Flood Potential Outlook
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
944
FGUS75 KCYS 182157
ESFCYS
NEC007-013-033-045-105-123-157-165-WYC001-007-009-015-021-027-031-
141900-
Probabilistic Hydrologic Outlook
National Weather Service Cheyenne WY
257 PM MST Thu Feb 18 2025
...Spring Flood and Water Resources Outlook Number 1...
...Below-Average Potential for Ice Jam Flooding This Spring...
...Near-Average Potential for Spring Snow melt Runoff Flooding...
This Spring Flood and Water Resources Outlook is the first of three
routine issuances for the Cheyenne Hydrologic Service Area which
comprises seven counties in southeast Wyoming and eight counties in
the Nebraska panhandle. This outlook includes the North Platte River
main stem and its tributaries (the Laramie, Encampment, and Medicine
Bow Rivers), the Niobrara, White and Little Snake Rivers.
.Flood Outlook Summary...
There is a below-average potential for flooding early this spring
due to low-elevation snow melt, ice break up, and ice jams. These
normally occur between February and April. The winter has brought
extended periods of above-normal temperatures along with limited
low-elevation snow pack. This limits the chances for flooding due to
during periods of ice break-up on area lakes and rivers.
The potential for flooding due to snow melt runoff in southeast
Wyoming and the Nebraska Panhandle this spring is near-normal.
At this time, the near average snowpack in the Laramie, Snowy, and
Sierra Madre ranges indicates there are no areas particularly
susceptible to flooding due to snow melt. However, there remains
considerable opportunity for further accumulation for snowpack
before the expected high-elevation snow melt in May and June.
However, even a smaller snowpack can generate flooding if there is a
period of extremely warm temperatures and/or if significant rainfall
comes before the ground thaws. Once the ground has thawed, the flood
potential for the rest of the spring and early summer will be below
average.
While the snow pack is currently near average. The potential for
flooding, early or late in the season, will depend on future
snowfall, temperature patterns, and spring rainfall. All of these
factors affect the total amount of water stored in the snow pack and
the speed with which it is released to the rivers.
.Observed and Forecast Temperatures and Precipitation...
Weather patterns since November have been warmer and dryer than
average across the area. The short term forecast calls for cooler
temperatures with accumulating snowfall. Outlooks by the Climate
Prediction Center (CPC)for the period from 6 to 14 days indicate
conditions that favor above-normal temperatures and near to below
normal precipitation. The latest 3-month outlook for March, April,
and May indicates no strong signal for above or below-normal
temperatures or precipitation.
.Snow Cover and Liquid Water Content...
Mountain snow pack across southeast Wyoming is near normal for most
of Wyoming. In southeastern Wyoming Basin snow water equivalents,
measured at the Natural Resource Conservation Service (NRCS) SNOTEL
stations, ranged from 48 percent of median in the Crow Creek basin
in southeast Wyoming to 114 percent of median in the Medicine Bow
River basin. There remain almost 2 months until the median date of
peak snow pack in most basins across the area. March and April can
have a disproportionate affect on the final snow pack accumulation for
the season. Warm windy temperatures or late winter and early spring
storms can cause dramatic, late-season, changes in total snow pack.
Snow cover across the Nebraska Panhandle counties is light and
inconsistent. It is heavier in the southwestern Panhandle than in
the north. Snow pack there contains relatively small amounts of
water and should not be a major factor in Spring flooding.
.Soil Conditions and Drought...
Soil moisture in the area, as portrayed by the CPC, is extremely low.
Soil moisture percentiles range from less than the 5th percentile in
the most drought affected areas to the 30th percentile.
According to the National Drought Monitor, Severe (D-2) to Extreme (D-3)
Drought conditions dominate the southeast portions of Wyoming and the
Panhandle of Nebraska. In these areas drought has worsened fairly
steadily since mid-summer.
.Lake and River Conditions...
It was an exceptionally warm winter through December but January was
extremely cold. The cold weather has continued into February. However
there has not been an abundance of moisture along with the cold weather.
Most of the higher elevations lakes are iced over, although the ice
thickness might be less than in most years. Lower elevations rivers and
lakes have frozen during the January cold with only moderate thaws
during recent warm spells.
.Climate Outlooks...
The latest outlooks issued by the Climate Prediction Center show
strong signals in favor of above-normal temperatures in the 6-10 day
period with a moderate signal for below-normal precipitation.
Stretching out to 8-14 days, the signal for above-normal temperatures
weakens to moderate but remains quite pronounced. A weak signal for
above-normal precipitation develops in this time period. The 3-month
outlook for the period from March through May shows a weak signal for
above-normal temperatures a weak signal for below-normal
percipitation.
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:02/15/2025 - 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
-------- ----- ----- ----- : --- --- --- --- --- ---
:Encampment River
Encampment 6.5 7.5 8.5 : <5 <5 <5 <5 <5 <5
:North Platte River
Saratoga 8.5 9.5 10.5 : 17 40 <5 17 <5 <5
Sinclair 9.0 10.0 11.0 : 8 31 <5 17 <5 6
:Medicine Box River
Hanna 6.0 7.0 8.0 : <5 <5 <5 <5 <5 <5
:North Platte River
Glenrock 7.0 8.0 9.0 : <5 <5 <5 <5 <5 <5
Orin 8.0 9.0 10.0 : <5 <5 <5 <5 <5 <5
:Laramie River
Woods Landing 6.0 6.5 7.0 : <5 5 <5 <5 <5 <5
Laramie 9.0 10.0 11.0 : 10 21 <5 6 <5 <5
Bosler 7.5 8.5 9.5 : <5 8 <5 <5 <5 <5
Fort Laramie 7.0 8.0 9.0 : <5 7 <5 <5 <5 <5
:North Platte River
Henry 5.5 6.5 7.5 : <5 <5 <5 <5 <5 <5
Mitchell 7.5 8.5 9.5 : <5 13 <5 8 <5 5
Minatare 7.5 8.5 9.5 : <5 7 <5 <5 <5 <5
Bridgeport 9.5 10.0 10.5 : <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:02/15/2025 - 09/30/2025
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment 3.6 3.6 4.2 4.5 5.1 5.5 5.8
:North Platte River
Saratoga 5.1 5.5 6.2 7.3 7.8 8.8 9.0
Sinclair 4.3 4.7 5.5 6.7 7.5 8.9 9.3
:Medicine Box River
Hanna 2.8 2.8 3.3 4.1 4.3 4.9 5.0
:North Platte River
Glenrock 2.4 2.5 2.6 2.7 2.8 3.0 3.5
Orin 4.5 4.5 4.6 4.8 4.9 5.1 5.6
:Laramie River
Woods Landing 2.0 2.0 2.5 3.0 3.5 4.0 4.7
Laramie 4.5 4.9 6.2 7.6 8.3 9.0 9.5
Bosler 1.2 1.3 1.9 3.4 5.6 6.2 6.6
Fort Laramie 2.8 3.0 3.3 3.5 3.5 3.5 4.2
:North Platte River
Henry 3.4 3.5 3.6 3.7 3.8 3.9 4.0
Mitchell 2.6 2.7 2.8 2.9 3.5 6.0 6.5
Minatare 3.5 3.7 3.9 4.2 4.6 5.9 6.2
Bridgeport 4.8 4.8 5.0 5.3 5.6 6.5 6.8
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:02/15/2025 - 09/30/2025
LOCATION 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment 1.8 1.8 1.8 1.7 1.6 1.6 1.5
:North Platte River
Saratoga 3.4 3.4 3.4 3.4 3.2 3.0 2.9
Sinclair 3.1 3.1 3.1 3.0 2.9 2.6 2.4
:Medicine Box River
Hanna 2.0 2.0 1.9 1.8 1.8 1.8 1.5
:North Platte River
Glenrock 0.9 0.8 0.8 0.7 0.6 0.5 0.4
Orin 3.5 3.5 3.5 3.5 3.3 3.2 3.1
:Laramie River
Woods Landing 1.2 1.2 1.2 0.5 0.3 0.3 0.3
Laramie 3.4 3.3 3.3 3.3 3.3 3.2 3.2
Bosler 0.9 0.8 0.7 0.7 0.7 0.7 0.7
Fort Laramie 2.4 2.4 2.3 2.3 2.3 2.3 2.3
:North Platte River
Henry 2.0 2.0 2.0 2.0 2.0 2.0 2.0
Mitchell 0.3 0.1 0.1 0.1 0.1 0.1 0.1
Minatare 1.5 1.5 1.4 1.4 1.4 1.3 1.3
Bridgeport 3.9 3.8 3.7 3.6 3.5 3.5 3.5
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 the National Weather Service`s Advanced
Hydrologic Prediction Service.
Visit our web site weather.gov/cys for more weather and water
information.
The next outlook will be issued February 27.
$$
AJA