Flood Potential Outlook
Issued by NWS Bismarck, ND

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FGUS73 KBIS 261539
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PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
1038 AM CDT THU APR 26 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 April 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...
Little to no snow remains across the James and Missouri River
basins of North Dakota. In general, the area lost its snowpack
in an orderly fashion with little flooding and the region`s risk
going forward is near normal to below normal for flooding.

The one area not covered in the below probability tables with a
greater than normal risk of high water is the Yellowstone and
Missouri Rivers west of Williston. The mountain snowpack remains
robust and will most likely cause at least some minor flooding
along the Yellowstone and Missouri Rivers from the Montana border
over into the Williston area.

...Current Conditions...
Rivers, lakes, and reservoirs are all faring well after a fairly
orderly spring melt season. Soil moisture levels are still below
normal, especially at depth, and this creates some concerns for
the upcoming growing season. However, this spring seems to have
done well with partitioning the available snowmelt between runoff
and infiltration into the ground.

...Weather Outlook...
The near term 6-10 and 8-14 day outlooks depict a below to near
normal temperature pattern with a near normal to below normal
precipitation outcome. Looking out at the one-month outlook, the
area is slightly favored for a below normal temperature outcome
with again a slight favoring for an above normal precipitation
pattern. The longer term three-month outlook shows the region with
an equal chance for above normal, near normal, and below normal
temperatures and 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:  04/28/2018  - 07/27/2018

                                       :    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 :  13   20   <5   <5   <5   <5
:Beaver Creek
Linton              12.0   14.0   16.0 :   8   20    7    9    6    7
:Little Muddy River
Williston           10.0   12.0   14.0 :  27   27   18   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 :  10    7   <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 :  10   12   <5   <5   <5   <5
:Spring Creek
Zap                 14.0   18.0   20.0 :   5   20   <5    8   <5   <5
:Knife River
Hazen               21.0   24.0   25.0 :  <5   17   <5    6   <5   <5
:Heart River
Mandan              17.0   23.0   28.0 :   5    7   <5   <5   <5   <5
:Apple Creek
Menoken             15.0   16.0   17.0 :  26   49   23   39    8   17

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: 04/28/2018  - 07/27/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               6.5    6.5    6.5    6.5    7.3    8.6   10.5
:James River
Grace City            5.5    5.5    5.5    5.5    7.0    8.9   10.9
Lamoure               8.8    8.8    8.8    8.8    8.8   10.8   13.3
:Cannonball River
Regent                5.1    5.1    6.1    6.7    8.3   10.0   12.1
:Cedar Creek
Raleigh               1.4    2.3    3.4    4.5    5.6    6.3    6.5
:Cannonball River
Breien                3.4    4.6    6.5    7.1    8.7   10.4   10.8
:Beaver Creek
Linton                5.1    5.1    5.2    7.2   10.2   11.8   17.5
:Little Muddy River
Williston             6.4    6.4    6.4    6.4   10.6   12.6   13.5
:Little Missouri
Marmarth              5.4    5.4    5.4    5.4    5.9   14.2   16.7
:Little Missouri River
Medora                6.5    6.5    6.5    6.5    6.7   14.8   17.7
Watford City          3.2    3.2    3.2    3.2    3.6   10.2   13.0
:Knife River
Manning               7.3    7.3    7.5    8.8   11.0   14.8   16.0
:Spring Creek
Zap                   4.9    4.9    5.3    8.6    9.9   11.9   14.3
:Knife River
Hazen                 1.6    1.7    4.1    9.9   11.8   14.4   14.6
:Heart River
Mandan                0.6    0.6    1.8    3.6    6.8    7.2   17.8
:Apple Creek
Menoken               5.5    5.5    5.5    8.7   15.2   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:  04/28/2018  - 07/27/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               5.9    5.9    5.9    5.8    5.8    5.8    5.8
:James River
Grace City            4.5    4.4    4.3    4.2    4.2    4.2    4.2
Lamoure               8.0    8.0    7.8    7.8    7.8    7.8    7.8
:Cannonball River
Regent                4.7    4.6    4.6    4.6    4.5    4.5    4.5
:Cedar Creek
Raleigh               0.7    0.7    0.7    0.5    0.3    0.3    0.3
:Cannonball River
Breien                2.6    2.6    2.5    2.5    2.4    2.4    2.4
:Beaver Creek
Linton                4.7    4.6    4.5    4.4    4.4    4.3    4.3
:Little Muddy River
Williston             4.9    4.9    4.8    4.8    4.8    4.8    4.8
:Little Missouri
Marmarth              1.6    1.5    1.4    1.3    1.3    1.3    1.3
:Little Missouri River
Medora                1.3    1.3    1.3    1.3    1.3    1.3    1.3
Watford City         -0.1   -0.1   -0.2   -0.3   -0.3   -0.4   -0.4
:Knife River
Manning               6.4    6.4    6.3    6.3    6.3    6.3    6.3
:Spring Creek
Zap                   4.8    4.8    4.8    4.8    4.8    4.8    4.8
:Knife River
Hazen                 1.1    1.0    1.0    0.9    0.8    0.8    0.7
:Heart River
Mandan               -0.1   -0.3   -0.4   -0.5   -0.6   -0.7   -0.7
:Apple Creek
Menoken               5.2    5.1    5.0    4.8    4.5    4.3    4.2

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 May 24th.

$$

ajs



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