National Weather Service United States Department of Commerce

 

Figure 1: Snow Water Equivalent Image. (Courtesy of NOHRSC)
Figure 2: USGS Current Streamflow Analysis
Figure 3: 180 Day Percentage of Mean Precipitation Analysis (Courtesy of Midwest Climate Center)
Figure 4: Palmer Drought Severity Index
Figure 5: Soil Moisture (mm)
Figure 6: Three Month Temperature Outlook
Figure 7: Three Month Precipitation Outlook

NWS
St. Louis, Missouri

Spring Flood Outlook
Issued: February 25, 2021

Snow Water EquivalentCurrent Snow Water Equivalent

Streamflow AnalysisUSGS Stream Analysis

  30 Day Rainfall DeparturePrecipitation 30 Day Percentage of Mean

Soil Moisture PercentileCurrent Soil Moisture

1-Month Precip Outlook3 Month Precipitation Outlook

1-Month Temp Outlook3 Month Temperature Outlook

3-Month Precip Outlook3 Month Precipitation Outlook

3-Month Temp Outlook3 Month Temperature Outlook

Probabilistic Hydrologic Outlook
National Weather Service ST. LOUIS MO
230 PM CST THU FEB 25 2021

...Spring Flood and Water Resources Outlook Number 2...
...Minor flooding likely along the Mississippi, Missouri, and
   Illinois Rivers...
...Most local streams have a near normal flood risk this spring...

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 its confluence with the LaMoine River to its confluence with the
Mississippi River, and for tributary rivers in eastern Missouri, and
west central and southwest Illinois.

There is no ongoing flooding anywhere within the St. Louis Service
Area, so probabilities within this outlook are not skewed by any
ongoing flooding.

This outlook is based on current streamflows and soil moisture over
the area, and upstream snowpack, particularly in the Mississippi,
Missouri, and Illinois river basins. The statistics are based on
about 30 to 60 years of historical rainfall and stream crests.  More
than normal rainfall could cause higher-than-expected crests at
individual forecast locations, while less than normal rainfall could
keep streams from reaching "likely" crests.

The Mississippi and Missouri rivers are experiencing near normal
streamflow for this time of year, while flows along the Illinois
River have experienced well below normal streamflow through most of
the past winter.  This is providing a low to mostly average starting
point for these rivers to accept future runoff.  Soils have dried out
considerably across the Midwest since last summer, leaving local
areas with near to below normal soil moisture.  Drier soils are the
rule from Minnesota and the Dakotas through western Kansas.  This
will provide the upper Mississippi River and middle Missouri River
basins with additional storage, which acts as a deterrent to
flooding.  Finally, snowpack and snow water equivalent in this
snowpack are well below average from northern Wisconsin, most of
Minnesota, and the Dakotas. In fact, the Plains states north through
the Dakotas are essentially snow-free, except for a small area over
southeastern Nebraska.  However, this snow water equivalent is well
above average from southern Nebraska through much of Iowa, northern
Illinois, and southern Wisconsin.  Due to close proximity of this
above normal snowpack, look for a likelihood of minor flooding for
the Illinois, Missouri, and Mississippi rivers.  However, given the
below normal snowpack in other portions of these basins, the
likelihood of significant (moderate or greater) flooding is not as
great, and in many locations the threat of significant flooding is
well below historical averages for the spring months.

For local basins, the chances for flooding at most locations
throughout the St. Louis service area are near or above average.
Minor flooding is likely along the Fabius rivers, the Middle Fork
Salt River, the Cuivre River, the Meramec River, the Bourbeuse River,
the Big River, the Moreau River, and the Kaskaskia River. Soil
moisture and wintertime precipitation have left these areas with
moist soils, but not much different from normal.  Most local forecast
points have minor flood probabilities close to or slightly above
normal, while these locations have near normal probabilites for
significant flooding.

In the near term, the Climate Prediction Center calls for above
normal temperatures throughout the bi-state region and near normal
precipitation chances in the 6 to 10 day outlook. By days 8 through
14, temperatures should remain above normal, while there`s a slightly
better than average chance of above normal precipitation.  For the
month of March, there`s a slightly better than average chance of
warmer than normal temperatures across the bi-state region.  March
precipitation should be close to normal over eastern Missouri while
Illinois has a better than average chance of above normal
precipitation.  Looking ahead to the next 3 months of March through
May, temperatures are expected to be above normal throughout the St.
Louis service area, while precipitation chances will be very similar
to March: near normal chances for typical precipitation amounts for
the spring months in Missouri and better chances for above normal
precipitation across Illinois.

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:  03/01/2021 - 05/30/2021

                                       :    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              15.0   20.0   25.0 :  70   63   16   16   <5   <5
LaGrange            17.0   23.0   25.0 :  52   52    9   10   <5   <5
Quincy              19.0   22.0   26.0 :  56   56   24   27    9   10
Lock & Dam 21       18.0   21.0   25.0 :  55   53   24   26    9   10
Hannibal            17.0   22.0   24.0 :  69   61   15   15    9   10
Saverton            16.0   20.0   24.0 :  73   64   31   38   10   11
Louisiana           15.0   20.0   25.0 :  84   71   28   33    6    8
Clarksville         25.0   31.0   33.0 :  84   72   26   28   14   14
Winfield            26.0   30.0   34.0 :  79   65   37   40    9   10
Grafton             20.0   24.0   29.0 :  68   72   28   36    7    6
Mel Price LD        21.0   29.0   34.0 :  72   73   24   40   <5    6
St. Louis           30.0   35.0   40.0 :  56   66   27   47    7   11
Chester             27.0   35.0   40.0 :  81   79   39   57   17   27
:North Fabius River
Ewing               11.0   17.0   20.0 :  63   54   15   15   10   10
:Middle Fabius River
Ewing               12.0   17.0   20.0 :  56   50   14   14    8    8
:South Fabius River
Taylor              10.0   14.0   19.0 :  52   52   17   17   <5   <5
:North River
Palmyra             13.0   16.0   22.0 :  24   27   11   11   <5   <5
:Mid Fork Salt River
Holliday            17.0   22.0   26.0 :  51   51    6    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 :  51   51   24   24    7    7
Old Monroe          24.0   27.0   30.0 :  55   61   28   25   14   14
:Dardenne Creek
St. Peters          18.0   20.0   23.0 :  30   30   17   16   <5   <5
:Meramec River
Steelville          12.0   20.0   25.0 :  48   41   <5   <5   <5   <5
Sullivan            11.0   20.0   29.0 :  71   67   15   12   <5   <5
:Bourbeuse River
Union               15.0   22.0   26.0 :  52   51   11   11   <5   <5
:Meramec River
Pacific             15.0   23.0   27.0 :  44   43    7    7   <5   <5
:Big River
Byrnesville         16.0   20.0   28.0 :  55   49   24   22   <5   <5
:Meramec River
Eureka              19.0   26.0   31.0 :  46   44   18   17    7    7
Valley Park         18.0   21.0   27.0 :  46   50   37   42   18   19
Fenton              23.0   29.0   32.0 :  47   56   16   20   10   12
Arnold              24.0   35.0   38.0 :  81   76   25   30   17   24
:Kaskaskia River
Vandalia            18.0   24.0   26.0 :  74   82   34   35   17   19
Carlyle TW         423.5  431.0  435.0 :  23   43   <5   <5   <5   <5
:La Moine River
Ripley              22.0   23.0   27.0 :  42   41   33   35   11   12
:Moreau River
Jefferson City      17.0   25.0   29.0 :  79   87   40   40   17   15
:Maries River
Westphalia          10.0   15.0   20.0 :  42   52   18   19   <5   <5
:Gasconade River
Rich Fountain       20.0   25.0   30.0 :  34   34   24   26    5    6
:Missouri River
Jefferson City      23.0   25.0   30.0 :  43   60   31   53   14   17
:Osage River
St. Thomas          23.0   30.0   35.0 :  14   16   <5   <5   <5   <5
Mari-Osa Campgrou   19.0   22.0   25.0 :  36   64   17   27    8   13
:Missouri River
Chamois             17.0   28.0   31.0 :  71   77   11   11    6    6
Hermann             21.0   26.0   33.0 :  76   81   33   57   12   13
Washington          20.0   28.0   31.0 :  57   69   13   16    9   10
St. Charles         25.0   30.0   36.0 :  64   71   23   33    8    9

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: 03/01/2021 - 05/30/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton               10.9   11.9   14.3   16.3   18.3   21.7   23.0
LaGrange             11.8   12.8   15.2   17.2   19.2   22.6   23.9
Quincy               14.2   14.9   17.4   19.4   21.8   25.6   27.6
Lock & Dam 21        12.3   13.2   16.2   18.2   20.5   24.6   26.9
Hannibal             13.8   14.6   16.2   18.4   20.4   23.6   26.5
Saverton             12.0   13.2   15.8   18.4   20.9   24.1   26.5
Louisiana            12.7   13.7   15.9   18.3   20.5   23.1   25.3
Clarksville          22.0   23.4   26.0   28.9   31.1   33.7   35.5
Winfield             22.2   23.6   26.2   29.0   31.1   33.5   35.6
Grafton              16.1   16.6   18.3   21.7   24.6   28.4   29.7
Mel Price LD         15.4   17.1   20.9   24.2   28.7   31.2   33.5
St. Louis            17.9   21.4   26.6   30.8   35.9   39.1   41.3
Chester              20.0   24.4   29.1   32.8   37.6   42.3   44.1
:North Fabius River
Ewing                 6.8    7.2    9.5   12.3   14.7   19.9   21.4
:Middle Fabius River
Ewing                 5.8    6.8    9.1   12.6   15.3   19.2   21.8
:South Fabius River
Taylor                5.6    6.5    8.0   10.1   13.2   16.4   18.3
:North River
Palmyra               6.3    6.9    8.7   10.4   12.9   16.5   18.1
:Mid Fork Salt River
Holliday             10.6   11.3   14.6   17.1   18.3   20.8   22.0
:Salt River
New London            5.7    7.4    9.2    9.9   11.2   13.1   13.4
:Cuivre River
Troy                 12.0   13.2   16.8   21.6   24.9   27.1   29.7
Old Monroe           17.6   20.1   22.0   24.5   27.6   30.6   31.3
:Dardenne Creek
St. Peters            8.4    9.5   11.9   15.2   19.1   20.6   22.0
:Meramec River
Steelville            3.8    5.7    8.1   11.7   14.4   16.2   19.9
Sullivan              7.5    7.9   10.2   14.4   18.4   21.6   26.3
:Bourbeuse River
Union                 8.9   10.5   11.8   15.2   18.7   22.9   25.4
:Meramec River
Pacific               7.3    7.7   11.4   14.8   18.6   22.3   26.3
:Big River
Byrnesville           8.5    9.9   12.2   16.6   19.7   22.9   25.7
:Meramec River
Eureka               10.2   10.7   14.4   17.8   23.6   29.3   35.6
Valley Park           8.2    9.3   13.4   17.2   25.5   31.8   36.6
Fenton               14.0   16.2   19.7   22.4   27.4   32.1   36.1
Arnold               18.7   19.9   25.8   29.5   34.8   39.0   41.2
:Kaskaskia River
Vandalia             12.8   14.0   17.2   22.6   25.3   27.1   28.7
Carlyle TW          415.9  416.5  418.3  420.2  423.4  424.0  424.7
:La Moine River
Ripley               10.9   12.4   16.3   19.8   24.7   27.4   28.3
:Moreau River
Jefferson City        9.5   13.7   17.6   22.0   27.2   33.6   40.1
:Maries River
Westphalia            2.5    3.6    5.0    8.4   13.2   16.5   18.4
:Gasconade River
Rich Fountain         5.5    8.3   10.5   16.0   24.1   28.4   31.0
:Missouri River
Jefferson City       11.1   14.8   19.0   21.7   25.6   33.1   36.0
:Osage River
St. Thomas            7.9    8.7   11.9   13.4   16.6   24.9   27.1
Mari-Osa Campgrou    10.5   11.7   15.0   17.6   19.6   24.7   29.0
:Missouri River
Chamois               9.2   12.3   16.7   19.1   22.5   28.3   31.2
Hermann              14.1   18.3   21.1   24.5   27.2   34.3   36.0
Washington           10.6   14.3   17.1   20.8   23.6   30.6   34.5
St. Charles          17.9   21.1   23.4   26.7   29.1   35.4   37.4

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: 03/01/2021 - 05/30/2021
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton                4.7    4.6    4.4    4.2    4.0    3.5    3.1
LaGrange              5.6    5.5    5.3    5.0    4.8    4.4    4.0
Quincy               11.8   11.8   11.7   11.6   11.5   11.2   11.0
Lock & Dam 21         5.3    5.2    5.0    4.7    4.5    4.1    3.7
Hannibal             10.4   10.4   10.2   10.1   10.0    9.9    9.8
Saverton              6.2    6.1    5.9    5.6    5.3    4.9    4.7
Louisiana            12.0   12.0   11.9   11.9   11.9   11.9   11.9
Clarksville          16.5   16.4   16.1   15.7   15.3   14.7   14.2
Winfield             16.3   16.2   15.9   15.6   15.0   14.5   14.1
Grafton              15.2   15.2   15.2   15.1   15.0   14.8   14.7
Mel Price LD          7.7    7.5    7.3    6.8    6.1    5.1    4.5
St. Louis             7.1    7.0    6.6    5.6    4.4    3.2    1.7
Chester              10.9   10.7   10.3    9.3    7.9    6.6    4.9
:North Fabius River
Ewing                 3.8    3.7    3.5    3.4    3.2    3.1    3.0
:Middle Fabius River
Ewing                 3.3    3.2    3.1    3.0    2.9    2.8    2.8
:South Fabius River
Taylor                2.3    2.2    2.0    2.0    1.8    1.7    1.6
:North River
Palmyra               4.5    4.5    4.5    4.3    4.2    4.1    3.8
:Mid Fork Salt River
Holliday              3.9    3.9    3.9    3.9    3.9    3.8    3.7
:Salt River
New London            6.2    5.1    4.8    3.9    2.4    2.1    2.1
:Cuivre River
Troy                  6.3    6.2    5.9    5.6    5.4    5.3    5.2
Old Monroe           12.5   12.3   12.0   11.5   10.8   10.2    9.8
:Dardenne Creek
St. Peters            1.7    1.7    1.4    1.3    1.2    1.1    1.1
:Meramec River
Steelville            2.1    2.0    1.8    1.6    1.5    1.4    1.3
Sullivan              3.3    3.2    2.9    2.7    2.6    2.4    2.3
:Bourbeuse River
Union                 2.7    2.6    2.5    2.4    2.3    2.1    2.0
:Big River
Byrnesville           3.6    3.3    2.9    2.5    2.1    2.0    1.8
:Meramec River
Eureka                4.4    4.3    4.0    3.7    3.5    3.3    3.2
Fenton                4.5    4.2    3.6    2.7    2.1    1.7    1.5
Arnold                8.2    8.1    7.9    7.5    7.2    6.7    6.6
:Kaskaskia River
Vandalia              6.7    5.3    3.5    3.1    2.9    2.7    2.6
Carlyle TW          415.7  415.6  413.3  411.2  411.2  411.2  411.2
:La Moine River
Ripley                5.9    5.8    5.5    5.2    4.9    4.7    4.5
:Moreau River
Jefferson City        2.2    2.1    2.1    2.0    1.9    1.8    1.8
:Maries River
Westphalia            1.9    1.8    1.6    1.4    1.3    1.1    1.1
:Gasconade River
Rich Fountain         4.2    4.2    3.9    3.7    3.3    3.1    3.0
:Missouri River
Jefferson City        5.7    5.4    5.1    5.0    4.4    3.9    3.7
:Osage River
St. Thomas            3.2    3.2    2.8    2.5    2.5    2.1    1.5
:Missouri River
Hermann               6.6    5.9    5.6    5.5    5.5    5.3    4.8
Washington            3.5    2.9    2.6    2.4    2.4    2.2    1.6
St. Charles          10.4    9.7    9.4    9.3    9.2    9.0    8.4

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 outlook update will be issued in two weeks, on Thursday,
March 11th.

$$
Fuchs