Flood Potential Outlook
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
020
FGUS75 KRIW 271810
ESFRIW
WYC003-013-017-019-023-025-029-035-037-039-043-130000-
Probabilistic Hydrologic Outlook
National Weather Service Riverton WY
1100 AM MST Thu Feb 27 2025
...Spring Flood and Water Resource Outlook...
...Below Average Flood Potential This Spring For Central Wyoming But
Confidence Remains Low...
This spring flood and water resource outlook is for the greater
Missouri River Basin portion of the Riverton Hydrologic Service Area
(HSA), which covers northern and central Wyoming east of the
Continental Divide.
.Flood Outlook Summary...
There is currently low confidence in the flood potential for this
spring. There are still two months of snow accumulation remaining,
and additional snow and rain will greatly influence river flows. The
speed of the spring warm-up also greatly influences how much water
makes it into rivers, with a slower and more modest warm-up allowing
more water to be absorbed by the ground after frost melts. In short,
many important variables are still unknown in February.
All that being said, high elevation snowpack is currently near to
slightly below average east of the Continental Divide. Low elevation
snowpack is also minimal for central Wyoming basins. Statistical
analysis and probabilistic forecasts in the tables below indicate
near normal to below normal chances for flooding. This lines up well
with local experience given current near to slightly below normal
snowpack conditions.
.Temperatures and Precipitation...
Temperatures over the past three months have been above normal for
most of central Wyoming. A lack of deep lower-elevation snowpack and
infrequent arctic air masses being advected in from the north have
allowed temperatures to remain relatively mild.
Precipitation over the past three months has been below normal
overall for central Wyoming. Basins have had below normal
precipitation overall, while the mountains have had near normal
precipitation.
.Snow Cover and Liquid Water Content...
High-elevation SWE ranges from 77 to 104 percent of normal in the
HUC6 basins, and overall is near to slightly below average. The
lowest values are in the Powder and Lower North Platte basins, with
values near 80 percent of normal. On the other hand, the Wind and
Sweetwater basins sit near 100 percent of normal.
Low-elevation snowpack is below normal for most basins. The snowiest
basin is the Bighorn Basin, where northern portions of the basin
have snow depths in the 1 to 4 inch range, with 0.5 to 1 inches of
SWE. Most other basins have minimal SWE and a trace to a few inches
of snow depth.
Its worth noting that for most locations across central Wyoming,
there are two more months of snow accumulation, with peak mountain
snow depths not occurring until mid-April to mid-May. Late winter
into spring is normally one of the wetter times of the year, so the
snow cover and SWE values listed above could quickly become non-
representative.
.Soil Conditions and Frost Depths...
Soil moisture for most of central Wyoming is in the 5 to 240 percent
range. Exceptions to this are in the Yellowstone and Shoshone
basins, where soil moisture is higher, and ranges from 40 to 70
percent. For most of the last month, frost depths have been at least
3 feet based on the Riverton, WY measurement, but recent quick
thawing has occurred due to warm temperatures.
.Lake and River Conditions...
A majority of the higher elevation lakes and streams across the
region are ice covered while lower elevation rivers have some open
water areas.
A majority of river gauges are ice affected, but those few that are
operating indicate normal to slightly below normal flows for this
time of year. Its worth noting that the spring melt has not begun
yet, so most of the observed river flows are not representative of
spring conditions at this time.
.Weather Outlooks...
The Climate Prediction Center`s monthly outlook for March indicates
a near normal precipitation, along with near normal temperatures.
The seasonal precipitation outlook covering meteorological spring
trends toward a slightly higher than average chance of below normal
precipitation, while the seasonal temperature outlook trends toward
a slightly higher than average chance of below normal temperatures.
.Numerical River Outlooks...
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.
...Table 1--Probabilities for minor, moderate, and major flooding...
Valid Period: 03/01/2025 - 09/30/2025
: 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
-------- ----- ----- ----- : --- --- --- --- --- ---
:Wind River
Dubois 5.0 5.5 6.0 : <5 22 <5 12 <5 6
Red Creek 9.5 10.0 10.5 : <5 <5 <5 <5 <5 <5
Crowheart 10.0 10.5 11.0 : <5 <5 <5 <5 <5 <5
Kinnear 9.0 10.0 11.0 : <5 8 <5 <5 <5 <5
Riverton 9.0 11.0 12.0 : <5 23 <5 8 <5 <5
:Little Wind River
Riverton 8.0 10.0 11.0 : 8 16 <5 <5 <5 <5
:Bighorn River
Basin 10.5 11.0 13.0 : <5 9 <5 8 <5 <5
Greybull 92.0 93.5 95.0 : <5 10 <5 7 <5 <5
:North Fork Shoshone River
Wapiti 8.0 9.0 10.0 : <5 14 <5 6 <5 <5
:South Fork Shoshone River
Buffalo Bill Rese 9.5 10.5 12.0 : <5 5 <5 <5 <5 <5
:Shoshone River
Lovell 11.0 11.5 12.0 : <5 20 <5 15 <5 12
:Yellowstone River
Fishing Bridge 9.0 10.0 11.0 : <5 <5 <5 <5 <5 <5
:Lamar River
Tower Junction 15.0 16.0 17.0 : <5 <5 <5 <5 <5 <5
:Powder River
Sussex 11.0 12.0 13.0 : 5 13 <5 11 <5 10
:North Platte River
Casper 8.0 9.0 10.0 : <5 <5 <5 <5 <5 <5
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: 03/01/2025 - 09/30/2025
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Wind River
Dubois 2.9 3.0 3.3 3.5 4.1 4.5 5.0
Red Creek 4.2 4.4 4.9 5.4 6.1 6.9 7.0
Crowheart 6.1 6.3 6.7 7.2 7.8 8.3 8.3
Kinnear 3.1 3.3 4.4 5.5 6.3 7.0 7.1
Riverton 3.1 3.1 3.2 4.8 6.5 7.4 7.6
:Little Wind River
Riverton 2.9 3.0 3.8 5.1 6.4 7.4 8.8
:Bighorn River
Basin 3.8 3.9 4.4 5.1 6.0 6.6 7.6
Greybull 82.3 82.4 83.2 84.7 85.8 86.9 87.8
:North Fork Shoshone River
Wapiti 5.1 5.3 5.4 5.7 6.2 6.7 7.8
:South Fork Shoshone River
Buffalo Bill Rese 5.5 5.7 6.1 6.7 7.1 7.9 8.3
:Shoshone River
Lovell 5.1 5.2 5.3 5.5 6.1 9.0 9.3
:Yellowstone River
Fishing Bridge 3.2 3.3 3.5 3.7 4.2 4.6 4.7
:Lamar River
Tower Junction 4.9 5.0 5.5 6.3 6.8 7.5 8.6
:Powder River
Sussex 2.6 2.9 3.3 4.3 6.3 8.1 10.7
:North Platte River
Casper 2.4 2.6 2.7 2.9 3.0 3.1 3.7
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: 03/01/2025 - 09/30/2025
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Wind River
Dubois 2.3 2.3 2.3 2.3 2.3 2.3 2.3
Red Creek 2.1 2.1 2.1 2.1 2.0 2.0 2.0
Crowheart 3.9 3.9 3.8 3.7 3.3 3.0 3.0
Kinnear 3.0 3.0 3.0 3.0 3.0 3.0 3.0
Riverton 2.0 2.0 2.0 2.0 2.0 2.0 2.0
:Little Wind River
Riverton 1.8 1.8 1.8 1.7 1.6 1.5 1.5
:Bighorn River
Basin 3.2 3.2 3.0 3.0 3.0 3.0 3.0
Greybull 81.4 81.3 81.2 81.0 80.7 80.6 80.5
:North Fork Shoshone River
Wapiti 2.5 2.5 2.5 2.5 2.5 2.5 2.5
:South Fork Shoshone River
Buffalo Bill Rese 3.6 3.4 3.4 3.1 3.0 2.9 2.9
:Shoshone River
Lovell 3.2 3.1 3.1 3.0 3.0 3.0 3.0
:Yellowstone River
Fishing Bridge 2.2 2.2 2.2 2.2 2.1 2.1 2.1
:Lamar River
Tower Junction 0.7 0.7 0.7 0.7 0.7 0.7 0.7
:Powder River
Sussex 2.3 2.3 2.2 2.2 2.1 2.1 2.1
:North Platte River
Casper 0.6 0.5 0.4 0.3 0.2 0.1 0.1
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.
Visit our web site weather.gov/riw for more weather and water
information.
This is the second scheduled 2025 spring flood and water resources
outlook for the greater Missouri River Basin. The next outlook is
scheduled for March 13, 2025.
$$
VandenBoogart