Flood Potential Outlook
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
000
FGUS75 KRIW 141712
ESFRIW
WYC003-013-017-019-023-025-029-035-037-039-043-010000-
Probabilistic Hydrologic Outlook
National Weather Service Riverton WY
1110 AM MST Thu Mar 14 2024
...Spring Flood and Water Resource Outlook...
...Below Average Flood Potential This Spring For Western And Central
Wyoming But Confidence Remains Low...
This spring flood and water resource outlook is for the Riverton
Hydrologic Service Area (HSA), which covers western and central
Wyoming.
.Flood Outlook Summary...
Confidence remains low in the flood potential outlook for this
spring. There are still one to 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 mid
March.
All that being said, high elevation snowpack varies across our HSA
east of the Continental Divide. Mountains that feed the Shoshone and
Upper Bighorn Basins contain above normal SWE, while the Wind River
Range remains near normal. The Bighorn Range has below to well below
normal snowpack. Low elevation snowpack is below average for most
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
below normal snowpack conditions.
.Temperatures and Precipitation...
Temperatures over the past three months have been above to much
above normal for most of central and western Wyoming. A lack of deep
lower-elevation snowpack and absence of cold air advection bringing
in Arctic air masses has allowed temperatures to remain mild. The
Wind River Basin is the one exception, where temperatures have been
near normal over the past three months.
Precipitation over the past three months has varied across the
region. The Bighorn Basin and Wind River Basin have seen near to
slightly above normal precipitation. Most mountain ranges, the Upper
Yellowstone Basin, and the Powder River Basin have had below to much
below normal precipitation.
.Snow Cover and Liquid Water Content...
High-elevation SWE ranges from 55 to 170 percent of normal. The
lowest values are in the Upper Yellowstone Basin, North Platte
Basin, and eastern Powder River Basin, with values between 55 to 80
percent of normal. The western Bighorn Basin sits between 120 to 170
percent of normal and the Wind River Basin sits right around normal.
Low-elevation snowpack is below normal for most basins. The snowiest
basin is the Wind River Basin, where far southwest portions of the
basin have snow depth in the 4 to 8 inch range, with a trace to up
to 2 inches of SWE. Most of the Wind River Basin, and other central
Wyoming basins have less than 1 inch of SWE and a trace to a few
inches of snow depth.
Its worth noting that for most locations across central Wyoming,
there are around one to 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 80 to 95 percent
range. Exceptions to this are in the Upper Yellowstone Basin and
around the North Platte River near Casper, where soil moisture is
lower, and ranges from 40 to 60 percent. In the last month, frost
depths have been about 1 to 2 feet for central Wyoming.
.Lake and River Conditions...
A majority of the higher elevation lakes and streams across the
region are ice covered while many lower elevation rivers have some
open water areas with some being completely ice free.
A majority of river gauges are ice affected, but those that are
operating indicate normal to slightly above 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 slightly higher than average chance of above normal precipitation,
along with a slightly higher than average chance of above normal
temperatures. The seasonal precipitation outlook covering
meteorological spring trends toward equal chances of above or below
normal precipitation, which is another way of saying that
climatological normals are the best forecast. The seasonal
temperature outlook covering meteorological spring trends toward a
slightly higher than average chance of above 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: 03/16/2024 - 09/30/2024
: 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
-------- ----- ----- ----- : --- --- --- --- --- ---
:Wind River
Dubois 5.0 5.5 6.0 : 21 22 9 12 6 6
Red Creek 9.5 10.0 10.5 : <5 <5 <5 <5 <5 <5
Crowheart 10.0 10.5 11.0 : 5 17 <5 7 <5 <5
Kinnear 9.0 10.0 11.0 : <5 9 <5 <5 <5 <5
Riverton 9.0 11.0 12.0 : 20 25 <5 8 <5 <5
:Little Wind River
Riverton 8.0 10.0 11.0 : 21 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 : 8 16 5 10 <5 <5
:South Fork Shoshone River
Buffalo Bill Rese 9.5 10.5 12.0 : <5 6 <5 <5 <5 <5
:Shoshone River
Lovell 11.0 11.5 12.0 : <5 20 <5 13 <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: 03/16/2024 - 09/30/2024
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Wind River
Dubois 3.9 4.0 4.0 4.3 4.9 5.4 6.1
Red Creek 5.7 6.1 6.3 7.0 7.4 8.0 8.1
Crowheart 8.4 8.5 8.7 9.2 9.5 9.9 10.0
Kinnear 6.3 6.4 6.7 7.3 7.8 8.3 8.5
Riverton 5.7 6.2 6.7 7.8 8.7 9.6 10.0
:Little Wind River
Riverton 4.4 5.0 5.7 6.5 7.7 8.9 10.1
:Bighorn River
Basin 5.2 5.2 5.5 7.4 8.7 9.4 9.6
Greybull 84.5 84.8 85.5 88.3 89.7 91.0 91.4
:North Fork Shoshone River
Wapiti 5.7 5.9 6.1 6.3 6.7 7.5 9.1
:South Fork Shoshone River
Buffalo Bill Rese 6.7 6.8 7.1 7.7 8.4 8.6 9.0
:Shoshone River
Lovell 8.3 8.3 8.3 9.2 9.6 9.9 10.0
:Yellowstone River
Fishing Bridge 6.1 6.2 6.4 6.5 7.1 7.4 7.7
:Lamar River
Tower Junction 5.5 5.6 6.0 6.6 7.3 8.1 9.0
:Powder River
Sussex 3.1 3.2 3.5 4.5 6.6 8.2 11.0
:North Platte River
Casper 3.4 3.4 3.4 3.4 3.5 3.9 4.8
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: 03/16/2024 - 09/30/2024
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 2.1 2.1 2.1
Crowheart 5.0 5.0 5.0 5.0 5.0 5.0 4.9
Kinnear 3.2 3.2 3.1 3.1 3.1 3.1 3.1
Riverton 1.9 1.9 1.8 1.4 1.1 1.1 1.1
:Little Wind River
Riverton 2.4 2.4 2.4 2.2 2.1 2.1 2.1
:Bighorn River
Basin 4.0 3.9 3.8 3.6 3.1 3.0 3.0
Greybull 82.4 82.4 82.4 82.1 81.4 81.1 80.9
:North Fork Shoshone River
Wapiti 2.8 2.8 2.8 2.8 2.8 2.8 2.8
:South Fork Shoshone River
Buffalo Bill Rese 4.1 4.1 4.0 4.0 3.8 3.3 3.0
:Shoshone River
Lovell 4.1 3.7 3.4 3.3 3.3 3.3 3.3
:Yellowstone River
Fishing Bridge 2.7 2.7 2.7 2.7 2.7 2.7 2.7
:Lamar River
Tower Junction 0.8 0.8 0.8 0.8 0.8 0.8 0.8
:Powder River
Sussex 2.7 2.7 2.7 2.6 2.6 2.5 2.5
:North Platte River
Casper 0.6 0.6 0.6 0.6 0.6 0.5 0.5
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 then
National Weather Service`s Advanced Hydrologic Prediction Service.
Visit our web site weather.gov/riw for more weather and water
information.
This is the third scheduled spring flood and water resources outlook for
2024.
$$
Hensley
- National Weather Service
- Topeka, KS Weather Forecast Office
- 1116 NE Strait Avenue
- Topeka, KS 66616-1667
- 785-234-2592
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