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: March 1, 2018

Snow Water EquivalentCurrent Snow Water Equivalent

Streamflow AnalysisUSGS Stream Analysis

  30 Day Rainfall DeparturePrecipitation 30 Day Percentage of Mean

 Palmer Drought IndexPalmer Drought Index

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
340 PM CST Thu Mar 01 2018

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

This updated 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.

Minor flooding is occurring or forecast to occur in the next few
days along the Kaskaskia River, so the 90-day modeling was adjusted
to account for the likelihood of flooding beyond the current flood
event.  Elsewhere, flooding is not occurring and model adjustment is
not necessary.

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.

...Typical flood potential across local tributaries...

After more than 4 months of below average precipitation across
Missouri and Illinois and since the initial spring flood outlook,
the last half of February produced considerable rainfall across the
St. Louis Hydrologic Service Area.  Totals over the last 2 weeks of
the month ranged from a little over 2 inches in the Quincy area up
to near 10 inches in southern Callaway County and southeastern
Washington County, Missouri near Caledonia.  This rainfall produced
minor to moderate flooding throughout the Meramec and Kaskaskia
river basins.  Drought conditions which ranged from abnormally dry
in northeastern Missouri and west central Illinois now cover a
smaller area ranging from abnormally dry over much of the area to
moderate drought over a small area southwest of St. Louis.  In just
2 weeks, this rainfall has totally changed the tone of this spring
flood outlook update. Now, there are near average chances of
flooding on local tributaries throughout the St. Louis Hydrologic
Service Area over the next 90 days.  Flood probabilities do not vary
by more 4 percent below the average over central Missouri to 8
percent above the average in northeastern Missouri.

...Elevated flood risk on the Mississippi and Illnois Rivers...

However, it`s a different story for the upper Mississippi and
Illinois rivers.  While the local area has experienced significant
rainfall to compensate for a prolonged precipitation deficit with
respect to seasonal norms, the upper Mississippi River basin has
experienced near to above normal snowfall after recent snowfall the
past couple of weeks boosted relatively light totals during a fairly
uneventful winter through early February.  Snow cover has receded
northward to the Minnesota-Iowa border, then northeastward to the
Green Bay area.  In most of Minnesota and northern Wisconsin, snow
water equivalents and snow depths are now mostly above what is
typically observed at the beginning of March.  With recent heavy
rainfall over the Midwest the last 2 weeks, streamflows feeding the
Mississippi River from Illinois and Iowa are above the seasonal
average.  This will leave the Mississippi River from near Canton,
Missouri south to Winfield, Missouri with an above average chance of
flooding the next 3 months.  For the Illinois River, it`s a similar
story.  Heavy rainfall and melting snowpack in the headwaters near
the Chicago area have resulted in widespread flooding that has
extended downstream into the lower Illinois River basin.  With the
Illinois River already in flood, any additional rainfall could pose
additional flood risk to communities between Meredosia and Hardin,
Illinois.  Along the Missouri River, the flood risk across central
and eastern Misouri remains below normal. While the heavy rainfall
of last weekend has generated minor flooding along the Gasconade
River, tributaries near and upstream of the Kansas City area remain
low, leaving the lower Missouri River with lower than average flood
potential this spring. Precipitation this winter has provided above
normal precipitation across Nebraska, but below average across most
of Iowa and 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
temperatures and precipitation to be mostly below average in the 6
to 10 day outlook.  However, in the 8 to 14 day outlook,
temperatures and precipitation are both expected to be near to above
average.  For the month of March, the updated outlook calls for the
most likely outcome to be above average temperatures and
precipitation.  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:  03/11/2018 - 06/02/2018

                                       :    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 :  84   66   27   17   <5   <5
LaGrange            18.0   23.0   25.0 :  54   42   11    9   <5   <5
Quincy              17.0   22.0   26.0 :  83   67   31   28   11    9
Quincy LD21         17.0   21.0   25.0 :  76   60   30   28   11    9
Hannibal            16.0   22.0   24.0 :  82   68   24   16   15    9
Saverton LD22       16.0   20.0   22.0 :  80   65   43   38   28   24
Louisiana           15.0   20.0   25.0 :  85   73   37   34    7    6
Clarksville LD24    25.0   31.0   33.0 :  86   73   32   32   22   12
Winfield LD25       26.0   30.0   34.0 :  81   68   51   39   13    9
:North Fabius River
Ewing               11.0   14.0   18.0 :  53   52   22   26   10   11
:Middle Fabius River
Ewing               12.0   17.0   19.5 :  49   45   14   13    9    9
:South Fabius River
Taylor               9.5   14.0   19.0 :  53   54   14   14   <5   <5
:North River
Palmyra             13.0   16.0   22.0 :  49   51   32   32   <5   <5
:Mid Fork Salt River
Holliday            17.0   22.0   26.0 :  43   45    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 :  48   49   24   28    8    8
Old Monroe          24.0   27.0   30.0 :  65   57   34   28   14   11
:Dardenne Creek
St. Peters          18.0   20.0   23.0 :  28   28   18   18   <5   <5
:Bourbeuse River
Union               15.0   22.0   26.0 :  49   49   10   10   <5   <5
:Big River
Byrnesville         16.0   20.0   28.0 :  63   61   25   22   <5   <5
:Meramec River
Steelville          12.0   20.0   25.0 :  46   40   <5    6   <5   <5
Sullivan            11.0   20.0   29.0 :  74   71   14   13   <5   <5
Pacific             15.0   23.0   27.0 :  46   46    8    9   <5   <5
Eureka              19.0   26.0   31.0 :  43   41   20   17    9    9
:Kaskaskia River
Vandalia            18.0   24.0   26.0 :  80   75   28   24   11   11
Carlyle TW         423.5  431.0  435.0 :  37   41   <5   <5   <5   <5
:La Moine River
Ripley              22.0   23.0   27.0 :  51   46   44   42   14   13
:Moreau River
Jefferson City      17.0   25.0   29.0 :  75   79   32   31   15   12
:Maries River
Westphalia          10.0   15.0   20.0 :  37   41   12   11   <5   <5
:Gasconade River
Rich Fountain       20.0   25.0   30.0 :  32   26   12    8   <5   <5
:Black River
Annapolis            8.0   15.0   25.0 :  38   53   12   12   <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: 03/11/2018 - 06/02/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20          12.3   12.6   15.2   17.3   20.6   22.2   23.8
LaGrange             13.2   13.5   16.1   18.2   21.5   23.1   24.7
Quincy               15.3   15.5   18.2   20.6   24.3   26.2   28.4
Quincy LD21          13.8   14.3   17.1   19.3   23.2   25.2   27.7
Hannibal             14.7   15.0   17.0   19.2   21.9   24.2   27.0
Saverton LD22        13.3   13.8   16.8   19.4   22.4   24.7   27.0
Louisiana            13.6   14.2   16.8   19.5   21.9   23.8   25.6
Clarksville LD24     23.3   24.1   27.1   30.0   32.5   34.3   35.8
Winfield LD25        23.4   24.2   27.2   30.1   32.4   34.3   35.9
:North Fabius River
Ewing                 5.3    6.5    8.7   11.2   13.7   18.6   20.6
:Middle Fabius River
Ewing                 5.2    6.3    8.5   11.9   15.0   18.8   21.4
:South Fabius River
Taylor                5.2    6.3    7.4    9.7   12.2   15.0   17.4
:North River
Palmyra               6.9    7.7    9.9   12.9   16.4   19.9   21.2
:Mid Fork Salt River
Holliday              9.0   10.0   13.6   16.6   17.9   20.6   22.0
:Salt River
New London            6.0    6.8    9.1    9.2   10.3   14.3   16.8
:Cuivre River
Troy                 12.0   13.3   16.4   20.4   25.0   27.6   29.6
Old Monroe           18.6   20.7   22.7   25.3   28.4   31.6   31.9
:Dardenne Creek
St. Peters            8.8    9.5   11.2   14.9   18.8   21.1   22.1
:Bourbeuse River
Union                 9.3   11.0   12.4   14.9   18.8   22.3   25.3
:Big River
Byrnesville           8.4   10.9   13.8   17.0   19.9   22.5   24.6
:Meramec River
Steelville            3.4    5.4    8.1   11.5   13.9   16.1   19.6
Sullivan              7.5    8.2   10.6   14.1   17.9   21.0   25.0
Pacific               4.6    7.4   10.4   14.7   19.0   22.6   24.9
Eureka                8.3    9.6   12.7   17.1   24.7   30.7   33.2
:Kaskaskia River
Vandalia             15.4   16.0   18.4   21.4   24.2   26.1   27.0
Carlyle TW          420.5  420.9  421.5  422.8  424.1  424.7  425.9
:La Moine River
Ripley               12.6   14.8   18.5   22.1   25.9   27.8   28.6
:Moreau River
Jefferson City        9.7   12.3   17.1   20.2   25.9   30.7   34.9
:Maries River
Westphalia            3.3    3.9    5.3    9.1   12.9   15.7   17.8
:Gasconade River
Rich Fountain         8.0    9.2   11.2   16.5   21.7   25.8   27.6
:Black River
Annapolis             5.4    6.3    7.1    8.0   10.4   15.0   19.8

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: 03/11/2018 - 06/02/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Mississippi River
Canton LD20           8.7    8.1    7.3    6.3    5.0    4.4    3.6
LaGrange              9.6    9.0    8.2    7.2    5.9    5.3    4.5
Quincy               12.8   12.7   12.5   12.3   11.9   11.7   11.3
Quincy LD21           9.5    8.8    8.0    6.8    5.6    5.0    4.2
Hannibal             12.3   12.0   11.5   11.0   10.6   10.2    9.9
Saverton LD22         9.4    9.0    8.3    7.3    6.5    5.9    5.0
Louisiana            12.1   12.1   12.0   12.0   12.0   11.9   11.9
Clarksville LD24     19.8   19.4   18.6   17.5   16.5   15.7   14.6
Winfield LD25        19.8   19.4   18.5   17.3   16.4   15.5   14.5
:North Fabius River
Ewing                 3.8    3.7    3.5    3.4    3.2    3.0    2.9
:Middle Fabius River
Ewing                 3.2    3.2    3.1    3.0    2.9    2.8    2.7
:South Fabius River
Taylor                2.4    2.2    2.1    1.9    1.8    1.6    1.5
:North River
Palmyra               4.1    4.1    4.0    3.9    3.8    3.5    3.4
:Mid Fork Salt River
Holliday              4.2    4.1    4.0    4.0    3.9    3.8    3.8
:Salt River
New London            5.5    5.0    4.8    4.1    2.9    2.1    2.1
:Cuivre River
Troy                  6.3    6.1    5.8    5.5    5.3    5.1    5.0
Old Monroe           15.4   15.1   14.5   13.4   12.4   11.5   10.1
:Dardenne Creek
St. Peters            1.8    1.8    1.6    1.5    1.4    1.3    1.3
:Bourbeuse River
Union                 2.7    2.6    2.4    2.3    2.1    2.0    1.9
:Big River
Byrnesville           3.7    3.4    2.9    2.6    2.3    2.2    2.0
:Meramec River
Steelville            2.4    2.2    1.9    1.7    1.6    1.4    1.3
Sullivan              4.5    4.2    3.8    3.7    3.5    3.4    3.3
Eureka                4.3    4.1    3.8    3.5    3.4    3.2    3.1
:Kaskaskia River
Vandalia              9.8    9.5    4.2    3.2    3.0    2.8    2.7
Carlyle TW          421.3  420.8  418.8  415.4  411.2  411.2  411.2
:La Moine River
Ripley                6.6    5.6    5.0    4.6    4.3    4.1    4.0
:Moreau River
Jefferson City        2.4    2.3    2.1    2.0    1.9    1.7    1.6
:Maries River
Westphalia            1.9    1.8    1.5    1.3    1.2    1.1    1.0
:Gasconade River
Rich Fountain         5.1    4.9    4.5    4.1    3.8    3.7    3.5

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 last week of this month.