Flood Potential Outlook
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
838
FGUS75 KCYS 262300
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
400 PM MST Wed Feb 26 2025
...Spring Flood and Water Resources Outlook Number 2...
...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 second 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 below-normal temperatures along with limited
low-elevation snow pack. This limits the chances for flooding due to
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 near
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 seen mixed temperature regimes
with periods of much above and much below normal warmth. It has been
a relatively dry year in the lower elevations but the mountains have
seen near normal snowpack accumulation. The short term forecast
calls for warmer temperatures with high winds and little
precipitation. Outlooks by the Climate Prediction Center (CPC)for
the period from 6 to 10 days indicate conditions that favor
near-normal temperatures and above normal precipitation. The
extended short-term outlook (8-14 days) show equal chances of above-
normal, below-normal, and near-normal temperatures. The precipitation
outlook for that period shows a weak signal favoring above-normal
precipitation in Wyoming, but no signal in Nebraska. The latest
3-month outlook for March, April, and May indicates no strong signal
for above or below-normal temperatures. There is a weak signal for
below-normal precipitation.
.Snow Cover and Liquid Water Content...
Mountain snow pack across southeast Wyoming is near normal for most
of southeastern Wyoming. Basin snow water equivalents, measured at
the Natural Resource Conservation Service (NRCS) SNOTEL stations,
ranged from 49 percent of median in the Crow Creek basin
in southeast Wyoming to 110 percent of median in the Medicine Bow
River basin. There remain almost a month and a half until 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. Extreme conditions in late winter and
early spring storms can cause dramatic, late-season, changes in total
snow pack.
Snow cover across the Nebraska Panhandle counties is all but absent.
.Soil Conditions and Drought...
Soil moisture in the area, as portrayed by the CPC, has improved in the
last two weeks. Considerable snowmelt and warm temperatures allowed some
moisture to infiltrate the soil column. That being said, soil moisture
remains below normal. Soil moisture percentiles range from less than the
5th percentile in Carbon and Albany Counties in Wyoming to the 30th
percentile in the Nebraska Panhandle.
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 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...
Outlooks by the Climate Prediction Center (CPC) for the period
from 6 to 10 days indicate conditions that favor near-normal
temperatures and above-normal precipitation. The extended short-
term outlooks (8-14 days) show equal chances of above-normal,
below-normal, and near-normal temperatures. The precipitation
outlook for that period shows a weak signal favoring above-normal
precipitation in Wyoming but no signal in Nebraska. The latest
three-month outlook for March, April, and May indicates no strong
signal for above or below-normal temperatures. There is a weak
signal favoring below-normal precipitation.
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: 03/01/2025 - 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
-------- ----- ----- ----- : --- --- --- --- --- ---
: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 : 14 40 <5 17 <5 <5
Sinclair 9.0 10.0 11.0 : <5 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 : 5 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: 03/01/2025 - 09/30/2025
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment 3.4 3.5 4.0 4.4 5.0 5.5 5.8
:North Platte River
Saratoga 4.7 5.1 5.8 6.7 7.5 8.7 8.7
Sinclair 4.0 4.4 5.0 6.1 7.0 8.7 8.8
:Medicine Box River
Hanna 2.6 2.7 3.1 3.9 4.1 4.7 4.9
:North Platte River
Glenrock 2.3 2.5 2.6 2.7 2.8 3.0 3.5
Orin 4.5 4.5 4.6 4.7 4.8 5.1 5.5
:Laramie River
Woods Landing 1.8 1.9 2.1 2.7 3.3 3.9 4.2
Laramie 4.2 4.5 5.0 7.0 8.0 8.7 9.0
Bosler 1.0 1.1 1.5 2.5 5.0 5.9 6.2
Fort Laramie 2.7 2.9 3.2 3.5 3.5 3.5 3.8
:North Platte River
Henry 3.4 3.5 3.6 3.7 3.8 3.9 3.9
Mitchell 2.6 2.7 2.8 2.9 3.5 5.8 6.2
Minatare 3.5 3.7 3.9 4.1 4.6 5.8 5.9
Bridgeport 4.8 4.8 5.0 5.2 5.6 6.5 6.6
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: 03/01/2025 - 09/30/2025
LOCATION 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment 1.8 1.8 1.7 1.7 1.6 1.5 1.5
:North Platte River
Saratoga 3.5 3.5 3.5 3.3 3.0 2.9 2.9
Sinclair 3.1 3.1 3.1 3.0 2.6 2.4 2.3
: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 0.7 0.7 0.5 0.4 0.3
Orin 3.5 3.5 3.5 3.5 3.3 3.1 2.9
:Laramie River
Woods Landing 1.2 1.2 0.9 0.3 0.3 0.3 0.3
Laramie 3.4 3.4 3.4 3.3 3.2 3.2 3.2
Bosler 0.8 0.8 0.7 0.7 0.7 0.7 0.7
Fort Laramie 2.4 2.3 2.3 2.3 2.3 2.3 2.3
:North Platte River
Henry 2.1 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 1.4 1.4
Bridgeport 3.9 3.8 3.6 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 by the middle of March.
$$
AJA