Text Products for ESF Issued by BIS

Flood Potential Outlook
Issued by NWS Bismarck, ND
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FGUS73 KBIS 291739
ESFBIS
NDC001-007-011-015-021-025-029-031-033-037-041-043-045-047-051-053-
055-057-059-061-065-083-085-087-089-093-103-105-021745-

Probabilistic Hydrologic Outlook
National Weather Service Bismarck ND
1139 AM CST Thu Feb 29 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 2 March
through 31 May, 2024. This is the second 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...
Despite a few inches of snow scattered around since the first Spring
FLood Outlook, the overall risk of widespread flooding remains very
low going into spring. Nonetheless, as the region moves into the
month of March, spring rains still represent the lion`s share of the
risk reflected in the tables. March is the transition month for the
region from normal daytime highs of below freezing temperatures
during the first week, to average daytime highs well above freezing
by the last week of the month. Thus, the risks below are more due to
spring rains on well frozen ground than they are for actual runoff
from melting snow. Similarly, the flood risk is also tied directly
to the soil conditions. The surface of the ground across much of
North Dakota remains wet and frozen. Once the ground begins to thaw,
the risk of flooding will fall even further as a thawed surface to
the ground will allow more infiltration of rain and meltwater than
the current frozen ground.

Perhaps the greater risk going into spring is the existing long-term
trend of below normal precipitation. If this trend continues,
increased and expanded drought designations are a real concern given
the lack of snow across North Dakota.

...Missouri and Yellowstone Rivers...
In western North Dakota the Missouri and Yellowstone rivers above
Lake Sakakawea are back down to normal water levels for this time of
year despite having recently experienced modest runoff.

The overall snowpack on the plains and headwaters area of Montana
continues to trend well below normal for this time of year, and
remains in contention for the lowest observed Snow-Water Equivalent
(SWE) going into spring for the Missouri and Yellowstone rivers in
the past 30 years.

However, an ice jam has formed in the Bismarck/Mandan area of the
Missouri River below Garrison Dam. As of 29 February, it is
currently just below the defined flood stage. Nonetheless, it has
already created minor impacts and created plenty of angst over its
potential to pose a real problem. This ice jam should resolve in the
coming few days as warmer weather once again envelopes the area, but
until then it does pose a risk for damaging high water.

...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 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 basins 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 as the ground thaws and the region enters
its growing season.

...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. Those few exceptions are generally in the areas
with well frozen ground where runoff from a nominal snowpack
exceeded expectations.

...Soil Conditions...
Soil moisture values 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 around the middle of March.

...Weather Outlook...
The Climate Prediction Center 6-10 day outlooks favor near normal in
the western part of the state to warmer than normal temperatures for
central and eastern North Dakota. Precipitation for the same period
is expected to be below normal in the northwestern two-thirds of the
state and slightly above normal in the southeastern one-third of the
state. The weeks 3-4 outlooks favor above normal temperatures
state-wide, with an equal chances designation for above normal, near
normal, or below normal precipitation for all but the southeastern
corner which has a slight favoring for above normal precipitation.
Overall, North Dakota is favored for an above normal temperature
outcome during March, with an equal chance for above normal, near
normal, or below normal precipitation. The longer 3-month outlook
for March, April and May combined favors above normal temperatures
with an equal chance for above normal, near normal, or below normal
precipitation. In general, this is consistent with the expectation
that the El Nino affected winter season will fade into an ENSO
neutral pattern by late spring to early summer.

...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: 03/02/2024  - 05/31/2024

                                       :    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 :  <5   17   <5    8   <5   <5
:Missouri River
Williston           22.0   24.0   26.0 :   5   31   <5   10   <5    8
: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 :  10   58   <5   <5   <5   <5
:Beaver Creek
Linton              12.0   14.0   16.0 :  <5   45   <5   31   <5   13
:Little Muddy River
Williston           10.0   12.0   14.0 :   6   69   <5   35   <5   10
:Little Missouri River
Marmarth            18.0   23.0   30.0 :  <5    6   <5   <5   <5   <5
Medora              15.0   18.0   20.0 :  <5   18   <5    8   <5    6
Watford City        20.0   24.0   30.0 :  <5   14   <5    5   <5   <5
:Knife River
Manning             15.0   17.0   20.0 :  <5   24   <5   <5   <5   <5
:Spring Creek
Zap                 14.0   18.0   20.0 :   9   29    6   17    5   11
:Knife River
Hazen               21.0   24.0   25.0 :  11   43    8   25   <5   23
:Heart River
Mandan              27.0   33.0   38.0 :  <5   23   <5   <5   <5   <5
:Apple Creek
Menoken             15.0   16.0   17.0 :  24   58   16   53   <5   34

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: 03/02/2024  - 05/31/2024
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem
Pingree               5.2    5.2    5.2    5.2    5.7    7.8    8.7
:James River
Grace City            4.1    4.1    4.1    4.1    5.0    5.9    6.4
LaMoure               7.4    7.4    7.4    7.5    8.3    9.2   10.4
:Missouri River
Williston            16.8   17.3   18.0   18.6   19.3   20.4   21.8
:Cannonball River
Regent                5.2    5.2    5.6    6.4    7.9    8.8    9.7
:Cedar Creek
Raleigh               1.0    1.1    2.2    3.2    4.4    5.3    5.7
:Cannonball River
Breien                2.8    3.1    3.9    5.9    8.3   10.0   10.7
:Beaver Creek
Linton                4.3    4.4    4.5    5.4    6.4   10.1   11.5
:Little Muddy River
Williston             4.3    4.3    4.8    5.6    7.7    9.0   10.5
:Little Missouri River
Marmarth              1.1    1.1    1.1    1.3    3.7    7.0   10.6
Medora                1.5    1.5    1.5    2.3    3.9    7.2   11.0
Watford City          7.1    7.1    7.1    7.8    9.7   11.9   14.7
:Knife River
Manning               6.4    6.4    6.4    7.6    9.3   10.8   14.1
:Spring Creek
Zap                   4.8    4.9    5.3    6.6    8.1   12.4   19.3
:Knife River
Hazen                 0.6    0.9    3.9    7.8   12.2   22.9   24.4
:Heart River
Mandan               11.2   12.3   13.1   15.3   19.2   21.4   25.3
:Apple Creek
Menoken               4.7    5.1    5.8    7.7   15.0   16.5   16.6

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: 03/02/2024  - 05/31/2024
LOCATION              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Pipestem
Pingree               5.1    5.1    5.1    5.1    5.1    5.1    5.1
:James River
Grace City            4.1    4.1    4.1    4.1    4.1    4.1    4.1
LaMoure               7.1    7.1    7.1    7.1    7.1    7.1    7.1
:Missouri River
:Cannonball River
Regent                5.0    5.0    5.0    5.0    5.0    5.0    5.0
:Cedar Creek
Raleigh               0.6    0.4    0.3    0.3    0.3    0.3    0.3
:Cannonball River
Breien                2.2    2.2    2.2    2.1    2.1    2.0    2.0
:Beaver Creek
Linton                4.3    4.2    4.2    4.2    4.2    4.2    4.2
:Little Muddy River
Williston             4.3    4.3    4.3    4.3    4.3    4.3    4.3
:Little Missouri River
Marmarth              1.1    1.1    1.1    1.0    1.0    0.9    0.9
Medora                1.5    1.5    1.4    1.4    1.3    1.3    1.3
Watford City          7.1    7.1    7.1    7.0    7.0    6.8    6.8
:Knife River
Manning               6.4    6.4    6.3    6.3    6.2    6.2    6.2
:Spring Creek
Zap                   4.8    4.8    4.8    4.8    4.8    4.8    4.8
:Knife River
Hazen                 0.6    0.6    0.5    0.5    0.4    0.3    0.3
:Heart River
Mandan               11.0   10.9   10.9   10.9   10.8   10.7   10.7
:Apple Creek
Menoken               3.9    3.9    3.9    3.8    3.7    3.5    3.4

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 14 March.


$$

Schlag
National Weather Service Weather Forecast Office
