Flood Potential Outlook
Issued by NWS Bismarck, ND

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FGUS73 KBIS 242118
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NDC001-007-011-015-021-025-029-031-033-037-041-043-045-047-051-
053-055-057-059-065-083-085-087-089-093-103-105-281800-

PROBABILISTIC HYDROLOGIC OUTLOOK
NATIONAL WEATHER SERVICE BISMARCK ND
430 PM CDT FRI APR 24 2015


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

This probability based Spring Flood and Water Resources Outlook is
for the James and Missouri River Basins of western and central North
Dakota, covering the time period of late April through late July.

The following message has four distinct sections. The first provides
text. on the notable highlights of the probabilities found in this
outlook. The second gives the current probabilities based on
existing conditions (CS) and the normal, or historical (HS) risk of
those locations reaching their respective Minor, Moderate, or Major
flood categories. The third section provides the current
probabilities of the river reaching the listed stages. Finally, the
fourth section contains the probability of each site falling to the
specified levels

...FLOOD OUTLOOK OVERVIEW HIGHLIGHTS...
Overall, the threat of flooding for late April through late July
appears near normal to below normal as the potential mode of flooding
has transitioned from the snow melt period through spring rains and into summer
thunderstorms.

...CURRENT CONDITIONS...

Soil moisture levels are generally on the low end of normal to below normal across
the region as dry weather has so far dominated over the typical spring shower season.
In general, all rivers and streams, as of late April are in the low end of normal to
below normal for this time of year.

...WEATHER OUTLOOK...

Climate outlooks from the Climate Prediction Center tend to favor above normal
temperatures through the end of April with a shift towards a greater than normal
chance of precipitation for the last week of April. However, looking at the longer
term 1-month and 3-month outlooks, the region has an equal chance for below normal,
near normal, or above normal temperatures and precipitation. However, as we enter
early summer and the thunderstorm season, precipitation patterns become highly
variable and localized.

...SUMMARY OF HYDROLOGIC CONDITIONS AND RISKS...

As we have exited the spring snow melt season and are in the middle of the spring
showers season, current hydrologic conditions as of late March suggest near normal
chances for flooding at any given point across the Missouri River basin. Again,
while the highly localized and variable precipitation patterns associated with spring
and summer showers and thunderstorms have lower predictability in the longer term
outlooks, these events are incorporated into the probabilities
below.


...LONG-RANGE PROBABILISTIC RIVER OUTLOOK BY FLOOD CATEGORY...

The table below give both the Conditional Simulation (CS) risk of
flooding based on current condtions and the Historical Simulation
(HS) risk of flooding. Risks of reaching Minor, Moderat, and Major
flood categories are presented.



                    JAMES AND MISSOURI RIVER BASINS
                    LONG-RANGE PROBABILISTIC OUTLOOK

        PROBABILITIES FOR MINOR...MODERATE AND MAJOR FLOODING
                    FROM  4/25/2015 TO 7/24/2015

TABLE 1                                  : CURRENT AND HISTORICAL
                                         : CHANCES OF EXCEEDING FLOOD
                                         : CATEGORY IN PERCENT (%)
                         CATEGORICAL     :
                      FLOOD STAGES (FT)  :  MINOR   MODERATE  MAJOR
LOCATION            MINOR    MOD   MAJOR :  CS HS    CS HS    CS HS
--------            ------ ------ ------ : --- ---  --- ---  --- ---
Little Muddy Creek.....
  Williston           10.0   12.0   14.0 :  28  28   17   23  <5   6
Little Missouri River.....
  Marmarth            18.0   23.0   30.0 :  <5   5   <5  <5   <5  <5
  Medora              15.0   18.0   20.0 :   8   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 :  30  20   15   8    7   5
Knife River.....
  Hazen               21.0   24.0   25.0 :  33  17   13   6    5  <5
Heart River.....
  Mandan              17.0   23.0   28.0 :  <5  <5   <5  <5   <5  <5
Apple Creek.....
  Menoken             15.0   16.0   17.0 :  42  53   27  35   12  17
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 :  46  23   <5  <5   <5  <5
Beaver Creek.....
  Linton              12.0   14.0   16.0 :  11  20    7   9   <5  <5
James River.....
  Grace City          12.0   14.0   15.0 :  <5  <5   <5  <5   <5   5
Pipestem Creek.....
  Pingree             11.0   13.0   15.0 :  <5  <5   <5  <5   <5  <5
James River.....
  LaMoure             14.0   16.0   18.0 :  <6   9   <5   6   <5  <5

LEGEND:
    CS  =  Conditional Simulation
    HS  =  Historical Simulation
    FT  =  Feet above gage zero datum



...LONG-RANGE PROBABILISTIC OUTLOOK BY RIVER STAGE...
The table below gives the current 95 through 5 percent probabilities
for exceeding river stages at the listed Forecast Points during the
valid period of this outlook.

For example: During the valid time period, there is a 50% chance for
             the Little Muddy Creek near Williston to rise above a
             stage of 6.2 ft and only a 10% chance it will rise
             above a stage of 12.5 ft.


                    JAMES AND MISSOURI RIVER BASINS
                    LONG-RANGE PROBABILISTIC OUTLOOK
           PROBABILITIES FOR EXCEEDING LISTED RIVER STAGES
                     FROM  4/25/2015 TO 7/24/2015

TABLE 2

LOCATION               95%    90%    75%    50%    25%    10%    05%
--------             ------ ------ ------ ------ ------ ------ ------
Little Muddy Creek.....
  Williston            4.6    4.6    4.6    6.2   10.9   12.5   13.4
Little Missouri River.....
  Marmarth             1.4    1.4    1.4    3.3    9.0   12.4   13.9
  Medora               2.0    2.0    2.6    5.8   10.0   13.4   15.1
  Watford City        -0.1   -0.1    1.1    3.8    6.8    9.2   11.1
Knife River.....
  Manning              6.4    6.4    7.0    9.2   10.6   14.9   16.0
SPRING CREEK.....
  Zap                  5.4    5.4    6.4   12.2   15.1   19.3   20.8
Knife River.....
  Hazen                2.4    2.9    7.6   18.3   22.6   24.4   25.1
Heart River.....
  Mandan               0.6    1.1    3.4    5.9    8.2    9.2   13.5
Apple Creek.....
  Menoken              6.8    6.8    6.8   12.7   16.3   17.3   19.0
Cannonball River.....
  Regent               5.4    5.4    6.7    7.7   11.0   14.0   14.8
Cedar Creek.....
  Raleigh              2.8    3.4    5.1    6.0    7.9    8.7   10.8
Cannonball River.....
  Breien               5.5    5.8    8.1    9.8   11.8   13.8   16.7
Beaver Creek.....
  Linton               4.6    4.7    5.1    6.7   10.5   12.4   15.5
James River.....
  Grace City           4.2    4.2    4.2    4.4    5.7    7.0   10.1
Pipestem Creek.....
  Pingree              5.0    5.0    5.0    5.0    5.7    7.0    8.8
James River.....
  LaMoure              7.3    7.3    7.3    7.3    7.5   10.6   15.3


...TABLE 3--NONEXCEEDANCE PROBABILITIES...

The table below represents the likelihood of the river remaining
above the listed stages. For example, at the Little Missouri River
near Medora, there is a 95% chance the river will remain above
2.0 ft and only a 5% chance it will fall below 1.6 ft.


                    JAMES AND MISSOURI RIVER BASINS
                    LONG-RANGE PROBABILISTIC OUTLOOK
                  CHANCE OF FALLING BELOW STAGES (FT)
                         AT SPECIFIC LOCATIONS
                      FROM  4/25/2015 TO 7/24/2015

LOCATION              95%    90%    75%    50%    25%    10%    05%
--------            ------ ------ ------ ------ ------ ------ ------
Little Muddy Creek.....
  Williston           4.6/    4.5    4.4    4.3    4.3    4.3    4.3

Little Missouri River.....
  Marmarth            1.3    1.3    1.3    1.2    1.1    1.1    1.1
  Medora              2.0    1.9    1.8    1.7    1.7    1.6    1.6
  Watford City       -0.4   -0.4   -0.6   -1.1   -1.1   -1.1   -1.1

Knife River.....
  Manning             6.3    6.3    6.3    6.3    5.5    5.5    5.5

SPRING CREEK.....
  Zap                 5.1    5.1    5.0    5.0    5.0    5.0    5.0

Knife River.....
  Hazen               1.7    1.6    1.5    1.5    1.4    1.4    1.4

Heart River.....
  Mandan              -0.7   -1.1   -1.6   -1.6   -1.6   -1.6   -1.6

Apple Creek.....
  Menoken             5.5    5.4    5.3    5.3    5.2    5.2    5.2

Cannonball River.....
  Regent              5.2    5.2    5.2    5.2    5.2    5.2    5.2

Cedar Creek.....
  Raleigh             1.1    1.1    1.1    1.1    1.1    1.1    1.1

Cannonball River.....
  Breien              2.3    2.3    2.2    2.1    2.1    2.0    2.0

Beaver Creek.....
  Linton              4.5    4.4    4.3    4.2    4.2    4.2    4.2

James River.....
  Grace City          4.2    4.2    4.2    4.2    4.2    4.2    4.2

Pipestem Creek.....
  Pingree             4.9    4.9    4.8    4.8    4.8    4.8    4.8

James River.....
  LaMoure             7.0    7.0    6.9    6.7    6.7    6.6    6.6


...THE OUTLOOK PRODUCTION PROCESS...
This long-range probabilistic outlook is based on a series of peak
river levels, or crests, takeing from the forecast hydrograph results
of the NWS Ensemble Streamflow Prediction Model (ESP). The model
is run for multiple scenarios starting at current river, snow, and
soil conditions using 25 or more years of past precipitation and
temperature conditions in the historical record. These crests can
then be ranked from lowest to highest, and assigned an exceedance
probability. For example, using a series of 50 years, the lowest
ranked cerst has 49 crests above it. As 95% of the crests are above
this value, it is assigned a 95% Probability Of Exceedance (POE).

The probabilities can be used for risk management by comparing this
year`s current temperature and preciptitation outlooks with those
of past year used in the hydrologic outlook. They can also be used
as an indication of the range of crests expected during the valid
period of the outlook.

By providing a range of peak river level probabilities, the NWS is
contributing to the region`s Impact-Based Decision Support Services
that help with long-range flood planning and response readiness.
This outlook is a part of the National Weather Service`s Advanced
Hydrologic Prediction Services (AHPS).

This outlook was produced using precipitation and temperatures for
the years 1979 through 2003.


... ADDITIONAL INFORMATION SOURCES...

The AHPS long-range probabilistic hydrologic outlooks are issued
near the end of each month. However, the Spring Flood and Water
Resources Outlooks are issued several times in advance of the
critical spring melt season starting in mid-lake February and
going through Marck...or until the melt season is in full effect.

This outlook is also available in graphic form on the NWS website
along with explanations that help in interpreting them. They are
available at:

        WWW.WEATHER.GOV/BISMARCK OR WEATHER.GOV/BIS

Click on the "Rivers and Lakes" tab above the map, or the AHPS
link in the blue banner on the left side of the screen.

Current river conditions for all forecast points are available
on our website, as well as forecast when the location is near or
above flood stage.

If you have any questions, contact the NWS at 701-250-4495.

$$



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