Flood Potential Outlook
Issued by NWS Cheyenne, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9
000
FGUS75 KCYS 071736
ESFCYS
WYC001-007-009-015-021-027-031-NEC007-013-033-045-105-123-157-165-
210000-

Probabilistic Hydrologic Outlook
National Weather Service Cheyenne, WY
1035 AM MST Thu Mar 7 2019

...Spring 2019 Flood and Water Resources Outlook Update...

This outlook is for the Cheyenne Hydrologic Service Area which
encompasses seven counties in south central and southeast Wyoming
and seven counties in the Nebraska Panhandle. The outlook includes
the North Platte River mainstem and its tributaries (the Laramie and
Medicine Bow Rivers), tributaries to the Missouri River (Niobrara
and White Rivers) of extreme northwest Nebraska, and the Little
Snake River.

The outlook is a generalized summary of spring flood potential.
Above normal future precipitation combined with heavy rain and rapid
snowmelt will increase the current flood potential. Below normal
future precipitation and gradual freezing and thawing will decrease
the flood potential.

...Current water precipitation averages 85 to 110 percent of normal
across south central and southeast Wyoming, and 50 to 85 percent for
the Nebraska Panhandle...

...Carryover reservoir storages are 80 to 110 percent of average...

...Abnormally dry conditions continue across south central and
extreme southeast Wyoming into the southern Nebraska Panhandle...

...Near average snowmelt streamflow volumes are forecast for basins
in southeast Wyoming and the Nebraska Panhandle...

...Low risk of flooding from snowmelt runoff this spring...

Mountain snow water equivalents (SWEs) in south central and
southeast Wyoming averaged 85 to 110 percent of normal since
February 21. The higher SWEs were observed in the Laramie and Upper
North Platte River basins as well as portions of the Niobrara and
White River basins in the northern Nebraska Panhandle. Frost depths
averaged between 12 and 20 inches. Soil moisture values averaged
between 100 and 200 mm, with deficits around 20 mm across extreme
southern and southeast Wyoming. Moderate drought (D1) was removed
from southern Carbon County as 2 to 5 inches of liquid precipitation
fell over that area during the past 30 days. Abnormally dry (D0)
conditions persisted over much of south central into far southeast
Wyoming, and into the southern Nebraska Panhandle.

The Wyoming Bureau of Reclamation`s March forecast predicts near
average spring snowmelt runoff for the North Platte River Basin.
Total April through July runoff in the North Platte River Basin
above Glendo Dam is expected to be 890,000 acre-ft, or 98 percent of
the 30-year average. As of February 28, storage capacity in the
North Platte Reservoirs was 1,759,773 acre-ft, or 110 percent of the
30-year average. Total capacity of the North Platte Reservoir system
is approximately 2.8 million acre-ft.

...Spring 2019 Climate Outlook...

The outlook for March issued February 28 by the Climate Prediction
Center indicates cool and wet conditions continuing with above
normal precipitation and below normal temperatures. The 90-day
outlook for March through May predicts above normal precipitation
and equal chances of above, normal and below normal temperatures.
The Seasonal Drought Outlook for March indicates an improvement of
drought conditions across southern Wyoming.

...Probabilities of Minor, Moderate and Major Flooding...

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:  03/09/2019  - 06/07/2019

                                       :    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   31    5   10   <5   <5
Sinclair             9.0   10.0   11.0 :   8   23   <5    8   <5   <5
:Medicine Bow 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    8   <5   <5   <5   <5
Bosler               7.5    8.5    9.5 :  <5   <5   <5   <5   <5   <5
Fort Laramie         7.0    8.0    9.0 :  <5   <5   <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    5   <5   <5   <5   <5
Minatare             7.5    8.5    9.5 :  <5   <5   <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: 03/09/2019  - 06/07/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment            3.8    3.9    4.1    4.3    4.8    5.2    5.3
:North Platte River
Saratoga              5.9    6.2    6.6    7.1    8.1    8.6    9.3
Sinclair              5.2    5.5    6.0    6.7    8.0    8.8    9.6
:Medicine Bow River
Hanna                 3.2    3.5    3.7    4.1    4.5    4.9    5.0
:North Platte River
Glenrock              2.1    2.1    2.2    2.3    2.6    3.1    3.5
Orin                  4.2    4.2    4.3    4.3    4.6    5.0    5.7
:Laramie River
Woods Landing         2.0    2.1    2.3    2.7    3.3    3.7    4.4
Laramie               5.2    5.4    6.0    6.9    7.7    8.3    8.8
Bosler                1.5    1.6    2.2    3.6    5.1    5.8    6.0
Fort Laramie          3.0    3.0    3.5    3.9    4.5    5.1    5.8
:North Platte River
Henry                 2.3    2.4    2.4    2.6    3.0    3.3    4.9
Mitchell              1.2    1.2    1.8    2.3    3.4    4.2    6.9
Minatare              2.4    2.5    2.8    3.5    4.2    4.8    6.5
Bridgeport            3.8    3.8    4.1    4.6    5.2    5.6    6.9

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: 03/09/2019  - 06/07/2019
Location              95%    90%    75%    50%    25%    10%     5%
--------            ------ ------ ------ ------ ------ ------ ------
:Encampment River
Encampment            1.7    1.7    1.7    1.7    1.7    1.6    1.5
:North Platte River
Saratoga              3.0    3.0    3.0    3.0    3.0    3.0    3.0
Sinclair              3.1    3.1    3.1    3.1    3.1    3.1    3.0
:Medicine Bow River
Hanna                 2.1    2.1    2.1    2.1    2.1    2.1    2.1
:North Platte River
Glenrock              1.0    0.9    0.9    0.9    0.8    0.8    0.8
Orin                  3.6    3.6    3.6    3.6    3.5    3.5    3.5
:Laramie River
Woods Landing         1.2    1.2    1.2    1.2    1.2    1.1    0.3
Laramie               2.6    2.6    2.6    2.6    2.6    2.6    2.5
Bosler                1.0    1.0    0.9    0.8    0.7    0.7    0.7
Fort Laramie          2.6    2.6    2.6    2.6    2.6    2.6    2.6
:North Platte River
Henry                 2.0    2.0    2.0    2.0    1.9    1.9    1.9
Mitchell              0.9    0.5    0.3    0.2    0.2    0.2    0.2
Minatare              2.1    2.1    2.1    1.6    1.5    1.4    1.3
Bridgeport            3.7    3.7    3.7    3.4    3.4    3.2    3.2

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.

...Related Internet Sites...

Visit our web site weather.gov/cys for more weather and water
information.

USGS Wyoming Drought Watch...
http://wy.water.usgs.gov/projects/drought/

U.S. Drought Monitor...https://www.drought.gov

NOAA Drought Page...https://www.drought.noaa.gov

Climate Prediction Center...https://www.cpc.ncep.noaa.gov

Additional River and Reservoir Information...

Advanced Hydrologic Prediction Service (AHPS)...
https://www.water.gov/ahps2/index.php?WFO=cys

NRCS Wyoming...http://www.wy.nrcs.usda.gov

USGS...https://water.usgs.gov

USBR...https://www.usbr.gov

Water Resource Data System (WRDS)...http://www.wrds.uwyo.edu

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.