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000
FGUS73 KBIS 151424
ESFBIS
NDC001-007-011-015-021-025-029-031-033-037-041-043-045-047-051-053-
055-057-059-061-065-083-085-087-089-093-103-105-171400-

Probabilistic Hydrologic Outlook
National Weather Service Bismarck ND
824 AM CST Thu Feb 15 2024

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

This Spring Flood and Water Resources Outlook is for the James and
Missouri basins of North Dakota, covering the period of 17 February
through 17 May, 2024. This is the first in a three-part Spring Flood
and Water Resources Outlook series.

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 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...
At this point, the overall flood risk across the James and Missouri
basins of North Dakota is below normal to well below normal for the
upcoming spring. This is largely due to the well below normal Snow-
Water Equivalent (SWE) in place at over the halfway point in the
snow accumulation season. The lone consideration for enhanced runoff
this spring is an unusually wet and frozen surface of the ground
that extends from eastern Sioux and Morton counties east and north
including the majority of the James River basin. This wet and now
well frozen ground is the direct result of a freezing rain event
that placed up to an inch of frozen rain across parts of the
southern James River basin. Not long after the freezing rain event,
an unusually warm period melted off much of the SWE across the
Missouri and James River basins of North Dakota, leading to an even
broader wetting of the ground surface.

The current risk of flooding is generally tied to the risk of an
early spring rain falling on the frozen wet soils. This would lead
to significantly more runoff than normally expected for a given rain
event. Once the soils warm up and allow infiltration of rain and
meltwater, the actual flood risks will fall even farther, all other
contributors being equal.

In reality, increased drought designations and overall worsening of
drought conditions are likely to be more of a concern going forward
since little hope for a change in current precipitation trends are
found in the current climate outlooks.

...Missouri and Yellowstone Rivers...
Both the Missouri and Yellowstone rivers are at normal water levels
for this time of year despite having recently experienced modest
runoff in western North Dakota and the plains of Montana.

The overall snowpack on the plains and headwaters area of Montana is
well behind normal for this time of year, and is in fact the lowest
SWE observed in the past 30 years. However, the relatively small
runoff event in February along the Missouri and Yellowstone rives in
Montana has greatly lessened the risk of ice related problems
upstream of Williston on the Missouri and Yellowstone rivers as
some stretches of each river are now widely ice free.

Even under the relatively low probability of above normal spring
runoff above Garrison Dam, the reservoirs of Fort Peck and Sakakawea
have above normal storage available for any excess runoff.

Below Garrison Dam, the Missouri River remains ice covered from
roughly Wilton on down through the Bismarck/Mandan area. Near term
temperatures going into late February suggest the river will
continue to slowly lose ice, but at this point it is not likely to
be ice free in the Bismarck/Mandan until sometime in the third full
week, or maybe even the last week of February.

...Snowpack Conditions...
Overall snowpack across the Missouri and James River basins of North
Dakota is well below normal for this time of year with generally a
trace to well under an inch of Snow-Water Equivalent (SWE) on the
ground.

...Current Drought Conditions... A steady, but slow expansion of D0
(Unusually Dry) drought is likely to continue across much of the
Missouri and James River basin in response to the growing snow
deficit. However, actual impacts are not yet being felt as the
region is still in the winter season. A continuation of the dry
pattern in place will increase drought concerns going into spring.

...Reservoirs and Natural Wetlands...
With only a few exceptions all man-made reservoirs, livestock dams,
and natural wetlands are at, or below, their normal water levels for
this time of year.

...Soil Conditions... Soils across the Missouri and James basins are
generally near normal going down to near 40 inches (100 cm), but the
ground surface is much wetter than normal due to early winter rain
and melting snow. This has created a wet and frozen ground surface
that is near impermeable to infiltration of future rain or
meltwater. The importance of this hard, frozen ground cannot be
overstated. Any early spring rain that falls before this soil thaws
will create an unusually high amount of runoff for a given rainfall
total. It is expected that these soils will largely remain
impermeable until some time in early March.

...Weather Outlook... The Climate Prediction Center 6-10 day
outlooks favor warmer and drier than normal, while the 8-14 day
outlooks hold the favoring for warmer than normal, and precipitation
goes to the equal chances category for above normal, near normal, or
below normal precipitation. The outlooks for the entire month of
February is for an above normal temperature outcome with
precipitation being in the equal chances category for above normal,
near normal, or below normal precipitation. The longer term three-
month outlook for February, March and April continues the favoring
for above normal temperatures and equal chances designation for
precipitation. In general, this somewhat suggests there`s an overall
favoring for an earlier than normal spring melt season, but does not
rule out a late spring snowstorm.

...Ice Conditions...
All small lakes and wetlands are covered with ice of highly
variable, but somewhat less than normal thickness for this time of
year. Recent warm weather has also been softening ice on the small
lakes, especially near the shoreline. Some small rivers in western
North Dakota lost much of their ice during a warm spell that
included a modest amount of runoff. This suggests that the risk of
ice jams is likely below normal on many of the western North Dakota
streams.

...Spring Flood Outlook Release Dates...
The NWS has set the release dates for the Spring Flood and Water
Resources Outlook series as follows:

First issuance:  February 15, 2024
First update:    February 29, 2024
Final update:    March 14, 2024

After the official Spring Flood and Water Resource Outlook series,
the NWS will return to its routine, monthly issuance of Flood and
Water Resource Outlooks on March 28, 2024 unless the spring melt is
already in full swing.


In Table 1 below, the current (CS) and historical (HS) or normal
probabilities of exceeding minor...moderate...and major flood stage
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 greater 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.

...Table 1--Probabilities for minor...moderate and major flooding...
                     Valid Period: 02/17/2024  - 05/17/2024


                                       :    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
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    8
LaMoure             14.0   16.0   18.0 :  10   17   <5    8   <5   <5
:Missouri River
Williston           22.0   24.0   26.0 :  <5   20   <5    8   <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    9   <5    5   <5   <5
:Cannonball River
Breien              10.0   20.0   23.0 :  12   55   <5   <5   <5   <5
:Beaver Creek
Linton              12.0   14.0   16.0 :  <5   42   <5   28   <5   13
:Little Muddy River
Williston           10.0   12.0   14.0 :   8   60   <5   32   <5   10
:Little Missouri River
Marmarth            18.0   23.0   30.0 :  <5   <5   <5   <5   <5   <5
Medora              15.0   18.0   20.0 :  <5   15   <5    8   <5   <5
Watford City        20.0   24.0   30.0 :  <5   13   <5   <5   <5   <5
:Knife River
Manning             15.0   17.0   20.0 :  <5   20   <5   <5   <5   <5
:Spring Creek
Zap                 14.0   18.0   20.0 :   8   22   <5   14   <5    8
:Knife River
Hazen               21.0   24.0   25.0 :  11   40    7   25    5   20
:Heart River
Mandan              27.0   33.0   38.0 :   7   19   <5   <5   <5   <5
:Apple Creek
Menoken             15.0   16.0   17.0 :  37   55   17   52    8   31

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: 02/17/2024  - 05/17/2024

Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem
Pingree               5.0    5.0    5.0    5.5    6.3    9.2   10.4
:James River
Grace City            4.0    4.0    4.1    4.4    5.9    6.3    9.8
LaMoure               7.3    7.3    7.3    8.2    9.6   13.9   15.5
:Missouri River
Williston            16.3   16.5   17.0   17.8   18.6   19.3   20.3
:Cannonball River
Regent                5.2    5.9    6.3    6.9    7.8    9.0    9.6
:Cedar Creek
Raleigh               1.0    1.4    2.8    3.4    4.8    5.4    5.5
:Cannonball River
Breien                3.9    4.2    5.3    6.3    8.7   10.6   11.5
:Beaver Creek
Linton                4.4    4.6    4.9    5.7    6.7    9.4   11.2
:Little Muddy River
Williston             4.9    5.1    5.3    5.9    7.4    9.5   11.2
:Little Missouri River
Marmarth              1.3    1.3    1.3    2.0    3.0    5.3    6.4
Medora                1.5    1.5    1.6    2.5    3.7    6.0    7.0
Watford City          8.0    8.0    8.0    8.4    9.5   11.8   12.9
:Knife River
Manning               6.3    6.3    6.3    7.3    8.6   13.0   14.2
:Spring Creek
Zap                   4.7    5.1    5.7    6.7    8.3   11.2   17.5
:Knife River
Hazen                 2.0    4.2    6.6    9.7   15.4   22.6   25.1
:Heart River
Mandan               11.4   12.7   14.4   16.5   20.5   24.3   27.5
:Apple Creek
Menoken               5.0    5.4    7.0   12.0   15.4   16.7   17.5

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: 02/17/2024  - 05/17/2024

LOCATION              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem
Pingree               5.0    5.0    5.0    4.9    4.9    4.9    4.9
:James River
Grace City            4.0    4.0    4.0    4.0    4.0    4.0    4.0
LaMoure               7.1    7.0    7.0    7.0    7.0    7.0    7.0
:Missouri River
:Cannonball River
Regent                5.0    5.0    5.0    5.0    5.0    5.0    5.0
:Cedar Creek
Raleigh               0.5    0.5    0.4    0.3    0.3    0.3    0.3
:Cannonball River
Breien                2.3    2.3    2.2    2.2    2.2    2.2    2.1
:Beaver Creek
Linton                4.3    4.3    4.2    4.2    4.2    4.2    4.2
:Little Muddy River
Williston             4.6    4.6    4.6    4.6    4.6    4.5    4.5
:Little Missouri River
Marmarth              1.3    1.3    1.3    1.3    1.2    1.2    1.2
Medora                1.4    1.4    1.4    1.4    1.4    1.4    1.4
Watford City          7.1    7.1    7.1    7.0    7.0    6.9    6.9
:Knife River
Manning               6.1    6.1    6.1    6.0    6.0    5.9    5.9
:Spring Creek
Zap                   4.6    4.6    4.6    4.6    4.6    4.6    4.5
:Knife River
Hazen                 0.6    0.6    0.6    0.6    0.6    0.5    0.4
:Heart River
Mandan                9.4    9.4    9.4    9.4    9.2    9.0    9.0
:Apple Creek
Menoken               4.0    4.0    3.9    3.9    3.9    3.7    3.6

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 February 29th, 2024.


$$

Schlag