Flood Potential Outlook
Issued by NWS Bismarck, ND

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000
FGUS73 KBIS 241618
ESFBIS

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
1117 AM CDT THU MAY 24 2018


...FLOOD AND WATER RESOURCES OUTLOOK...

This probabilistic Flood and Water Resources outlook is for
the Missouri and James River basins of North Dakota and covers
the period of late May through late July.

The following message has four sections. The first provides some
text on the highlights of this outlook and conditions affecting
the local hydrology. The second section gives the current and
normal/historical risks of flooding as determined by the Ensemble
Streamflow Forecast model of the National Weather Service. The
third section gives the current probabilities for reaching flood
stage at the listed forecast locations. And finally, the fourth
section covers the risk of the river sites falling below the
listed stages.

...Flood Outlook Highlights...
Most small rivers and streams are near normal to slightly below
normal for this time of year. Low soil moisture values remain a
concern for agriculture, and will continue to reduce expected
runoff from normal rainfall.

One of the items of interest not included in the tables below is the
runoff for the Missouri and Yellowstone Rivers. Mountain snowpack in
the headwaters of both the Yellowstone and Missouri River basins
remains above normal. While this suggests a very robust runoff along
the Yellowstone and Missouri rivers in western North Dakota, it is
not enough to create concerns downstream of Garrison Dam.

...Current Conditions...
The vast majority of rivers, streams, and reservoirs are well within
their normal range for this time of year. Soil moisture tends to be
below normal and is expected to have the potential to lessen expected
runoff from a given rain event.

...Weather Outlook...
The near term 6-10 and 8-14 day outlooks depict a well above
normal chance for warmer than normal temperatures with above normal
precipitation. The one-month outlook for June has a greater than
normal probability for above normal temperatures and an equal chance
probability for above normal, near normal, and below 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.


                 Chance of Exceeding Stages at Specific Locations
                     Valid Period:  05/26/2018  - 08/24/2018

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Pipestem Creek
Pingree             11.0   13.0   15.0 :  <5   <5   <5   <5   <5   <5
:James River
Grace City          12.0   14.0   15.0 :   5   <5   <5   <5   <5   <5
Lamoure             14.0   16.0   18.0 :   5   <5   <5   <5   <5   <5
:Cannonball River
Regent              22.0   24.0   26.0 :  <5   <5   <5   <5   <5   <5
:Cedar Creek
Raleigh             12.0   14.0   16.0 :  <5   <5   <5   <5   <5   <5
:Cannonball River
Breien              10.0   20.0   23.0 :   9   17   <5   <5   <5   <5
:Beaver Creek
Linton              12.0   14.0   16.0 :  14   20    7    9    6    7
:Little Muddy River
Williston           10.0   12.0   14.0 :  28   26   13   23   <5    6
:Little Missouri
Marmarth            18.0   23.0   30.0 :  <5   <5   <5   <5   <5   <5
:Little Missouri River
Medora              15.0   18.0   20.0 :  <5   <5   <5   <5   <5   <5
Watford City        20.0   24.0   30.0 :  <5   <5   <5   <5   <5   <5
:Knife River
Manning             15.0   17.0   20.0 :  11   12   <5   <5   <5   <5
:Spring Creek
Zap                 14.0   18.0   20.0 :   5   11   <5    8   <5   <5
:Knife River
Hazen               21.0   24.0   25.0 :  <5   10   <5    5   <5   <5
:Heart River
Mandan              17.0   23.0   28.0 :   6    6   <5   <5   <5   <5
:Apple Creek
Menoken             15.0   16.0   17.0 :  23   39   19   30    8   21

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: 05/26/2018  - 08/24/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               5.3    5.3    5.3    5.3    6.7    9.2    9.5
:James River
Grace City            5.4    5.4    5.4    5.4    6.6    9.7   11.3
Lamoure               8.2    8.2    8.2    8.2    8.6   10.2   13.4
:Cannonball River
Regent                5.4    5.4    5.9    7.2    7.9   10.4   12.8
:Cedar Creek
Raleigh               1.2    1.5    2.4    4.2    5.5    6.6    7.2
:Cannonball River
Breien                3.1    3.6    5.6    7.2    8.2   10.0   11.4
:Beaver Creek
Linton                5.0    5.0    5.2    6.4    9.9   12.1   17.5
:Little Muddy River
Williston             4.7    4.7    4.7    6.1   10.5   12.6   13.7
:Little Missouri
Marmarth              2.1    2.1    2.1    2.3    4.2    7.3   11.5
:Little Missouri River
Medora                2.7    2.7    2.7    3.3    5.5    8.3   12.3
Watford City          0.5    0.5    0.6    1.4    3.5    4.7    7.9
:Knife River
Manning               6.4    6.4    6.5    7.7   11.3   15.4   16.3
:Spring Creek
Zap                   4.8    4.9    5.2    5.7    8.6   11.4   14.4
:Knife River
Hazen                 0.7    0.8    2.1    4.8   11.1   13.5   15.1
:Heart River
Mandan                0.1    0.3    0.4    2.8    4.2    8.2   18.8
:Apple Creek
Menoken               5.9    5.9    5.9    6.7   12.5   16.9   18.7

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:  05/26/2018  - 08/24/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               5.2    5.2    5.2    5.2    5.2    5.2    5.2
:James River
Grace City            5.1    5.1    5.1    5.1    5.1    5.1    5.1
Lamoure               7.8    7.8    7.7    7.5    7.4    7.4    7.4
:Cannonball River
Regent                5.3    5.3    5.3    5.3    5.3    5.3    5.3
:Cedar Creek
Raleigh               0.9    0.7    0.3    0.3    0.3    0.3    0.3
:Cannonball River
Breien                2.7    2.6    2.5    2.4    2.4    2.4    2.4
:Beaver Creek
Linton                4.6    4.6    4.5    4.3    4.3    4.3    4.3
:Little Muddy River
Williston             4.6    4.4    4.3    4.1    4.1    4.1    4.1
:Little Missouri
Marmarth              0.9    0.9    0.9    0.9    0.9    0.9    0.9
:Little Missouri River
Medora                1.3    1.3    1.3    1.3    1.3    1.3    1.3
Watford City          0.0   -0.0   -0.1   -0.1   -0.1   -0.1   -0.1
:Knife River
Manning               6.3    6.3    5.5    5.5    5.5    5.5    5.5
:Spring Creek
Zap                   4.8    4.8    4.8    4.8    4.8    4.8    4.8
:Knife River
Hazen                 0.3    0.3    0.3    0.3    0.3    0.3    0.3
:Heart River
Mandan               -0.3   -0.4   -0.5   -0.6   -0.6   -0.6   -0.6
:Apple Creek
Menoken               5.1    5.0    4.8    4.6    4.5    4.4    4.3

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/bis for more weather and water
information.

The next outlook will be issued on June 28th.

$$

ajs


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