Flood Potential Outlook
Issued by NWS Sioux Falls, SD

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FGUS73 KFSD 071643
ESFFSD

Probabilistic Hydrologic Outlook
National Weather Service Sioux Falls SD
900 AM CST Thu Mar 07 2019

...Spring Flood Outlook...

This spring flood outlook is for the rivers and streams in southeast
South Dakota, southwest Minnesota, northwest Iowa, and extreme
northeast Nebraska.

Due to the very wet conditions across the area late last summer into
last fall, and the increasing snow pack over the last 6 to 8 weeks,
the chances for minor, moderate, or major flooding are above to
much above normal this spring.

The flood threat through this spring, both in location and severity,
will largely be determined by future rain or snow fall and how fast
the melting of the snowpack occurs.

The outlook for the next 2 weeks shows that near normal
precipitation is expected through mid March with likely below normal
temperatures. The 30 day outlook for March shows equal chances for
above normal, normal, or below normal precipitation, and increased
chances for below normal temperatures. The 90 day outlook for March
through May shows equal chances for above normal, normal, or below
normal precipitation, and normal to above normal temperatures.

For most of the rivers in the area, the chances for minor, moderate,
or major flooding are above to much above normal. The areas with the
most increased chances of major flooding are the middle and lower
portions of the James River, all of the Vermillion River, the Big
Sioux River below Brookings, the Rock River, the middle portions of
the Floyd River, the entire Little Sioux River, the upper Des
Moines River, and the upper Redwood River.

...Current Snow Conditions...

The current snow pack is widespread for all areas along and north of
Interstate 90. Depths are generally 15 to 25 inches in that area,
with some locations between Highway 14 and SD Highway 34/MN Highway
30 having 30 to 40 inches of snow on the ground. The water content
of the snow pack in this area is generally 2 1/2 to 4 inches, with a
few localized areas of 4 to 6+ inches. Areas south of I-90 generally
have less than 12 inches of snow on the ground, with a water content
of 1 to 2 inches.

...Current Soil Conditions...

Soils in the area are generally frozen to 1 to 3 feet deep. With the
wet conditions last fall heading into the freeze-up, the soils were
fairly well saturated as they froze, which will make them much more
impervious to soaking up much of the snow melt as it occurs. There
is some uncertainty as to the current level of the soil saturation
as we head into spring, and this will play a very big role in how
severe the flooding will be over the next 2 to 3 months.

...Current River Conditions...

River levels and flows are above normal across the region. All
rivers are still ice covered. Ice jams are possible as we head into
the spring as the increased flows will raise and break up the river
ice before it melts.

...Probabilistic Outlooks...

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:  03/10/2019  - 06/08/2019

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Floyd River
Sheldon             12.0   14.0   16.0 :  89   26   34   10   <5   <5
Alton               12.0   16.0   18.0 : >98   36   89   17   58   10
Le Mars             20.0   21.0   24.0 : >98   23   96   16   66   13
:West Branch Floyd River
Struble             14.0   15.0   16.0 :  64   15   38    7   11   <5
:Floyd River
Merrill             12.0   14.0   16.0 :  83   12   54    9   44   <5
James               26.0   30.0   34.0 :  42   <5   13   <5   <5   <5
:Little Sioux River
Milford             12.0   14.0   16.0 : >98   89  >98   79   91   67
Spencer             10.0   14.0   16.0 : >98   71   68   22   30    5
:Ocheyedan River
Spencer              8.0    9.5   10.5 :  96   46   84   35   64   13
:Little Sioux River
Linn Grove          18.0   19.5   21.0 : >98   69   92   47   74   21
Cherokee            17.0   21.0   24.0 : >98   60   90   29   48    6
Correctionville     19.0   21.0   23.0 :  80   17   61   15   45    7
:West Fork Ditch
Hornick             20.0   22.0   27.0 :  90   38   79   26   36    5
:Perry Creek
Sioux City          24.0   26.0   28.0 :   8   <5    7   <5    5   <5
:Big Sioux River
Brookings            9.0   10.5   12.0 : >98   60   96   46   79   31
Dell Rapids         12.0   14.0   15.0 : >98   44   84   40   70   32
Sioux Falls I-90    12.0   15.0   17.0 : >98   48   71   33   47   12
:Skunk Creek
Sioux Falls         11.5   15.0   17.0 :  65   13   31   <5   24   <5
:Big Sioux River
Sioux Falls N Cliff 16.0   18.0   31.0 : >98   44   89   41   <5   <5
:Split Rock Creek
Corson               8.5   11.0   14.0 : >98   38   91   25   65   14
:Rock River
Luverne             10.0   12.0   14.0 :  80   22   54   12   <5   <5
Rock Rapids         13.0   16.0   19.0 :  96   53   82   25   65   19
Rock Valley         16.0   17.0   19.0 :  81   24   69   22   58   18
:Big Sioux River
Hawarden            20.5   24.0   27.0 : >98   61  >98   48   91   35
Akron               16.0   18.0   20.0 : >98   64  >98   53  >98   39
Sioux City          32.0   38.0   41.0 :  52   11   25   <5   19   <5
:James River
Huron               11.0   13.0   15.0 : >98   43   95   35   81   30
Forestburg          12.0   14.0   16.0 : >98   41   84   35   63   22
Mitchell            17.0   20.0   22.0 : >98   49   79   33   57   21
:Firesteel Creek
Mount Vernon         8.0   13.0   15.0 :  66   41   18   16   10   12
:James River
Scotland            13.0   14.0   16.0 : >98   56  >98   50   84   36
Yankton             12.0   14.0   16.0 :  84   35   77   33   70   28
:West Fork Vermillion River
Parker               9.0   10.0   11.0 :  27   10   24    7   12    6
:East Fork Vermillion River
Parker              12.0   14.0   16.0 :  72   33   37   14   16   <5
:Vermillion River
Davis               11.0   13.0   15.0 : >98   49   70   34   27   11
Wakonda             14.0   15.5   17.0 :  94   48   82   39   66   34
Vermillion          21.0   22.0   30.0 :  60   29   55   25   15   <5
:Redwood River
Marshall            14.0   15.0   16.5 :  95   16   78   11   51    8
:West Fork Des Moines River
Jackson             12.0   12.5   14.0 :  85   11   59   <5   12   <5
:Missouri River
South Sioux City    30.0   33.0   36.0 :  25    5   11   <5   <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: 03/10/2019  - 06/08/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Floyd River
Sheldon              10.1   11.3   12.7   13.4   14.4   15.2   15.8
Alton                14.0   15.7   17.1   18.3   19.5   20.7   21.7
Le Mars              21.3   22.4   23.6   24.5   25.1   25.4   25.9
:West Branch Floyd River
Struble              12.0   12.5   13.5   14.8   15.5   16.0   17.0
:Floyd River
Merrill               9.7   10.4   12.7   14.7   17.1   17.6   17.7
James                17.9   18.9   20.8   23.8   28.5   30.5   31.6
:Little Sioux River
Milford              15.6   16.0   17.2   20.2   23.3   27.9   31.3
Spencer              12.0   12.4   13.5   15.1   16.3   17.9   19.3
:Ocheyedan River
Spencer               8.1    8.9   10.1   11.2   12.3   13.3   15.1
:Little Sioux River
Linn Grove           19.3   19.6   21.0   22.9   23.8   24.9   25.9
Cherokee             20.1   21.0   22.0   23.8   24.8   26.5   27.7
Correctionville      16.7   18.1   20.1   22.1   24.7   26.9   28.1
:West Fork Ditch
Hornick              19.4   20.0   22.1   24.6   28.0   29.3   32.2
:Perry Creek
Sioux City            9.4   10.2   11.7   13.0   16.5   21.2   28.0
:Big Sioux River
Brookings            10.8   11.2   12.2   12.9   13.5   13.9   14.4
Dell Rapids          12.9   13.2   14.6   16.2   16.7   17.8   18.2
Sioux Falls I-90     13.0   13.2   14.6   16.9   17.5   18.6   19.0
:Skunk Creek
Sioux Falls           9.1    9.5   10.3   12.7   16.7   18.8   19.5
:Big Sioux River
Sioux Falls N Cliff  17.0   17.6   20.7   24.6   26.6   28.0   28.2
:Split Rock Creek
Corson               10.3   11.1   12.0   15.3   18.2   19.7   22.2
:Rock River
Luverne               8.4    9.4   10.4   12.1   13.0   13.6   13.9
Rock Rapids          13.6   15.0   16.9   21.6   24.6   27.0   28.5
Rock Valley          13.2   14.2   16.4   19.4   21.1   22.4   23.1
:Big Sioux River
Hawarden             26.4   27.1   29.6   33.6   36.6   41.8   44.5
Akron                20.6   21.0   22.3   23.6   24.4   25.6   25.9
Sioux City           23.4   24.3   27.2   33.5   38.0   45.0   48.2
:James River
Huron                12.9   13.8   15.7   18.1   20.0   21.6   24.0
Forestburg           12.9   13.7   15.1   16.7   18.4   20.9   22.9
Mitchell             18.5   18.9   20.4   22.4   23.7   26.1   29.1
:Firesteel Creek
Mount Vernon          4.2    5.0    6.3    9.2   12.2   15.0   16.2
:James River
Scotland             14.5   15.1   17.8   19.6   20.6   22.7   24.8
Yankton               9.5   10.5   14.8   18.0   19.9   23.5   27.0
:West Fork Vermillion River
Parker                3.3    3.4    4.0    6.2    9.8   11.2   11.3
:East Fork Vermillion River
Parker               10.2   10.4   11.3   13.2   15.1   16.5   17.5
:Vermillion River
Davis                11.3   11.6   12.5   14.2   15.2   15.9   16.2
Wakonda              13.8   14.5   16.4   17.1   17.4   17.6   17.6
Vermillion           12.4   13.2   15.6   22.9   27.1   30.4   30.6
:Redwood River
Marshall             14.0   14.5   15.2   16.6   17.6   18.1   18.8
:West Fork Des Moines River
Jackson              11.7   11.9   12.2   12.7   13.2   14.3   15.5
:Missouri River
South Sioux City     16.6   17.4   20.5   26.0   30.2   33.6   34.7

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: 03/10/2019  - 06/08/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Floyd River
Sheldon               4.0    4.0    4.0    4.0    4.0    4.0    4.0
Alton                 5.9    5.9    5.9    5.9    5.8    5.8    5.7
Le Mars               9.9    9.9    9.9    9.9    9.8    9.3    9.0
:West Branch Floyd River
Struble               4.7    4.7    4.7    4.7    4.5    4.4    4.3
:Floyd River
Merrill               1.2    1.2    1.2    1.2    1.2    1.0    0.8
James                 9.9    9.9    9.9    9.9    9.9    9.6    9.5
:Little Sioux River
Milford               7.7    7.7    7.7    7.7    7.6    7.6    7.6
Spencer               5.1    5.1    5.1    5.1    5.1    5.0    5.0
:Ocheyedan River
Spencer               3.0    3.0    3.0    3.0    3.0    2.9    2.9
:Little Sioux River
Linn Grove           16.1   16.1   16.1   16.1   16.1   16.1   16.1
Cherokee              8.2    8.1    8.1    8.1    8.1    8.1    8.0
Correctionville       6.0    6.0    6.0    6.0    6.0    5.9    5.9
:West Fork Ditch
Hornick               6.8    6.8    6.8    6.8    6.4    6.2    6.0
:Perry Creek
Sioux City            7.1    7.1    7.1    7.1    7.1    7.1    7.0
:Big Sioux River
Brookings             2.6    2.6    2.6    2.6    2.6    2.6    2.6
Dell Rapids           3.8    3.8    3.8    3.8    3.8    3.8    3.8
Sioux Falls I-90      7.8    7.8    7.8    7.8    7.8    7.8    7.7
:Skunk Creek
Sioux Falls           3.8    3.8    3.8    3.8    3.8    3.8    3.8
:Big Sioux River
Sioux Falls N Cliff   5.7    5.7    5.7    5.7    5.6    5.6    5.6
:Split Rock Creek
Corson                2.0    2.0    2.0    2.0    2.0    2.0    2.0
:Rock River
Luverne               3.8    3.8    3.8    3.8    3.8    3.8    3.8
Rock Rapids           8.2    8.2    8.2    8.2    8.1    8.1    8.1
Rock Valley           4.1    4.1    4.1    4.1    4.1    4.1    4.0
:Big Sioux River
Hawarden             12.4   12.4   12.4   12.4   12.4   12.4   12.4
Akron                 6.8    6.8    6.8    6.8    6.8    6.8    6.8
Sioux City           11.0   11.0   11.0   11.0   11.0   11.0   11.0
:James River
Huron                 9.0    9.0    9.0    9.0    9.0    9.0    9.0
Forestburg            4.1    4.1    4.1    4.1    4.1    4.1    4.1
Mitchell              9.8    9.8    9.8    9.8    9.8    9.8    9.8
:Firesteel Creek
Mount Vernon          2.2    2.2    2.2    2.2    2.2    2.2    2.2
:James River
Scotland              4.4    4.4    4.4    4.4    4.4    4.4    4.4
Yankton               2.8    2.8    2.8    2.8    2.8    2.8    2.8
:West Fork Vermillion River
Parker                0.6    0.6    0.6    0.6    0.6    0.6    0.5
:East Fork Vermillion River
Parker                3.6    3.6    3.6    3.6    3.6    3.6    3.6
:Vermillion River
Davis                 2.7    2.7    2.7    2.7    2.7    2.7    2.7
Wakonda               3.8    3.8    3.8    3.8    3.8    3.8    3.8
Vermillion            2.5    2.4    2.4    2.4    2.4    2.4    2.4
:Redwood River
Marshall              6.8    6.8    6.8    6.8    6.8    6.8    6.8
:West Fork Des Moines River
Jackson               7.8    7.8    7.8    7.8    7.7    7.7    7.7
:Missouri River
South Sioux City      8.5    8.5    8.5    8.5    8.5    8.5    8.5

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/fsd for more weather and water
information.

The next outlook will be issued toward the end of March unless
conditions or forecasts change significantly before then.

$$

Gillispie



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