Flood Potential Outlook
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
101
FGUS75 KCYS 131710
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
1110 AM MST Wed Mar 13 2025
...Spring Flood and Water Resources Outlook Number 3...
...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 third 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 near-average potential for flooding early this Spring
due to low-elevation snow melt. Snow-pack in the lower elevations
is near normal for late winter. Ice-jam flooding in late winter or
early spring normally occurs during the break up of river ice
between February and April. The winter has brought extended
periods of below-normal temperatures following warm temperatures in
December. We should see near-normal 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 to
slightly below normal. At this time, the near average snowpack in
the Laramie, Snowy, and Sierra Madre ranges indicates there are
limited areas susceptible to flooding due to snow melt. The only
area with a notably large snow-pack is around Medicine Bow Peak in
the Snowy Range. This source area may warrant extra attention
during the later runoff season. There remains considerable
opportunity for further accumulation of snowpack before the expected
high-elevation snow melt in May and June.
While the snow-pack is currently near normal the long-term hydrologic
models indicate a below-normal probability of flooding this Spring.
This may reflect the drought conditions of late fall and the ability of
dry soils to absorb the runoff produced by a near-normal snow-pack.
It should be noted that even a smaller snowpack can generate
flooding if there is a period of extremely warm temperatures and/or
if significant rainfall comes during periods of rapid snowmelt.
Otherwise, the flood potential for 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. Precipitation in the North
Platte basin during February was quite generous and brought the
seasonal snowpack very close to the long-term median. The short term
forecast calls for cooler temperatures, high winds, and some
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) shows conditions that favor
near-normal temperatures and above normal precipitation. 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. 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 108 percent of median in the Medicine Bow
River basin. There remains almost a month 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 slightly
during February and March. Soils thawed early this year and have allowed
considerable snowmelt 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 extremely cold
after that. Temperatures moderated slightly in February. Precipitation
in February was near normal in the plains but was well above normal in
the mountains. Most of the higher elevations lakes remain iced over.
Lower elevations rivers and lakes have frozen during the January and
February 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 and extreme western 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: 03/15/2025 - 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 6 17 <5 <5
Sinclair 9.0 10.0 11.0 : 14 31 6 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 : 14 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 14 <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: 03/15/2025 - 09/30/2025
Location 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment 3.8 4.1 4.4 4.7 5.2 5.4 6.0
:North Platte River
Saratoga 5.4 6.1 6.7 7.5 8.1 9.3 9.6
Sinclair 4.6 5.3 6.0 7.0 7.9 9.7 10.2
:Medicine Box River
Hanna 3.2 3.3 3.7 4.2 4.4 4.9 5.3
:North Platte River
Glenrock 2.5 2.6 2.7 2.8 2.9 3.1 3.6
Orin 4.5 4.6 4.7 4.8 4.9 5.1 5.6
:Laramie River
Woods Landing 2.0 2.2 2.6 3.2 3.6 4.3 5.0
Laramie 4.7 5.3 7.0 8.0 8.4 9.2 9.6
Bosler 1.4 1.4 2.6 4.9 5.8 6.6 7.1
Fort Laramie 2.8 3.1 3.3 3.5 3.5 4.1 5.3
:North Platte River
Henry 3.5 3.5 3.7 3.7 3.8 3.9 4.2
Mitchell 2.7 2.8 2.8 3.1 3.8 4.4 6.1
Minatare 3.5 3.7 3.9 4.2 4.8 5.1 5.8
Bridgeport 4.7 4.8 5.0 5.2 5.7 6.0 6.5
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: 03/15/2025 - 09/30/2025
LOCATION 95% 90% 75% 50% 25% 10% 5%
-------- ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment 1.8 1.8 1.8 1.7 1.7 1.6 1.5
:North Platte River
Saratoga 3.7 3.7 3.6 3.6 3.5 3.3 3.0
Sinclair 3.4 3.3 3.3 3.2 3.1 3.0 2.5
:Medicine Box River
Hanna 2.2 2.1 2.0 2.0 1.9 1.8 1.8
:North Platte River
Glenrock 0.9 0.9 0.8 0.7 0.6 0.5 0.5
Orin 3.5 3.5 3.5 3.5 3.4 3.3 3.2
:Laramie River
Woods Landing 1.3 1.2 1.2 1.1 0.3 0.3 0.3
Laramie 3.5 3.4 3.3 3.3 3.2 3.2 3.2
Bosler 0.9 0.8 0.7 0.7 0.7 0.7 0.6
Fort Laramie 2.3 2.3 2.3 2.3 2.3 2.3 2.3
:North Platte River
Henry 2.1 2.1 2.1 2.1 2.1 2.1 2.0
Mitchell 0.7 0.4 0.2 0.1 0.1 0.1 0.1
Minatare 1.6 1.6 1.5 1.5 1.5 1.5 1.5
Bridgeport 3.8 3.7 3.6 3.5 3.4 3.3 3.3
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 end of April.
$$
AJA