temperatures north of this line.

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:  02/18/2018 - 05/19/2018

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Mississippi River
Canton LD20         14.0   20.0   25.0 :  68   63   17   17   <5   <5
LaGrange            18.0   23.0   25.0 :  33   39    8    9   <5   <5
Quincy              17.0   22.0   26.0 :  66   63   23   26    9    9
Quincy LD21         17.0   21.0   25.0 :  47   56   22   25    9    9
Hannibal            16.0   22.0   24.0 :  68   65   16   16    9    9
Saverton LD22       16.0   20.0   22.0 :  56   60   28   36   18   21
Louisiana           15.0   20.0   25.0 :  70   70   26   32   <5    6
Clarksville LD24    25.0   31.0   33.0 :  70   70   24   28   12   12
Winfield LD25       26.0   30.0   34.0 :  60   64   30   38    9    9
:North Fabius River
Ewing               11.0   14.0   18.0 :  41   55   16   33    9   10
:Middle Fabius River
Ewing               12.0   17.0   19.5 :  39   50   10   13    7    8
:South Fabius River
Taylor               9.5   14.0   19.0 :  27   59    8   14   <5   <5
:North River
Palmyra             13.0   16.0   22.0 :  37   56   25   38   <5   <5
:Mid Fork Salt River
Holliday            17.0   22.0   26.0 :  28   52   <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 :  47   50   21   28    7    7
Old Monroe          24.0   27.0   30.0 :  41   56   21   28   12   11
:Dardenne Creek
St. Peters          18.0   20.0   23.0 :  28   32   17   17   <5   <5
:Bourbeuse River
Union               15.0   22.0   26.0 :  40   54    8   10   <5   <5
:Big River
Byrnesville         16.0   20.0   28.0 :  28   62   11   22   <5   <5
:Meramec River
Steelville          12.0   20.0   25.0 :  22   40   <5    8   <5   <5
Sullivan            11.0   20.0   29.0 :  28   72    8   11   <5   <5
Pacific             15.0   23.0   27.0 :  23   49   <5    8   <5   <5
Eureka              19.0   26.0   31.0 :  22   42   10   15   <5    8
:Kaskaskia River
Vandalia            18.0   24.0   26.0 :  63   82   18   27    8   12
Carlyle TW         423.5  431.0  435.0 :  10   43   <5   <5   <5   <5
:La Moine River
Ripley              22.0   23.0   27.0 :  40   48   28   41   12   15
:Moreau River
Jefferson City      17.0   25.0   29.0 :  31   79   12   33    8   13
:Maries River
Westphalia          10.0   15.0   20.0 :  20   43    5   11   <5   <5
:Gasconade River
Rich Fountain       20.0   25.0   30.0 :  10   24   <5    8   <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: 02/18/2018 - 05/19/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20           9.7   10.4   13.3   14.8   18.3   21.5   23.0
LaGrange             10.6   11.3   14.2   15.7   19.2   22.4   23.9
Quincy               13.2   13.9   16.1   17.8   21.7   25.3   27.2
Quincy LD21          10.7   11.9   15.0   16.6   20.5   24.2   26.5
Hannibal             12.9   13.7   15.3   16.6   20.4   23.3   25.7
Saverton LD22        10.5   11.7   14.3   16.2   20.9   23.8   25.9
Louisiana            12.1   12.6   14.7   16.3   20.3   23.0   24.6
Clarksville LD24     20.4   21.9   24.7   26.6   30.9   33.6   35.0
Winfield LD25        20.5   22.0   24.8   26.7   30.9   33.6   35.0
:North Fabius River
Ewing                 4.3    5.7    7.6    9.7   12.5   16.2   20.2
:Middle Fabius River
Ewing                 3.8    5.0    7.5   10.7   13.0   17.0   21.3
:South Fabius River
Taylor                4.0    4.7    5.9    7.9   10.3   13.2   17.2
:North River
Palmyra               4.8    6.2    7.8   10.8   16.0   19.0   20.2
:Mid Fork Salt River
Holliday              4.9    5.8    8.6   13.7   17.2   18.7   20.3
:Salt River
New London            2.5    2.7    4.0    8.9    9.3   13.1   14.6
:Cuivre River
Troy                 10.1   11.7   14.7   20.0   24.7   26.8   29.5
Old Monroe           15.9   17.3   19.7   22.0   26.6   30.4   30.8
:Dardenne Creek
St. Peters            8.3   10.0   12.2   16.0   18.8   21.0   21.6
:Bourbeuse River
Union                 3.4    7.0   10.5   13.8   17.6   21.0   24.4
:Big River
Byrnesville           3.9    5.0    7.0   10.7   17.1   20.8   22.6
:Meramec River
Steelville            1.6    1.6    2.5    6.2   10.6   14.4   17.7
Sullivan              3.5    3.6    4.4    7.7   12.0   17.8   22.1
Eureka                3.9    5.2    7.0   10.6   17.8   26.2   29.7
:Kaskaskia River
Vandalia              9.4   11.2   14.0   19.6   23.0   25.6   26.8
Carlyle TW          413.8  414.1  415.7  418.6  421.6  423.5  424.2
:La Moine River
Ripley                9.7   10.7   15.1   19.1   23.8   27.4   28.5
:Moreau River
Jefferson City        3.2    3.9    6.4   11.5   18.2   26.0   33.7
:Maries River
Westphalia            0.8    1.2    2.2    2.9    7.8   11.9   14.7
:Gasconade River
Rich Fountain         3.6    4.0    5.4    8.1   12.7   19.4   23.5

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: 02/18/2018 - 05/19/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20           3.6    3.5    3.3    3.1    3.0    2.9    2.7
LaGrange              4.5    4.4    4.2    4.0    3.9    3.8    3.6
Quincy               11.3   11.2   11.0   10.9   10.9   10.9   10.9
Quincy LD21           4.1    4.1    3.8    3.7    3.6    3.4    3.2
Hannibal              9.9    9.9    9.8    9.8    9.8    9.7    9.7
Saverton LD22         4.9    4.9    4.8    4.6    4.5    4.4    4.2
Louisiana            11.9   11.9   11.9   11.8   11.8   11.8   11.8
Clarksville LD24     14.6   14.5   14.3   14.1   14.0   13.8   13.7
Winfield LD25        14.5   14.4   14.2   14.0   13.8   13.7   13.5
:North Fabius River
Ewing                 3.3    3.2    3.1    3.0    2.9    2.8    2.6
:Middle Fabius River
Ewing                 2.9    2.9    2.8    2.7    2.6    2.5    2.3
:South Fabius River
Taylor                1.6    1.6    1.5    1.4    1.3    1.0    0.9
:North River
Palmyra               3.7    3.7    3.6    3.5    3.3    2.6    2.6
:Mid Fork Salt River
Holliday              4.0    4.0    4.0    3.9    3.8    3.7    3.7
:Salt River
New London            4.8    4.6    4.1    3.1    2.1    2.1    2.1
:Cuivre River
Troy                  5.7    5.6    5.3    5.2    5.1    4.9    4.8
Old Monroe           10.1   10.0    9.8    9.5    9.5    9.4    9.4
:Dardenne Creek
St. Peters            1.3    1.2    1.2    1.1    1.1    1.0    1.0
:Bourbeuse River
Union                 1.4    1.4    1.3    1.3    1.2    1.1    1.1
:Big River
Byrnesville           1.4    1.3    1.1    1.1    1.0    1.0    0.9
:Meramec River
Steelville            1.2    1.2    1.2    1.1    1.1    1.1    1.1
Sullivan              3.0    3.0    2.9    2.9    2.8    2.8    2.8
Eureka                2.9    2.8    2.8    2.8    2.8    2.7    2.7
:Kaskaskia River
Vandalia              4.5    3.7    3.2    2.7    2.4    2.3    2.2
Carlyle TW          413.5  413.3  411.4  411.2  411.2  411.2  411.2
:La Moine River
Ripley                4.7    4.5    4.3    4.1    4.0    3.8    3.8
:Moreau River
Jefferson City        1.5    1.5    1.5    1.4    1.4    1.4    1.4
:Maries River
Westphalia            0.5    0.5    0.5    0.4    0.3    0.3    0.3
:Gasconade River
Rich Fountain         3.2    3.2    3.2    3.1    3.1    3.1    3.0

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 outlook will be issued the Spring Flood Outlook update on
March 1st.

$$
Fuchs



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