National Weather Service United States Department of Commerce
PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
1210 PM CDT WED MAR 27 2019

...SPRING FLOOD AND WATER RESOURCES OUTLOOK...

This update to the Spring Flood and Water Resources Outlook is for
the Missouri and James River basins of North Dakota and covers the
period from late March through the end of June.

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...
Flood outlooks issued during the spring melt season, like this
one, can be difficult to interpret as sites that are currently
under a flood warning inflate the probabilities, those that are
not yet experiencing high water tend to be more representative of
the risk. Also, those that recently experienced high water tend
to have a very wet soil profile and this also leads to a higher
risk, even as that risk is very front loaded in the effective
time period.

In the northwest corner of North Dakota the Little Muddy River
has already experienced its spring flood, and as soils dry out,
the risk will essentially go to normal very quickly. The same
can be said for other small streams in the area, such as the
White Earth River, Little Knife River, and Deep Creek in
McLean County.

The Knife River and Spring Creek are done with their spring melt
season and are entering a period where they will quickly go
to a normal risk of flooding. This is due to the fact that there
is very little snow left to melt.

The Heart River is nearing the end of its spring snowmelt season.
If it weren`t for the icejam in the Mandan area, it would have
only a slightly elevated risk of more flooding. That long-term
risk is largely related to the discharge of stored flood waters
from Heart Butte Dam, which will keep the Heart above normal for
the next few weeks.

The Cannonball and Cedar Creek basin still have flood warnings
in effect, and there is more snow to melt. Minor to moderate
flooding will continue for the next several days before the risk
of higher water begins to fall around the first of April.

East of the Missouri River and south of I-94, Apple Creek near
Menoken has a very robust snowpack that has just begun melting.
Beaver Creek near Linton has a lot of snow left to melt.
Significant potential for moderate flooding is realistic, and
the added risk of ice problems suggests the risk of major flooding
cannot be ruled out.

Farther to the east and in the James River Basin, the headwaters
area down to Jamestown and Pipestem dams are now at normal to
somewhat above normal risk of at least some Minor flooding. This
risk increases downstream of Jamestown where a heavier snowpack
sitting on wet, frozen soils is expected to start developing runoff
over the coming days. The risk of overland flooding and high water
on the smaller creeks and streams across the area should be
considered well above normal. Were it not for the protection
afforded by Jamestown and Pipestem dams, flood risk along the
James south of Jamestown would be considerably higher. Weather
forecasts suggest the spring melt should be in full swing during
the first few days of April.

The Prairie Pothole region, including at least parts of Sheridan,
Wells, Kidder, Stutsman, Logan, McIntosh and Dickey counties
continue to have enough water in the snowpack to suggest overland
flooding will be a concern by this coming weekend, and through the
first week of April.

And lastly, the Missouri River itself. New this spring is the
inclusion of the Missouri River near Williston in the extended
streamflow predictive modeling. The Yellowstone and Missouri
Rivers west of Williston are currently in a significant flood
season. Water levels, mostly exacerbated by icejams, have reached
major flood stage and are expected to continue an erratic up and
down pattern over the last few days of March as ice exits the
area. Once this ice related high water exits, the Missouri River
near Williston will find itself in a near normal risk of extended
flooding due to snowmelt in the rockies, where there is a near
normal snowpack.

Importantly, the probabilities shown in Tables 1 and 2 do not
include the risks associated with icejam related flooding. Icejams
defy mathematical predictions, but are known to increase during
early and rapid spring runoffs where the ice becomes mobilized, only
to get stuck at some downstream constriction such as bridges and
bends in the river. One of the areas that may have a higher than
normal risk of icejams this spring is the Missouri River below
Garrison Dam. The exceptionally cold February and early March have
kept ice cover on the Missouri through March. In most years, much
of the ice had already left the Missouri River by early March. This
is not the case this year.

...Current Conditions...
Flood warnings remain in place at several forecast points across
western and central North Dakota. This pattern of one watershed
becoming active at a time is going to most likely change as more
widespread melting takes place over a larger part of North Dakota.
So far there has been near zero added precipitation on top of the
melting snowpack, and that trend is expected to continue for the
next week.

...Weather Outlook...
Below normal temperatures and near normal to slightly above normal
precipitation is favored in the 8-14 day outlook. Longer term,
the one-month and three-month outlooks slightly favor below
normal temperatures and hold the area in an equal chance designation
for above normal, near normal, or 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:  03/31/2019  - 06/29/2019

                                       :    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
--------           -----  -----  ----- : ---  ---  ---  ---  ---  ---
:Pipestem Creek
Pingree             11.0   13.0   15.0 :   9   12   <5   <5   <5   <5
:James River
Grace City          12.0   14.0   15.0 :  38   16   11    9    9    7
Lamoure             14.0   16.0   18.0 :  46   10   13    6    5   <5
:Missouri River
Williston           22.0   24.0   26.0 :  22   27    6   17    5    6
:Cannonball River
Regent              22.0   24.0   26.0 :  <5   <5   <5   <5   <5   <5
:Cedar Creek
Raleigh             12.0   14.0   16.0 : >98   <5  >98   <5   <5   <5
:Cannonball River
Breien              10.0   20.0   23.0 : >98   34  >98   <5   <5   <5
:Beaver Creek
Linton              12.0   14.0   16.0 : >98   29   34   12   11    8
:Little Muddy River
Williston           10.0   12.0   14.0 :  36   56    8   19   <5    9
:Little Missouri
Marmarth            18.0   23.0   30.0 :   6    5   <5   <5   <5   <5
:Little Missouri River
Medora              15.0   18.0   20.0 : >98   15    9    7    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    8   <5   <5   <5   <5
:Spring Creek
Zap                 14.0   18.0   20.0 :  15   10   <5   <5   <5   <5
:Knife River
Hazen               21.0   24.0   25.0 :   6   17   <5   11   <5    9
:Heart River
Mandan              17.0   23.0   28.0 :  <5   12   <5   <5   <5   <5
:Apple Creek
Menoken             15.0   16.0   17.0 :  49   42   33   34    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: 03/31/2019  - 06/29/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               9.2    9.2    9.3    9.5    9.9   10.6   11.6
:James River
Grace City           11.2   11.2   11.3   11.7   12.6   14.5   16.1
Lamoure              12.6   12.6   13.4   13.8   14.7   16.5   17.7
:Missouri River
Williston            20.2   20.2   20.2   20.6   21.8   23.2   25.3
:Cannonball River
Regent               11.4   11.4   11.4   11.6   12.6   16.2   19.0
:Cedar Creek
Raleigh              14.9   14.9   14.9   14.9   14.9   15.2   15.7
:Cannonball River
Breien               21.0   21.0   21.0   21.0   21.0   21.0   21.0
:Beaver Creek
Linton               13.0   13.0   13.3   13.8   14.5   16.1   16.9
:Little Muddy River
Williston             5.3    5.4    6.6    8.9   10.9   11.9   12.5
:Little Missouri
Marmarth             12.3   12.3   12.3   12.3   14.4   16.3   19.3
:Little Missouri River
Medora               16.0   16.0   16.0   16.0   16.0   17.9   20.1
Watford City         11.5   11.5   11.5   11.5   11.6   13.3   15.8
:Knife River
Manning               7.4    7.5    8.2   10.2   12.2   15.2   15.8
:Spring Creek
Zap                   6.2    6.2    6.9    9.4   12.1   14.5   16.0
:Knife River
Hazen                 6.8    6.8    7.9   11.0   15.7   18.9   21.9
:Heart River
Mandan               10.0   10.0   10.0   10.0   11.4   14.9   16.4
:Apple Creek
Menoken              11.0   11.0   11.9   14.7   16.1   16.6   17.6

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:  03/31/2019  - 06/29/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               5.2    5.1    5.1    5.0    5.0    5.0    5.0
:James River
Grace City            5.0    4.9    4.8    4.7    4.7    4.7    4.7
Lamoure               7.1    7.1    7.1    7.1    7.1    7.1    7.1
:Cannonball River
Regent                5.3    5.2    5.2    5.2    5.2    5.2    5.2
:Cedar Creek
Raleigh               1.7    1.6    1.4    1.4    1.3    1.3    1.3
:Cannonball River
Breien                3.6    3.5    3.3    3.2    3.2    3.2    3.1
:Beaver Creek
Linton                4.9    4.8    4.6    4.5    4.4    4.4    4.4
:Little Muddy River
Williston             4.8    4.7    4.7    4.6    4.6    4.6    4.5
:Little Missouri
Marmarth              1.8    1.7    1.6    1.4    1.3    1.3    1.3
:Little Missouri River
Medora                2.7    2.4    2.3    2.1    2.1    2.1    2.0
Watford City          0.4    0.1   -0.0   -0.1   -0.2   -0.2   -0.3
:Knife River
Manning               6.5    6.5    6.4    6.4    6.4    6.4    5.6
:Spring Creek
Zap                   4.8    4.8    4.8    4.8    4.8    4.8    4.8
:Knife River
Hazen                 1.3    1.1    1.0    0.9    0.6    0.6    0.5
:Heart River
Mandan                0.7    0.2   -0.0   -0.3   -0.5   -0.5   -0.6
:Apple Creek
Menoken               4.1    4.1    4.1    4.1    4.1    4.1    4.0

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.