Flood Potential Outlook
Issued by NWS Bismarck, ND

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13
000
FGUS73 KBIS 151843
ESFBIS

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
937 AM CST THU FEB 15 2018


...SPRING 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 mid-February through mid-May.

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...
This issuance of the monthly Probabilistic Hydrologic Outlook
provides an early look at the spring melt season. Due to below
normal snowfall, dry soils, and more available space in native
wetlands, the risk of widespread flooding this spring is well below
normal. While the spring melt season is still too far in the
future to rule out at least some flooding, it would take well above
normal precipitation going forward to bring the risk up to
historically normal levels. At this point, the moisture deficits of
last summer and fall, and this winter, enhance the risk of drought
intensification once we get past the spring melt season. So while it
is still a little early for spring prognostications, the risks seem
to be tilted more in favor of a lack of normal spring runoff than of
widespread flooding.

One of the things not included in the below table is the runoff for
the Missouri and Yellowstone Rivers. While we are about half through
the snow accumulation season for the mountains, it is actually above
normal in the headwaters for both the Yellowstone and Missouri River
Basins. However, this alone does not suggest a troublesome runoff
event as previous high runoff years included significant spring rains
on the plains of Montana and North Dakota.

High water due to ice jams is also not included in the below tables.
However, the lack of a significant snowpack suggests small rivers of
western and central North Dakota will have trouble generating enough
runoff to lift and mobilize the ice. To create ice problems would
require significant, and early, spring rains.

...Current Conditions...
Rivers, lakes, and reservoirs are near to slightly below normal
for this time of the year. Most of North Dakota remains well below
normal for snow cover with near zero water equivalent in the
southernmost tier of counties to a widespread 0.25 - 0.5 inches of
water across most of central and western North Dakota. The heaviest
snowpack is in the upper James River Basin, and that is still below
normal at about an inch of water. Soil moisture levels are also well
below normal across most of the state. Similarly, wetlands tend to
be down from the recent highs of the past several years. Western and
central parts of the state are currently under moderate to severe
drought designations, mostly due to the dry summer and fall.

...Weather Outlook... The near term 6-10 and 8-14 day generally
favor a cooler than normal pattern with near normal precipitation.
This tilt towards cooler than normal temperatures continues through
the one-month outlook with a slight favoring of above normal
precipitation for western North Dakota, and near normal precipitation
for the rest of the state. Looking longer term at the three-month
outlook and we see a slight favoring of below normal temperatures
in the western half of North Dakota with an overall slightly
enhanced chance for above 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:  02/17/2018  - 05/18/2018

                                       :    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   12   <5   <5   <5   <5
:James River
Grace City          12.0   14.0   15.0 :  <5   15   <5    9   <5    7
Lamoure             14.0   16.0   18.0 :  <5    9   <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 :  25   48   <5   <5   <5   <5
:Beaver Creek
Linton              12.0   14.0   16.0 :   5   30   <5    7   <5   <5
:Little Muddy River
Williston           10.0   12.0   14.0 :  <5   49   <5   27   <5   14
: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    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 :  <5   21   <5   <5   <5   <5
:Spring Creek
Zap                 14.0   18.0   20.0 :  <5   24   <5    9   <5    6
:Knife River
Hazen               21.0   24.0   25.0 :  <5   32   <5   18   <5   11
:Heart River
Mandan              17.0   23.0   28.0 :  <5    9   <5   <5   <5   <5
:Apple Creek
Menoken             15.0   16.0   17.0 :  20   54    8   48   <5   28

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: 02/17/2018  - 05/18/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               4.9    4.9    5.0    5.3    5.8    7.8    9.1
:James River
Grace City            4.2    4.3    4.5    4.9    6.1    7.2    8.4
Lamoure               6.7    6.7    6.9    7.2    7.5    8.2    9.4
:Cannonball River
Regent                5.0    5.3    6.1    6.7    7.7    8.8    9.4
:Cedar Creek
Raleigh               1.1    1.8    3.4    4.7    6.2    7.3    8.0
:Cannonball River
Breien                3.0    3.4    5.9    8.0   10.0   12.1   13.6
:Beaver Creek
Linton                4.4    4.6    5.0    5.4    7.1    9.7   11.9
:Little Muddy River
Williston             4.5    4.5    4.5    5.2    6.3    8.2    8.8
:Little Missouri
Marmarth              2.0    2.5    3.4    4.2    5.9    9.6   13.6
:Little Missouri River
Medora                2.6    3.3    4.6    5.6    7.1    9.2   13.9
Watford City          0.1    0.4    1.4    2.1    3.3    5.0    9.3
:Knife River
Manning               6.3    6.3    6.3    7.3    9.1    9.9   10.2
:Spring Creek
Zap                   5.0    5.0    5.3    6.5    9.0   11.0   12.3
:Knife River
Hazen                 1.1    1.1    3.1    6.0   10.4   13.8   15.7
:Heart River
Mandan               -0.1    0.2    1.8    3.0    4.9    6.8    9.4
:Apple Creek
Menoken               5.1    5.3    6.0    7.9   14.5   15.6   16.5

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:  02/17/2018  - 05/18/2018
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem Creek
Pingree               4.9    4.9    4.9    4.9    4.9    4.9    4.9
:James River
Grace City            4.2    4.2    4.2    4.2    4.2    4.2    4.2
Lamoure               6.6    6.6    6.6    6.6    6.6    6.6    6.6
:Cannonball River
Regent                4.4    4.4    4.4    4.4    4.4    4.4    4.4
:Cedar Creek
Raleigh               0.7    0.7    0.7    0.7    0.3    0.3    0.3
:Cannonball River
Breien                2.4    2.4    2.4    2.4    2.4    2.4    2.4
:Beaver Creek
Linton                4.3    4.3    4.3    4.3    4.3    4.2    4.2
:Little Muddy River
Williston             4.5    4.5    4.4    4.4    4.4    4.3    4.3
:Little Missouri
Marmarth              1.0    1.0    1.0    1.0    1.0    1.0    0.9
:Little Missouri River
Medora                1.4    1.4    1.4    1.4    1.4    1.4    1.3
Watford City         -0.6   -0.6   -0.6   -0.6   -0.6   -0.8   -1.0
:Knife River
Manning               6.3    6.3    6.3    6.3    6.3    5.9    5.5
:Spring Creek
Zap                   5.0    5.0    4.9    4.9    4.9    4.9    4.9
:Knife River
Hazen                 1.1    1.1    1.1    1.1    1.0    0.9    0.9
:Heart River
Mandan               -0.5   -0.5   -0.5   -0.5   -0.5   -0.7   -0.8
:Apple Creek
Menoken               4.2    4.2    4.2    4.2    4.2    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.

The next outlook will be issued on March 1st, 2018.

$$

ajs



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.